Kernel Mode Setting (KMS)

Drivers must initialize the mode setting core by calling drm_mode_config_init() on the DRM device. The function initializes the struct drm_device mode_config field and never fails. Once done, mode configuration must be setup by initializing the following fields.

  • int min_width, min_height; int max_width, max_height; Minimum and maximum width and height of the frame buffers in pixel units.
  • struct drm_mode_config_funcs *funcs; Mode setting functions.

Overview

digraph "KMS" {
   node [shape=box]

   subgraph cluster_static {
       style=dashed
       label="Static Objects"

       node [bgcolor=grey style=filled]
       "drm_plane A" -> "drm_crtc"
       "drm_plane B" -> "drm_crtc"
       "drm_crtc" -> "drm_encoder A"
       "drm_crtc" -> "drm_encoder B"
   }

   subgraph cluster_user_created {
       style=dashed
       label="Userspace-Created"

       node [shape=oval]
       "drm_framebuffer 1" -> "drm_plane A"
       "drm_framebuffer 2" -> "drm_plane B"
   }

   subgraph cluster_connector {
       style=dashed
       label="Hotpluggable"

       "drm_encoder A" -> "drm_connector A"
       "drm_encoder B" -> "drm_connector B"
   }
}

KMS Display Pipeline Overview

The basic object structure KMS presents to userspace is fairly simple. Framebuffers (represented by struct drm_framebuffer, see Frame Buffer Abstraction) feed into planes. One or more (or even no) planes feed their pixel data into a CRTC (represented by struct drm_crtc, see CRTC Abstraction) for blending. The precise blending step is explained in more detail in Plane Composition Properties and related chapters.

For the output routing the first step is encoders (represented by struct drm_encoder, see Encoder Abstraction). Those are really just internal artifacts of the helper libraries used to implement KMS drivers. Besides that they make it unecessarily more complicated for userspace to figure out which connections between a CRTC and a connector are possible, and what kind of cloning is supported, they serve no purpose in the userspace API. Unfortunately encoders have been exposed to userspace, hence can’t remove them at this point. Futhermore the exposed restrictions are often wrongly set by drivers, and in many cases not powerful enough to express the real restrictions. A CRTC can be connected to multiple encoders, and for an active CRTC there must be at least one encoder.

The final, and real, endpoint in the display chain is the connector (represented by struct drm_connector, see Connector Abstraction). Connectors can have different possible encoders, but the kernel driver selects which encoder to use for each connector. The use case is DVI, which could switch between an analog and a digital encoder. Encoders can also drive multiple different connectors. There is exactly one active connector for every active encoder.

Internally the output pipeline is a bit more complex and matches today’s hardware more closely:

digraph "Output Pipeline" {
   node [shape=box]

   subgraph {
       "drm_crtc" [bgcolor=grey style=filled]
   }

   subgraph cluster_internal {
       style=dashed
       label="Internal Pipeline"
       {
           node [bgcolor=grey style=filled]
           "drm_encoder A";
           "drm_encoder B";
           "drm_encoder C";
       }

       {
           node [bgcolor=grey style=filled]
           "drm_encoder B" -> "drm_bridge B"
           "drm_encoder C" -> "drm_bridge C1"
           "drm_bridge C1" -> "drm_bridge C2";
       }
   }

   "drm_crtc" -> "drm_encoder A"
   "drm_crtc" -> "drm_encoder B"
   "drm_crtc" -> "drm_encoder C"


   subgraph cluster_output {
       style=dashed
       label="Outputs"

       "drm_encoder A" -> "drm_connector A";
       "drm_bridge B" -> "drm_connector B";
       "drm_bridge C2" -> "drm_connector C";

       "drm_panel"
   }
}

KMS Output Pipeline

Internally two additional helper objects come into play. First, to be able to share code for encoders (sometimes on the same SoC, sometimes off-chip) one or more Bridges (represented by struct drm_bridge) can be linked to an encoder. This link is static and cannot be changed, which means the cross-bar (if there is any) needs to be mapped between the CRTC and any encoders. Often for drivers with bridges there’s no code left at the encoder level. Atomic drivers can leave out all the encoder callbacks to essentially only leave a dummy routing object behind, which is needed for backwards compatibility since encoders are exposed to userspace.

The second object is for panels, represented by struct drm_panel, see Panel Helper Reference. Panels do not have a fixed binding point, but are generally linked to the driver private structure that embeds struct drm_connector.

Note that currently the bridge chaining and interactions with connectors and panels are still in-flux and not really fully sorted out yet.

KMS Core Structures and Functions

struct drm_mode_config_funcs

basic driver provided mode setting functions

Definition

struct drm_mode_config_funcs {
  struct drm_framebuffer *(*fb_create)(struct drm_device *dev,struct drm_file *file_priv, const struct drm_mode_fb_cmd2 *mode_cmd);
  const struct drm_format_info *(*get_format_info)(const struct drm_mode_fb_cmd2 *mode_cmd);
  void (*output_poll_changed)(struct drm_device *dev);
  enum drm_mode_status (*mode_valid)(struct drm_device *dev, const struct drm_display_mode *mode);
  int (*atomic_check)(struct drm_device *dev, struct drm_atomic_state *state);
  int (*atomic_commit)(struct drm_device *dev,struct drm_atomic_state *state, bool nonblock);
  struct drm_atomic_state *(*atomic_state_alloc)(struct drm_device *dev);
  void (*atomic_state_clear)(struct drm_atomic_state *state);
  void (*atomic_state_free)(struct drm_atomic_state *state);
};

Members

fb_create

Create a new framebuffer object. The core does basic checks on the requested metadata, but most of that is left to the driver. See struct drm_mode_fb_cmd2 for details.

If the parameters are deemed valid and the backing storage objects in the underlying memory manager all exist, then the driver allocates a new drm_framebuffer structure, subclassed to contain driver-specific information (like the internal native buffer object references). It also needs to fill out all relevant metadata, which should be done by calling drm_helper_mode_fill_fb_struct().

The initialization is finalized by calling drm_framebuffer_init(), which registers the framebuffer and makes it accessible to other threads.

RETURNS:

A new framebuffer with an initial reference count of 1 or a negative error code encoded with ERR_PTR().

get_format_info

Allows a driver to return custom format information for special fb layouts (eg. ones with auxiliary compression control planes).

RETURNS:

The format information specific to the given fb metadata, or NULL if none is found.

output_poll_changed

Callback used by helpers to inform the driver of output configuration changes.

Drivers implementing fbdev emulation with the helpers can call drm_fb_helper_hotplug_changed from this hook to inform the fbdev helper of output changes.

FIXME:

Except that there’s no vtable for device-level helper callbacks there’s no reason this is a core function.

mode_valid
Device specific validation of display modes. Can be used to reject modes that can never be supported. Only device wide constraints can be checked here. crtc/encoder/bridge/connector specific constraints should be checked in the .:c:func:mode_valid() hook for each specific object.
atomic_check

This is the only hook to validate an atomic modeset update. This function must reject any modeset and state changes which the hardware or driver doesn’t support. This includes but is of course not limited to:

  • Checking that the modes, framebuffers, scaling and placement requirements and so on are within the limits of the hardware.
  • Checking that any hidden shared resources are not oversubscribed. This can be shared PLLs, shared lanes, overall memory bandwidth, display fifo space (where shared between planes or maybe even CRTCs).
  • Checking that virtualized resources exported to userspace are not oversubscribed. For various reasons it can make sense to expose more planes, crtcs or encoders than which are physically there. One example is dual-pipe operations (which generally should be hidden from userspace if when lockstepped in hardware, exposed otherwise), where a plane might need 1 hardware plane (if it’s just on one pipe), 2 hardware planes (when it spans both pipes) or maybe even shared a hardware plane with a 2nd plane (if there’s a compatible plane requested on the area handled by the other pipe).
  • Check that any transitional state is possible and that if requested, the update can indeed be done in the vblank period without temporarily disabling some functions.
  • Check any other constraints the driver or hardware might have.
  • This callback also needs to correctly fill out the drm_crtc_state in this update to make sure that drm_atomic_crtc_needs_modeset() reflects the nature of the possible update and returns true if and only if the update cannot be applied without tearing within one vblank on that CRTC. The core uses that information to reject updates which require a full modeset (i.e. blanking the screen, or at least pausing updates for a substantial amount of time) if userspace has disallowed that in its request.
  • The driver also does not need to repeat basic input validation like done for the corresponding legacy entry points. The core does that before calling this hook.

See the documentation of atomic_commit for an exhaustive list of error conditions which don’t have to be checked at the in this callback.

See the documentation for struct drm_atomic_state for how exactly an atomic modeset update is described.

Drivers using the atomic helpers can implement this hook using drm_atomic_helper_check(), or one of the exported sub-functions of it.

RETURNS:

0 on success or one of the below negative error codes:

  • -EINVAL, if any of the above constraints are violated.
  • -EDEADLK, when returned from an attempt to acquire an additional drm_modeset_lock through drm_modeset_lock().
  • -ENOMEM, if allocating additional state sub-structures failed due to lack of memory.
  • -EINTR, -EAGAIN or -ERESTARTSYS, if the IOCTL should be restarted. This can either be due to a pending signal, or because the driver needs to completely bail out to recover from an exceptional situation like a GPU hang. From a userspace point all errors are treated equally.
atomic_commit

This is the only hook to commit an atomic modeset update. The core guarantees that atomic_check has been called successfully before calling this function, and that nothing has been changed in the interim.

See the documentation for struct drm_atomic_state for how exactly an atomic modeset update is described.

Drivers using the atomic helpers can implement this hook using drm_atomic_helper_commit(), or one of the exported sub-functions of it.

Nonblocking commits (as indicated with the nonblock parameter) must do any preparatory work which might result in an unsuccessful commit in the context of this callback. The only exceptions are hardware errors resulting in -EIO. But even in that case the driver must ensure that the display pipe is at least running, to avoid compositors crashing when pageflips don’t work. Anything else, specifically committing the update to the hardware, should be done without blocking the caller. For updates which do not require a modeset this must be guaranteed.

The driver must wait for any pending rendering to the new framebuffers to complete before executing the flip. It should also wait for any pending rendering from other drivers if the underlying buffer is a shared dma-buf. Nonblocking commits must not wait for rendering in the context of this callback.

An application can request to be notified when the atomic commit has completed. These events are per-CRTC and can be distinguished by the CRTC index supplied in drm_event to userspace.

The drm core will supply a struct drm_event in each CRTC’s drm_crtc_state.event. See the documentation for drm_crtc_state.event for more details about the precise semantics of this event.

NOTE:

Drivers are not allowed to shut down any display pipe successfully enabled through an atomic commit on their own. Doing so can result in compositors crashing if a page flip is suddenly rejected because the pipe is off.

RETURNS:

0 on success or one of the below negative error codes:

  • -EBUSY, if a nonblocking updated is requested and there is an earlier updated pending. Drivers are allowed to support a queue of outstanding updates, but currently no driver supports that. Note that drivers must wait for preceding updates to complete if a synchronous update is requested, they are not allowed to fail the commit in that case.
  • -ENOMEM, if the driver failed to allocate memory. Specifically this can happen when trying to pin framebuffers, which must only be done when committing the state.
  • -ENOSPC, as a refinement of the more generic -ENOMEM to indicate that the driver has run out of vram, iommu space or similar GPU address space needed for framebuffer.
  • -EIO, if the hardware completely died.
  • -EINTR, -EAGAIN or -ERESTARTSYS, if the IOCTL should be restarted. This can either be due to a pending signal, or because the driver needs to completely bail out to recover from an exceptional situation like a GPU hang. From a userspace point of view all errors are treated equally.

This list is exhaustive. Specifically this hook is not allowed to return -EINVAL (any invalid requests should be caught in atomic_check) or -EDEADLK (this function must not acquire additional modeset locks).

atomic_state_alloc

This optional hook can be used by drivers that want to subclass struct drm_atomic_state to be able to track their own driver-private global state easily. If this hook is implemented, drivers must also implement atomic_state_clear and atomic_state_free.

Subclassing of drm_atomic_state is deprecated in favour of using drm_private_state and drm_private_obj.

RETURNS:

A new drm_atomic_state on success or NULL on failure.

atomic_state_clear

This hook must clear any driver private state duplicated into the passed-in drm_atomic_state. This hook is called when the caller encountered a drm_modeset_lock deadlock and needs to drop all already acquired locks as part of the deadlock avoidance dance implemented in drm_modeset_backoff().

Any duplicated state must be invalidated since a concurrent atomic update might change it, and the drm atomic interfaces always apply updates as relative changes to the current state.

Drivers that implement this must call drm_atomic_state_default_clear() to clear common state.

Subclassing of drm_atomic_state is deprecated in favour of using drm_private_state and drm_private_obj.

atomic_state_free

This hook needs driver private resources and the drm_atomic_state itself. Note that the core first calls drm_atomic_state_clear() to avoid code duplicate between the clear and free hooks.

Drivers that implement this must call drm_atomic_state_default_release() to release common resources.

Subclassing of drm_atomic_state is deprecated in favour of using drm_private_state and drm_private_obj.

Description

Some global (i.e. not per-CRTC, connector, etc) mode setting functions that involve drivers.

struct drm_mode_config

Mode configuration control structure

Definition

struct drm_mode_config {
  struct mutex mutex;
  struct drm_modeset_lock connection_mutex;
  struct drm_modeset_acquire_ctx *acquire_ctx;
  struct mutex idr_mutex;
  struct idr crtc_idr;
  struct idr tile_idr;
  struct mutex fb_lock;
  int num_fb;
  struct list_head fb_list;
  spinlock_t connector_list_lock;
  int num_connector;
  struct ida connector_ida;
  struct list_head connector_list;
  struct llist_head connector_free_list;
  struct work_struct connector_free_work;
  int num_encoder;
  struct list_head encoder_list;
  int num_total_plane;
  struct list_head plane_list;
  int num_crtc;
  struct list_head crtc_list;
  struct list_head property_list;
  int min_width, min_height;
  int max_width, max_height;
  const struct drm_mode_config_funcs *funcs;
  resource_size_t fb_base;
  bool poll_enabled;
  bool poll_running;
  bool delayed_event;
  struct delayed_work output_poll_work;
  struct mutex blob_lock;
  struct list_head property_blob_list;
  struct drm_property *edid_property;
  struct drm_property *dpms_property;
  struct drm_property *path_property;
  struct drm_property *tile_property;
  struct drm_property *link_status_property;
  struct drm_property *plane_type_property;
  struct drm_property *prop_src_x;
  struct drm_property *prop_src_y;
  struct drm_property *prop_src_w;
  struct drm_property *prop_src_h;
  struct drm_property *prop_crtc_x;
  struct drm_property *prop_crtc_y;
  struct drm_property *prop_crtc_w;
  struct drm_property *prop_crtc_h;
  struct drm_property *prop_fb_id;
  struct drm_property *prop_in_fence_fd;
  struct drm_property *prop_out_fence_ptr;
  struct drm_property *prop_crtc_id;
  struct drm_property *prop_active;
  struct drm_property *prop_mode_id;
  struct drm_property *dvi_i_subconnector_property;
  struct drm_property *dvi_i_select_subconnector_property;
  struct drm_property *tv_subconnector_property;
  struct drm_property *tv_select_subconnector_property;
  struct drm_property *tv_mode_property;
  struct drm_property *tv_left_margin_property;
  struct drm_property *tv_right_margin_property;
  struct drm_property *tv_top_margin_property;
  struct drm_property *tv_bottom_margin_property;
  struct drm_property *tv_brightness_property;
  struct drm_property *tv_contrast_property;
  struct drm_property *tv_flicker_reduction_property;
  struct drm_property *tv_overscan_property;
  struct drm_property *tv_saturation_property;
  struct drm_property *tv_hue_property;
  struct drm_property *scaling_mode_property;
  struct drm_property *aspect_ratio_property;
  struct drm_property *degamma_lut_property;
  struct drm_property *degamma_lut_size_property;
  struct drm_property *ctm_property;
  struct drm_property *gamma_lut_property;
  struct drm_property *gamma_lut_size_property;
  struct drm_property *suggested_x_property;
  struct drm_property *suggested_y_property;
  struct drm_property *non_desktop_property;
  struct drm_property *panel_orientation_property;
  uint32_t preferred_depth, prefer_shadow;
  bool async_page_flip;
  bool allow_fb_modifiers;
  struct drm_property *modifiers_property;
  uint32_t cursor_width, cursor_height;
  struct drm_atomic_state *suspend_state;
  const struct drm_mode_config_helper_funcs *helper_private;
};

Members

mutex

This is the big scary modeset BKL which protects everything that isn’t protect otherwise. Scope is unclear and fuzzy, try to remove anything from under it’s protection and move it into more well-scoped locks.

The one important thing this protects is the use of acquire_ctx.

connection_mutex

This protects connector state and the connector to encoder to CRTC routing chain.

For atomic drivers specifically this protects drm_connector.state.

acquire_ctx
Global implicit acquire context used by atomic drivers for legacy IOCTLs. Deprecated, since implicit locking contexts make it impossible to use driver-private struct drm_modeset_lock. Users of this must hold mutex.
idr_mutex
Mutex for KMS ID allocation and management. Protects both crtc_idr and tile_idr.
crtc_idr
Main KMS ID tracking object. Use this idr for all IDs, fb, crtc, connector, modes - just makes life easier to have only one.
tile_idr
Use this idr for allocating new IDs for tiled sinks like use in some high-res DP MST screens.
fb_lock
Mutex to protect fb the global fb_list and num_fb.
num_fb
Number of entries on fb_list.
fb_list
List of all struct drm_framebuffer.
connector_list_lock
Protects num_connector and connector_list and connector_free_list.
num_connector
Number of connectors on this device. Protected by connector_list_lock.
connector_ida
ID allocator for connector indices.
connector_list
List of connector objects linked with drm_connector.head. Protected by connector_list_lock. Only use drm_for_each_connector_iter() and struct drm_connector_list_iter to walk this list.
connector_free_list
List of connector objects linked with drm_connector.free_head. Protected by connector_list_lock. Used by drm_for_each_connector_iter() and struct drm_connector_list_iter to savely free connectors using connector_free_work.
connector_free_work
Work to clean up connector_free_list.
num_encoder
Number of encoders on this device. This is invariant over the lifetime of a device and hence doesn’t need any locks.
encoder_list
List of encoder objects linked with drm_encoder.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.
num_total_plane
Number of universal (i.e. with primary/curso) planes on this device. This is invariant over the lifetime of a device and hence doesn’t need any locks.
plane_list
List of plane objects linked with drm_plane.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.
num_crtc
Number of CRTCs on this device linked with drm_crtc.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.
crtc_list
List of CRTC objects linked with drm_crtc.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.
property_list
List of property type objects linked with drm_property.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.
min_width
minimum pixel width on this device
min_height
minimum pixel height on this device
max_width
maximum pixel width on this device
max_height
maximum pixel height on this device
funcs
core driver provided mode setting functions
fb_base
base address of the framebuffer
poll_enabled
track polling support for this device
poll_running
track polling status for this device
delayed_event
track delayed poll uevent deliver for this device
output_poll_work
delayed work for polling in process context
blob_lock
Mutex for blob property allocation and management, protects property_blob_list and drm_file.blobs.
property_blob_list
List of all the blob property objects linked with drm_property_blob.head. Protected by blob_lock.
edid_property
Default connector property to hold the EDID of the currently connected sink, if any.
dpms_property
Default connector property to control the connector’s DPMS state.
path_property
Default connector property to hold the DP MST path for the port.
tile_property
Default connector property to store the tile position of a tiled screen, for sinks which need to be driven with multiple CRTCs.
link_status_property
Default connector property for link status of a connector
plane_type_property
Default plane property to differentiate CURSOR, PRIMARY and OVERLAY legacy uses of planes.
prop_src_x
Default atomic plane property for the plane source position in the connected drm_framebuffer.
prop_src_y
Default atomic plane property for the plane source position in the connected drm_framebuffer.
prop_src_w
Default atomic plane property for the plane source position in the connected drm_framebuffer.
prop_src_h
Default atomic plane property for the plane source position in the connected drm_framebuffer.
prop_crtc_x
Default atomic plane property for the plane destination position in the drm_crtc is is being shown on.
prop_crtc_y
Default atomic plane property for the plane destination position in the drm_crtc is is being shown on.
prop_crtc_w
Default atomic plane property for the plane destination position in the drm_crtc is is being shown on.
prop_crtc_h
Default atomic plane property for the plane destination position in the drm_crtc is is being shown on.
prop_fb_id
Default atomic plane property to specify the drm_framebuffer.
prop_in_fence_fd
Sync File fd representing the incoming fences for a Plane.
prop_out_fence_ptr
Sync File fd pointer representing the outgoing fences for a CRTC. Userspace should provide a pointer to a value of type s32, and then cast that pointer to u64.
prop_crtc_id
Default atomic plane property to specify the drm_crtc.
prop_active
Default atomic CRTC property to control the active state, which is the simplified implementation for DPMS in atomic drivers.
prop_mode_id
Default atomic CRTC property to set the mode for a CRTC. A 0 mode implies that the CRTC is entirely disabled - all connectors must be of and active must be set to disabled, too.
dvi_i_subconnector_property
Optional DVI-I property to differentiate between analog or digital mode.
dvi_i_select_subconnector_property
Optional DVI-I property to select between analog or digital mode.
tv_subconnector_property
Optional TV property to differentiate between different TV connector types.
tv_select_subconnector_property
Optional TV property to select between different TV connector types.
tv_mode_property
Optional TV property to select the output TV mode.
tv_left_margin_property
Optional TV property to set the left margin.
tv_right_margin_property
Optional TV property to set the right margin.
tv_top_margin_property
Optional TV property to set the right margin.
tv_bottom_margin_property
Optional TV property to set the right margin.
tv_brightness_property
Optional TV property to set the brightness.
tv_contrast_property
Optional TV property to set the contrast.
tv_flicker_reduction_property
Optional TV property to control the flicker reduction mode.
tv_overscan_property
Optional TV property to control the overscan setting.
tv_saturation_property
Optional TV property to set the saturation.
tv_hue_property
Optional TV property to set the hue.
scaling_mode_property
Optional connector property to control the upscaling, mostly used for built-in panels.
aspect_ratio_property
Optional connector property to control the HDMI infoframe aspect ratio setting.
degamma_lut_property
Optional CRTC property to set the LUT used to convert the framebuffer’s colors to linear gamma.
degamma_lut_size_property
Optional CRTC property for the size of the degamma LUT as supported by the driver (read-only).
ctm_property
Optional CRTC property to set the matrix used to convert colors after the lookup in the degamma LUT.
gamma_lut_property
Optional CRTC property to set the LUT used to convert the colors, after the CTM matrix, to the gamma space of the connected screen.
gamma_lut_size_property
Optional CRTC property for the size of the gamma LUT as supported by the driver (read-only).
suggested_x_property
Optional connector property with a hint for the position of the output on the host’s screen.
suggested_y_property
Optional connector property with a hint for the position of the output on the host’s screen.
non_desktop_property
Optional connector property with a hint that device isn’t a standard display, and the console/desktop, should not be displayed on it.
panel_orientation_property
Optional connector property indicating how the lcd-panel is mounted inside the casing (e.g. normal or upside-down).
preferred_depth
preferred RBG pixel depth, used by fb helpers
prefer_shadow
hint to userspace to prefer shadow-fb rendering
async_page_flip
Does this device support async flips on the primary plane?
allow_fb_modifiers
Whether the driver supports fb modifiers in the ADDFB2.1 ioctl call.
modifiers_property
Plane property to list support modifier/format combination.
cursor_width
hint to userspace for max cursor width
cursor_height
hint to userspace for max cursor height
suspend_state
Atomic state when suspended. Set by drm_mode_config_helper_suspend() and cleared by drm_mode_config_helper_resume().
helper_private
mid-layer private data

Description

Core mode resource tracking structure. All CRTC, encoders, and connectors enumerated by the driver are added here, as are global properties. Some global restrictions are also here, e.g. dimension restrictions.

void drm_mode_config_reset(struct drm_device * dev)

call ->reset callbacks

Parameters

struct drm_device * dev
drm device

Description

This functions calls all the crtc’s, encoder’s and connector’s ->reset callback. Drivers can use this in e.g. their driver load or resume code to reset hardware and software state.

void drm_mode_config_init(struct drm_device * dev)

initialize DRM mode_configuration structure

Parameters

struct drm_device * dev
DRM device

Description

Initialize dev‘s mode_config structure, used for tracking the graphics configuration of dev.

Since this initializes the modeset locks, no locking is possible. Which is no problem, since this should happen single threaded at init time. It is the driver’s problem to ensure this guarantee.

void drm_mode_config_cleanup(struct drm_device * dev)

free up DRM mode_config info

Parameters

struct drm_device * dev
DRM device

Description

Free up all the connectors and CRTCs associated with this DRM device, then free up the framebuffers and associated buffer objects.

Note that since this /should/ happen single-threaded at driver/device teardown time, no locking is required. It’s the driver’s job to ensure that this guarantee actually holds true.

FIXME: cleanup any dangling user buffer objects too

Modeset Base Object Abstraction

digraph {
   node [shape=box]

   "drm_property A" -> "drm_mode_object A"
   "drm_property A" -> "drm_mode_object B"
   "drm_property B" -> "drm_mode_object A"
}

Mode Objects and Properties

The base structure for all KMS objects is struct drm_mode_object. One of the base services it provides is tracking properties, which are especially important for the atomic IOCTL (see Atomic Mode Setting). The somewhat surprising part here is that properties are not directly instantiated on each object, but free-standing mode objects themselves, represented by struct drm_property, which only specify the type and value range of a property. Any given property can be attached multiple times to different objects using drm_object_attach_property().

struct drm_mode_object

base structure for modeset objects

Definition

struct drm_mode_object {
  uint32_t id;
  uint32_t type;
  struct drm_object_properties *properties;
  struct kref refcount;
  void (*free_cb)(struct kref *kref);
};

Members

id
userspace visible identifier
type
type of the object, one of DRM_MODE_OBJECT_*
properties
properties attached to this object, including values
refcount
reference count for objects which with dynamic lifetime
free_cb
free function callback, only set for objects with dynamic lifetime

Description

Base structure for modeset objects visible to userspace. Objects can be looked up using drm_mode_object_find(). Besides basic uapi interface properties like id and type it provides two services:

struct drm_object_properties

property tracking for drm_mode_object

Definition

struct drm_object_properties {
  int count;
  struct drm_property *properties[DRM_OBJECT_MAX_PROPERTY];
  uint64_t values[DRM_OBJECT_MAX_PROPERTY];
};

Members

count
number of valid properties, must be less than or equal to DRM_OBJECT_MAX_PROPERTY.
properties

Array of pointers to drm_property.

NOTE: if we ever start dynamically destroying properties (ie. not at drm_mode_config_cleanup() time), then we’d have to do a better job of detaching property from mode objects to avoid dangling property pointers:

values

Array to store the property values, matching properties. Do not read/write values directly, but use drm_object_property_get_value() and drm_object_property_set_value().

Note that atomic drivers do not store mutable properties in this array, but only the decoded values in the corresponding state structure. The decoding is done using the drm_crtc.atomic_get_property and drm_crtc.atomic_set_property hooks for struct drm_crtc. For struct drm_plane the hooks are drm_plane_funcs.atomic_get_property and drm_plane_funcs.atomic_set_property. And for struct drm_connector the hooks are drm_connector_funcs.atomic_get_property and drm_connector_funcs.atomic_set_property .

Hence atomic drivers should not use drm_object_property_set_value() and drm_object_property_get_value() on mutable objects, i.e. those without the DRM_MODE_PROP_IMMUTABLE flag set.

struct drm_mode_object * drm_mode_object_find(struct drm_device * dev, struct drm_file * file_priv, uint32_t id, uint32_t type)

look up a drm object with static lifetime

Parameters

struct drm_device * dev
drm device
struct drm_file * file_priv
drm file
uint32_t id
id of the mode object
uint32_t type
type of the mode object

Description

This function is used to look up a modeset object. It will acquire a reference for reference counted objects. This reference must be dropped again by callind drm_mode_object_put().

void drm_mode_object_put(struct drm_mode_object * obj)

release a mode object reference

Parameters

struct drm_mode_object * obj
DRM mode object

Description

This function decrements the object’s refcount if it is a refcounted modeset object. It is a no-op on any other object. This is used to drop references acquired with drm_mode_object_get().

void drm_mode_object_get(struct drm_mode_object * obj)

acquire a mode object reference

Parameters

struct drm_mode_object * obj
DRM mode object

Description

This function increments the object’s refcount if it is a refcounted modeset object. It is a no-op on any other object. References should be dropped again by calling drm_mode_object_put().

void drm_object_attach_property(struct drm_mode_object * obj, struct drm_property * property, uint64_t init_val)

attach a property to a modeset object

Parameters

struct drm_mode_object * obj
drm modeset object
struct drm_property * property
property to attach
uint64_t init_val
initial value of the property

Description

This attaches the given property to the modeset object with the given initial value. Currently this function cannot fail since the properties are stored in a statically sized array.

int drm_object_property_set_value(struct drm_mode_object * obj, struct drm_property * property, uint64_t val)

set the value of a property

Parameters

struct drm_mode_object * obj
drm mode object to set property value for
struct drm_property * property
property to set
uint64_t val
value the property should be set to

Description

This function sets a given property on a given object. This function only changes the software state of the property, it does not call into the driver’s ->set_property callback.

Note that atomic drivers should not have any need to call this, the core will ensure consistency of values reported back to userspace through the appropriate ->atomic_get_property callback. Only legacy drivers should call this function to update the tracked value (after clamping and other restrictions have been applied).

Return

Zero on success, error code on failure.

int drm_object_property_get_value(struct drm_mode_object * obj, struct drm_property * property, uint64_t * val)

retrieve the value of a property

Parameters

struct drm_mode_object * obj
drm mode object to get property value from
struct drm_property * property
property to retrieve
uint64_t * val
storage for the property value

Description

This function retrieves the softare state of the given property for the given property. Since there is no driver callback to retrieve the current property value this might be out of sync with the hardware, depending upon the driver and property.

Atomic drivers should never call this function directly, the core will read out property values through the various ->atomic_get_property callbacks.

Return

Zero on success, error code on failure.

Atomic Mode Setting

digraph {
   node [shape=box]

   subgraph cluster_state {
       style=dashed
       label="Free-standing state"

       "drm_atomic_state" -> "duplicated drm_plane_state A"
       "drm_atomic_state" -> "duplicated drm_plane_state B"
       "drm_atomic_state" -> "duplicated drm_crtc_state"
       "drm_atomic_state" -> "duplicated drm_connector_state"
       "drm_atomic_state" -> "duplicated driver private state"
   }

   subgraph cluster_current {
       style=dashed
       label="Current state"

       "drm_device" -> "drm_plane A"
       "drm_device" -> "drm_plane B"
       "drm_device" -> "drm_crtc"
       "drm_device" -> "drm_connector"
       "drm_device" -> "driver private object"

       "drm_plane A" -> "drm_plane_state A"
       "drm_plane B" -> "drm_plane_state B"
       "drm_crtc" -> "drm_crtc_state"
       "drm_connector" -> "drm_connector_state"
       "driver private object" -> "driver private state"
   }

   "drm_atomic_state" -> "drm_device" [label="atomic_commit"]
   "duplicated drm_plane_state A" -> "drm_device"[style=invis]
}

Mode Objects and Properties

Atomic provides transactional modeset (including planes) updates, but a bit differently from the usual transactional approach of try-commit and rollback:

  • Firstly, no hardware changes are allowed when the commit would fail. This allows us to implement the DRM_MODE_ATOMIC_TEST_ONLY mode, which allows userspace to explore whether certain configurations would work or not.
  • This would still allow setting and rollback of just the software state, simplifying conversion of existing drivers. But auditing drivers for correctness of the atomic_check code becomes really hard with that: Rolling back changes in data structures all over the place is hard to get right.
  • Lastly, for backwards compatibility and to support all use-cases, atomic updates need to be incremental and be able to execute in parallel. Hardware doesn’t always allow it, but where possible plane updates on different CRTCs should not interfere, and not get stalled due to output routing changing on different CRTCs.

Taken all together there’s two consequences for the atomic design:

  • The overall state is split up into per-object state structures: struct drm_plane_state for planes, struct drm_crtc_state for CRTCs and struct drm_connector_state for connectors. These are the only objects with userspace-visible and settable state. For internal state drivers can subclass these structures through embeddeding, or add entirely new state structures for their globally shared hardware functions.
  • An atomic update is assembled and validated as an entirely free-standing pile of structures within the drm_atomic_state container. Driver private state structures are also tracked in the same structure; see the next chapter. Only when a state is committed is it applied to the driver and modeset objects. This way rolling back an update boils down to releasing memory and unreferencing objects like framebuffers.

Read on in this chapter, and also in Atomic Modeset Helper Functions Reference for more detailed coverage of specific topics.

Handling Driver Private State

Very often the DRM objects exposed to userspace in the atomic modeset api (drm_connector, drm_crtc and drm_plane) do not map neatly to the underlying hardware. Especially for any kind of shared resources (e.g. shared clocks, scaler units, bandwidth and fifo limits shared among a group of planes or CRTCs, and so on) it makes sense to model these as independent objects. Drivers then need to do similar state tracking and commit ordering for such private (since not exposed to userpace) objects as the atomic core and helpers already provide for connectors, planes and CRTCs.

To make this easier on drivers the atomic core provides some support to track driver private state objects using struct drm_private_obj, with the associated state struct drm_private_state.

Similar to userspace-exposed objects, private state structures can be acquired by calling drm_atomic_get_private_obj_state(). Since this function does not take care of locking, drivers should wrap it for each type of private state object they have with the required call to drm_modeset_lock() for the corresponding drm_modeset_lock.

All private state structures contained in a drm_atomic_state update can be iterated using for_each_oldnew_private_obj_in_state(), for_each_new_private_obj_in_state() and for_each_old_private_obj_in_state(). Drivers are recommended to wrap these for each type of driver private state object they have, filtering on drm_private_obj.funcs using for_each_if(), at least if they want to iterate over all objects of a given type.

An earlier way to handle driver private state was by subclassing struct drm_atomic_state. But since that encourages non-standard ways to implement the check/commit split atomic requires (by using e.g. “check and rollback or commit instead” of “duplicate state, check, then either commit or release duplicated state) it is deprecated in favour of using drm_private_state.

Atomic Mode Setting Function Reference

struct drm_crtc_commit

track modeset commits on a CRTC

Definition

struct drm_crtc_commit {
  struct drm_crtc *crtc;
  struct kref ref;
  struct completion flip_done;
  struct completion hw_done;
  struct completion cleanup_done;
  struct list_head commit_entry;
  struct drm_pending_vblank_event *event;
  bool abort_completion;
};

Members

crtc
DRM CRTC for this commit.
ref
Reference count for this structure. Needed to allow blocking on completions without the risk of the completion disappearing meanwhile.
flip_done
Will be signaled when the hardware has flipped to the new set of buffers. Signals at the same time as when the drm event for this commit is sent to userspace, or when an out-fence is singalled. Note that for most hardware, in most cases this happens after hw_done is signalled.
hw_done

Will be signalled when all hw register changes for this commit have been written out. Especially when disabling a pipe this can be much later than than flip_done, since that can signal already when the screen goes black, whereas to fully shut down a pipe more register I/O is required.

Note that this does not need to include separately reference-counted resources like backing storage buffer pinning, or runtime pm management.

cleanup_done
Will be signalled after old buffers have been cleaned up by calling drm_atomic_helper_cleanup_planes(). Since this can only happen after a vblank wait completed it might be a bit later. This completion is useful to throttle updates and avoid hardware updates getting ahead of the buffer cleanup too much.
commit_entry
Entry on the per-CRTC drm_crtc.commit_list. Protected by $drm_crtc.commit_lock.
event
drm_pending_vblank_event pointer to clean up private events.
abort_completion
A flag that’s set after drm_atomic_helper_setup_commit takes a second reference for the completion of $drm_crtc_state.event. It’s used by the free code to remove the second reference if commit fails.

Description

This structure is used to track pending modeset changes and atomic commit on a per-CRTC basis. Since updating the list should never block this structure is reference counted to allow waiters to safely wait on an event to complete, without holding any locks.

It has 3 different events in total to allow a fine-grained synchronization between outstanding updates:

atomic commit thread                    hardware

write new state into hardware   ---->   ...
signal hw_done
                                        switch to new state on next
...                                     v/hblank

wait for buffers to show up             ...

...                                     send completion irq
                                        irq handler signals flip_done
cleanup old buffers

signal cleanup_done

wait for flip_done              <----
clean up atomic state

The important bit to know is that cleanup_done is the terminal event, but the ordering between flip_done and hw_done is entirely up to the specific driver and modeset state change.

For an implementation of how to use this look at drm_atomic_helper_setup_commit() from the atomic helper library.

struct drm_private_state_funcs

atomic state functions for private objects

Definition

struct drm_private_state_funcs {
  struct drm_private_state *(*atomic_duplicate_state)(struct drm_private_obj *obj);
  void (*atomic_destroy_state)(struct drm_private_obj *obj, struct drm_private_state *state);
};

Members

atomic_duplicate_state

Duplicate the current state of the private object and return it. It is an error to call this before obj->state has been initialized.

RETURNS:

Duplicated atomic state or NULL when obj->state is not initialized or allocation failed.

atomic_destroy_state
Frees the private object state created with atomic_duplicate_state.

Description

These hooks are used by atomic helpers to create, swap and destroy states of private objects. The structure itself is used as a vtable to identify the associated private object type. Each private object type that needs to be added to the atomic states is expected to have an implementation of these hooks and pass a pointer to it’s drm_private_state_funcs struct to drm_atomic_get_private_obj_state().

struct drm_private_obj

base struct for driver private atomic object

Definition

struct drm_private_obj {
  struct drm_private_state *state;
  const struct drm_private_state_funcs *funcs;
};

Members

state
Current atomic state for this driver private object.
funcs
Functions to manipulate the state of this driver private object, see drm_private_state_funcs.

Description

A driver private object is initialized by calling drm_atomic_private_obj_init() and cleaned up by calling drm_atomic_private_obj_fini().

Currently only tracks the state update functions and the opaque driver private state itself, but in the future might also track which drm_modeset_lock is required to duplicate and update this object’s state.

struct drm_private_state

base struct for driver private object state

Definition

struct drm_private_state {
  struct drm_atomic_state *state;
};

Members

state
backpointer to global drm_atomic_state

Description

Currently only contains a backpointer to the overall atomic update, but in the future also might hold synchronization information similar to e.g. drm_crtc.commit.

struct drm_atomic_state

the global state object for atomic updates

Definition

struct drm_atomic_state {
  struct kref ref;
  struct drm_device *dev;
  bool allow_modeset : 1;
  bool legacy_cursor_update : 1;
  bool async_update : 1;
  struct __drm_planes_state *planes;
  struct __drm_crtcs_state *crtcs;
  int num_connector;
  struct __drm_connnectors_state *connectors;
  int num_private_objs;
  struct __drm_private_objs_state *private_objs;
  struct drm_modeset_acquire_ctx *acquire_ctx;
  struct drm_crtc_commit *fake_commit;
  struct work_struct commit_work;
};

Members

ref
count of all references to this state (will not be freed until zero)
dev
parent DRM device
allow_modeset
allow full modeset
legacy_cursor_update
hint to enforce legacy cursor IOCTL semantics
async_update
hint for asynchronous plane update
planes
pointer to array of structures with per-plane data
crtcs
pointer to array of CRTC pointers
num_connector
size of the connectors and connector_states arrays
connectors
pointer to array of structures with per-connector data
num_private_objs
size of the private_objs array
private_objs
pointer to array of private object pointers
acquire_ctx
acquire context for this atomic modeset state update
fake_commit

Used for signaling unbound planes/connectors. When a connector or plane is not bound to any CRTC, it’s still important to preserve linearity to prevent the atomic states from being freed to early.

This commit (if set) is not bound to any crtc, but will be completed when drm_atomic_helper_commit_hw_done() is called.

commit_work
Work item which can be used by the driver or helpers to execute the commit without blocking.

Description

States are added to an atomic update by calling drm_atomic_get_crtc_state(), drm_atomic_get_plane_state(), drm_atomic_get_connector_state(), or for private state structures, drm_atomic_get_private_obj_state().

struct drm_crtc_commit * drm_crtc_commit_get(struct drm_crtc_commit * commit)

acquire a reference to the CRTC commit

Parameters

struct drm_crtc_commit * commit
CRTC commit

Description

Increases the reference of commit.

Return

The pointer to commit, with reference increased.

void drm_crtc_commit_put(struct drm_crtc_commit * commit)

release a reference to the CRTC commmit

Parameters

struct drm_crtc_commit * commit
CRTC commit

Description

This releases a reference to commit which is freed after removing the final reference. No locking required and callable from any context.

struct drm_atomic_state * drm_atomic_state_get(struct drm_atomic_state * state)

acquire a reference to the atomic state

Parameters

struct drm_atomic_state * state
The atomic state

Description

Returns a new reference to the state

void drm_atomic_state_put(struct drm_atomic_state * state)

release a reference to the atomic state

Parameters

struct drm_atomic_state * state
The atomic state

Description

This releases a reference to state which is freed after removing the final reference. No locking required and callable from any context.

struct drm_crtc_state * drm_atomic_get_existing_crtc_state(struct drm_atomic_state * state, struct drm_crtc * crtc)

get crtc state, if it exists

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_crtc * crtc
crtc to grab

Description

This function returns the crtc state for the given crtc, or NULL if the crtc is not part of the global atomic state.

This function is deprecated, drm_atomic_get_old_crtc_state or drm_atomic_get_new_crtc_state should be used instead.

struct drm_crtc_state * drm_atomic_get_old_crtc_state(struct drm_atomic_state * state, struct drm_crtc * crtc)

get old crtc state, if it exists

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_crtc * crtc
crtc to grab

Description

This function returns the old crtc state for the given crtc, or NULL if the crtc is not part of the global atomic state.

struct drm_crtc_state * drm_atomic_get_new_crtc_state(struct drm_atomic_state * state, struct drm_crtc * crtc)

get new crtc state, if it exists

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_crtc * crtc
crtc to grab

Description

This function returns the new crtc state for the given crtc, or NULL if the crtc is not part of the global atomic state.

struct drm_plane_state * drm_atomic_get_existing_plane_state(struct drm_atomic_state * state, struct drm_plane * plane)

get plane state, if it exists

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_plane * plane
plane to grab

Description

This function returns the plane state for the given plane, or NULL if the plane is not part of the global atomic state.

This function is deprecated, drm_atomic_get_old_plane_state or drm_atomic_get_new_plane_state should be used instead.

struct drm_plane_state * drm_atomic_get_old_plane_state(struct drm_atomic_state * state, struct drm_plane * plane)

get plane state, if it exists

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_plane * plane
plane to grab

Description

This function returns the old plane state for the given plane, or NULL if the plane is not part of the global atomic state.

struct drm_plane_state * drm_atomic_get_new_plane_state(struct drm_atomic_state * state, struct drm_plane * plane)

get plane state, if it exists

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_plane * plane
plane to grab

Description

This function returns the new plane state for the given plane, or NULL if the plane is not part of the global atomic state.

struct drm_connector_state * drm_atomic_get_existing_connector_state(struct drm_atomic_state * state, struct drm_connector * connector)

get connector state, if it exists

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_connector * connector
connector to grab

Description

This function returns the connector state for the given connector, or NULL if the connector is not part of the global atomic state.

This function is deprecated, drm_atomic_get_old_connector_state or drm_atomic_get_new_connector_state should be used instead.

struct drm_connector_state * drm_atomic_get_old_connector_state(struct drm_atomic_state * state, struct drm_connector * connector)

get connector state, if it exists

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_connector * connector
connector to grab

Description

This function returns the old connector state for the given connector, or NULL if the connector is not part of the global atomic state.

struct drm_connector_state * drm_atomic_get_new_connector_state(struct drm_atomic_state * state, struct drm_connector * connector)

get connector state, if it exists

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_connector * connector
connector to grab

Description

This function returns the new connector state for the given connector, or NULL if the connector is not part of the global atomic state.

const struct drm_plane_state * __drm_atomic_get_current_plane_state(struct drm_atomic_state * state, struct drm_plane * plane)

get current plane state

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_plane * plane
plane to grab

Description

This function returns the plane state for the given plane, either from state, or if the plane isn’t part of the atomic state update, from plane. This is useful in atomic check callbacks, when drivers need to peek at, but not change, state of other planes, since it avoids threading an error code back up the call chain.

WARNING:

Note that this function is in general unsafe since it doesn’t check for the required locking for access state structures. Drivers must ensure that it is safe to access the returned state structure through other means. One common example is when planes are fixed to a single CRTC, and the driver knows that the CRTC lock is held already. In that case holding the CRTC lock gives a read-lock on all planes connected to that CRTC. But if planes can be reassigned things get more tricky. In that case it’s better to use drm_atomic_get_plane_state and wire up full error handling.

Return

Read-only pointer to the current plane state.

for_each_oldnew_connector_in_state(__state, connector, old_connector_state, new_connector_state, __i)

iterate over all connectors in an atomic update

Parameters

__state
struct drm_atomic_state pointer
connector
struct drm_connector iteration cursor
old_connector_state
struct drm_connector_state iteration cursor for the old state
new_connector_state
struct drm_connector_state iteration cursor for the new state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all connectors in an atomic update, tracking both old and new state. This is useful in places where the state delta needs to be considered, for example in atomic check functions.

for_each_old_connector_in_state(__state, connector, old_connector_state, __i)

iterate over all connectors in an atomic update

Parameters

__state
struct drm_atomic_state pointer
connector
struct drm_connector iteration cursor
old_connector_state
struct drm_connector_state iteration cursor for the old state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all connectors in an atomic update, tracking only the old state. This is useful in disable functions, where we need the old state the hardware is still in.

for_each_new_connector_in_state(__state, connector, new_connector_state, __i)

iterate over all connectors in an atomic update

Parameters

__state
struct drm_atomic_state pointer
connector
struct drm_connector iteration cursor
new_connector_state
struct drm_connector_state iteration cursor for the new state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all connectors in an atomic update, tracking only the new state. This is useful in enable functions, where we need the new state the hardware should be in when the atomic commit operation has completed.

for_each_oldnew_crtc_in_state(__state, crtc, old_crtc_state, new_crtc_state, __i)

iterate over all CRTCs in an atomic update

Parameters

__state
struct drm_atomic_state pointer
crtc
struct drm_crtc iteration cursor
old_crtc_state
struct drm_crtc_state iteration cursor for the old state
new_crtc_state
struct drm_crtc_state iteration cursor for the new state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all CRTCs in an atomic update, tracking both old and new state. This is useful in places where the state delta needs to be considered, for example in atomic check functions.

for_each_old_crtc_in_state(__state, crtc, old_crtc_state, __i)

iterate over all CRTCs in an atomic update

Parameters

__state
struct drm_atomic_state pointer
crtc
struct drm_crtc iteration cursor
old_crtc_state
struct drm_crtc_state iteration cursor for the old state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all CRTCs in an atomic update, tracking only the old state. This is useful in disable functions, where we need the old state the hardware is still in.

for_each_new_crtc_in_state(__state, crtc, new_crtc_state, __i)

iterate over all CRTCs in an atomic update

Parameters

__state
struct drm_atomic_state pointer
crtc
struct drm_crtc iteration cursor
new_crtc_state
struct drm_crtc_state iteration cursor for the new state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all CRTCs in an atomic update, tracking only the new state. This is useful in enable functions, where we need the new state the hardware should be in when the atomic commit operation has completed.

for_each_oldnew_plane_in_state(__state, plane, old_plane_state, new_plane_state, __i)

iterate over all planes in an atomic update

Parameters

__state
struct drm_atomic_state pointer
plane
struct drm_plane iteration cursor
old_plane_state
struct drm_plane_state iteration cursor for the old state
new_plane_state
struct drm_plane_state iteration cursor for the new state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all planes in an atomic update, tracking both old and new state. This is useful in places where the state delta needs to be considered, for example in atomic check functions.

for_each_oldnew_plane_in_state_reverse(__state, plane, old_plane_state, new_plane_state, __i)

iterate over all planes in an atomic update in reverse order

Parameters

__state
struct drm_atomic_state pointer
plane
struct drm_plane iteration cursor
old_plane_state
struct drm_plane_state iteration cursor for the old state
new_plane_state
struct drm_plane_state iteration cursor for the new state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all planes in an atomic update in reverse order, tracking both old and new state. This is useful in places where the state delta needs to be considered, for example in atomic check functions.

for_each_old_plane_in_state(__state, plane, old_plane_state, __i)

iterate over all planes in an atomic update

Parameters

__state
struct drm_atomic_state pointer
plane
struct drm_plane iteration cursor
old_plane_state
struct drm_plane_state iteration cursor for the old state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all planes in an atomic update, tracking only the old state. This is useful in disable functions, where we need the old state the hardware is still in.

for_each_new_plane_in_state(__state, plane, new_plane_state, __i)

iterate over all planes in an atomic update

Parameters

__state
struct drm_atomic_state pointer
plane
struct drm_plane iteration cursor
new_plane_state
struct drm_plane_state iteration cursor for the new state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all planes in an atomic update, tracking only the new state. This is useful in enable functions, where we need the new state the hardware should be in when the atomic commit operation has completed.

for_each_oldnew_private_obj_in_state(__state, obj, old_obj_state, new_obj_state, __i)

iterate over all private objects in an atomic update

Parameters

__state
struct drm_atomic_state pointer
obj
struct drm_private_obj iteration cursor
old_obj_state
struct drm_private_state iteration cursor for the old state
new_obj_state
struct drm_private_state iteration cursor for the new state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all private objects in an atomic update, tracking both old and new state. This is useful in places where the state delta needs to be considered, for example in atomic check functions.

for_each_old_private_obj_in_state(__state, obj, old_obj_state, __i)

iterate over all private objects in an atomic update

Parameters

__state
struct drm_atomic_state pointer
obj
struct drm_private_obj iteration cursor
old_obj_state
struct drm_private_state iteration cursor for the old state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all private objects in an atomic update, tracking only the old state. This is useful in disable functions, where we need the old state the hardware is still in.

for_each_new_private_obj_in_state(__state, obj, new_obj_state, __i)

iterate over all private objects in an atomic update

Parameters

__state
struct drm_atomic_state pointer
obj
struct drm_private_obj iteration cursor
new_obj_state
struct drm_private_state iteration cursor for the new state
__i
int iteration cursor, for macro-internal use

Description

This iterates over all private objects in an atomic update, tracking only the new state. This is useful in enable functions, where we need the new state the hardware should be in when the atomic commit operation has completed.

bool drm_atomic_crtc_needs_modeset(const struct drm_crtc_state * state)

compute combined modeset need

Parameters

const struct drm_crtc_state * state
drm_crtc_state for the CRTC

Description

To give drivers flexibility struct drm_crtc_state has 3 booleans to track whether the state CRTC changed enough to need a full modeset cycle: mode_changed, active_changed and connectors_changed. This helper simply combines these three to compute the overall need for a modeset for state.

The atomic helper code sets these booleans, but drivers can and should change them appropriately to accurately represent whether a modeset is really needed. In general, drivers should avoid full modesets whenever possible.

For example if the CRTC mode has changed, and the hardware is able to enact the requested mode change without going through a full modeset, the driver should clear mode_changed in its drm_mode_config_funcs.atomic_check implementation.

void drm_atomic_state_default_release(struct drm_atomic_state * state)

release memory initialized by drm_atomic_state_init

Parameters

struct drm_atomic_state * state
atomic state

Description

Free all the memory allocated by drm_atomic_state_init. This should only be used by drivers which are still subclassing drm_atomic_state and haven’t switched to drm_private_state yet.

int drm_atomic_state_init(struct drm_device * dev, struct drm_atomic_state * state)

init new atomic state

Parameters

struct drm_device * dev
DRM device
struct drm_atomic_state * state
atomic state

Description

Default implementation for filling in a new atomic state. This should only be used by drivers which are still subclassing drm_atomic_state and haven’t switched to drm_private_state yet.

struct drm_atomic_state * drm_atomic_state_alloc(struct drm_device * dev)

allocate atomic state

Parameters

struct drm_device * dev
DRM device

Description

This allocates an empty atomic state to track updates.

void drm_atomic_state_default_clear(struct drm_atomic_state * state)

clear base atomic state

Parameters

struct drm_atomic_state * state
atomic state

Description

Default implementation for clearing atomic state. This should only be used by drivers which are still subclassing drm_atomic_state and haven’t switched to drm_private_state yet.

void drm_atomic_state_clear(struct drm_atomic_state * state)

clear state object

Parameters

struct drm_atomic_state * state
atomic state

Description

When the w/w mutex algorithm detects a deadlock we need to back off and drop all locks. So someone else could sneak in and change the current modeset configuration. Which means that all the state assembled in state is no longer an atomic update to the current state, but to some arbitrary earlier state. Which could break assumptions the driver’s drm_mode_config_funcs.atomic_check likely relies on.

Hence we must clear all cached state and completely start over, using this function.

void __drm_atomic_state_free(struct kref * ref)

free all memory for an atomic state

Parameters

struct kref * ref
This atomic state to deallocate

Description

This frees all memory associated with an atomic state, including all the per-object state for planes, crtcs and connectors.

struct drm_crtc_state * drm_atomic_get_crtc_state(struct drm_atomic_state * state, struct drm_crtc * crtc)

get crtc state

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_crtc * crtc
crtc to get state object for

Description

This function returns the crtc state for the given crtc, allocating it if needed. It will also grab the relevant crtc lock to make sure that the state is consistent.

Return

Either the allocated state or the error code encoded into the pointer. When the error is EDEADLK then the w/w mutex code has detected a deadlock and the entire atomic sequence must be restarted. All other errors are fatal.

int drm_atomic_set_mode_for_crtc(struct drm_crtc_state * state, const struct drm_display_mode * mode)

set mode for CRTC

Parameters

struct drm_crtc_state * state
the CRTC whose incoming state to update
const struct drm_display_mode * mode
kernel-internal mode to use for the CRTC, or NULL to disable

Description

Set a mode (originating from the kernel) on the desired CRTC state and update the enable property.

Return

Zero on success, error code on failure. Cannot return -EDEADLK.

int drm_atomic_set_mode_prop_for_crtc(struct drm_crtc_state * state, struct drm_property_blob * blob)

set mode for CRTC

Parameters

struct drm_crtc_state * state
the CRTC whose incoming state to update
struct drm_property_blob * blob
pointer to blob property to use for mode

Description

Set a mode (originating from a blob property) on the desired CRTC state. This function will take a reference on the blob property for the CRTC state, and release the reference held on the state’s existing mode property, if any was set.

Return

Zero on success, error code on failure. Cannot return -EDEADLK.

int drm_atomic_crtc_set_property(struct drm_crtc * crtc, struct drm_crtc_state * state, struct drm_property * property, uint64_t val)

set property on CRTC

Parameters

struct drm_crtc * crtc
the drm CRTC to set a property on
struct drm_crtc_state * state
the state object to update with the new property value
struct drm_property * property
the property to set
uint64_t val
the new property value

Description

This function handles generic/core properties and calls out to driver’s drm_crtc_funcs.atomic_set_property for driver properties. To ensure consistent behavior you must call this function rather than the driver hook directly.

Return

Zero on success, error code on failure

struct drm_plane_state * drm_atomic_get_plane_state(struct drm_atomic_state * state, struct drm_plane * plane)

get plane state

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_plane * plane
plane to get state object for

Description

This function returns the plane state for the given plane, allocating it if needed. It will also grab the relevant plane lock to make sure that the state is consistent.

Return

Either the allocated state or the error code encoded into the pointer. When the error is EDEADLK then the w/w mutex code has detected a deadlock and the entire atomic sequence must be restarted. All other errors are fatal.

void drm_atomic_private_obj_init(struct drm_private_obj * obj, struct drm_private_state * state, const struct drm_private_state_funcs * funcs)

initialize private object

Parameters

struct drm_private_obj * obj
private object
struct drm_private_state * state
initial private object state
const struct drm_private_state_funcs * funcs
pointer to the struct of function pointers that identify the object type

Description

Initialize the private object, which can be embedded into any driver private object that needs its own atomic state.

void drm_atomic_private_obj_fini(struct drm_private_obj * obj)

finalize private object

Parameters

struct drm_private_obj * obj
private object

Description

Finalize the private object.

struct drm_private_state * drm_atomic_get_private_obj_state(struct drm_atomic_state * state, struct drm_private_obj * obj)

get private object state

Parameters

struct drm_atomic_state * state
global atomic state
struct drm_private_obj * obj
private object to get the state for

Description

This function returns the private object state for the given private object, allocating the state if needed. It does not grab any locks as the caller is expected to care of any required locking.

Return

Either the allocated state or the error code encoded into a pointer.

struct drm_connector_state * drm_atomic_get_connector_state(struct drm_atomic_state * state, struct drm_connector * connector)

get connector state

Parameters

struct drm_atomic_state * state
global atomic state object
struct drm_connector * connector
connector to get state object for

Description

This function returns the connector state for the given connector, allocating it if needed. It will also grab the relevant connector lock to make sure that the state is consistent.

Return

Either the allocated state or the error code encoded into the pointer. When the error is EDEADLK then the w/w mutex code has detected a deadlock and the entire atomic sequence must be restarted. All other errors are fatal.

int drm_atomic_set_crtc_for_plane(struct drm_plane_state * plane_state, struct drm_crtc * crtc)

set crtc for plane

Parameters

struct drm_plane_state * plane_state
the plane whose incoming state to update
struct drm_crtc * crtc
crtc to use for the plane

Description

Changing the assigned crtc for a plane requires us to grab the lock and state for the new crtc, as needed. This function takes care of all these details besides updating the pointer in the state object itself.

Return

0 on success or can fail with -EDEADLK or -ENOMEM. When the error is EDEADLK then the w/w mutex code has detected a deadlock and the entire atomic sequence must be restarted. All other errors are fatal.

void drm_atomic_set_fb_for_plane(struct drm_plane_state * plane_state, struct drm_framebuffer * fb)

set framebuffer for plane

Parameters

struct drm_plane_state * plane_state
atomic state object for the plane
struct drm_framebuffer * fb
fb to use for the plane

Description

Changing the assigned framebuffer for a plane requires us to grab a reference to the new fb and drop the reference to the old fb, if there is one. This function takes care of all these details besides updating the pointer in the state object itself.

void drm_atomic_set_fence_for_plane(struct drm_plane_state * plane_state, struct dma_fence * fence)

set fence for plane

Parameters

struct drm_plane_state * plane_state
atomic state object for the plane
struct dma_fence * fence
dma_fence to use for the plane

Description

Helper to setup the plane_state fence in case it is not set yet. By using this drivers doesn’t need to worry if the user choose implicit or explicit fencing.

This function will not set the fence to the state if it was set via explicit fencing interfaces on the atomic ioctl. In that case it will drop the reference to the fence as we are not storing it anywhere. Otherwise, if drm_plane_state.fence is not set this function we just set it with the received implicit fence. In both cases this function consumes a reference for fence.

int drm_atomic_set_crtc_for_connector(struct drm_connector_state * conn_state, struct drm_crtc * crtc)

set crtc for connector

Parameters

struct drm_connector_state * conn_state
atomic state object for the connector
struct drm_crtc * crtc
crtc to use for the connector

Description

Changing the assigned crtc for a connector requires us to grab the lock and state for the new crtc, as needed. This function takes care of all these details besides updating the pointer in the state object itself.

Return

0 on success or can fail with -EDEADLK or -ENOMEM. When the error is EDEADLK then the w/w mutex code has detected a deadlock and the entire atomic sequence must be restarted. All other errors are fatal.

int drm_atomic_add_affected_connectors(struct drm_atomic_state * state, struct drm_crtc * crtc)

add connectors for crtc

Parameters

struct drm_atomic_state * state
atomic state
struct drm_crtc * crtc
DRM crtc

Description

This function walks the current configuration and adds all connectors currently using crtc to the atomic configuration state. Note that this function must acquire the connection mutex. This can potentially cause unneeded seralization if the update is just for the planes on one crtc. Hence drivers and helpers should only call this when really needed (e.g. when a full modeset needs to happen due to some change).

Return

0 on success or can fail with -EDEADLK or -ENOMEM. When the error is EDEADLK then the w/w mutex code has detected a deadlock and the entire atomic sequence must be restarted. All other errors are fatal.

int drm_atomic_add_affected_planes(struct drm_atomic_state * state, struct drm_crtc * crtc)

add planes for crtc

Parameters

struct drm_atomic_state * state
atomic state
struct drm_crtc * crtc
DRM crtc

Description

This function walks the current configuration and adds all planes currently used by crtc to the atomic configuration state. This is useful when an atomic commit also needs to check all currently enabled plane on crtc, e.g. when changing the mode. It’s also useful when re-enabling a CRTC to avoid special code to force-enable all planes.

Since acquiring a plane state will always also acquire the w/w mutex of the current CRTC for that plane (if there is any) adding all the plane states for a CRTC will not reduce parallism of atomic updates.

Return

0 on success or can fail with -EDEADLK or -ENOMEM. When the error is EDEADLK then the w/w mutex code has detected a deadlock and the entire atomic sequence must be restarted. All other errors are fatal.

int drm_atomic_check_only(struct drm_atomic_state * state)

check whether a given config would work

Parameters

struct drm_atomic_state * state
atomic configuration to check

Description

Note that this function can return -EDEADLK if the driver needed to acquire more locks but encountered a deadlock. The caller must then do the usual w/w backoff dance and restart. All other errors are fatal.

Return

0 on success, negative error code on failure.

int drm_atomic_commit(struct drm_atomic_state * state)

commit configuration atomically

Parameters

struct drm_atomic_state * state
atomic configuration to check

Description

Note that this function can return -EDEADLK if the driver needed to acquire more locks but encountered a deadlock. The caller must then do the usual w/w backoff dance and restart. All other errors are fatal.

This function will take its own reference on state. Callers should always release their reference with drm_atomic_state_put().

Return

0 on success, negative error code on failure.

int drm_atomic_nonblocking_commit(struct drm_atomic_state * state)

atomic nonblocking commit

Parameters

struct drm_atomic_state * state
atomic configuration to check

Description

Note that this function can return -EDEADLK if the driver needed to acquire more locks but encountered a deadlock. The caller must then do the usual w/w backoff dance and restart. All other errors are fatal.

This function will take its own reference on state. Callers should always release their reference with drm_atomic_state_put().

Return

0 on success, negative error code on failure.

void drm_state_dump(struct drm_device * dev, struct drm_printer * p)

dump entire device atomic state

Parameters

struct drm_device * dev
the drm device
struct drm_printer * p
where to print the state to

Description

Just for debugging. Drivers might want an option to dump state to dmesg in case of error irq’s. (Hint, you probably want to ratelimit this!)

The caller must drm_modeset_lock_all(), or if this is called from error irq handler, it should not be enabled by default. (Ie. if you are debugging errors you might not care that this is racey. But calling this without all modeset locks held is not inherently safe.)

void drm_atomic_clean_old_fb(struct drm_device * dev, unsigned plane_mask, int ret)
  • Unset old_fb pointers and set plane->fb pointers.

Parameters

struct drm_device * dev
drm device to check.
unsigned plane_mask
plane mask for planes that were updated.
int ret
return value, can be -EDEADLK for a retry.

Description

Before doing an update drm_plane.old_fb is set to drm_plane.fb, but before dropping the locks old_fb needs to be set to NULL and plane->fb updated. This is a common operation for each atomic update, so this call is split off as a helper.

int drm_atomic_replace_property_blob_from_id(struct drm_device * dev, struct drm_property_blob ** blob, uint64_t blob_id, ssize_t expected_size, ssize_t expected_elem_size, bool * replaced)

lookup the new blob and replace the old one with it

Parameters

struct drm_device * dev
DRM device
struct drm_property_blob ** blob
a pointer to the member blob to be replaced
uint64_t blob_id
ID of the new blob
ssize_t expected_size
total expected size of the blob data (in bytes)
ssize_t expected_elem_size
expected element size of the blob data (in bytes)
bool * replaced
did the blob get replaced?

Description

Replace blob with another blob with the ID blob_id. If blob_id is zero blob becomes NULL.

If expected_size is positive the new blob length is expected to be equal to expected_size bytes. If expected_elem_size is positive the new blob length is expected to be a multiple of expected_elem_size bytes. Otherwise an error is returned.

replaced will indicate to the caller whether the blob was replaced or not. If the old and new blobs were in fact the same blob replaced will be false otherwise it will be true.

Return

Zero on success, error code on failure.

int drm_atomic_crtc_get_property(struct drm_crtc * crtc, const struct drm_crtc_state * state, struct drm_property * property, uint64_t * val)

get property value from CRTC state

Parameters

struct drm_crtc * crtc
the drm CRTC to set a property on
const struct drm_crtc_state * state
the state object to get the property value from
struct drm_property * property
the property to set
uint64_t * val
return location for the property value

Description

This function handles generic/core properties and calls out to driver’s drm_crtc_funcs.atomic_get_property for driver properties. To ensure consistent behavior you must call this function rather than the driver hook directly.

Return

Zero on success, error code on failure

int drm_atomic_crtc_check(struct drm_crtc * crtc, struct drm_crtc_state * state)

check crtc state

Parameters

struct drm_crtc * crtc
crtc to check
struct drm_crtc_state * state
crtc state to check

Description

Provides core sanity checks for crtc state.

Return

Zero on success, error code on failure

int drm_atomic_plane_set_property(struct drm_plane * plane, struct drm_plane_state * state, struct drm_property * property, uint64_t val)

set property on plane

Parameters

struct drm_plane * plane
the drm plane to set a property on
struct drm_plane_state * state
the state object to update with the new property value
struct drm_property * property
the property to set
uint64_t val
the new property value

Description

This function handles generic/core properties and calls out to driver’s drm_plane_funcs.atomic_set_property for driver properties. To ensure consistent behavior you must call this function rather than the driver hook directly.

Return

Zero on success, error code on failure

int drm_atomic_plane_get_property(struct drm_plane * plane, const struct drm_plane_state * state, struct drm_property * property, uint64_t * val)

get property value from plane state

Parameters

struct drm_plane * plane
the drm plane to set a property on
const struct drm_plane_state * state
the state object to get the property value from
struct drm_property * property
the property to set
uint64_t * val
return location for the property value

Description

This function handles generic/core properties and calls out to driver’s drm_plane_funcs.atomic_get_property for driver properties. To ensure consistent behavior you must call this function rather than the driver hook directly.

Return

Zero on success, error code on failure

int drm_atomic_plane_check(struct drm_plane * plane, struct drm_plane_state * state)

check plane state

Parameters

struct drm_plane * plane
plane to check
struct drm_plane_state * state
plane state to check

Description

Provides core sanity checks for plane state.

Return

Zero on success, error code on failure

int drm_atomic_connector_set_property(struct drm_connector * connector, struct drm_connector_state * state, struct drm_property * property, uint64_t val)

set property on connector.

Parameters

struct drm_connector * connector
the drm connector to set a property on
struct drm_connector_state * state
the state object to update with the new property value
struct drm_property * property
the property to set
uint64_t val
the new property value

Description

This function handles generic/core properties and calls out to driver’s drm_connector_funcs.atomic_set_property for driver properties. To ensure consistent behavior you must call this function rather than the driver hook directly.

Return

Zero on success, error code on failure

int drm_atomic_connector_get_property(struct drm_connector * connector, const struct drm_connector_state * state, struct drm_property * property, uint64_t * val)

get property value from connector state

Parameters

struct drm_connector * connector
the drm connector to set a property on
const struct drm_connector_state * state
the state object to get the property value from
struct drm_property * property
the property to set
uint64_t * val
return location for the property value

Description

This function handles generic/core properties and calls out to driver’s drm_connector_funcs.atomic_get_property for driver properties. To ensure consistent behavior you must call this function rather than the driver hook directly.

Return

Zero on success, error code on failure

CRTC Abstraction

A CRTC represents the overall display pipeline. It receives pixel data from drm_plane and blends them together. The drm_display_mode is also attached to the CRTC, specifying display timings. On the output side the data is fed to one or more drm_encoder, which are then each connected to one drm_connector.

To create a CRTC, a KMS drivers allocates and zeroes an instances of struct drm_crtc (possibly as part of a larger structure) and registers it with a call to drm_crtc_init_with_planes().

The CRTC is also the entry point for legacy modeset operations, see drm_crtc_funcs.set_config, legacy plane operations, see drm_crtc_funcs.page_flip and drm_crtc_funcs.cursor_set2, and other legacy operations like drm_crtc_funcs.gamma_set. For atomic drivers all these features are controlled through drm_property and drm_mode_config_funcs.atomic_check and drm_mode_config_funcs.atomic_check.

CRTC Functions Reference

struct drm_crtc_state

mutable CRTC state

Definition

struct drm_crtc_state {
  struct drm_crtc *crtc;
  bool enable;
  bool active;
  bool planes_changed : 1;
  bool mode_changed : 1;
  bool active_changed : 1;
  bool connectors_changed : 1;
  bool zpos_changed : 1;
  bool color_mgmt_changed : 1;
  u32 plane_mask;
  u32 connector_mask;
  u32 encoder_mask;
  struct drm_display_mode adjusted_mode;
  struct drm_display_mode mode;
  struct drm_property_blob *mode_blob;
  struct drm_property_blob *degamma_lut;
  struct drm_property_blob *ctm;
  struct drm_property_blob *gamma_lut;
  u32 target_vblank;
  u32 pageflip_flags;
  struct drm_pending_vblank_event *event;
  struct drm_crtc_commit *commit;
  struct drm_atomic_state *state;
};

Members

crtc
backpointer to the CRTC
enable
whether the CRTC should be enabled, gates all other state
active
whether the CRTC is actively displaying (used for DPMS)
planes_changed
planes on this crtc are updated
mode_changed
mode or enable has been changed
active_changed
active has been toggled.
connectors_changed
connectors to this crtc have been updated
zpos_changed
zpos values of planes on this crtc have been updated
color_mgmt_changed
color management properties have changed (degamma or gamma LUT or CSC matrix)
plane_mask
bitmask of (1 << drm_plane_index(plane)) of attached planes
connector_mask
bitmask of (1 << drm_connector_index(connector)) of attached connectors
encoder_mask
bitmask of (1 << drm_encoder_index(encoder)) of attached encoders
adjusted_mode
Internal display timings which can be used by the driver to handle differences between the mode requested by userspace in mode and what is actually programmed into the hardware. It is purely driver implementation defined what exactly this adjusted mode means. Usually it is used to store the hardware display timings used between the CRTC and encoder blocks.
mode

Display timings requested by userspace. The driver should try to match the refresh rate as close as possible (but note that it’s undefined what exactly is close enough, e.g. some of the HDMI modes only differ in less than 1% of the refresh rate). The active width and height as observed by userspace for positioning planes must match exactly.

For external connectors where the sink isn’t fixed (like with a built-in panel), this mode here should match the physical mode on the wire to the last details (i.e. including sync polarities and everything).

mode_blob
drm_property_blob for mode
degamma_lut
Lookup table for converting framebuffer pixel data before apply the color conversion matrix ctm. See drm_crtc_enable_color_mgmt(). The blob (if not NULL) is an array of struct drm_color_lut.
ctm
Color transformation matrix. See drm_crtc_enable_color_mgmt(). The blob (if not NULL) is a struct drm_color_ctm.
gamma_lut
Lookup table for converting pixel data after the color conversion matrix ctm. See drm_crtc_enable_color_mgmt(). The blob (if not NULL) is an array of struct drm_color_lut.
target_vblank
Target vertical blank period when a page flip should take effect.
pageflip_flags
DRM_MODE_PAGE_FLIP_* flags, as passed to the page flip ioctl. Zero in any other case.
event

Optional pointer to a DRM event to signal upon completion of the state update. The driver must send out the event when the atomic commit operation completes. There are two cases:

  • The event is for a CRTC which is being disabled through this atomic commit. In that case the event can be send out any time after the hardware has stopped scanning out the current framebuffers. It should contain the timestamp and counter for the last vblank before the display pipeline was shut off. The simplest way to achieve that is calling drm_crtc_send_vblank_event() somewhen after drm_crtc_vblank_off() has been called.
  • For a CRTC which is enabled at the end of the commit (even when it undergoes an full modeset) the vblank timestamp and counter must be for the vblank right before the first frame that scans out the new set of buffers. Again the event can only be sent out after the hardware has stopped scanning out the old buffers.
  • Events for disabled CRTCs are not allowed, and drivers can ignore that case.

This can be handled by the drm_crtc_send_vblank_event() function, which the driver should call on the provided event upon completion of the atomic commit. Note that if the driver supports vblank signalling and timestamping the vblank counters and timestamps must agree with the ones returned from page flip events. With the current vblank helper infrastructure this can be achieved by holding a vblank reference while the page flip is pending, acquired through drm_crtc_vblank_get() and released with drm_crtc_vblank_put(). Drivers are free to implement their own vblank counter and timestamp tracking though, e.g. if they have accurate timestamp registers in hardware.

For hardware which supports some means to synchronize vblank interrupt delivery with committing display state there’s also drm_crtc_arm_vblank_event(). See the documentation of that function for a detailed discussion of the constraints it needs to be used safely.

If the device can’t notify of flip completion in a race-free way at all, then the event should be armed just after the page flip is committed. In the worst case the driver will send the event to userspace one frame too late. This doesn’t allow for a real atomic update, but it should avoid tearing.

commit
This tracks how the commit for this update proceeds through the various phases. This is never cleared, except when we destroy the state, so that subsequent commits can synchronize with previous ones.
state
backpointer to global drm_atomic_state

Description

Note that the distinction between enable and active is rather subtile: Flipping active while enable is set without changing anything else may never return in a failure from the drm_mode_config_funcs.atomic_check callback. Userspace assumes that a DPMS On will always succeed. In other words: enable controls resource assignment, active controls the actual hardware state.

The three booleans active_changed, connectors_changed and mode_changed are intended to indicate whether a full modeset is needed, rather than strictly describing what has changed in a commit. See also: drm_atomic_crtc_needs_modeset()

struct drm_crtc_funcs

control CRTCs for a given device

Definition

struct drm_crtc_funcs {
  void (*reset)(struct drm_crtc *crtc);
  int (*cursor_set)(struct drm_crtc *crtc, struct drm_file *file_priv, uint32_t handle, uint32_t width, uint32_t height);
  int (*cursor_set2)(struct drm_crtc *crtc, struct drm_file *file_priv,uint32_t handle, uint32_t width, uint32_t height, int32_t hot_x, int32_t hot_y);
  int (*cursor_move)(struct drm_crtc *crtc, int x, int y);
  int (*gamma_set)(struct drm_crtc *crtc, u16 *r, u16 *g, u16 *b,uint32_t size, struct drm_modeset_acquire_ctx *ctx);
  void (*destroy)(struct drm_crtc *crtc);
  int (*set_config)(struct drm_mode_set *set, struct drm_modeset_acquire_ctx *ctx);
  int (*page_flip)(struct drm_crtc *crtc,struct drm_framebuffer *fb,struct drm_pending_vblank_event *event,uint32_t flags, struct drm_modeset_acquire_ctx *ctx);
  int (*page_flip_target)(struct drm_crtc *crtc,struct drm_framebuffer *fb,struct drm_pending_vblank_event *event,uint32_t flags, uint32_t target, struct drm_modeset_acquire_ctx *ctx);
  int (*set_property)(struct drm_crtc *crtc, struct drm_property *property, uint64_t val);
  struct drm_crtc_state *(*atomic_duplicate_state)(struct drm_crtc *crtc);
  void (*atomic_destroy_state)(struct drm_crtc *crtc, struct drm_crtc_state *state);
  int (*atomic_set_property)(struct drm_crtc *crtc,struct drm_crtc_state *state,struct drm_property *property, uint64_t val);
  int (*atomic_get_property)(struct drm_crtc *crtc,const struct drm_crtc_state *state,struct drm_property *property, uint64_t *val);
  int (*late_register)(struct drm_crtc *crtc);
  void (*early_unregister)(struct drm_crtc *crtc);
  int (*set_crc_source)(struct drm_crtc *crtc, const char *source, size_t *values_cnt);
  void (*atomic_print_state)(struct drm_printer *p, const struct drm_crtc_state *state);
  u32 (*get_vblank_counter)(struct drm_crtc *crtc);
  int (*enable_vblank)(struct drm_crtc *crtc);
  void (*disable_vblank)(struct drm_crtc *crtc);
};

Members

reset

Reset CRTC hardware and software state to off. This function isn’t called by the core directly, only through drm_mode_config_reset(). It’s not a helper hook only for historical reasons.

Atomic drivers can use drm_atomic_helper_crtc_reset() to reset atomic state using this hook.

cursor_set

Update the cursor image. The cursor position is relative to the CRTC and can be partially or fully outside of the visible area.

Note that contrary to all other KMS functions the legacy cursor entry points don’t take a framebuffer object, but instead take directly a raw buffer object id from the driver’s buffer manager (which is either GEM or TTM for current drivers).

This entry point is deprecated, drivers should instead implement universal plane support and register a proper cursor plane using drm_crtc_init_with_planes().

This callback is optional

RETURNS:

0 on success or a negative error code on failure.

cursor_set2

Update the cursor image, including hotspot information. The hotspot must not affect the cursor position in CRTC coordinates, but is only meant as a hint for virtualized display hardware to coordinate the guests and hosts cursor position. The cursor hotspot is relative to the cursor image. Otherwise this works exactly like cursor_set.

This entry point is deprecated, drivers should instead implement universal plane support and register a proper cursor plane using drm_crtc_init_with_planes().

This callback is optional.

RETURNS:

0 on success or a negative error code on failure.

cursor_move

Update the cursor position. The cursor does not need to be visible when this hook is called.

This entry point is deprecated, drivers should instead implement universal plane support and register a proper cursor plane using drm_crtc_init_with_planes().

This callback is optional.

RETURNS:

0 on success or a negative error code on failure.

gamma_set

Set gamma on the CRTC.

This callback is optional.

Atomic drivers who want to support gamma tables should implement the atomic color management support, enabled by calling drm_crtc_enable_color_mgmt(), which then supports the legacy gamma interface through the drm_atomic_helper_legacy_gamma_set() compatibility implementation.

destroy
Clean up plane resources. This is only called at driver unload time through drm_mode_config_cleanup() since a CRTC cannot be hotplugged in DRM.
set_config

This is the main legacy entry point to change the modeset state on a CRTC. All the details of the desired configuration are passed in a struct drm_mode_set - see there for details.

Drivers implementing atomic modeset should use drm_atomic_helper_set_config() to implement this hook.

RETURNS:

0 on success or a negative error code on failure.

page_flip

Legacy entry point to schedule a flip to the given framebuffer.

Page flipping is a synchronization mechanism that replaces the frame buffer being scanned out by the CRTC with a new frame buffer during vertical blanking, avoiding tearing (except when requested otherwise through the DRM_MODE_PAGE_FLIP_ASYNC flag). When an application requests a page flip the DRM core verifies that the new frame buffer is large enough to be scanned out by the CRTC in the currently configured mode and then calls this hook with a pointer to the new frame buffer.

The driver must wait for any pending rendering to the new framebuffer to complete before executing the flip. It should also wait for any pending rendering from other drivers if the underlying buffer is a shared dma-buf.

An application can request to be notified when the page flip has completed. The drm core will supply a struct drm_event in the event parameter in this case. This can be handled by the drm_crtc_send_vblank_event() function, which the driver should call on the provided event upon completion of the flip. Note that if the driver supports vblank signalling and timestamping the vblank counters and timestamps must agree with the ones returned from page flip events. With the current vblank helper infrastructure this can be achieved by holding a vblank reference while the page flip is pending, acquired through drm_crtc_vblank_get() and released with drm_crtc_vblank_put(). Drivers are free to implement their own vblank counter and timestamp tracking though, e.g. if they have accurate timestamp registers in hardware.

This callback is optional.

NOTE:

Very early versions of the KMS ABI mandated that the driver must block (but not reject) any rendering to the old framebuffer until the flip operation has completed and the old framebuffer is no longer visible. This requirement has been lifted, and userspace is instead expected to request delivery of an event and wait with recycling old buffers until such has been received.

RETURNS:

0 on success or a negative error code on failure. Note that if a page flip operation is already pending the callback should return -EBUSY. Pageflips on a disabled CRTC (either by setting a NULL mode or just runtime disabled through DPMS respectively the new atomic “ACTIVE” state) should result in an -EINVAL error code. Note that drm_atomic_helper_page_flip() checks this already for atomic drivers.

page_flip_target

Same as page_flip but with an additional parameter specifying the absolute target vertical blank period (as reported by drm_crtc_vblank_count()) when the flip should take effect.

Note that the core code calls drm_crtc_vblank_get before this entry point, and will call drm_crtc_vblank_put if this entry point returns any non-0 error code. It’s the driver’s responsibility to call drm_crtc_vblank_put after this entry point returns 0, typically when the flip completes.

set_property

This is the legacy entry point to update a property attached to the CRTC.

This callback is optional if the driver does not support any legacy driver-private properties. For atomic drivers it is not used because property handling is done entirely in the DRM core.

RETURNS:

0 on success or a negative error code on failure.

atomic_duplicate_state

Duplicate the current atomic state for this CRTC and return it. The core and helpers guarantee that any atomic state duplicated with this hook and still owned by the caller (i.e. not transferred to the driver by calling drm_mode_config_funcs.atomic_commit) will be cleaned up by calling the atomic_destroy_state hook in this structure.

Atomic drivers which don’t subclass struct drm_crtc_state should use drm_atomic_helper_crtc_duplicate_state(). Drivers that subclass the state structure to extend it with driver-private state should use __drm_atomic_helper_crtc_duplicate_state() to make sure shared state is duplicated in a consistent fashion across drivers.

It is an error to call this hook before drm_crtc.state has been initialized correctly.

NOTE:

If the duplicate state references refcounted resources this hook must acquire a reference for each of them. The driver must release these references again in atomic_destroy_state.

RETURNS:

Duplicated atomic state or NULL when the allocation failed.

atomic_destroy_state
Destroy a state duplicated with atomic_duplicate_state and release or unreference all resources it references
atomic_set_property

Decode a driver-private property value and store the decoded value into the passed-in state structure. Since the atomic core decodes all standardized properties (even for extensions beyond the core set of properties which might not be implemented by all drivers) this requires drivers to subclass the state structure.

Such driver-private properties should really only be implemented for truly hardware/vendor specific state. Instead it is preferred to standardize atomic extension and decode the properties used to expose such an extension in the core.

Do not call this function directly, use drm_atomic_crtc_set_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

NOTE:

This function is called in the state assembly phase of atomic modesets, which can be aborted for any reason (including on userspace’s request to just check whether a configuration would be possible). Drivers MUST NOT touch any persistent state (hardware or software) or data structures except the passed in state parameter.

Also since userspace controls in which order properties are set this function must not do any input validation (since the state update is incomplete and hence likely inconsistent). Instead any such input validation must be done in the various atomic_check callbacks.

RETURNS:

0 if the property has been found, -EINVAL if the property isn’t implemented by the driver (which should never happen, the core only asks for properties attached to this CRTC). No other validation is allowed by the driver. The core already checks that the property value is within the range (integer, valid enum value, ...) the driver set when registering the property.

atomic_get_property

Reads out the decoded driver-private property. This is used to implement the GETCRTC IOCTL.

Do not call this function directly, use drm_atomic_crtc_get_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

RETURNS:

0 on success, -EINVAL if the property isn’t implemented by the driver (which should never happen, the core only asks for properties attached to this CRTC).

late_register

This optional hook can be used to register additional userspace interfaces attached to the crtc like debugfs interfaces. It is called late in the driver load sequence from drm_dev_register(). Everything added from this callback should be unregistered in the early_unregister callback.

Returns:

0 on success, or a negative error code on failure.

early_unregister
This optional hook should be used to unregister the additional userspace interfaces attached to the crtc from late_register. It is called from drm_dev_unregister(), early in the driver unload sequence to disable userspace access before data structures are torndown.
set_crc_source

Changes the source of CRC checksums of frames at the request of userspace, typically for testing purposes. The sources available are specific of each driver and a NULL value indicates that CRC generation is to be switched off.

When CRC generation is enabled, the driver should call drm_crtc_add_crc_entry() at each frame, providing any information that characterizes the frame contents in the crcN arguments, as provided from the configured source. Drivers must accept an “auto” source name that will select a default source for this CRTC.

Note that “auto” can depend upon the current modeset configuration, e.g. it could pick an encoder or output specific CRC sampling point.

This callback is optional if the driver does not support any CRC generation functionality.

RETURNS:

0 on success or a negative error code on failure.

atomic_print_state

If driver subclasses struct drm_crtc_state, it should implement this optional hook for printing additional driver specific state.

Do not call this directly, use drm_atomic_crtc_print_state() instead.

get_vblank_counter

Driver callback for fetching a raw hardware vblank counter for the CRTC. It’s meant to be used by new drivers as the replacement of drm_driver.get_vblank_counter hook.

This callback is optional. If a device doesn’t have a hardware counter, the driver can simply leave the hook as NULL. The DRM core will account for missed vblank events while interrupts where disabled based on system timestamps.

Wraparound handling and loss of events due to modesetting is dealt with in the DRM core code, as long as drivers call drm_crtc_vblank_off() and drm_crtc_vblank_on() when disabling or enabling a CRTC.

See also drm_device.vblank_disable_immediate and drm_device.max_vblank_count.

Returns:

Raw vblank counter value.

enable_vblank

Enable vblank interrupts for the CRTC. It’s meant to be used by new drivers as the replacement of drm_driver.enable_vblank hook.

Returns:

Zero on success, appropriate errno if the vblank interrupt cannot be enabled.

disable_vblank
Disable vblank interrupts for the CRTC. It’s meant to be used by new drivers as the replacement of drm_driver.disable_vblank hook.

Description

The drm_crtc_funcs structure is the central CRTC management structure in the DRM. Each CRTC controls one or more connectors (note that the name CRTC is simply historical, a CRTC may control LVDS, VGA, DVI, TV out, etc. connectors, not just CRTs).

Each driver is responsible for filling out this structure at startup time, in addition to providing other modesetting features, like i2c and DDC bus accessors.

struct drm_crtc

central CRTC control structure

Definition

struct drm_crtc {
  struct drm_device *dev;
  struct device_node *port;
  struct list_head head;
  char *name;
  struct drm_modeset_lock mutex;
  struct drm_mode_object base;
  struct drm_plane *primary;
  struct drm_plane *cursor;
  unsigned index;
  int cursor_x;
  int cursor_y;
  bool enabled;
  struct drm_display_mode mode;
  struct drm_display_mode hwmode;
  int x, y;
  const struct drm_crtc_funcs *funcs;
  uint32_t gamma_size;
  uint16_t *gamma_store;
  const struct drm_crtc_helper_funcs *helper_private;
  struct drm_object_properties properties;
  struct drm_crtc_state *state;
  struct list_head commit_list;
  spinlock_t commit_lock;
#ifdef CONFIG_DEBUG_FS;
  struct dentry *debugfs_entry;
#endif;
  struct drm_crtc_crc crc;
  unsigned int fence_context;
  spinlock_t fence_lock;
  unsigned long fence_seqno;
  char timeline_name[32];
};

Members

dev
parent DRM device
port
OF node used by drm_of_find_possible_crtcs()
head
list management
name
human readable name, can be overwritten by the driver
mutex

This provides a read lock for the overall CRTC state (mode, dpms state, ...) and a write lock for everything which can be update without a full modeset (fb, cursor data, CRTC properties ...). A full modeset also need to grab drm_mode_config.connection_mutex.

For atomic drivers specifically this protects state.

base
base KMS object for ID tracking etc.
primary
primary plane for this CRTC
cursor
cursor plane for this CRTC
index
Position inside the mode_config.list, can be used as an array index. It is invariant over the lifetime of the CRTC.
cursor_x
current x position of the cursor, used for universal cursor planes
cursor_y
current y position of the cursor, used for universal cursor planes
enabled
is this CRTC enabled?
mode
current mode timings
hwmode
mode timings as programmed to hw regs
x
x position on screen
y
y position on screen
funcs
CRTC control functions
gamma_size
size of gamma ramp
gamma_store
gamma ramp values
helper_private
mid-layer private data
properties
property tracking for this CRTC
state

Current atomic state for this CRTC.

This is protected by mutex. Note that nonblocking atomic commits access the current CRTC state without taking locks. Either by going through the struct drm_atomic_state pointers, see for_each_oldnew_crtc_in_state(), for_each_old_crtc_in_state() and for_each_new_crtc_in_state(). Or through careful ordering of atomic commit operations as implemented in the atomic helpers, see struct drm_crtc_commit.

commit_list

List of drm_crtc_commit structures tracking pending commits. Protected by commit_lock. This list holds its own full reference, as does the ongoing commit.

“Note that the commit for a state change is also tracked in drm_crtc_state.commit. For accessing the immediately preceding commit in an atomic update it is recommended to just use that pointer in the old CRTC state, since accessing that doesn’t need any locking or list-walking. commit_list should only be used to stall for framebuffer cleanup that’s signalled through drm_crtc_commit.cleanup_done.”

commit_lock
Spinlock to protect commit_list.
debugfs_entry
Debugfs directory for this CRTC.
crc
Configuration settings of CRC capture.
fence_context
timeline context used for fence operations.
fence_lock
spinlock to protect the fences in the fence_context.
fence_seqno
Seqno variable used as monotonic counter for the fences created on the CRTC’s timeline.
timeline_name
The name of the CRTC’s fence timeline.

Description

Each CRTC may have one or more connectors associated with it. This structure allows the CRTC to be controlled.

struct drm_mode_set

new values for a CRTC config change

Definition

struct drm_mode_set {
  struct drm_framebuffer *fb;
  struct drm_crtc *crtc;
  struct drm_display_mode *mode;
  uint32_t x;
  uint32_t y;
  struct drm_connector **connectors;
  size_t num_connectors;
};

Members

fb
framebuffer to use for new config
crtc
CRTC whose configuration we’re about to change
mode
mode timings to use
x
position of this CRTC relative to fb
y
position of this CRTC relative to fb
connectors
array of connectors to drive with this CRTC if possible
num_connectors
size of connectors array

Description

This represents a modeset configuration for the legacy SETCRTC ioctl and is also used internally. Atomic drivers instead use drm_atomic_state.

unsigned int drm_crtc_index(const struct drm_crtc * crtc)

find the index of a registered CRTC

Parameters

const struct drm_crtc * crtc
CRTC to find index for

Description

Given a registered CRTC, return the index of that CRTC within a DRM device’s list of CRTCs.

uint32_t drm_crtc_mask(const struct drm_crtc * crtc)

find the mask of a registered CRTC

Parameters

const struct drm_crtc * crtc
CRTC to find mask for

Description

Given a registered CRTC, return the mask bit of that CRTC for an encoder’s possible_crtcs field.

struct drm_crtc * drm_crtc_find(struct drm_device * dev, struct drm_file * file_priv, uint32_t id)

look up a CRTC object from its ID

Parameters

struct drm_device * dev
DRM device
struct drm_file * file_priv
drm file to check for lease against.
uint32_t id
drm_mode_object ID

Description

This can be used to look up a CRTC from its userspace ID. Only used by drivers for legacy IOCTLs and interface, nowadays extensions to the KMS userspace interface should be done using drm_property.

drm_for_each_crtc(crtc, dev)

iterate over all CRTCs

Parameters

crtc
a struct drm_crtc as the loop cursor
dev
the struct drm_device

Description

Iterate over all CRTCs of dev.

struct drm_crtc * drm_crtc_from_index(struct drm_device * dev, int idx)

find the registered CRTC at an index

Parameters

struct drm_device * dev
DRM device
int idx
index of registered CRTC to find for

Description

Given a CRTC index, return the registered CRTC from DRM device’s list of CRTCs with matching index. This is the inverse of drm_crtc_index(). It’s useful in the vblank callbacks (like drm_driver.enable_vblank or drm_driver.disable_vblank), since that still deals with indices instead of pointers to struct drm_crtc.”

int drm_crtc_force_disable(struct drm_crtc * crtc)

Forcibly turn off a CRTC

Parameters

struct drm_crtc * crtc
CRTC to turn off

Note

This should only be used by non-atomic legacy drivers.

Return

Zero on success, error code on failure.

int drm_crtc_force_disable_all(struct drm_device * dev)

Forcibly turn off all enabled CRTCs

Parameters

struct drm_device * dev
DRM device whose CRTCs to turn off

Description

Drivers may want to call this on unload to ensure that all displays are unlit and the GPU is in a consistent, low power state. Takes modeset locks.

Note

This should only be used by non-atomic legacy drivers. For an atomic version look at drm_atomic_helper_shutdown().

Return

Zero on success, error code on failure.

int drm_crtc_init_with_planes(struct drm_device * dev, struct drm_crtc * crtc, struct drm_plane * primary, struct drm_plane * cursor, const struct drm_crtc_funcs * funcs, const char * name, ...)

Initialise a new CRTC object with specified primary and cursor planes.

Parameters

struct drm_device * dev
DRM device
struct drm_crtc * crtc
CRTC object to init
struct drm_plane * primary
Primary plane for CRTC
struct drm_plane * cursor
Cursor plane for CRTC
const struct drm_crtc_funcs * funcs
callbacks for the new CRTC
const char * name
printf style format string for the CRTC name, or NULL for default name
...
variable arguments

Description

Inits a new object created as base part of a driver crtc object. Drivers should use this function instead of drm_crtc_init(), which is only provided for backwards compatibility with drivers which do not yet support universal planes). For really simple hardware which has only 1 plane look at drm_simple_display_pipe_init() instead.

Return

Zero on success, error code on failure.

void drm_crtc_cleanup(struct drm_crtc * crtc)

Clean up the core crtc usage

Parameters

struct drm_crtc * crtc
CRTC to cleanup

Description

This function cleans up crtc and removes it from the DRM mode setting core. Note that the function does not free the crtc structure itself, this is the responsibility of the caller.

int drm_mode_set_config_internal(struct drm_mode_set * set)

helper to call drm_mode_config_funcs.set_config

Parameters

struct drm_mode_set * set
modeset config to set

Description

This is a little helper to wrap internal calls to the drm_mode_config_funcs.set_config driver interface. The only thing it adds is correct refcounting dance.

This should only be used by non-atomic legacy drivers.

Return

Zero on success, negative errno on failure.

int drm_crtc_check_viewport(const struct drm_crtc * crtc, int x, int y, const struct drm_display_mode * mode, const struct drm_framebuffer * fb)

Checks that a framebuffer is big enough for the CRTC viewport

Parameters

const struct drm_crtc * crtc
CRTC that framebuffer will be displayed on
int x
x panning
int y
y panning
const struct drm_display_mode * mode
mode that framebuffer will be displayed under
const struct drm_framebuffer * fb
framebuffer to check size of

Frame Buffer Abstraction

Frame buffers are abstract memory objects that provide a source of pixels to scanout to a CRTC. Applications explicitly request the creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls and receive an opaque handle that can be passed to the KMS CRTC control, plane configuration and page flip functions.

Frame buffers rely on the underlying memory manager for allocating backing storage. When creating a frame buffer applications pass a memory handle (or a list of memory handles for multi-planar formats) through the struct drm_mode_fb_cmd2 argument. For drivers using GEM as their userspace buffer management interface this would be a GEM handle. Drivers are however free to use their own backing storage object handles, e.g. vmwgfx directly exposes special TTM handles to userspace and so expects TTM handles in the create ioctl and not GEM handles.

Framebuffers are tracked with struct drm_framebuffer. They are published using drm_framebuffer_init() - after calling that function userspace can use and access the framebuffer object. The helper function drm_helper_mode_fill_fb_struct() can be used to pre-fill the required metadata fields.

The lifetime of a drm framebuffer is controlled with a reference count, drivers can grab additional references with drm_framebuffer_get() and drop them again with drm_framebuffer_put(). For driver-private framebuffers for which the last reference is never dropped (e.g. for the fbdev framebuffer when the struct struct drm_framebuffer is embedded into the fbdev helper struct) drivers can manually clean up a framebuffer at module unload time with drm_framebuffer_unregister_private(). But doing this is not recommended, and it’s better to have a normal free-standing struct drm_framebuffer.

Frame Buffer Functions Reference

struct drm_framebuffer_funcs

framebuffer hooks

Definition

struct drm_framebuffer_funcs {
  void (*destroy)(struct drm_framebuffer *framebuffer);
  int (*create_handle)(struct drm_framebuffer *fb,struct drm_file *file_priv, unsigned int *handle);
  int (*dirty)(struct drm_framebuffer *framebuffer,struct drm_file *file_priv, unsigned flags,unsigned color, struct drm_clip_rect *clips, unsigned num_clips);
};

Members

destroy
Clean up framebuffer resources, specifically also unreference the backing storage. The core guarantees to call this function for every framebuffer successfully created by calling drm_mode_config_funcs.fb_create. Drivers must also call drm_framebuffer_cleanup() to release DRM core resources for this framebuffer.
create_handle

Create a buffer handle in the driver-specific buffer manager (either GEM or TTM) valid for the passed-in struct drm_file. This is used by the core to implement the GETFB IOCTL, which returns (for sufficiently priviledged user) also a native buffer handle. This can be used for seamless transitions between modesetting clients by copying the current screen contents to a private buffer and blending between that and the new contents.

GEM based drivers should call drm_gem_handle_create() to create the handle.

RETURNS:

0 on success or a negative error code on failure.

dirty

Optional callback for the dirty fb IOCTL.

Userspace can notify the driver via this callback that an area of the framebuffer has changed and should be flushed to the display hardware. This can also be used internally, e.g. by the fbdev emulation, though that’s not the case currently.

See documentation in drm_mode.h for the struct drm_mode_fb_dirty_cmd for more information as all the semantics and arguments have a one to one mapping on this function.

RETURNS:

0 on success or a negative error code on failure.

struct drm_framebuffer

frame buffer object

Definition

struct drm_framebuffer {
  struct drm_device *dev;
  struct list_head head;
  struct drm_mode_object base;
  char comm[TASK_COMM_LEN];
  const struct drm_format_info *format;
  const struct drm_framebuffer_funcs *funcs;
  unsigned int pitches[4];
  unsigned int offsets[4];
  uint64_t modifier;
  unsigned int width;
  unsigned int height;
  int flags;
  int hot_x;
  int hot_y;
  struct list_head filp_head;
  struct drm_gem_object *obj[4];
};

Members

dev
DRM device this framebuffer belongs to
head
Place on the drm_mode_config.fb_list, access protected by drm_mode_config.fb_lock.
base
base modeset object structure, contains the reference count.
comm
Name of the process allocating the fb, used for fb dumping.
format
framebuffer format information
funcs
framebuffer vfunc table
pitches
Line stride per buffer. For userspace created object this is copied from drm_mode_fb_cmd2.
offsets

Offset from buffer start to the actual pixel data in bytes, per buffer. For userspace created object this is copied from drm_mode_fb_cmd2.

Note that this is a linear offset and does not take into account tiling or buffer laytou per modifier. It meant to be used when the actual pixel data for this framebuffer plane starts at an offset, e.g. when multiple planes are allocated within the same backing storage buffer object. For tiled layouts this generally means it offsets must at least be tile-size aligned, but hardware often has stricter requirements.

This should not be used to specifiy x/y pixel offsets into the buffer data (even for linear buffers). Specifying an x/y pixel offset is instead done through the source rectangle in struct drm_plane_state.

modifier
Data layout modifier. This is used to describe tiling, or also special layouts (like compression) of auxiliary buffers. For userspace created object this is copied from drm_mode_fb_cmd2.
width
Logical width of the visible area of the framebuffer, in pixels.
height
Logical height of the visible area of the framebuffer, in pixels.
flags
Framebuffer flags like DRM_MODE_FB_INTERLACED or DRM_MODE_FB_MODIFIERS.
hot_x
X coordinate of the cursor hotspot. Used by the legacy cursor IOCTL when the driver supports cursor through a DRM_PLANE_TYPE_CURSOR universal plane.
hot_y
Y coordinate of the cursor hotspot. Used by the legacy cursor IOCTL when the driver supports cursor through a DRM_PLANE_TYPE_CURSOR universal plane.
filp_head
Placed on drm_file.fbs, protected by drm_file.fbs_lock.
obj

GEM objects backing the framebuffer, one per plane (optional).

This is used by the GEM framebuffer helpers, see e.g. drm_gem_fb_create().

Description

Note that the fb is refcounted for the benefit of driver internals, for example some hw, disabling a CRTC/plane is asynchronous, and scanout does not actually complete until the next vblank. So some cleanup (like releasing the reference(s) on the backing GEM bo(s)) should be deferred. In cases like this, the driver would like to hold a ref to the fb even though it has already been removed from userspace perspective. See drm_framebuffer_get() and drm_framebuffer_put().

The refcount is stored inside the mode object base.

void drm_framebuffer_get(struct drm_framebuffer * fb)

acquire a framebuffer reference

Parameters

struct drm_framebuffer * fb
DRM framebuffer

Description

This function increments the framebuffer’s reference count.

void drm_framebuffer_put(struct drm_framebuffer * fb)

release a framebuffer reference

Parameters

struct drm_framebuffer * fb
DRM framebuffer

Description

This function decrements the framebuffer’s reference count and frees the framebuffer if the reference count drops to zero.

void drm_framebuffer_reference(struct drm_framebuffer * fb)

acquire a framebuffer reference

Parameters

struct drm_framebuffer * fb
DRM framebuffer

Description

This is a compatibility alias for drm_framebuffer_get() and should not be used by new code.

void drm_framebuffer_unreference(struct drm_framebuffer * fb)

release a framebuffer reference

Parameters

struct drm_framebuffer * fb
DRM framebuffer

Description

This is a compatibility alias for drm_framebuffer_put() and should not be used by new code.

uint32_t drm_framebuffer_read_refcount(const struct drm_framebuffer * fb)

read the framebuffer reference count.

Parameters

const struct drm_framebuffer * fb
framebuffer

Description

This functions returns the framebuffer’s reference count.

void drm_framebuffer_assign(struct drm_framebuffer ** p, struct drm_framebuffer * fb)

store a reference to the fb

Parameters

struct drm_framebuffer ** p
location to store framebuffer
struct drm_framebuffer * fb
new framebuffer (maybe NULL)

Description

This functions sets the location to store a reference to the framebuffer, unreferencing the framebuffer that was previously stored in that location.

int drm_framebuffer_init(struct drm_device * dev, struct drm_framebuffer * fb, const struct drm_framebuffer_funcs * funcs)

initialize a framebuffer

Parameters

struct drm_device * dev
DRM device
struct drm_framebuffer * fb
framebuffer to be initialized
const struct drm_framebuffer_funcs * funcs
... with these functions

Description

Allocates an ID for the framebuffer’s parent mode object, sets its mode functions & device file and adds it to the master fd list.

IMPORTANT: This functions publishes the fb and makes it available for concurrent access by other users. Which means by this point the fb _must_ be fully set up - since all the fb attributes are invariant over its lifetime, no further locking but only correct reference counting is required.

Return

Zero on success, error code on failure.

struct drm_framebuffer * drm_framebuffer_lookup(struct drm_device * dev, struct drm_file * file_priv, uint32_t id)

look up a drm framebuffer and grab a reference

Parameters

struct drm_device * dev
drm device
struct drm_file * file_priv
drm file to check for lease against.
uint32_t id
id of the fb object

Description

If successful, this grabs an additional reference to the framebuffer - callers need to make sure to eventually unreference the returned framebuffer again, using drm_framebuffer_put().

void drm_framebuffer_unregister_private(struct drm_framebuffer * fb)

unregister a private fb from the lookup idr

Parameters

struct drm_framebuffer * fb
fb to unregister

Description

Drivers need to call this when cleaning up driver-private framebuffers, e.g. those used for fbdev. Note that the caller must hold a reference of it’s own, i.e. the object may not be destroyed through this call (since it’ll lead to a locking inversion).

NOTE

This function is deprecated. For driver-private framebuffers it is not recommended to embed a framebuffer struct info fbdev struct, instead, a framebuffer pointer is preferred and drm_framebuffer_put() should be called when the framebuffer is to be cleaned up.

void drm_framebuffer_cleanup(struct drm_framebuffer * fb)

remove a framebuffer object

Parameters

struct drm_framebuffer * fb
framebuffer to remove

Description

Cleanup framebuffer. This function is intended to be used from the drivers drm_framebuffer_funcs.destroy callback. It can also be used to clean up driver private framebuffers embedded into a larger structure.

Note that this function does not remove the fb from active usage - if it is still used anywhere, hilarity can ensue since userspace could call getfb on the id and get back -EINVAL. Obviously no concern at driver unload time.

Also, the framebuffer will not be removed from the lookup idr - for user-created framebuffers this will happen in in the rmfb ioctl. For driver-private objects (e.g. for fbdev) drivers need to explicitly call drm_framebuffer_unregister_private.

void drm_framebuffer_remove(struct drm_framebuffer * fb)

remove and unreference a framebuffer object

Parameters

struct drm_framebuffer * fb
framebuffer to remove

Description

Scans all the CRTCs and planes in dev‘s mode_config. If they’re using fb, removes it, setting it to NULL. Then drops the reference to the passed-in framebuffer. Might take the modeset locks.

Note that this function optimizes the cleanup away if the caller holds the last reference to the framebuffer. It is also guaranteed to not take the modeset locks in this case.

int drm_framebuffer_plane_width(int width, const struct drm_framebuffer * fb, int plane)

width of the plane given the first plane

Parameters

int width
width of the first plane
const struct drm_framebuffer * fb
the framebuffer
int plane
plane index

Return

The width of plane, given that the width of the first plane is width.

int drm_framebuffer_plane_height(int height, const struct drm_framebuffer * fb, int plane)

height of the plane given the first plane

Parameters

int height
height of the first plane
const struct drm_framebuffer * fb
the framebuffer
int plane
plane index

Return

The height of plane, given that the height of the first plane is height.

DRM Format Handling

struct drm_format_info

information about a DRM format

Definition

struct drm_format_info {
  u32 format;
  u8 depth;
  u8 num_planes;
  u8 cpp[3];
  u8 hsub;
  u8 vsub;
  bool has_alpha;
};

Members

format
4CC format identifier (DRM_FORMAT_*)
depth
Color depth (number of bits per pixel excluding padding bits), valid for a subset of RGB formats only. This is a legacy field, do not use in new code and set to 0 for new formats.
num_planes
Number of color planes (1 to 3)
cpp
Number of bytes per pixel (per plane)
hsub
Horizontal chroma subsampling factor
vsub
Vertical chroma subsampling factor
has_alpha
Does the format embeds an alpha component?
struct drm_format_name_buf

name of a DRM format

Definition

struct drm_format_name_buf {
  char str[32];
};

Members

str
string buffer containing the format name
uint32_t drm_mode_legacy_fb_format(uint32_t bpp, uint32_t depth)

compute drm fourcc code from legacy description

Parameters

uint32_t bpp
bits per pixels
uint32_t depth
bit depth per pixel

Description

Computes a drm fourcc pixel format code for the given bpp/depth values. Useful in fbdev emulation code, since that deals in those values.

const char * drm_get_format_name(uint32_t format, struct drm_format_name_buf * buf)

fill a string with a drm fourcc format’s name

Parameters

uint32_t format
format to compute name of
struct drm_format_name_buf * buf
caller-supplied buffer
const struct drm_format_info * drm_format_info(u32 format)

query information for a given format

Parameters

u32 format
pixel format (DRM_FORMAT_*)

Description

The caller should only pass a supported pixel format to this function. Unsupported pixel formats will generate a warning in the kernel log.

Return

The instance of struct drm_format_info that describes the pixel format, or NULL if the format is unsupported.

const struct drm_format_info * drm_get_format_info(struct drm_device * dev, const struct drm_mode_fb_cmd2 * mode_cmd)

query information for a given framebuffer configuration

Parameters

struct drm_device * dev
DRM device
const struct drm_mode_fb_cmd2 * mode_cmd
metadata from the userspace fb creation request

Return

The instance of struct drm_format_info that describes the pixel format, or NULL if the format is unsupported.

int drm_format_num_planes(uint32_t format)

get the number of planes for format

Parameters

uint32_t format
pixel format (DRM_FORMAT_*)

Return

The number of planes used by the specified pixel format.

int drm_format_plane_cpp(uint32_t format, int plane)

determine the bytes per pixel value

Parameters

uint32_t format
pixel format (DRM_FORMAT_*)
int plane
plane index

Return

The bytes per pixel value for the specified plane.

int drm_format_horz_chroma_subsampling(uint32_t format)

get the horizontal chroma subsampling factor

Parameters

uint32_t format
pixel format (DRM_FORMAT_*)

Return

The horizontal chroma subsampling factor for the specified pixel format.

int drm_format_vert_chroma_subsampling(uint32_t format)

get the vertical chroma subsampling factor

Parameters

uint32_t format
pixel format (DRM_FORMAT_*)

Return

The vertical chroma subsampling factor for the specified pixel format.

int drm_format_plane_width(int width, uint32_t format, int plane)

width of the plane given the first plane

Parameters

int width
width of the first plane
uint32_t format
pixel format
int plane
plane index

Return

The width of plane, given that the width of the first plane is width.

int drm_format_plane_height(int height, uint32_t format, int plane)

height of the plane given the first plane

Parameters

int height
height of the first plane
uint32_t format
pixel format
int plane
plane index

Return

The height of plane, given that the height of the first plane is height.

Dumb Buffer Objects

The KMS API doesn’t standardize backing storage object creation and leaves it to driver-specific ioctls. Furthermore actually creating a buffer object even for GEM-based drivers is done through a driver-specific ioctl - GEM only has a common userspace interface for sharing and destroying objects. While not an issue for full-fledged graphics stacks that include device-specific userspace components (in libdrm for instance), this limit makes DRM-based early boot graphics unnecessarily complex.

Dumb objects partly alleviate the problem by providing a standard API to create dumb buffers suitable for scanout, which can then be used to create KMS frame buffers.

To support dumb objects drivers must implement the drm_driver.dumb_create operation. drm_driver.dumb_destroy defaults to drm_gem_dumb_destroy() if not set and drm_driver.dumb_map_offset defaults to drm_gem_dumb_map_offset(). See the callbacks for further details.

Note that dumb objects may not be used for gpu acceleration, as has been attempted on some ARM embedded platforms. Such drivers really must have a hardware-specific ioctl to allocate suitable buffer objects.

Plane Abstraction

A plane represents an image source that can be blended with or overlayed on top of a CRTC during the scanout process. Planes take their input data from a drm_framebuffer object. The plane itself specifies the cropping and scaling of that image, and where it is placed on the visible are of a display pipeline, represented by drm_crtc. A plane can also have additional properties that specify how the pixels are positioned and blended, like rotation or Z-position. All these properties are stored in drm_plane_state.

To create a plane, a KMS drivers allocates and zeroes an instances of struct drm_plane (possibly as part of a larger structure) and registers it with a call to drm_universal_plane_init().

Cursor and overlay planes are optional. All drivers should provide one primary plane per CRTC to avoid surprising userspace too much. See enum drm_plane_type for a more in-depth discussion of these special uapi-relevant plane types. Special planes are associated with their CRTC by calling drm_crtc_init_with_planes().

The type of a plane is exposed in the immutable “type” enumeration property, which has one of the following values: “Overlay”, “Primary”, “Cursor”.

Plane Functions Reference

struct drm_plane_state

mutable plane state

Definition

struct drm_plane_state {
  struct drm_plane *plane;
  struct drm_crtc *crtc;
  struct drm_framebuffer *fb;
  struct dma_fence *fence;
  int32_t crtc_x;
  int32_t crtc_y;
  uint32_t crtc_w, crtc_h;
  uint32_t src_x, src_y;
  uint32_t src_h, src_w;
  unsigned int rotation;
  unsigned int zpos;
  unsigned int normalized_zpos;
  enum drm_color_encoding color_encoding;
  enum drm_color_range color_range;
  struct drm_rect src, dst;
  bool visible;
  struct drm_crtc_commit *commit;
  struct drm_atomic_state *state;
};

Members

plane
backpointer to the plane
crtc
Currently bound CRTC, NULL if disabled. Do not this write directly, use drm_atomic_set_crtc_for_plane()
fb
Currently bound framebuffer. Do not write this directly, use drm_atomic_set_fb_for_plane()
fence
Optional fence to wait for before scanning out fb. Do not write this directly, use drm_atomic_set_fence_for_plane()
crtc_x
Left position of visible portion of plane on crtc, signed dest location allows it to be partially off screen.
crtc_y
Upper position of visible portion of plane on crtc, signed dest location allows it to be partially off screen.
crtc_w
width of visible portion of plane on crtc
crtc_h
height of visible portion of plane on crtc
src_x
left position of visible portion of plane within plane (in 16.16)
src_y
upper position of visible portion of plane within plane (in 16.16)
src_h
height of visible portion of plane (in 16.16)
src_w
width of visible portion of plane (in 16.16)
rotation
rotation of the plane
zpos
priority of the given plane on crtc (optional) Note that multiple active planes on the same crtc can have an identical zpos value. The rule to solving the conflict is to compare the plane object IDs; the plane with a higher ID must be stacked on top of a plane with a lower ID.
normalized_zpos
normalized value of zpos: unique, range from 0 to N-1 where N is the number of active planes for given crtc. Note that the driver must call drm_atomic_normalize_zpos() to update this before it can be trusted.
color_encoding
Color encoding for non RGB formats
color_range
Color range for non RGB formats
src
clipped source coordinates of the plane (in 16.16)
dst
clipped destination coordinates of the plane
visible
Visibility of the plane. This can be false even if fb!=NULL and crtc!=NULL, due to clipping.
commit

Tracks the pending commit to prevent use-after-free conditions, and for async plane updates.

May be NULL.

state
backpointer to global drm_atomic_state
struct drm_plane_funcs

driver plane control functions

Definition

struct drm_plane_funcs {
  int (*update_plane)(struct drm_plane *plane,struct drm_crtc *crtc, struct drm_framebuffer *fb,int crtc_x, int crtc_y,unsigned int crtc_w, unsigned int crtc_h,uint32_t src_x, uint32_t src_y,uint32_t src_w, uint32_t src_h, struct drm_modeset_acquire_ctx *ctx);
  int (*disable_plane)(struct drm_plane *plane, struct drm_modeset_acquire_ctx *ctx);
  void (*destroy)(struct drm_plane *plane);
  void (*reset)(struct drm_plane *plane);
  int (*set_property)(struct drm_plane *plane, struct drm_property *property, uint64_t val);
  struct drm_plane_state *(*atomic_duplicate_state)(struct drm_plane *plane);
  void (*atomic_destroy_state)(struct drm_plane *plane, struct drm_plane_state *state);
  int (*atomic_set_property)(struct drm_plane *plane,struct drm_plane_state *state,struct drm_property *property, uint64_t val);
  int (*atomic_get_property)(struct drm_plane *plane,const struct drm_plane_state *state,struct drm_property *property, uint64_t *val);
  int (*late_register)(struct drm_plane *plane);
  void (*early_unregister)(struct drm_plane *plane);
  void (*atomic_print_state)(struct drm_printer *p, const struct drm_plane_state *state);
  bool (*format_mod_supported)(struct drm_plane *plane, uint32_t format, uint64_t modifier);
};

Members

update_plane

This is the legacy entry point to enable and configure the plane for the given CRTC and framebuffer. It is never called to disable the plane, i.e. the passed-in crtc and fb paramters are never NULL.

The source rectangle in frame buffer memory coordinates is given by the src_x, src_y, src_w and src_h parameters (as 16.16 fixed point values). Devices that don’t support subpixel plane coordinates can ignore the fractional part.

The destination rectangle in CRTC coordinates is given by the crtc_x, crtc_y, crtc_w and crtc_h parameters (as integer values). Devices scale the source rectangle to the destination rectangle. If scaling is not supported, and the source rectangle size doesn’t match the destination rectangle size, the driver must return a -<errorname>EINVAL</errorname> error.

Drivers implementing atomic modeset should use drm_atomic_helper_update_plane() to implement this hook.

RETURNS:

0 on success or a negative error code on failure.

disable_plane

This is the legacy entry point to disable the plane. The DRM core calls this method in response to a DRM_IOCTL_MODE_SETPLANE IOCTL call with the frame buffer ID set to 0. Disabled planes must not be processed by the CRTC.

Drivers implementing atomic modeset should use drm_atomic_helper_disable_plane() to implement this hook.

RETURNS:

0 on success or a negative error code on failure.

destroy
Clean up plane resources. This is only called at driver unload time through drm_mode_config_cleanup() since a plane cannot be hotplugged in DRM.
reset

Reset plane hardware and software state to off. This function isn’t called by the core directly, only through drm_mode_config_reset(). It’s not a helper hook only for historical reasons.

Atomic drivers can use drm_atomic_helper_plane_reset() to reset atomic state using this hook.

set_property

This is the legacy entry point to update a property attached to the plane.

This callback is optional if the driver does not support any legacy driver-private properties. For atomic drivers it is not used because property handling is done entirely in the DRM core.

RETURNS:

0 on success or a negative error code on failure.

atomic_duplicate_state

Duplicate the current atomic state for this plane and return it. The core and helpers guarantee that any atomic state duplicated with this hook and still owned by the caller (i.e. not transferred to the driver by calling drm_mode_config_funcs.atomic_commit) will be cleaned up by calling the atomic_destroy_state hook in this structure.

Atomic drivers which don’t subclass struct drm_plane_state should use drm_atomic_helper_plane_duplicate_state(). Drivers that subclass the state structure to extend it with driver-private state should use __drm_atomic_helper_plane_duplicate_state() to make sure shared state is duplicated in a consistent fashion across drivers.

It is an error to call this hook before drm_plane.state has been initialized correctly.

NOTE:

If the duplicate state references refcounted resources this hook must acquire a reference for each of them. The driver must release these references again in atomic_destroy_state.

RETURNS:

Duplicated atomic state or NULL when the allocation failed.

atomic_destroy_state
Destroy a state duplicated with atomic_duplicate_state and release or unreference all resources it references
atomic_set_property

Decode a driver-private property value and store the decoded value into the passed-in state structure. Since the atomic core decodes all standardized properties (even for extensions beyond the core set of properties which might not be implemented by all drivers) this requires drivers to subclass the state structure.

Such driver-private properties should really only be implemented for truly hardware/vendor specific state. Instead it is preferred to standardize atomic extension and decode the properties used to expose such an extension in the core.

Do not call this function directly, use drm_atomic_plane_set_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

NOTE:

This function is called in the state assembly phase of atomic modesets, which can be aborted for any reason (including on userspace’s request to just check whether a configuration would be possible). Drivers MUST NOT touch any persistent state (hardware or software) or data structures except the passed in state parameter.

Also since userspace controls in which order properties are set this function must not do any input validation (since the state update is incomplete and hence likely inconsistent). Instead any such input validation must be done in the various atomic_check callbacks.

RETURNS:

0 if the property has been found, -EINVAL if the property isn’t implemented by the driver (which shouldn’t ever happen, the core only asks for properties attached to this plane). No other validation is allowed by the driver. The core already checks that the property value is within the range (integer, valid enum value, ...) the driver set when registering the property.

atomic_get_property

Reads out the decoded driver-private property. This is used to implement the GETPLANE IOCTL.

Do not call this function directly, use drm_atomic_plane_get_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

RETURNS:

0 on success, -EINVAL if the property isn’t implemented by the driver (which should never happen, the core only asks for properties attached to this plane).

late_register

This optional hook can be used to register additional userspace interfaces attached to the plane like debugfs interfaces. It is called late in the driver load sequence from drm_dev_register(). Everything added from this callback should be unregistered in the early_unregister callback.

Returns:

0 on success, or a negative error code on failure.

early_unregister
This optional hook should be used to unregister the additional userspace interfaces attached to the plane from late_register. It is called from drm_dev_unregister(), early in the driver unload sequence to disable userspace access before data structures are torndown.
atomic_print_state

If driver subclasses struct drm_plane_state, it should implement this optional hook for printing additional driver specific state.

Do not call this directly, use drm_atomic_plane_print_state() instead.

format_mod_supported

This optional hook is used for the DRM to determine if the given format/modifier combination is valid for the plane. This allows the DRM to generate the correct format bitmask (which formats apply to which modifier).

Returns:

True if the given modifier is valid for that format on the plane. False otherwise.

enum drm_plane_type

uapi plane type enumeration

Constants

DRM_PLANE_TYPE_OVERLAY
Overlay planes represent all non-primary, non-cursor planes. Some drivers refer to these types of planes as “sprites” internally.
DRM_PLANE_TYPE_PRIMARY
Primary planes represent a “main” plane for a CRTC. Primary planes are the planes operated upon by CRTC modesetting and flipping operations described in the drm_crtc_funcs.page_flip and drm_crtc_funcs.set_config hooks.
DRM_PLANE_TYPE_CURSOR
Cursor planes represent a “cursor” plane for a CRTC. Cursor planes are the planes operated upon by the DRM_IOCTL_MODE_CURSOR and DRM_IOCTL_MODE_CURSOR2 IOCTLs.

Description

For historical reasons not all planes are made the same. This enumeration is used to tell the different types of planes apart to implement the different uapi semantics for them. For userspace which is universal plane aware and which is using that atomic IOCTL there’s no difference between these planes (beyong what the driver and hardware can support of course).

For compatibility with legacy userspace, only overlay planes are made available to userspace by default. Userspace clients may set the DRM_CLIENT_CAP_UNIVERSAL_PLANES client capability bit to indicate that they wish to receive a universal plane list containing all plane types. See also drm_for_each_legacy_plane().

WARNING: The values of this enum is UABI since they’re exposed in the “type” property.

struct drm_plane

central DRM plane control structure

Definition

struct drm_plane {
  struct drm_device *dev;
  struct list_head head;
  char *name;
  struct drm_modeset_lock mutex;
  struct drm_mode_object base;
  uint32_t possible_crtcs;
  uint32_t *format_types;
  unsigned int format_count;
  bool format_default;
  uint64_t *modifiers;
  unsigned int modifier_count;
  struct drm_crtc *crtc;
  struct drm_framebuffer *fb;
  struct drm_framebuffer *old_fb;
  const struct drm_plane_funcs *funcs;
  struct drm_object_properties properties;
  enum drm_plane_type type;
  unsigned index;
  const struct drm_plane_helper_funcs *helper_private;
  struct drm_plane_state *state;
  struct drm_property *zpos_property;
  struct drm_property *rotation_property;
  struct drm_property *color_encoding_property;
  struct drm_property *color_range_property;
};

Members

dev
DRM device this plane belongs to
head
for list management
name
human readable name, can be overwritten by the driver
mutex

Protects modeset plane state, together with the drm_crtc.mutex of CRTC this plane is linked to (when active, getting activated or getting disabled).

For atomic drivers specifically this protects state.

base
base mode object
possible_crtcs
pipes this plane can be bound to
format_types
array of formats supported by this plane
format_count
number of formats supported
format_default
driver hasn’t supplied supported formats for the plane
modifiers
array of modifiers supported by this plane
modifier_count
number of modifiers supported
crtc
Currently bound CRTC, only really meaningful for non-atomic drivers. Atomic drivers should instead check drm_plane_state.crtc.
fb
Currently bound framebuffer, only really meaningful for non-atomic drivers. Atomic drivers should instead check drm_plane_state.fb.
old_fb
Temporary tracking of the old fb while a modeset is ongoing. Used by drm_mode_set_config_internal() to implement correct refcounting.
funcs
helper functions
properties
property tracking for this plane
type
type of plane (overlay, primary, cursor)
index
Position inside the mode_config.list, can be used as an array index. It is invariant over the lifetime of the plane.
helper_private
mid-layer private data
state

Current atomic state for this plane.

This is protected by mutex. Note that nonblocking atomic commits access the current plane state without taking locks. Either by going through the struct drm_atomic_state pointers, see for_each_oldnew_plane_in_state(), for_each_old_plane_in_state() and for_each_new_plane_in_state(). Or through careful ordering of atomic commit operations as implemented in the atomic helpers, see struct drm_crtc_commit.

zpos_property
zpos property for this plane
rotation_property
rotation property for this plane
color_encoding_property
Optional “COLOR_ENCODING” enum property for specifying color encoding for non RGB formats. See drm_plane_create_color_properties().
color_range_property
Optional “COLOR_RANGE” enum property for specifying color range for non RGB formats. See drm_plane_create_color_properties().
unsigned int drm_plane_index(struct drm_plane * plane)

find the index of a registered plane

Parameters

struct drm_plane * plane
plane to find index for

Description

Given a registered plane, return the index of that plane within a DRM device’s list of planes.

struct drm_plane * drm_plane_find(struct drm_device * dev, struct drm_file * file_priv, uint32_t id)

find a drm_plane

Parameters

struct drm_device * dev
DRM device
struct drm_file * file_priv
drm file to check for lease against.
uint32_t id
plane id

Description

Returns the plane with id, NULL if it doesn’t exist. Simple wrapper around drm_mode_object_find().

drm_for_each_plane_mask(plane, dev, plane_mask)

iterate over planes specified by bitmask

Parameters

plane
the loop cursor
dev
the DRM device
plane_mask
bitmask of plane indices

Description

Iterate over all planes specified by bitmask.

drm_for_each_legacy_plane(plane, dev)

iterate over all planes for legacy userspace

Parameters

plane
the loop cursor
dev
the DRM device

Description

Iterate over all legacy planes of dev, excluding primary and cursor planes. This is useful for implementing userspace apis when userspace is not universal plane aware. See also enum drm_plane_type.

drm_for_each_plane(plane, dev)

iterate over all planes

Parameters

plane
the loop cursor
dev
the DRM device

Description

Iterate over all planes of dev, include primary and cursor planes.

int drm_universal_plane_init(struct drm_device * dev, struct drm_plane * plane, uint32_t possible_crtcs, const struct drm_plane_funcs * funcs, const uint32_t * formats, unsigned int format_count, const uint64_t * format_modifiers, enum drm_plane_type type, const char * name, ...)

Initialize a new universal plane object

Parameters

struct drm_device * dev
DRM device
struct drm_plane * plane
plane object to init
uint32_t possible_crtcs
bitmask of possible CRTCs
const struct drm_plane_funcs * funcs
callbacks for the new plane
const uint32_t * formats
array of supported formats (DRM_FORMAT_*)
unsigned int format_count
number of elements in formats
const uint64_t * format_modifiers
array of struct drm_format modifiers terminated by DRM_FORMAT_MOD_INVALID
enum drm_plane_type type
type of plane (overlay, primary, cursor)
const char * name
printf style format string for the plane name, or NULL for default name
...
variable arguments

Description

Initializes a plane object of type type.

Return

Zero on success, error code on failure.

int drm_plane_init(struct drm_device * dev, struct drm_plane * plane, uint32_t possible_crtcs, const struct drm_plane_funcs * funcs, const uint32_t * formats, unsigned int format_count, bool is_primary)

Initialize a legacy plane

Parameters

struct drm_device * dev
DRM device
struct drm_plane * plane
plane object to init
uint32_t possible_crtcs
bitmask of possible CRTCs
const struct drm_plane_funcs * funcs
callbacks for the new plane
const uint32_t * formats
array of supported formats (DRM_FORMAT_*)
unsigned int format_count
number of elements in formats
bool is_primary
plane type (primary vs overlay)

Description

Legacy API to initialize a DRM plane.

New drivers should call drm_universal_plane_init() instead.

Return

Zero on success, error code on failure.

void drm_plane_cleanup(struct drm_plane * plane)

Clean up the core plane usage

Parameters

struct drm_plane * plane
plane to cleanup

Description

This function cleans up plane and removes it from the DRM mode setting core. Note that the function does not free the plane structure itself, this is the responsibility of the caller.

struct drm_plane * drm_plane_from_index(struct drm_device * dev, int idx)

find the registered plane at an index

Parameters

struct drm_device * dev
DRM device
int idx
index of registered plane to find for

Description

Given a plane index, return the registered plane from DRM device’s list of planes with matching index. This is the inverse of drm_plane_index().

void drm_plane_force_disable(struct drm_plane * plane)

Forcibly disable a plane

Parameters

struct drm_plane * plane
plane to disable

Description

Forces the plane to be disabled.

Used when the plane’s current framebuffer is destroyed, and when restoring fbdev mode.

Note that this function is not suitable for atomic drivers, since it doesn’t wire through the lock acquisition context properly and hence can’t handle retries or driver private locks. You probably want to use drm_atomic_helper_disable_plane() or drm_atomic_helper_disable_planes_on_crtc() instead.

int drm_mode_plane_set_obj_prop(struct drm_plane * plane, struct drm_property * property, uint64_t value)

set the value of a property

Parameters

struct drm_plane * plane
drm plane object to set property value for
struct drm_property * property
property to set
uint64_t value
value the property should be set to

Description

This functions sets a given property on a given plane object. This function calls the driver’s ->set_property callback and changes the software state of the property if the callback succeeds.

Return

Zero on success, error code on failure.

Display Modes Function Reference

enum drm_mode_status

hardware support status of a mode

Constants

MODE_OK
Mode OK
MODE_HSYNC
hsync out of range
MODE_VSYNC
vsync out of range
MODE_H_ILLEGAL
mode has illegal horizontal timings
MODE_V_ILLEGAL
mode has illegal horizontal timings
MODE_BAD_WIDTH
requires an unsupported linepitch
MODE_NOMODE
no mode with a matching name
MODE_NO_INTERLACE
interlaced mode not supported
MODE_NO_DBLESCAN
doublescan mode not supported
MODE_NO_VSCAN
multiscan mode not supported
MODE_MEM
insufficient video memory
MODE_VIRTUAL_X
mode width too large for specified virtual size
MODE_VIRTUAL_Y
mode height too large for specified virtual size
MODE_MEM_VIRT
insufficient video memory given virtual size
MODE_NOCLOCK
no fixed clock available
MODE_CLOCK_HIGH
clock required is too high
MODE_CLOCK_LOW
clock required is too low
MODE_CLOCK_RANGE
clock/mode isn’t in a ClockRange
MODE_BAD_HVALUE
horizontal timing was out of range
MODE_BAD_VVALUE
vertical timing was out of range
MODE_BAD_VSCAN
VScan value out of range
MODE_HSYNC_NARROW
horizontal sync too narrow
MODE_HSYNC_WIDE
horizontal sync too wide
MODE_HBLANK_NARROW
horizontal blanking too narrow
MODE_HBLANK_WIDE
horizontal blanking too wide
MODE_VSYNC_NARROW
vertical sync too narrow
MODE_VSYNC_WIDE
vertical sync too wide
MODE_VBLANK_NARROW
vertical blanking too narrow
MODE_VBLANK_WIDE
vertical blanking too wide
MODE_PANEL
exceeds panel dimensions
MODE_INTERLACE_WIDTH
width too large for interlaced mode
MODE_ONE_WIDTH
only one width is supported
MODE_ONE_HEIGHT
only one height is supported
MODE_ONE_SIZE
only one resolution is supported
MODE_NO_REDUCED
monitor doesn’t accept reduced blanking
MODE_NO_STEREO
stereo modes not supported
MODE_NO_420
ycbcr 420 modes not supported
MODE_STALE
mode has become stale
MODE_BAD
unspecified reason
MODE_ERROR
error condition

Description

This enum is used to filter out modes not supported by the driver/hardware combination.

struct drm_display_mode

DRM kernel-internal display mode structure

Definition

struct drm_display_mode {
  struct list_head head;
  struct drm_mode_object base;
  char name[DRM_DISPLAY_MODE_LEN];
  enum drm_mode_status status;
  unsigned int type;
  int clock;
  int hdisplay;
  int hsync_start;
  int hsync_end;
  int htotal;
  int hskew;
  int vdisplay;
  int vsync_start;
  int vsync_end;
  int vtotal;
  int vscan;
  unsigned int flags;
  int width_mm;
  int height_mm;
  int crtc_clock;
  int crtc_hdisplay;
  int crtc_hblank_start;
  int crtc_hblank_end;
  int crtc_hsync_start;
  int crtc_hsync_end;
  int crtc_htotal;
  int crtc_hskew;
  int crtc_vdisplay;
  int crtc_vblank_start;
  int crtc_vblank_end;
  int crtc_vsync_start;
  int crtc_vsync_end;
  int crtc_vtotal;
  int *private;
  int private_flags;
  int vrefresh;
  int hsync;
  enum hdmi_picture_aspect picture_aspect_ratio;
};

Members

head
struct list_head for mode lists.
base

A display mode is a normal modeset object, possibly including public userspace id.

FIXME:

This can probably be removed since the entire concept of userspace managing modes explicitly has never landed in upstream kernel mode setting support.

name
Human-readable name of the mode, filled out with drm_mode_set_name().
status
Status of the mode, used to filter out modes not supported by the hardware. See enum drm_mode_status.
type

A bitmask of flags, mostly about the source of a mode. Possible flags are:

  • DRM_MODE_TYPE_PREFERRED: Preferred mode, usually the native resolution of an LCD panel. There should only be one preferred mode per connector at any given time.
  • DRM_MODE_TYPE_DRIVER: Mode created by the driver, which is all of them really. Drivers must set this bit for all modes they create and expose to userspace.
  • DRM_MODE_TYPE_USERDEF: Mode defined via kernel command line

Plus a big list of flags which shouldn’t be used at all, but are still around since these flags are also used in the userspace ABI. We no longer accept modes with these types though:

  • DRM_MODE_TYPE_BUILTIN: Meant for hard-coded modes, unused. Use DRM_MODE_TYPE_DRIVER instead.
  • DRM_MODE_TYPE_DEFAULT: Again a leftover, use DRM_MODE_TYPE_PREFERRED instead.
  • DRM_MODE_TYPE_CLOCK_C and DRM_MODE_TYPE_CRTC_C: Define leftovers which are stuck around for hysterical raisins only. No one has an idea what they were meant for. Don’t use.
clock
Pixel clock in kHz.
hdisplay
horizontal display size
hsync_start
horizontal sync start
hsync_end
horizontal sync end
htotal
horizontal total size
hskew
horizontal skew?!
vdisplay
vertical display size
vsync_start
vertical sync start
vsync_end
vertical sync end
vtotal
vertical total size
vscan
vertical scan?!
flags

Sync and timing flags:

  • DRM_MODE_FLAG_PHSYNC: horizontal sync is active high.
  • DRM_MODE_FLAG_NHSYNC: horizontal sync is active low.
  • DRM_MODE_FLAG_PVSYNC: vertical sync is active high.
  • DRM_MODE_FLAG_NVSYNC: vertical sync is active low.
  • DRM_MODE_FLAG_INTERLACE: mode is interlaced.
  • DRM_MODE_FLAG_DBLSCAN: mode uses doublescan.
  • DRM_MODE_FLAG_CSYNC: mode uses composite sync.
  • DRM_MODE_FLAG_PCSYNC: composite sync is active high.
  • DRM_MODE_FLAG_NCSYNC: composite sync is active low.
  • DRM_MODE_FLAG_HSKEW: hskew provided (not used?).
  • DRM_MODE_FLAG_BCAST: <deprecated>
  • DRM_MODE_FLAG_PIXMUX: <deprecated>
  • DRM_MODE_FLAG_DBLCLK: double-clocked mode.
  • DRM_MODE_FLAG_CLKDIV2: half-clocked mode.

Additionally there’s flags to specify how 3D modes are packed:

  • DRM_MODE_FLAG_3D_NONE: normal, non-3D mode.
  • DRM_MODE_FLAG_3D_FRAME_PACKING: 2 full frames for left and right.
  • DRM_MODE_FLAG_3D_FIELD_ALTERNATIVE: interleaved like fields.
  • DRM_MODE_FLAG_3D_LINE_ALTERNATIVE: interleaved lines.
  • DRM_MODE_FLAG_3D_SIDE_BY_SIDE_FULL: side-by-side full frames.
  • DRM_MODE_FLAG_3D_L_DEPTH: ?
  • DRM_MODE_FLAG_3D_L_DEPTH_GFX_GFX_DEPTH: ?
  • DRM_MODE_FLAG_3D_TOP_AND_BOTTOM: frame split into top and bottom parts.
  • DRM_MODE_FLAG_3D_SIDE_BY_SIDE_HALF: frame split into left and right parts.
width_mm
Addressable size of the output in mm, projectors should set this to 0.
height_mm
Addressable size of the output in mm, projectors should set this to 0.
crtc_clock

Actual pixel or dot clock in the hardware. This differs from the logical clock when e.g. using interlacing, double-clocking, stereo modes or other fancy stuff that changes the timings and signals actually sent over the wire.

This is again in kHz.

Note that with digital outputs like HDMI or DP there’s usually a massive confusion between the dot clock and the signal clock at the bit encoding level. Especially when a 8b/10b encoding is used and the difference is exactly a factor of 10.

crtc_hdisplay
hardware mode horizontal display size
crtc_hblank_start
hardware mode horizontal blank start
crtc_hblank_end
hardware mode horizontal blank end
crtc_hsync_start
hardware mode horizontal sync start
crtc_hsync_end
hardware mode horizontal sync end
crtc_htotal
hardware mode horizontal total size
crtc_hskew
hardware mode horizontal skew?!
crtc_vdisplay
hardware mode vertical display size
crtc_vblank_start
hardware mode vertical blank start
crtc_vblank_end
hardware mode vertical blank end
crtc_vsync_start
hardware mode vertical sync start
crtc_vsync_end
hardware mode vertical sync end
crtc_vtotal
hardware mode vertical total size
private
Pointer for driver private data. This can only be used for mode objects passed to drivers in modeset operations. It shouldn’t be used by atomic drivers since they can store any additional data by subclassing state structures.
private_flags
Similar to private, but just an integer.
vrefresh

Vertical refresh rate, for debug output in human readable form. Not used in a functional way.

This value is in Hz.

hsync

Horizontal refresh rate, for debug output in human readable form. Not used in a functional way.

This value is in kHz.

picture_aspect_ratio
Field for setting the HDMI picture aspect ratio of a mode.

Description

The horizontal and vertical timings are defined per the following diagram.

          Active                 Front           Sync           Back
         Region                 Porch                          Porch
<-----------------------><----------------><-------------><-------------->
  //////////////////////|
 ////////////////////// |
//////////////////////  |..................               ................
                                           _______________
<----- [hv]display ----->
<------------- [hv]sync_start ------------>
<--------------------- [hv]sync_end --------------------->
<-------------------------------- [hv]total ----------------------------->*

This structure contains two copies of timings. First are the plain timings, which specify the logical mode, as it would be for a progressive 1:1 scanout at the refresh rate userspace can observe through vblank timestamps. Then there’s the hardware timings, which are corrected for interlacing, double-clocking and similar things. They are provided as a convenience, and can be appropriately computed using drm_mode_set_crtcinfo().

For printing you can use DRM_MODE_FMT and DRM_MODE_ARG().

DRM_MODE_FMT()

printf string for struct drm_display_mode

Parameters

DRM_MODE_ARG(m)

printf arguments for struct drm_display_mode

Parameters

m
display mode
bool drm_mode_is_stereo(const struct drm_display_mode * mode)

check for stereo mode flags

Parameters

const struct drm_display_mode * mode
drm_display_mode to check

Return

True if the mode is one of the stereo modes (like side-by-side), false if not.

void drm_mode_debug_printmodeline(const struct drm_display_mode * mode)

print a mode to dmesg

Parameters

const struct drm_display_mode * mode
mode to print

Description

Describe mode using DRM_DEBUG.

struct drm_display_mode * drm_mode_create(struct drm_device * dev)

create a new display mode

Parameters

struct drm_device * dev
DRM device

Description

Create a new, cleared drm_display_mode with kzalloc, allocate an ID for it and return it.

Return

Pointer to new mode on success, NULL on error.

void drm_mode_destroy(struct drm_device * dev, struct drm_display_mode * mode)

remove a mode

Parameters

struct drm_device * dev
DRM device
struct drm_display_mode * mode
mode to remove

Description

Release mode‘s unique ID, then free it mode structure itself using kfree.

void drm_mode_probed_add(struct drm_connector * connector, struct drm_display_mode * mode)

add a mode to a connector’s probed_mode list

Parameters

struct drm_connector * connector
connector the new mode
struct drm_display_mode * mode
mode data

Description

Add mode to connector‘s probed_mode list for later use. This list should then in a second step get filtered and all the modes actually supported by the hardware moved to the connector‘s modes list.

struct drm_display_mode * drm_cvt_mode(struct drm_device * dev, int hdisplay, int vdisplay, int vrefresh, bool reduced, bool interlaced, bool margins)

create a modeline based on the CVT algorithm

Parameters

struct drm_device * dev
drm device
int hdisplay
hdisplay size
int vdisplay
vdisplay size
int vrefresh
vrefresh rate
bool reduced
whether to use reduced blanking
bool interlaced
whether to compute an interlaced mode
bool margins
whether to add margins (borders)

Description

This function is called to generate the modeline based on CVT algorithm according to the hdisplay, vdisplay, vrefresh. It is based from the VESA(TM) Coordinated Video Timing Generator by Graham Loveridge April 9, 2003 available at http://www.elo.utfsm.cl/~elo212/docs/CVTd6r1.xls

And it is copied from xf86CVTmode in xserver/hw/xfree86/modes/xf86cvt.c. What I have done is to translate it by using integer calculation.

Return

The modeline based on the CVT algorithm stored in a drm_display_mode object. The display mode object is allocated with drm_mode_create(). Returns NULL when no mode could be allocated.

struct drm_display_mode * drm_gtf_mode_complex(struct drm_device * dev, int hdisplay, int vdisplay, int vrefresh, bool interlaced, int margins, int GTF_M, int GTF_2C, int GTF_K, int GTF_2J)

create the modeline based on the full GTF algorithm

Parameters

struct drm_device * dev
drm device
int hdisplay
hdisplay size
int vdisplay
vdisplay size
int vrefresh
vrefresh rate.
bool interlaced
whether to compute an interlaced mode
int margins
desired margin (borders) size
int GTF_M
extended GTF formula parameters
int GTF_2C
extended GTF formula parameters
int GTF_K
extended GTF formula parameters
int GTF_2J
extended GTF formula parameters

Description

GTF feature blocks specify C and J in multiples of 0.5, so we pass them in here multiplied by two. For a C of 40, pass in 80.

Return

The modeline based on the full GTF algorithm stored in a drm_display_mode object. The display mode object is allocated with drm_mode_create(). Returns NULL when no mode could be allocated.

struct drm_display_mode * drm_gtf_mode(struct drm_device * dev, int hdisplay, int vdisplay, int vrefresh, bool interlaced, int margins)

create the modeline based on the GTF algorithm

Parameters

struct drm_device * dev
drm device
int hdisplay
hdisplay size
int vdisplay
vdisplay size
int vrefresh
vrefresh rate.
bool interlaced
whether to compute an interlaced mode
int margins
desired margin (borders) size

Description

return the modeline based on GTF algorithm

This function is to create the modeline based on the GTF algorithm. Generalized Timing Formula is derived from:

GTF Spreadsheet by Andy Morrish (1/5/97) available at http://www.vesa.org

And it is copied from the file of xserver/hw/xfree86/modes/xf86gtf.c. What I have done is to translate it by using integer calculation. I also refer to the function of fb_get_mode in the file of drivers/video/fbmon.c

Standard GTF parameters:

M = 600
C = 40
K = 128
J = 20

Return

The modeline based on the GTF algorithm stored in a drm_display_mode object. The display mode object is allocated with drm_mode_create(). Returns NULL when no mode could be allocated.

void drm_display_mode_from_videomode(const struct videomode * vm, struct drm_display_mode * dmode)

fill in dmode using vm,

Parameters

const struct videomode * vm
videomode structure to use as source
struct drm_display_mode * dmode
drm_display_mode structure to use as destination

Description

Fills out dmode using the display mode specified in vm.

void drm_display_mode_to_videomode(const struct drm_display_mode * dmode, struct videomode * vm)

fill in vm using dmode,

Parameters

const struct drm_display_mode * dmode
drm_display_mode structure to use as source
struct videomode * vm
videomode structure to use as destination

Description

Fills out vm using the display mode specified in dmode.

void drm_bus_flags_from_videomode(const struct videomode * vm, u32 * bus_flags)

extract information about pixelclk and DE polarity from videomode and store it in a separate variable

Parameters

const struct videomode * vm
videomode structure to use
u32 * bus_flags
information about pixelclk and DE polarity will be stored here

Description

Sets DRM_BUS_FLAG_DE_(LOW|HIGH) and DRM_BUS_FLAG_PIXDATA_(POS|NEG)EDGE in bus_flags according to DISPLAY_FLAGS found in vm

int of_get_drm_display_mode(struct device_node * np, struct drm_display_mode * dmode, u32 * bus_flags, int index)

get a drm_display_mode from devicetree

Parameters

struct device_node * np
device_node with the timing specification
struct drm_display_mode * dmode
will be set to the return value
u32 * bus_flags
information about pixelclk and DE polarity
int index
index into the list of display timings in devicetree

Description

This function is expensive and should only be used, if only one mode is to be read from DT. To get multiple modes start with of_get_display_timings and work with that instead.

Return

0 on success, a negative errno code when no of videomode node was found.

void drm_mode_set_name(struct drm_display_mode * mode)

set the name on a mode

Parameters

struct drm_display_mode * mode
name will be set in this mode

Description

Set the name of mode to a standard format which is <hdisplay>x<vdisplay> with an optional ‘i’ suffix for interlaced modes.

int drm_mode_hsync(const struct drm_display_mode * mode)

get the hsync of a mode

Parameters

const struct drm_display_mode * mode
mode

Return

modes‘s hsync rate in kHz, rounded to the nearest integer. Calculates the value first if it is not yet set.

int drm_mode_vrefresh(const struct drm_display_mode * mode)

get the vrefresh of a mode

Parameters

const struct drm_display_mode * mode
mode

Return

modes‘s vrefresh rate in Hz, rounded to the nearest integer. Calculates the value first if it is not yet set.

void drm_mode_get_hv_timing(const struct drm_display_mode * mode, int * hdisplay, int * vdisplay)

Fetches hdisplay/vdisplay for given mode

Parameters

const struct drm_display_mode * mode
mode to query
int * hdisplay
hdisplay value to fill in
int * vdisplay
vdisplay value to fill in

Description

The vdisplay value will be doubled if the specified mode is a stereo mode of the appropriate layout.

void drm_mode_set_crtcinfo(struct drm_display_mode * p, int adjust_flags)

set CRTC modesetting timing parameters

Parameters

struct drm_display_mode * p
mode
int adjust_flags
a combination of adjustment flags

Description

Setup the CRTC modesetting timing parameters for p, adjusting if necessary.

  • The CRTC_INTERLACE_HALVE_V flag can be used to halve vertical timings of interlaced modes.
  • The CRTC_STEREO_DOUBLE flag can be used to compute the timings for buffers containing two eyes (only adjust the timings when needed, eg. for “frame packing” or “side by side full”).
  • The CRTC_NO_DBLSCAN and CRTC_NO_VSCAN flags request that adjustment not be performed for doublescan and vscan > 1 modes respectively.
void drm_mode_copy(struct drm_display_mode * dst, const struct drm_display_mode * src)

copy the mode

Parameters

struct drm_display_mode * dst
mode to overwrite
const struct drm_display_mode * src
mode to copy

Description

Copy an existing mode into another mode, preserving the object id and list head of the destination mode.

struct drm_display_mode * drm_mode_duplicate(struct drm_device * dev, const struct drm_display_mode * mode)

allocate and duplicate an existing mode

Parameters

struct drm_device * dev
drm_device to allocate the duplicated mode for
const struct drm_display_mode * mode
mode to duplicate

Description

Just allocate a new mode, copy the existing mode into it, and return a pointer to it. Used to create new instances of established modes.

Return

Pointer to duplicated mode on success, NULL on error.

bool drm_mode_equal(const struct drm_display_mode * mode1, const struct drm_display_mode * mode2)

test modes for equality

Parameters

const struct drm_display_mode * mode1
first mode
const struct drm_display_mode * mode2
second mode

Description

Check to see if mode1 and mode2 are equivalent.

Return

True if the modes are equal, false otherwise.

bool drm_mode_equal_no_clocks(const struct drm_display_mode * mode1, const struct drm_display_mode * mode2)

test modes for equality

Parameters

const struct drm_display_mode * mode1
first mode
const struct drm_display_mode * mode2
second mode

Description

Check to see if mode1 and mode2 are equivalent, but don’t check the pixel clocks.

Return

True if the modes are equal, false otherwise.

bool drm_mode_equal_no_clocks_no_stereo(const struct drm_display_mode * mode1, const struct drm_display_mode * mode2)

test modes for equality

Parameters

const struct drm_display_mode * mode1
first mode
const struct drm_display_mode * mode2
second mode

Description

Check to see if mode1 and mode2 are equivalent, but don’t check the pixel clocks nor the stereo layout.

Return

True if the modes are equal, false otherwise.

enum drm_mode_status drm_mode_validate_driver(struct drm_device * dev, const struct drm_display_mode * mode)

make sure the mode is somewhat sane

Parameters

struct drm_device * dev
drm device
const struct drm_display_mode * mode
mode to check

Description

First do basic validation on the mode, and then allow the driver to check for device/driver specific limitations via the optional drm_mode_config_helper_funcs.mode_valid hook.

Return

The mode status

enum drm_mode_status drm_mode_validate_size(const struct drm_display_mode * mode, int maxX, int maxY)

make sure modes adhere to size constraints

Parameters

const struct drm_display_mode * mode
mode to check
int maxX
maximum width
int maxY
maximum height

Description

This function is a helper which can be used to validate modes against size limitations of the DRM device/connector. If a mode is too big its status member is updated with the appropriate validation failure code. The list itself is not changed.

Return

The mode status

enum drm_mode_status drm_mode_validate_ycbcr420(const struct drm_display_mode * mode, struct drm_connector * connector)

add ‘ycbcr420-only’ modes only when allowed

Parameters

const struct drm_display_mode * mode
mode to check
struct drm_connector * connector
drm connector under action

Description

This function is a helper which can be used to filter out any YCBCR420 only mode, when the source doesn’t support it.

Return

The mode status

void drm_mode_prune_invalid(struct drm_device * dev, struct list_head * mode_list, bool verbose)

remove invalid modes from mode list

Parameters

struct drm_device * dev
DRM device
struct list_head * mode_list
list of modes to check
bool verbose
be verbose about it

Description

This helper function can be used to prune a display mode list after validation has been completed. All modes who’s status is not MODE_OK will be removed from the list, and if verbose the status code and mode name is also printed to dmesg.

void drm_mode_sort(struct list_head * mode_list)

sort mode list

Parameters

struct list_head * mode_list
list of drm_display_mode structures to sort

Description

Sort mode_list by favorability, moving good modes to the head of the list.

void drm_mode_connector_list_update(struct drm_connector * connector)

update the mode list for the connector

Parameters

struct drm_connector * connector
the connector to update

Description

This moves the modes from the connector probed_modes list to the actual mode list. It compares the probed mode against the current list and only adds different/new modes.

This is just a helper functions doesn’t validate any modes itself and also doesn’t prune any invalid modes. Callers need to do that themselves.

bool drm_mode_parse_command_line_for_connector(const char * mode_option, struct drm_connector * connector, struct drm_cmdline_mode * mode)

parse command line modeline for connector

Parameters

const char * mode_option
optional per connector mode option
struct drm_connector * connector
connector to parse modeline for
struct drm_cmdline_mode * mode
preallocated drm_cmdline_mode structure to fill out

Description

This parses mode_option command line modeline for modes and options to configure the connector. If mode_option is NULL the default command line modeline in fb_mode_option will be parsed instead.

This uses the same parameters as the fb modedb.c, except for an extra force-enable, force-enable-digital and force-disable bit at the end:

<xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m][eDd]

The intermediate drm_cmdline_mode structure is required to store additional options from the command line modline like the force-enable/disable flag.

Return

True if a valid modeline has been parsed, false otherwise.

struct drm_display_mode * drm_mode_create_from_cmdline_mode(struct drm_device * dev, struct drm_cmdline_mode * cmd)

convert a command line modeline into a DRM display mode

Parameters

struct drm_device * dev
DRM device to create the new mode for
struct drm_cmdline_mode * cmd
input command line modeline

Return

Pointer to converted mode on success, NULL on error.

bool drm_mode_is_420_only(const struct drm_display_info * display, const struct drm_display_mode * mode)

if a given videomode can be only supported in YCBCR420 output format

Parameters

const struct drm_display_info * display
display under action
const struct drm_display_mode * mode
video mode to be tested.

Return

true if the mode can be supported in YCBCR420 format false if not.

bool drm_mode_is_420_also(const struct drm_display_info * display, const struct drm_display_mode * mode)

if a given videomode can be supported in YCBCR420 output format also (along with RGB/YCBCR444/422)

Parameters

const struct drm_display_info * display
display under action.
const struct drm_display_mode * mode
video mode to be tested.

Return

true if the mode can be support YCBCR420 format false if not.

bool drm_mode_is_420(const struct drm_display_info * display, const struct drm_display_mode * mode)

if a given videomode can be supported in YCBCR420 output format

Parameters

const struct drm_display_info * display
display under action.
const struct drm_display_mode * mode
video mode to be tested.

Return

true if the mode can be supported in YCBCR420 format false if not.

Connector Abstraction

In DRM connectors are the general abstraction for display sinks, and include als fixed panels or anything else that can display pixels in some form. As opposed to all other KMS objects representing hardware (like CRTC, encoder or plane abstractions) connectors can be hotplugged and unplugged at runtime. Hence they are reference-counted using drm_connector_get() and drm_connector_put().

KMS driver must create, initialize, register and attach at a struct drm_connector for each such sink. The instance is created as other KMS objects and initialized by setting the following fields. The connector is initialized with a call to drm_connector_init() with a pointer to the struct drm_connector_funcs and a connector type, and then exposed to userspace with a call to drm_connector_register().

Connectors must be attached to an encoder to be used. For devices that map connectors to encoders 1:1, the connector should be attached at initialization time with a call to drm_mode_connector_attach_encoder(). The driver must also set the drm_connector.encoder field to point to the attached encoder.

For connectors which are not fixed (like built-in panels) the driver needs to support hotplug notifications. The simplest way to do that is by using the probe helpers, see drm_kms_helper_poll_init() for connectors which don’t have hardware support for hotplug interrupts. Connectors with hardware hotplug support can instead use e.g. drm_helper_hpd_irq_event().

Connector Functions Reference

enum drm_connector_status

status for a drm_connector

Constants

connector_status_connected
The connector is definitely connected to a sink device, and can be enabled.
connector_status_disconnected
The connector isn’t connected to a sink device which can be autodetect. For digital outputs like DP or HDMI (which can be realiable probed) this means there’s really nothing there. It is driver-dependent whether a connector with this status can be lit up or not.
connector_status_unknown
The connector’s status could not be reliably detected. This happens when probing would either cause flicker (like load-detection when the connector is in use), or when a hardware resource isn’t available (like when load-detection needs a free CRTC). It should be possible to light up the connector with one of the listed fallback modes. For default configuration userspace should only try to light up connectors with unknown status when there’s not connector with connector_status_connected.

Description

This enum is used to track the connector status. There are no separate #defines for the uapi!

struct drm_scrambling

Definition

struct drm_scrambling {
  bool supported;
  bool low_rates;
};

Members

supported
scrambling supported for rates > 340 Mhz.
low_rates
scrambling supported for rates <= 340 Mhz.
struct drm_hdmi_info

runtime information about the connected HDMI sink

Definition

struct drm_hdmi_info {
  struct drm_scdc scdc;
  unsigned long y420_vdb_modes[BITS_TO_LONGS(128)];
  unsigned long y420_cmdb_modes[BITS_TO_LONGS(128)];
  u64 y420_cmdb_map;
  u8 y420_dc_modes;
};

Members

scdc
sink’s scdc support and capabilities
y420_vdb_modes
bitmap of modes which can support ycbcr420 output only (not normal RGB/YCBCR444/422 outputs). There are total 107 VICs defined by CEA-861-F spec, so the size is 128 bits to map upto 128 VICs;
y420_cmdb_modes
bitmap of modes which can support ycbcr420 output also, along with normal HDMI outputs. There are total 107 VICs defined by CEA-861-F spec, so the size is 128 bits to map upto 128 VICs;
y420_cmdb_map
bitmap of SVD index, to extraxt vcb modes
y420_dc_modes
bitmap of deep color support index

Description

Describes if a given display supports advanced HDMI 2.0 features. This information is available in CEA-861-F extension blocks (like HF-VSDB).

connector’s link_status property value

Constants

DRM_LINK_STATUS_GOOD
DP Link is Good as a result of successful link training
DRM_LINK_STATUS_BAD
DP Link is BAD as a result of link training failure

Description

This enum is used as the connector’s link status property value. It is set to the values defined in uapi.

enum drm_panel_orientation

panel_orientation info for drm_display_info

Constants

DRM_MODE_PANEL_ORIENTATION_UNKNOWN
The drm driver has not provided any panel orientation information (normal for non panels) in this case the “panel orientation” connector prop will not be attached.
DRM_MODE_PANEL_ORIENTATION_NORMAL
The top side of the panel matches the top side of the device’s casing.
DRM_MODE_PANEL_ORIENTATION_BOTTOM_UP
The top side of the panel matches the bottom side of the device’s casing, iow the panel is mounted upside-down.
DRM_MODE_PANEL_ORIENTATION_LEFT_UP
The left side of the panel matches the top side of the device’s casing.
DRM_MODE_PANEL_ORIENTATION_RIGHT_UP
The right side of the panel matches the top side of the device’s casing.

Description

This enum is used to track the (LCD) panel orientation. There are no separate #defines for the uapi!

struct drm_display_info

runtime data about the connected sink

Definition

struct drm_display_info {
  char name[DRM_DISPLAY_INFO_LEN];
  unsigned int width_mm;
  unsigned int height_mm;
  unsigned int pixel_clock;
  unsigned int bpc;
  enum subpixel_order subpixel_order;
#define DRM_COLOR_FORMAT_RGB444         (1<<0);
#define DRM_COLOR_FORMAT_YCRCB444       (1<<1);
#define DRM_COLOR_FORMAT_YCRCB422       (1<<2);
#define DRM_COLOR_FORMAT_YCRCB420       (1<<3);
  int panel_orientation;
  u32 color_formats;
  const u32 *bus_formats;
  unsigned int num_bus_formats;
#define DRM_BUS_FLAG_DE_LOW             (1<<0);
#define DRM_BUS_FLAG_DE_HIGH            (1<<1);
#define DRM_BUS_FLAG_PIXDATA_POSEDGE    (1<<2);
#define DRM_BUS_FLAG_PIXDATA_NEGEDGE    (1<<3);
#define DRM_BUS_FLAG_DATA_MSB_TO_LSB    (1<<4);
#define DRM_BUS_FLAG_DATA_LSB_TO_MSB    (1<<5);
  u32 bus_flags;
  int max_tmds_clock;
  bool dvi_dual;
  bool has_hdmi_infoframe;
  u8 edid_hdmi_dc_modes;
  u8 cea_rev;
  struct drm_hdmi_info hdmi;
  bool non_desktop;
};

Members

name
Name of the display.
width_mm
Physical width in mm.
height_mm
Physical height in mm.
pixel_clock
Maximum pixel clock supported by the sink, in units of 100Hz. This mismatches the clock in drm_display_mode (which is in kHZ), because that’s what the EDID uses as base unit.
bpc
Maximum bits per color channel. Used by HDMI and DP outputs.
subpixel_order
Subpixel order of LCD panels.
panel_orientation
Read only connector property for built-in panels, indicating the orientation of the panel vs the device’s casing. drm_connector_init() sets this to DRM_MODE_PANEL_ORIENTATION_UNKNOWN. When not UNKNOWN this gets used by the drm_fb_helpers to rotate the fb to compensate and gets exported as prop to userspace.
color_formats
HDMI Color formats, selects between RGB and YCrCb modes. Used DRM_COLOR_FORMAT_ defines, which are _not_ the same ones as used to describe the pixel format in framebuffers, and also don’t match the formats in bus_formats which are shared with v4l.
bus_formats
Pixel data format on the wire, somewhat redundant with color_formats. Array of size num_bus_formats encoded using MEDIA_BUS_FMT_ defines shared with v4l and media drivers.
num_bus_formats
Size of bus_formats array.
bus_flags
Additional information (like pixel signal polarity) for the pixel data on the bus, using DRM_BUS_FLAGS_ defines.
max_tmds_clock
Maximum TMDS clock rate supported by the sink in kHz. 0 means undefined.
dvi_dual
Dual-link DVI sink?
has_hdmi_infoframe
Does the sink support the HDMI infoframe?
edid_hdmi_dc_modes
Mask of supported hdmi deep color modes. Even more stuff redundant with bus_formats.
cea_rev
CEA revision of the HDMI sink.
hdmi
advance features of a HDMI sink.
non_desktop
Non desktop display (HMD).

Description

Describes a given display (e.g. CRT or flat panel) and its limitations. For fixed display sinks like built-in panels there’s not much difference between this and struct drm_connector. But for sinks with a real cable this structure is meant to describe all the things at the other end of the cable.

For sinks which provide an EDID this can be filled out by calling drm_add_edid_modes().

struct drm_tv_connector_state

TV connector related states

Definition

struct drm_tv_connector_state {
  enum drm_mode_subconnector subconnector;
  struct {
    unsigned int left;
    unsigned int right;
    unsigned int top;
    unsigned int bottom;
  } margins;
  unsigned int mode;
  unsigned int brightness;
  unsigned int contrast;
  unsigned int flicker_reduction;
  unsigned int overscan;
  unsigned int saturation;
  unsigned int hue;
};

Members

subconnector
selected subconnector
margins
margins
margins.left
left margin
margins.right
right margin
margins.top
top margin
margins.bottom
bottom margin
mode
TV mode
brightness
brightness in percent
contrast
contrast in percent
flicker_reduction
flicker reduction in percent
overscan
overscan in percent
saturation
saturation in percent
hue
hue in percent
struct drm_connector_state

mutable connector state

Definition

struct drm_connector_state {
  struct drm_connector *connector;
  struct drm_crtc *crtc;
  struct drm_encoder *best_encoder;
  enum drm_link_status link_status;
  struct drm_atomic_state *state;
  struct drm_crtc_commit *commit;
  struct drm_tv_connector_state tv;
  enum hdmi_picture_aspect picture_aspect_ratio;
  unsigned int scaling_mode;
  unsigned int content_protection;
};

Members

connector
backpointer to the connector
crtc

CRTC to connect connector to, NULL if disabled.

Do not change this directly, use drm_atomic_set_crtc_for_connector() instead.

best_encoder
can be used by helpers and drivers to select the encoder
link_status
Connector link_status to keep track of whether link is GOOD or BAD to notify userspace if retraining is necessary.
state
backpointer to global drm_atomic_state
commit

Tracks the pending commit to prevent use-after-free conditions.

Is only set when crtc is NULL.

tv
TV connector state
picture_aspect_ratio

Connector property to control the HDMI infoframe aspect ratio setting.

The DRM_MODE_PICTURE_ASPECT_* values much match the values for enum hdmi_picture_aspect

scaling_mode
Connector property to control the upscaling, mostly used for built-in panels.
content_protection
Connector property to request content protection. This is most commonly used for HDCP.
struct drm_connector_funcs

control connectors on a given device

Definition

struct drm_connector_funcs {
  int (*dpms)(struct drm_connector *connector, int mode);
  void (*reset)(struct drm_connector *connector);
  enum drm_connector_status (*detect)(struct drm_connector *connector, bool force);
  void (*force)(struct drm_connector *connector);
  int (*fill_modes)(struct drm_connector *connector, uint32_t max_width, uint32_t max_height);
  int (*set_property)(struct drm_connector *connector, struct drm_property *property, uint64_t val);
  int (*late_register)(struct drm_connector *connector);
  void (*early_unregister)(struct drm_connector *connector);
  void (*destroy)(struct drm_connector *connector);
  struct drm_connector_state *(*atomic_duplicate_state)(struct drm_connector *connector);
  void (*atomic_destroy_state)(struct drm_connector *connector, struct drm_connector_state *state);
  int (*atomic_set_property)(struct drm_connector *connector,struct drm_connector_state *state,struct drm_property *property, uint64_t val);
  int (*atomic_get_property)(struct drm_connector *connector,const struct drm_connector_state *state,struct drm_property *property, uint64_t *val);
  void (*atomic_print_state)(struct drm_printer *p, const struct drm_connector_state *state);
};

Members

dpms

Legacy entry point to set the per-connector DPMS state. Legacy DPMS is exposed as a standard property on the connector, but diverted to this callback in the drm core. Note that atomic drivers don’t implement the 4 level DPMS support on the connector any more, but instead only have an on/off “ACTIVE” property on the CRTC object.

This hook is not used by atomic drivers, remapping of the legacy DPMS property is entirely handled in the DRM core.

RETURNS:

0 on success or a negative error code on failure.

reset

Reset connector hardware and software state to off. This function isn’t called by the core directly, only through drm_mode_config_reset(). It’s not a helper hook only for historical reasons.

Atomic drivers can use drm_atomic_helper_connector_reset() to reset atomic state using this hook.

detect

Check to see if anything is attached to the connector. The parameter force is set to false whilst polling, true when checking the connector due to a user request. force can be used by the driver to avoid expensive, destructive operations during automated probing.

This callback is optional, if not implemented the connector will be considered as always being attached.

FIXME:

Note that this hook is only called by the probe helper. It’s not in the helper library vtable purely for historical reasons. The only DRM core entry point to probe connector state is fill_modes.

Note that the helper library will already hold drm_mode_config.connection_mutex. Drivers which need to grab additional locks to avoid races with concurrent modeset changes need to use drm_connector_helper_funcs.detect_ctx instead.

RETURNS:

drm_connector_status indicating the connector’s status.

force

This function is called to update internal encoder state when the connector is forced to a certain state by userspace, either through the sysfs interfaces or on the kernel cmdline. In that case the detect callback isn’t called.

FIXME:

Note that this hook is only called by the probe helper. It’s not in the helper library vtable purely for historical reasons. The only DRM core entry point to probe connector state is fill_modes.

fill_modes

Entry point for output detection and basic mode validation. The driver should reprobe the output if needed (e.g. when hotplug handling is unreliable), add all detected modes to drm_connector.modes and filter out any the device can’t support in any configuration. It also needs to filter out any modes wider or higher than the parameters max_width and max_height indicate.

The drivers must also prune any modes no longer valid from drm_connector.modes. Furthermore it must update drm_connector.status and drm_connector.edid. If no EDID has been received for this output connector->edid must be NULL.

Drivers using the probe helpers should use drm_helper_probe_single_connector_modes() or drm_helper_probe_single_connector_modes_nomerge() to implement this function.

RETURNS:

The number of modes detected and filled into drm_connector.modes.

set_property

This is the legacy entry point to update a property attached to the connector.

This callback is optional if the driver does not support any legacy driver-private properties. For atomic drivers it is not used because property handling is done entirely in the DRM core.

RETURNS:

0 on success or a negative error code on failure.

late_register

This optional hook can be used to register additional userspace interfaces attached to the connector, light backlight control, i2c, DP aux or similar interfaces. It is called late in the driver load sequence from drm_connector_register() when registering all the core drm connector interfaces. Everything added from this callback should be unregistered in the early_unregister callback.

This is called while holding drm_connector.mutex.

Returns:

0 on success, or a negative error code on failure.

early_unregister

This optional hook should be used to unregister the additional userspace interfaces attached to the connector from late_register(). It is called from drm_connector_unregister(), early in the driver unload sequence to disable userspace access before data structures are torndown.

This is called while holding drm_connector.mutex.

destroy
Clean up connector resources. This is called at driver unload time through drm_mode_config_cleanup(). It can also be called at runtime when a connector is being hot-unplugged for drivers that support connector hotplugging (e.g. DisplayPort MST).
atomic_duplicate_state

Duplicate the current atomic state for this connector and return it. The core and helpers guarantee that any atomic state duplicated with this hook and still owned by the caller (i.e. not transferred to the driver by calling drm_mode_config_funcs.atomic_commit) will be cleaned up by calling the atomic_destroy_state hook in this structure.

Atomic drivers which don’t subclass struct drm_connector_state should use drm_atomic_helper_connector_duplicate_state(). Drivers that subclass the state structure to extend it with driver-private state should use __drm_atomic_helper_connector_duplicate_state() to make sure shared state is duplicated in a consistent fashion across drivers.

It is an error to call this hook before drm_connector.state has been initialized correctly.

NOTE:

If the duplicate state references refcounted resources this hook must acquire a reference for each of them. The driver must release these references again in atomic_destroy_state.

RETURNS:

Duplicated atomic state or NULL when the allocation failed.

atomic_destroy_state
Destroy a state duplicated with atomic_duplicate_state and release or unreference all resources it references
atomic_set_property

Decode a driver-private property value and store the decoded value into the passed-in state structure. Since the atomic core decodes all standardized properties (even for extensions beyond the core set of properties which might not be implemented by all drivers) this requires drivers to subclass the state structure.

Such driver-private properties should really only be implemented for truly hardware/vendor specific state. Instead it is preferred to standardize atomic extension and decode the properties used to expose such an extension in the core.

Do not call this function directly, use drm_atomic_connector_set_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

NOTE:

This function is called in the state assembly phase of atomic modesets, which can be aborted for any reason (including on userspace’s request to just check whether a configuration would be possible). Drivers MUST NOT touch any persistent state (hardware or software) or data structures except the passed in state parameter.

Also since userspace controls in which order properties are set this function must not do any input validation (since the state update is incomplete and hence likely inconsistent). Instead any such input validation must be done in the various atomic_check callbacks.

RETURNS:

0 if the property has been found, -EINVAL if the property isn’t implemented by the driver (which shouldn’t ever happen, the core only asks for properties attached to this connector). No other validation is allowed by the driver. The core already checks that the property value is within the range (integer, valid enum value, ...) the driver set when registering the property.

atomic_get_property

Reads out the decoded driver-private property. This is used to implement the GETCONNECTOR IOCTL.

Do not call this function directly, use drm_atomic_connector_get_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

RETURNS:

0 on success, -EINVAL if the property isn’t implemented by the driver (which shouldn’t ever happen, the core only asks for properties attached to this connector).

atomic_print_state

If driver subclasses struct drm_connector_state, it should implement this optional hook for printing additional driver specific state.

Do not call this directly, use drm_atomic_connector_print_state() instead.

Description

Each CRTC may have one or more connectors attached to it. The functions below allow the core DRM code to control connectors, enumerate available modes, etc.

struct drm_connector

central DRM connector control structure

Definition

struct drm_connector {
  struct drm_device *dev;
  struct device *kdev;
  struct device_attribute *attr;
  struct list_head head;
  struct drm_mode_object base;
  char *name;
  struct mutex mutex;
  unsigned index;
  int connector_type;
  int connector_type_id;
  bool interlace_allowed;
  bool doublescan_allowed;
  bool stereo_allowed;
  bool ycbcr_420_allowed;
  bool registered;
  struct list_head modes;
  enum drm_connector_status status;
  struct list_head probed_modes;
  struct drm_display_info display_info;
  const struct drm_connector_funcs *funcs;
  struct drm_property_blob *edid_blob_ptr;
  struct drm_object_properties properties;
  struct drm_property *scaling_mode_property;
  struct drm_property *content_protection_property;
  struct drm_property_blob *path_blob_ptr;
  struct drm_property_blob *tile_blob_ptr;
#define DRM_CONNECTOR_POLL_HPD (1 << 0);
#define DRM_CONNECTOR_POLL_CONNECT (1 << 1);
#define DRM_CONNECTOR_POLL_DISCONNECT (1 << 2);
  uint8_t polled;
  int dpms;
  const struct drm_connector_helper_funcs *helper_private;
  struct drm_cmdline_mode cmdline_mode;
  enum drm_connector_force force;
  bool override_edid;
#define DRM_CONNECTOR_MAX_ENCODER 3;
  uint32_t encoder_ids[DRM_CONNECTOR_MAX_ENCODER];
  struct drm_encoder *encoder;
#define MAX_ELD_BYTES   128;
  uint8_t eld[MAX_ELD_BYTES];
  bool latency_present[2];
  int video_latency[2];
  int audio_latency[2];
  int null_edid_counter;
  unsigned bad_edid_counter;
  bool edid_corrupt;
  struct dentry *debugfs_entry;
  struct drm_connector_state *state;
  bool has_tile;
  struct drm_tile_group *tile_group;
  bool tile_is_single_monitor;
  uint8_t num_h_tile, num_v_tile;
  uint8_t tile_h_loc, tile_v_loc;
  uint16_t tile_h_size, tile_v_size;
  struct llist_node free_node;
};

Members

dev
parent DRM device
kdev
kernel device for sysfs attributes
attr
sysfs attributes
head
list management
base
base KMS object
name
human readable name, can be overwritten by the driver
mutex
Lock for general connector state, but currently only protects registered. Most of the connector state is still protected by drm_mode_config.mutex.
index
Compacted connector index, which matches the position inside the mode_config.list for drivers not supporting hot-add/removing. Can be used as an array index. It is invariant over the lifetime of the connector.
connector_type
one of the DRM_MODE_CONNECTOR_<foo> types from drm_mode.h
connector_type_id
index into connector type enum
interlace_allowed
can this connector handle interlaced modes?
doublescan_allowed
can this connector handle doublescan?
stereo_allowed
can this connector handle stereo modes?
ycbcr_420_allowed
This bool indicates if this connector is capable of handling YCBCR 420 output. While parsing the EDID blocks, its very helpful to know, if the source is capable of handling YCBCR 420 outputs.
registered
Is this connector exposed (registered) with userspace? Protected by mutex.
modes
Modes available on this connector (from fill_modes() + user). Protected by drm_mode_config.mutex.
status
One of the drm_connector_status enums (connected, not, or unknown). Protected by drm_mode_config.mutex.
probed_modes
These are modes added by probing with DDC or the BIOS, before filtering is applied. Used by the probe helpers. Protected by drm_mode_config.mutex.
display_info

Display information is filled from EDID information when a display is detected. For non hot-pluggable displays such as flat panels in embedded systems, the driver should initialize the drm_display_info.width_mm and drm_display_info.height_mm fields with the physical size of the display.

Protected by drm_mode_config.mutex.

funcs
connector control functions
edid_blob_ptr
DRM property containing EDID if present
properties
property tracking for this connector
scaling_mode_property
Optional atomic property to control the upscaling.
content_protection_property
DRM ENUM property for content protection
path_blob_ptr
DRM blob property data for the DP MST path property.
tile_blob_ptr
DRM blob property data for the tile property (used mostly by DP MST). This is meant for screens which are driven through separate display pipelines represented by drm_crtc, which might not be running with genlocked clocks. For tiled panels which are genlocked, like dual-link LVDS or dual-link DSI, the driver should try to not expose the tiling and virtualize both drm_crtc and drm_plane if needed.
polled

Connector polling mode, a combination of

DRM_CONNECTOR_POLL_HPD
The connector generates hotplug events and doesn’t need to be periodically polled. The CONNECT and DISCONNECT flags must not be set together with the HPD flag.
DRM_CONNECTOR_POLL_CONNECT
Periodically poll the connector for connection.
DRM_CONNECTOR_POLL_DISCONNECT
Periodically poll the connector for disconnection.

Set to 0 for connectors that don’t support connection status discovery.

dpms
current dpms state
helper_private
mid-layer private data
cmdline_mode
mode line parsed from the kernel cmdline for this connector
force
a DRM_FORCE_<foo> state for forced mode sets
override_edid
has the EDID been overwritten through debugfs for testing?
encoder_ids
valid encoders for this connector
encoder
Currently bound encoder driving this connector, if any. Only really meaningful for non-atomic drivers. Atomic drivers should instead look at drm_connector_state.best_encoder, and in case they need the CRTC driving this output, drm_connector_state.crtc.
eld
EDID-like data, if present
latency_present
AV delay info from ELD, if found
video_latency
video latency info from ELD, if found
audio_latency
audio latency info from ELD, if found
null_edid_counter
track sinks that give us all zeros for the EDID
bad_edid_counter
track sinks that give us an EDID with invalid checksum
edid_corrupt
indicates whether the last read EDID was corrupt
debugfs_entry
debugfs directory for this connector
state

Current atomic state for this connector.

This is protected by drm_mode_config.connection_mutex. Note that nonblocking atomic commits access the current connector state without taking locks. Either by going through the struct drm_atomic_state pointers, see for_each_oldnew_connector_in_state(), for_each_old_connector_in_state() and for_each_new_connector_in_state(). Or through careful ordering of atomic commit operations as implemented in the atomic helpers, see struct drm_crtc_commit.

has_tile
is this connector connected to a tiled monitor
tile_group
tile group for the connected monitor
tile_is_single_monitor
whether the tile is one monitor housing
num_h_tile
number of horizontal tiles in the tile group
num_v_tile
number of vertical tiles in the tile group
tile_h_loc
horizontal location of this tile
tile_v_loc
vertical location of this tile
tile_h_size
horizontal size of this tile.
tile_v_size
vertical size of this tile.
free_node
List used only by drm_connector_iter to be able to clean up a connector from any context, in conjunction with drm_mode_config.connector_free_work.

Description

Each connector may be connected to one or more CRTCs, or may be clonable by another connector if they can share a CRTC. Each connector also has a specific position in the broader display (referred to as a ‘screen’ though it could span multiple monitors).

struct drm_connector * drm_connector_lookup(struct drm_device * dev, struct drm_file * file_priv, uint32_t id)

lookup connector object

Parameters

struct drm_device * dev
DRM device
struct drm_file * file_priv
drm file to check for lease against.
uint32_t id
connector object id

Description

This function looks up the connector object specified by id add takes a reference to it.

void drm_connector_get(struct drm_connector * connector)

acquire a connector reference

Parameters

struct drm_connector * connector
DRM connector

Description

This function increments the connector’s refcount.

void drm_connector_put(struct drm_connector * connector)

release a connector reference

Parameters

struct drm_connector * connector
DRM connector

Description

This function decrements the connector’s reference count and frees the object if the reference count drops to zero.

void drm_connector_reference(struct drm_connector * connector)

acquire a connector reference

Parameters

struct drm_connector * connector
DRM connector

Description

This is a compatibility alias for drm_connector_get() and should not be used by new code.

void drm_connector_unreference(struct drm_connector * connector)

release a connector reference

Parameters

struct drm_connector * connector
DRM connector

Description

This is a compatibility alias for drm_connector_put() and should not be used by new code.

struct drm_tile_group

Tile group metadata

Definition

struct drm_tile_group {
  struct kref refcount;
  struct drm_device *dev;
  int id;
  u8 group_data[8];
};

Members

refcount
reference count
dev
DRM device
id
tile group id exposed to userspace
group_data
Sink-private data identifying this group

Description

group_data corresponds to displayid vend/prod/serial for external screens with an EDID.

struct drm_connector_list_iter

connector_list iterator

Definition

struct drm_connector_list_iter {
};

Members

Description

This iterator tracks state needed to be able to walk the connector_list within struct drm_mode_config. Only use together with drm_connector_list_iter_begin(), drm_connector_list_iter_end() and drm_connector_list_iter_next() respectively the convenience macro drm_for_each_connector_iter().

drm_for_each_connector_iter(connector, iter)

connector_list iterator macro

Parameters

connector
struct drm_connector pointer used as cursor
iter
struct drm_connector_list_iter

Description

Note that connector is only valid within the list body, if you want to use connector after calling drm_connector_list_iter_end() then you need to grab your own reference first using drm_connector_get().

int drm_connector_init(struct drm_device * dev, struct drm_connector * connector, const struct drm_connector_funcs * funcs, int connector_type)

Init a preallocated connector

Parameters

struct drm_device * dev
DRM device
struct drm_connector * connector
the connector to init
const struct drm_connector_funcs * funcs
callbacks for this connector
int connector_type
user visible type of the connector

Description

Initialises a preallocated connector. Connectors should be subclassed as part of driver connector objects.

Return

Zero on success, error code on failure.

int drm_mode_connector_attach_encoder(struct drm_connector * connector, struct drm_encoder * encoder)

attach a connector to an encoder

Parameters

struct drm_connector * connector
connector to attach
struct drm_encoder * encoder
encoder to attach connector to

Description

This function links up a connector to an encoder. Note that the routing restrictions between encoders and crtcs are exposed to userspace through the possible_clones and possible_crtcs bitmasks.

Return

Zero on success, negative errno on failure.

void drm_connector_cleanup(struct drm_connector * connector)

cleans up an initialised connector

Parameters

struct drm_connector * connector
connector to cleanup

Description

Cleans up the connector but doesn’t free the object.

int drm_connector_register(struct drm_connector * connector)

register a connector

Parameters

struct drm_connector * connector
the connector to register

Description

Register userspace interfaces for a connector

Return

Zero on success, error code on failure.

void drm_connector_unregister(struct drm_connector * connector)

unregister a connector

Parameters

struct drm_connector * connector
the connector to unregister

Description

Unregister userspace interfaces for a connector

const char * drm_get_connector_status_name(enum drm_connector_status status)

return a string for connector status

Parameters

enum drm_connector_status status
connector status to compute name of

Description

In contrast to the other drm_get_*_name functions this one here returns a const pointer and hence is threadsafe.

void drm_connector_list_iter_begin(struct drm_device * dev, struct drm_connector_list_iter * iter)

initialize a connector_list iterator

Parameters

struct drm_device * dev
DRM device
struct drm_connector_list_iter * iter
connector_list iterator

Description

Sets iter up to walk the drm_mode_config.connector_list of dev. iter must always be cleaned up again by calling drm_connector_list_iter_end(). Iteration itself happens using drm_connector_list_iter_next() or drm_for_each_connector_iter().

struct drm_connector * drm_connector_list_iter_next(struct drm_connector_list_iter * iter)

return next connector

Parameters

struct drm_connector_list_iter * iter
connectr_list iterator

Description

Returns the next connector for iter, or NULL when the list walk has completed.

void drm_connector_list_iter_end(struct drm_connector_list_iter * iter)

tear down a connector_list iterator

Parameters

struct drm_connector_list_iter * iter
connector_list iterator

Description

Tears down iter and releases any resources (like drm_connector references) acquired while walking the list. This must always be called, both when the iteration completes fully or when it was aborted without walking the entire list.

const char * drm_get_subpixel_order_name(enum subpixel_order order)

return a string for a given subpixel enum

Parameters

enum subpixel_order order
enum of subpixel_order

Description

Note you could abuse this and return something out of bounds, but that would be a caller error. No unscrubbed user data should make it here.

int drm_display_info_set_bus_formats(struct drm_display_info * info, const u32 * formats, unsigned int num_formats)

set the supported bus formats

Parameters

struct drm_display_info * info
display info to store bus formats in
const u32 * formats
array containing the supported bus formats
unsigned int num_formats
the number of entries in the fmts array

Description

Store the supported bus formats in display info structure. See MEDIA_BUS_FMT_* definitions in include/uapi/linux/media-bus-format.h for a full list of available formats.

int drm_mode_create_dvi_i_properties(struct drm_device * dev)

create DVI-I specific connector properties

Parameters

struct drm_device * dev
DRM device

Description

Called by a driver the first time a DVI-I connector is made.

int drm_mode_create_tv_properties(struct drm_device * dev, unsigned int num_modes, const char *const modes)

create TV specific connector properties

Parameters

struct drm_device * dev
DRM device
unsigned int num_modes
number of different TV formats (modes) supported
const char *const modes
array of pointers to strings containing name of each format

Description

Called by a driver’s TV initialization routine, this function creates the TV specific connector properties for a given device. Caller is responsible for allocating a list of format names and passing them to this routine.

int drm_mode_create_scaling_mode_property(struct drm_device * dev)

create scaling mode property

Parameters

struct drm_device * dev
DRM device

Description

Called by a driver the first time it’s needed, must be attached to desired connectors.

Atomic drivers should use drm_connector_attach_scaling_mode_property() instead to correctly assign drm_connector_state.picture_aspect_ratio in the atomic state.

int drm_connector_attach_scaling_mode_property(struct drm_connector * connector, u32 scaling_mode_mask)

attach atomic scaling mode property

Parameters

struct drm_connector * connector
connector to attach scaling mode property on.
u32 scaling_mode_mask
or’ed mask of BIT(DRM_MODE_SCALE_*).

Description

This is used to add support for scaling mode to atomic drivers. The scaling mode will be set to drm_connector_state.picture_aspect_ratio and can be used from drm_connector_helper_funcs->atomic_check for validation.

This is the atomic version of drm_mode_create_scaling_mode_property().

Return

Zero on success, negative errno on failure.

int drm_connector_attach_content_protection_property(struct drm_connector * connector)

attach content protection property

Parameters

struct drm_connector * connector
connector to attach CP property on.

Description

This is used to add support for content protection on select connectors. Content Protection is intentionally vague to allow for different underlying technologies, however it is most implemented by HDCP.

The content protection will be set to drm_connector_state.content_protection

Return

Zero on success, negative errno on failure.

int drm_mode_create_aspect_ratio_property(struct drm_device * dev)

create aspect ratio property

Parameters

struct drm_device * dev
DRM device

Description

Called by a driver the first time it’s needed, must be attached to desired connectors.

Return

Zero on success, negative errno on failure.

int drm_mode_create_suggested_offset_properties(struct drm_device * dev)

create suggests offset properties

Parameters

struct drm_device * dev
DRM device

Description

Create the the suggested x/y offset property for connectors.

int drm_mode_connector_set_path_property(struct drm_connector * connector, const char * path)

set tile property on connector

Parameters

struct drm_connector * connector
connector to set property on.
const char * path
path to use for property; must not be NULL.

Description

This creates a property to expose to userspace to specify a connector path. This is mainly used for DisplayPort MST where connectors have a topology and we want to allow userspace to give them more meaningful names.

Return

Zero on success, negative errno on failure.

int drm_mode_connector_set_tile_property(struct drm_connector * connector)

set tile property on connector

Parameters

struct drm_connector * connector
connector to set property on.

Description

This looks up the tile information for a connector, and creates a property for userspace to parse if it exists. The property is of the form of 8 integers using ‘:’ as a separator.

Return

Zero on success, errno on failure.

int drm_mode_connector_update_edid_property(struct drm_connector * connector, const struct edid * edid)

update the edid property of a connector

Parameters

struct drm_connector * connector
drm connector
const struct edid * edid
new value of the edid property

Description

This function creates a new blob modeset object and assigns its id to the connector’s edid property.

Return

Zero on success, negative errno on failure.

Set link status property of a connector

Parameters

struct drm_connector * connector
drm connector
uint64_t link_status
new value of link status property (0: Good, 1: Bad)

Description

In usual working scenario, this link status property will always be set to “GOOD”. If something fails during or after a mode set, the kernel driver may set this link status property to “BAD”. The caller then needs to send a hotplug uevent for userspace to re-check the valid modes through GET_CONNECTOR_IOCTL and retry modeset.

Note

Drivers cannot rely on userspace to support this property and issue a modeset. As such, they may choose to handle issues (like re-training a link) without userspace’s intervention.

The reason for adding this property is to handle link training failures, but it is not limited to DP or link training. For example, if we implement asynchronous setcrtc, this property can be used to report any failures in that.

int drm_connector_init_panel_orientation_property(struct drm_connector * connector, int width, int height)

initialize the connecters panel_orientation property

Parameters

struct drm_connector * connector
connector for which to init the panel-orientation property.
int width
width in pixels of the panel, used for panel quirk detection
int height
height in pixels of the panel, used for panel quirk detection

Description

This function should only be called for built-in panels, after setting connector->display_info.panel_orientation first (if known).

This function will check for platform specific (e.g. DMI based) quirks overriding display_info.panel_orientation first, then if panel_orientation is not DRM_MODE_PANEL_ORIENTATION_UNKNOWN it will attach the “panel orientation” property to the connector.

Return

Zero on success, negative errno on failure.

void drm_mode_put_tile_group(struct drm_device * dev, struct drm_tile_group * tg)

drop a reference to a tile group.

Parameters

struct drm_device * dev
DRM device
struct drm_tile_group * tg
tile group to drop reference to.

Description

drop reference to tile group and free if 0.

struct drm_tile_group * drm_mode_get_tile_group(struct drm_device * dev, char topology)

get a reference to an existing tile group

Parameters

struct drm_device * dev
DRM device
char topology
8-bytes unique per monitor.

Description

Use the unique bytes to get a reference to an existing tile group.

Return

tile group or NULL if not found.

struct drm_tile_group * drm_mode_create_tile_group(struct drm_device * dev, char topology)

create a tile group from a displayid description

Parameters

struct drm_device * dev
DRM device
char topology
8-bytes unique per monitor.

Description

Create a tile group for the unique monitor, and get a unique identifier for the tile group.

Return

new tile group or error.

Encoder Abstraction

Encoders represent the connecting element between the CRTC (as the overall pixel pipeline, represented by struct drm_crtc) and the connectors (as the generic sink entity, represented by struct drm_connector). An encoder takes pixel data from a CRTC and converts it to a format suitable for any attached connector. Encoders are objects exposed to userspace, originally to allow userspace to infer cloning and connector/CRTC restrictions. Unfortunately almost all drivers get this wrong, making the uabi pretty much useless. On top of that the exposed restrictions are too simple for today’s hardware, and the recommended way to infer restrictions is by using the DRM_MODE_ATOMIC_TEST_ONLY flag for the atomic IOCTL.

Otherwise encoders aren’t used in the uapi at all (any modeset request from userspace directly connects a connector with a CRTC), drivers are therefore free to use them however they wish. Modeset helper libraries make strong use of encoders to facilitate code sharing. But for more complex settings it is usually better to move shared code into a separate drm_bridge. Compared to encoders, bridges also have the benefit of being purely an internal abstraction since they are not exposed to userspace at all.

Encoders are initialized with drm_encoder_init() and cleaned up using drm_encoder_cleanup().

Encoder Functions Reference

struct drm_encoder_funcs

encoder controls

Definition

struct drm_encoder_funcs {
  void (*reset)(struct drm_encoder *encoder);
  void (*destroy)(struct drm_encoder *encoder);
  int (*late_register)(struct drm_encoder *encoder);
  void (*early_unregister)(struct drm_encoder *encoder);
};

Members

reset
Reset encoder hardware and software state to off. This function isn’t called by the core directly, only through drm_mode_config_reset(). It’s not a helper hook only for historical reasons.
destroy
Clean up encoder resources. This is only called at driver unload time through drm_mode_config_cleanup() since an encoder cannot be hotplugged in DRM.
late_register

This optional hook can be used to register additional userspace interfaces attached to the encoder like debugfs interfaces. It is called late in the driver load sequence from drm_dev_register(). Everything added from this callback should be unregistered in the early_unregister callback.

Returns:

0 on success, or a negative error code on failure.

early_unregister
This optional hook should be used to unregister the additional userspace interfaces attached to the encoder from late_register. It is called from drm_dev_unregister(), early in the driver unload sequence to disable userspace access before data structures are torndown.

Description

Encoders sit between CRTCs and connectors.

struct drm_encoder

central DRM encoder structure

Definition

struct drm_encoder {
  struct drm_device *dev;
  struct list_head head;
  struct drm_mode_object base;
  char *name;
  int encoder_type;
  unsigned index;
  uint32_t possible_crtcs;
  uint32_t possible_clones;
  struct drm_crtc *crtc;
  struct drm_bridge *bridge;
  const struct drm_encoder_funcs *funcs;
  const struct drm_encoder_helper_funcs *helper_private;
};

Members

dev
parent DRM device
head
list management
base
base KMS object
name
human readable name, can be overwritten by the driver
encoder_type

One of the DRM_MODE_ENCODER_<foo> types in drm_mode.h. The following encoder types are defined thus far:

  • DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A.
  • DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort.
  • DRM_MODE_ENCODER_LVDS for display panels, or in general any panel with a proprietary parallel connector.
  • DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video, Component, SCART).
  • DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
  • DRM_MODE_ENCODER_DSI for panels connected using the DSI serial bus.
  • DRM_MODE_ENCODER_DPI for panels connected using the DPI parallel bus.
  • DRM_MODE_ENCODER_DPMST for special fake encoders used to allow mutliple DP MST streams to share one physical encoder.
index
Position inside the mode_config.list, can be used as an array index. It is invariant over the lifetime of the encoder.
possible_crtcs

Bitmask of potential CRTC bindings, using drm_crtc_index() as the index into the bitfield. The driver must set the bits for all drm_crtc objects this encoder can be connected to before calling drm_encoder_init().

In reality almost every driver gets this wrong.

Note that since CRTC objects can’t be hotplugged the assigned indices are stable and hence known before registering all objects.

possible_clones

Bitmask of potential sibling encoders for cloning, using drm_encoder_index() as the index into the bitfield. The driver must set the bits for all drm_encoder objects which can clone a drm_crtc together with this encoder before calling drm_encoder_init(). Drivers should set the bit representing the encoder itself, too. Cloning bits should be set such that when two encoders can be used in a cloned configuration, they both should have each another bits set.

In reality almost every driver gets this wrong.

Note that since encoder objects can’t be hotplugged the assigned indices are stable and hence known before registering all objects.

crtc
Currently bound CRTC, only really meaningful for non-atomic drivers. Atomic drivers should instead check drm_connector_state.crtc.
bridge
bridge associated to the encoder
funcs
control functions
helper_private
mid-layer private data

Description

CRTCs drive pixels to encoders, which convert them into signals appropriate for a given connector or set of connectors.

unsigned int drm_encoder_index(struct drm_encoder * encoder)

find the index of a registered encoder

Parameters

struct drm_encoder * encoder
encoder to find index for

Description

Given a registered encoder, return the index of that encoder within a DRM device’s list of encoders.

bool drm_encoder_crtc_ok(struct drm_encoder * encoder, struct drm_crtc * crtc)

can a given crtc drive a given encoder?

Parameters

struct drm_encoder * encoder
encoder to test
struct drm_crtc * crtc
crtc to test

Description

Returns false if encoder can’t be driven by crtc, true otherwise.

struct drm_encoder * drm_encoder_find(struct drm_device * dev, struct drm_file * file_priv, uint32_t id)

find a drm_encoder

Parameters

struct drm_device * dev
DRM device
struct drm_file * file_priv
drm file to check for lease against.
uint32_t id
encoder id

Description

Returns the encoder with id, NULL if it doesn’t exist. Simple wrapper around drm_mode_object_find().

drm_for_each_encoder_mask(encoder, dev, encoder_mask)

iterate over encoders specified by bitmask

Parameters

encoder
the loop cursor
dev
the DRM device
encoder_mask
bitmask of encoder indices

Description

Iterate over all encoders specified by bitmask.

drm_for_each_encoder(encoder, dev)

iterate over all encoders

Parameters

encoder
the loop cursor
dev
the DRM device

Description

Iterate over all encoders of dev.

int drm_encoder_init(struct drm_device * dev, struct drm_encoder * encoder, const struct drm_encoder_funcs * funcs, int encoder_type, const char * name, ...)

Init a preallocated encoder

Parameters

struct drm_device * dev
drm device
struct drm_encoder * encoder
the encoder to init
const struct drm_encoder_funcs * funcs
callbacks for this encoder
int encoder_type
user visible type of the encoder
const char * name
printf style format string for the encoder name, or NULL for default name
...
variable arguments

Description

Initialises a preallocated encoder. Encoder should be subclassed as part of driver encoder objects. At driver unload time drm_encoder_cleanup() should be called from the driver’s drm_encoder_funcs.destroy hook.

Return

Zero on success, error code on failure.

void drm_encoder_cleanup(struct drm_encoder * encoder)

cleans up an initialised encoder

Parameters

struct drm_encoder * encoder
encoder to cleanup

Description

Cleans up the encoder but doesn’t free the object.

KMS Initialization and Cleanup

A KMS device is abstracted and exposed as a set of planes, CRTCs, encoders and connectors. KMS drivers must thus create and initialize all those objects at load time after initializing mode setting.

CRTCs (struct drm_crtc)

A CRTC is an abstraction representing a part of the chip that contains a pointer to a scanout buffer. Therefore, the number of CRTCs available determines how many independent scanout buffers can be active at any given time. The CRTC structure contains several fields to support this: a pointer to some video memory (abstracted as a frame buffer object), a display mode, and an (x, y) offset into the video memory to support panning or configurations where one piece of video memory spans multiple CRTCs.

CRTC Initialization

A KMS device must create and register at least one struct struct drm_crtc instance. The instance is allocated and zeroed by the driver, possibly as part of a larger structure, and registered with a call to drm_crtc_init() with a pointer to CRTC functions.

Cleanup

The DRM core manages its objects’ lifetime. When an object is not needed anymore the core calls its destroy function, which must clean up and free every resource allocated for the object. Every drm_*_init() call must be matched with a corresponding drm_*_cleanup() call to cleanup CRTCs (drm_crtc_cleanup()), planes (drm_plane_cleanup()), encoders (drm_encoder_cleanup()) and connectors (drm_connector_cleanup()). Furthermore, connectors that have been added to sysfs must be removed by a call to drm_connector_unregister() before calling drm_connector_cleanup().

Connectors state change detection must be cleanup up with a call to drm_kms_helper_poll_fini().

Output discovery and initialization example

void intel_crt_init(struct drm_device *dev)
{
    struct drm_connector *connector;
    struct intel_output *intel_output;

    intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
    if (!intel_output)
        return;

    connector = &intel_output->base;
    drm_connector_init(dev, &intel_output->base,
               &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);

    drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
             DRM_MODE_ENCODER_DAC);

    drm_mode_connector_attach_encoder(&intel_output->base,
                      &intel_output->enc);

    /* Set up the DDC bus. */
    intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
    if (!intel_output->ddc_bus) {
        dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
               "failed.\n");
        return;
    }

    intel_output->type = INTEL_OUTPUT_ANALOG;
    connector->interlace_allowed = 0;
    connector->doublescan_allowed = 0;

    drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
    drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);

    drm_connector_register(connector);
}

In the example above (taken from the i915 driver), a CRTC, connector and encoder combination is created. A device-specific i2c bus is also created for fetching EDID data and performing monitor detection. Once the process is complete, the new connector is registered with sysfs to make its properties available to applications.

KMS Locking

As KMS moves toward more fine grained locking, and atomic ioctl where userspace can indirectly control locking order, it becomes necessary to use ww_mutex and acquire-contexts to avoid deadlocks. But because the locking is more distributed around the driver code, we want a bit of extra utility/tracking out of our acquire-ctx. This is provided by struct drm_modeset_lock and struct drm_modeset_acquire_ctx.

For basic principles of ww_mutex, see: Documentation/locking/ww-mutex-design.txt

The basic usage pattern is to:

drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
retry:
foreach (lock in random_ordered_set_of_locks) {
    ret = drm_modeset_lock(lock, ctx)
    if (ret == -EDEADLK) {
        ret = drm_modeset_backoff(ctx);
        if (!ret)
            goto retry;
    }
    if (ret)
        goto out;
}
... do stuff ...
out:
drm_modeset_drop_locks(ctx);
drm_modeset_acquire_fini(ctx);

If all that is needed is a single modeset lock, then the struct drm_modeset_acquire_ctx is not needed and the locking can be simplified by passing a NULL instead of ctx in the drm_modeset_lock() call or calling drm_modeset_lock_single_interruptible(). To unlock afterwards call drm_modeset_unlock().

On top of these per-object locks using ww_mutex there’s also an overall drm_mode_config.mutex, for protecting everything else. Mostly this means probe state of connectors, and preventing hotplug add/removal of connectors.

Finally there’s a bunch of dedicated locks to protect drm core internal lists and lookup data structures.

struct drm_modeset_acquire_ctx

locking context (see ww_acquire_ctx)

Definition

struct drm_modeset_acquire_ctx {
  struct ww_acquire_ctx ww_ctx;
  struct drm_modeset_lock *contended;
  struct list_head locked;
  bool trylock_only;
  bool interruptible;
};

Members

ww_ctx
base acquire ctx
contended
used internally for -EDEADLK handling
locked
list of held locks
trylock_only
trylock mode used in atomic contexts/panic notifiers
interruptible
whether interruptible locking should be used.

Description

Each thread competing for a set of locks must use one acquire ctx. And if any lock fxn returns -EDEADLK, it must backoff and retry.

struct drm_modeset_lock

used for locking modeset resources.

Definition

struct drm_modeset_lock {
  struct ww_mutex mutex;
  struct list_head head;
};

Members

mutex
resource locking
head
used to hold it’s place on drm_atomi_state.locked list when part of an atomic update

Description

Used for locking CRTCs and other modeset resources.

void drm_modeset_lock_fini(struct drm_modeset_lock * lock)

cleanup lock

Parameters

struct drm_modeset_lock * lock
lock to cleanup
bool drm_modeset_is_locked(struct drm_modeset_lock * lock)

equivalent to mutex_is_locked()

Parameters

struct drm_modeset_lock * lock
lock to check
void drm_modeset_lock_all(struct drm_device * dev)

take all modeset locks

Parameters

struct drm_device * dev
DRM device

Description

This function takes all modeset locks, suitable where a more fine-grained scheme isn’t (yet) implemented. Locks must be dropped by calling the drm_modeset_unlock_all() function.

This function is deprecated. It allocates a lock acquisition context and stores it in drm_device.mode_config. This facilitate conversion of existing code because it removes the need to manually deal with the acquisition context, but it is also brittle because the context is global and care must be taken not to nest calls. New code should use the drm_modeset_lock_all_ctx() function and pass in the context explicitly.

void drm_modeset_unlock_all(struct drm_device * dev)

drop all modeset locks

Parameters

struct drm_device * dev
DRM device

Description

This function drops all modeset locks taken by a previous call to the drm_modeset_lock_all() function.

This function is deprecated. It uses the lock acquisition context stored in drm_device.mode_config. This facilitates conversion of existing code because it removes the need to manually deal with the acquisition context, but it is also brittle because the context is global and care must be taken not to nest calls. New code should pass the acquisition context directly to the drm_modeset_drop_locks() function.

void drm_warn_on_modeset_not_all_locked(struct drm_device * dev)

check that all modeset locks are locked

Parameters

struct drm_device * dev
device

Description

Useful as a debug assert.

void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx * ctx, uint32_t flags)

initialize acquire context

Parameters

struct drm_modeset_acquire_ctx * ctx
the acquire context
uint32_t flags
0 or DRM_MODESET_ACQUIRE_INTERRUPTIBLE

Description

When passing DRM_MODESET_ACQUIRE_INTERRUPTIBLE to flags, all calls to drm_modeset_lock() will perform an interruptible wait.

void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx * ctx)

cleanup acquire context

Parameters

struct drm_modeset_acquire_ctx * ctx
the acquire context
void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx * ctx)

drop all locks

Parameters

struct drm_modeset_acquire_ctx * ctx
the acquire context

Description

Drop all locks currently held against this acquire context.

int drm_modeset_backoff(struct drm_modeset_acquire_ctx * ctx)

deadlock avoidance backoff

Parameters

struct drm_modeset_acquire_ctx * ctx
the acquire context

Description

If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), you must call this function to drop all currently held locks and block until the contended lock becomes available.

This function returns 0 on success, or -ERESTARTSYS if this context is initialized with DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the wait has been interrupted.

void drm_modeset_lock_init(struct drm_modeset_lock * lock)

initialize lock

Parameters

struct drm_modeset_lock * lock
lock to init
int drm_modeset_lock(struct drm_modeset_lock * lock, struct drm_modeset_acquire_ctx * ctx)

take modeset lock

Parameters

struct drm_modeset_lock * lock
lock to take
struct drm_modeset_acquire_ctx * ctx
acquire ctx

Description

If ctx is not NULL, then its ww acquire context is used and the lock will be tracked by the context and can be released by calling drm_modeset_drop_locks(). If -EDEADLK is returned, this means a deadlock scenario has been detected and it is an error to attempt to take any more locks without first calling drm_modeset_backoff().

If the ctx is not NULL and initialized with DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with -ERESTARTSYS when interrupted.

If ctx is NULL then the function call behaves like a normal, uninterruptible non-nesting mutex_lock() call.

int drm_modeset_lock_single_interruptible(struct drm_modeset_lock * lock)

take a single modeset lock

Parameters

struct drm_modeset_lock * lock
lock to take

Description

This function behaves as drm_modeset_lock() with a NULL context, but performs interruptible waits.

This function returns 0 on success, or -ERESTARTSYS when interrupted.

void drm_modeset_unlock(struct drm_modeset_lock * lock)

drop modeset lock

Parameters

struct drm_modeset_lock * lock
lock to release
int drm_modeset_lock_all_ctx(struct drm_device * dev, struct drm_modeset_acquire_ctx * ctx)

take all modeset locks

Parameters

struct drm_device * dev
DRM device
struct drm_modeset_acquire_ctx * ctx
lock acquisition context

Description

This function takes all modeset locks, suitable where a more fine-grained scheme isn’t (yet) implemented.

Unlike drm_modeset_lock_all(), it doesn’t take the drm_mode_config.mutex since that lock isn’t required for modeset state changes. Callers which need to grab that lock too need to do so outside of the acquire context ctx.

Locks acquired with this function should be released by calling the drm_modeset_drop_locks() function on ctx.

Return

0 on success or a negative error-code on failure.

KMS Properties

Property Types and Blob Property Support

Properties as represented by drm_property are used to extend the modeset interface exposed to userspace. For the atomic modeset IOCTL properties are even the only way to transport metadata about the desired new modeset configuration from userspace to the kernel. Properties have a well-defined value range, which is enforced by the drm core. See the documentation of the flags member of struct drm_property for an overview of the different property types and ranges.

Properties don’t store the current value directly, but need to be instatiated by attaching them to a drm_mode_object with drm_object_attach_property().

Property values are only 64bit. To support bigger piles of data (like gamma tables, color correction matrices or large structures) a property can instead point at a drm_property_blob with that additional data.

Properties are defined by their symbolic name, userspace must keep a per-object mapping from those names to the property ID used in the atomic IOCTL and in the get/set property IOCTL.

struct drm_property_enum

symbolic values for enumerations

Definition

struct drm_property_enum {
  uint64_t value;
  struct list_head head;
  char name[DRM_PROP_NAME_LEN];
};

Members

value
numeric property value for this enum entry
head
list of enum values, linked to drm_property.enum_list
name
symbolic name for the enum

Description

For enumeration and bitmask properties this structure stores the symbolic decoding for each value. This is used for example for the rotation property.

struct drm_property

modeset object property

Definition

struct drm_property {
  struct list_head head;
  struct drm_mode_object base;
  uint32_t flags;
  char name[DRM_PROP_NAME_LEN];
  uint32_t num_values;
  uint64_t *values;
  struct drm_device *dev;
  struct list_head enum_list;
};

Members

head
per-device list of properties, for cleanup.
base
base KMS object
flags

Property flags and type. A property needs to be one of the following types:

DRM_MODE_PROP_RANGE
Range properties report their minimum and maximum admissible unsigned values. The KMS core verifies that values set by application fit in that range. The range is unsigned. Range properties are created using drm_property_create_range().
DRM_MODE_PROP_SIGNED_RANGE
Range properties report their minimum and maximum admissible unsigned values. The KMS core verifies that values set by application fit in that range. The range is signed. Range properties are created using drm_property_create_signed_range().
DRM_MODE_PROP_ENUM
Enumerated properties take a numerical value that ranges from 0 to the number of enumerated values defined by the property minus one, and associate a free-formed string name to each value. Applications can retrieve the list of defined value-name pairs and use the numerical value to get and set property instance values. Enum properties are created using drm_property_create_enum().
DRM_MODE_PROP_BITMASK
Bitmask properties are enumeration properties that additionally restrict all enumerated values to the 0..63 range. Bitmask property instance values combine one or more of the enumerated bits defined by the property. Bitmask properties are created using drm_property_create_bitmask().
DRM_MODE_PROB_OBJECT

Object properties are used to link modeset objects. This is used extensively in the atomic support to create the display pipeline, by linking drm_framebuffer to drm_plane, drm_plane to drm_crtc and drm_connector to drm_crtc. An object property can only link to a specific type of drm_mode_object, this limit is enforced by the core. Object properties are created using drm_property_create_object().

Object properties work like blob properties, but in a more general fashion. They are limited to atomic drivers and must have the DRM_MODE_PROP_ATOMIC flag set.

DRM_MODE_PROP_BLOB

Blob properties store a binary blob without any format restriction. The binary blobs are created as KMS standalone objects, and blob property instance values store the ID of their associated blob object. Blob properties are created by calling drm_property_create() with DRM_MODE_PROP_BLOB as the type.

Actual blob objects to contain blob data are created using drm_property_create_blob(), or through the corresponding IOCTL.

Besides the built-in limit to only accept blob objects blob properties work exactly like object properties. The only reasons blob properties exist is backwards compatibility with existing userspace.

In addition a property can have any combination of the below flags:

DRM_MODE_PROP_ATOMIC
Set for properties which encode atomic modeset state. Such properties are not exposed to legacy userspace.
DRM_MODE_PROP_IMMUTABLE
Set for properties where userspace cannot be changed by userspace. The kernel is allowed to update the value of these properties. This is generally used to expose probe state to usersapce, e.g. the EDID, or the connector path property on DP MST sinks.
name
symbolic name of the properties
num_values
size of the values array.
values
Array with limits and values for the property. The interpretation of these limits is dependent upon the type per flags.
dev
DRM device
enum_list
List of drm_prop_enum_list structures with the symbolic names for enum and bitmask values.

Description

This structure represent a modeset object property. It combines both the name of the property with the set of permissible values. This means that when a driver wants to use a property with the same name on different objects, but with different value ranges, then it must create property for each one. An example would be rotation of drm_plane, when e.g. the primary plane cannot be rotated. But if both the name and the value range match, then the same property structure can be instantiated multiple times for the same object. Userspace must be able to cope with this and cannot assume that the same symbolic property will have the same modeset object ID on all modeset objects.

Properties are created by one of the special functions, as explained in detail in the flags structure member.

To actually expose a property it must be attached to each object using drm_object_attach_property(). Currently properties can only be attached to drm_connector, drm_crtc and drm_plane.

Properties are also used as the generic metadatatransport for the atomic IOCTL. Everything that was set directly in structures in the legacy modeset IOCTLs (like the plane source or destination windows, or e.g. the links to the CRTC) is exposed as a property with the DRM_MODE_PROP_ATOMIC flag set.

struct drm_property_blob

Blob data for drm_property

Definition

struct drm_property_blob {
  struct drm_mode_object base;
  struct drm_device *dev;
  struct list_head head_global;
  struct list_head head_file;
  size_t length;
  void *data;
};

Members

base
base KMS object
dev
DRM device
head_global
entry on the global blob list in drm_mode_config.property_blob_list.
head_file
entry on the per-file blob list in drm_file.blobs list.
length
size of the blob in bytes, invariant over the lifetime of the object
data
actual data, embedded at the end of this structure

Description

Blobs are used to store bigger values than what fits directly into the 64 bits available for a drm_property.

Blobs are reference counted using drm_property_blob_get() and drm_property_blob_put(). They are created using drm_property_create_blob().

bool drm_property_type_is(struct drm_property * property, uint32_t type)

check the type of a property

Parameters

struct drm_property * property
property to check
uint32_t type
property type to compare with

Description

This is a helper function becauase the uapi encoding of property types is a bit special for historical reasons.

struct drm_property_blob * drm_property_reference_blob(struct drm_property_blob * blob)

acquire a blob property reference

Parameters

struct drm_property_blob * blob
DRM blob property

Description

This is a compatibility alias for drm_property_blob_get() and should not be used by new code.

void drm_property_unreference_blob(struct drm_property_blob * blob)

release a blob property reference

Parameters

struct drm_property_blob * blob
DRM blob property

Description

This is a compatibility alias for drm_property_blob_put() and should not be used by new code.

struct drm_property * drm_property_find(struct drm_device * dev, struct drm_file * file_priv, uint32_t id)

find property object

Parameters

struct drm_device * dev
DRM device
struct drm_file * file_priv
drm file to check for lease against.
uint32_t id
property object id

Description

This function looks up the property object specified by id and returns it.

struct drm_property * drm_property_create(struct drm_device * dev, u32 flags, const char * name, int num_values)

create a new property type

Parameters

struct drm_device * dev
drm device
u32 flags
flags specifying the property type
const char * name
name of the property
int num_values
number of pre-defined values

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property * drm_property_create_enum(struct drm_device * dev, u32 flags, const char * name, const struct drm_prop_enum_list * props, int num_values)

create a new enumeration property type

Parameters

struct drm_device * dev
drm device
u32 flags
flags specifying the property type
const char * name
name of the property
const struct drm_prop_enum_list * props
enumeration lists with property values
int num_values
number of pre-defined values

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Userspace is only allowed to set one of the predefined values for enumeration properties.

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property * drm_property_create_bitmask(struct drm_device * dev, u32 flags, const char * name, const struct drm_prop_enum_list * props, int num_props, uint64_t supported_bits)

create a new bitmask property type

Parameters

struct drm_device * dev
drm device
u32 flags
flags specifying the property type
const char * name
name of the property
const struct drm_prop_enum_list * props
enumeration lists with property bitflags
int num_props
size of the props array
uint64_t supported_bits
bitmask of all supported enumeration values

Description

This creates a new bitmask drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Compared to plain enumeration properties userspace is allowed to set any or’ed together combination of the predefined property bitflag values

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property * drm_property_create_range(struct drm_device * dev, u32 flags, const char * name, uint64_t min, uint64_t max)

create a new unsigned ranged property type

Parameters

struct drm_device * dev
drm device
u32 flags
flags specifying the property type
const char * name
name of the property
uint64_t min
minimum value of the property
uint64_t max
maximum value of the property

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Userspace is allowed to set any unsigned integer value in the (min, max) range inclusive.

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property * drm_property_create_signed_range(struct drm_device * dev, u32 flags, const char * name, int64_t min, int64_t max)

create a new signed ranged property type

Parameters

struct drm_device * dev
drm device
u32 flags
flags specifying the property type
const char * name
name of the property
int64_t min
minimum value of the property
int64_t max
maximum value of the property

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Userspace is allowed to set any signed integer value in the (min, max) range inclusive.

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property * drm_property_create_object(struct drm_device * dev, u32 flags, const char * name, uint32_t type)

create a new object property type

Parameters

struct drm_device * dev
drm device
u32 flags
flags specifying the property type
const char * name
name of the property
uint32_t type
object type from DRM_MODE_OBJECT_* defines

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Userspace is only allowed to set this to any property value of the given type. Only useful for atomic properties, which is enforced.

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property * drm_property_create_bool(struct drm_device * dev, u32 flags, const char * name)

create a new boolean property type

Parameters

struct drm_device * dev
drm device
u32 flags
flags specifying the property type
const char * name
name of the property

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

This is implemented as a ranged property with only {0, 1} as valid values.

Return

A pointer to the newly created property on success, NULL on failure.

int drm_property_add_enum(struct drm_property * property, int index, uint64_t value, const char * name)

add a possible value to an enumeration property

Parameters

struct drm_property * property
enumeration property to change
int index
index of the new enumeration
uint64_t value
value of the new enumeration
const char * name
symbolic name of the new enumeration

Description

This functions adds enumerations to a property.

It’s use is deprecated, drivers should use one of the more specific helpers to directly create the property with all enumerations already attached.

Return

Zero on success, error code on failure.

void drm_property_destroy(struct drm_device * dev, struct drm_property * property)

destroy a drm property

Parameters

struct drm_device * dev
drm device
struct drm_property * property
property to destry

Description

This function frees a property including any attached resources like enumeration values.

struct drm_property_blob * drm_property_create_blob(struct drm_device * dev, size_t length, const void * data)

Create new blob property

Parameters

struct drm_device * dev
DRM device to create property for
size_t length
Length to allocate for blob data
const void * data
If specified, copies data into blob

Description

Creates a new blob property for a specified DRM device, optionally copying data. Note that blob properties are meant to be invariant, hence the data must be filled out before the blob is used as the value of any property.

Return

New blob property with a single reference on success, or an ERR_PTR value on failure.

void drm_property_blob_put(struct drm_property_blob * blob)

release a blob property reference

Parameters

struct drm_property_blob * blob
DRM blob property

Description

Releases a reference to a blob property. May free the object.

struct drm_property_blob * drm_property_blob_get(struct drm_property_blob * blob)

acquire blob property reference

Parameters

struct drm_property_blob * blob
DRM blob property

Description

Acquires a reference to an existing blob property. Returns blob, which allows this to be used as a shorthand in assignments.

struct drm_property_blob * drm_property_lookup_blob(struct drm_device * dev, uint32_t id)

look up a blob property and take a reference

Parameters

struct drm_device * dev
drm device
uint32_t id
id of the blob property

Description

If successful, this takes an additional reference to the blob property. callers need to make sure to eventually unreference the returned property again, using drm_property_blob_put().

Return

NULL on failure, pointer to the blob on success.

int drm_property_replace_global_blob(struct drm_device * dev, struct drm_property_blob ** replace, size_t length, const void * data, struct drm_mode_object * obj_holds_id, struct drm_property * prop_holds_id)

replace existing blob property

Parameters

struct drm_device * dev
drm device
struct drm_property_blob ** replace
location of blob property pointer to be replaced
size_t length
length of data for new blob, or 0 for no data
const void * data
content for new blob, or NULL for no data
struct drm_mode_object * obj_holds_id
optional object for property holding blob ID
struct drm_property * prop_holds_id
optional property holding blob ID return 0 on success or error on failure

Description

This function will replace a global property in the blob list, optionally updating a property which holds the ID of that property.

If length is 0 or data is NULL, no new blob will be created, and the holding property, if specified, will be set to 0.

Access to the replace pointer is assumed to be protected by the caller, e.g. by holding the relevant modesetting object lock for its parent.

For example, a drm_connector has a ‘PATH’ property, which contains the ID of a blob property with the value of the MST path information. Calling this function with replace pointing to the connector’s path_blob_ptr, length and data set for the new path information, obj_holds_id set to the connector’s base object, and prop_holds_id set to the path property name, will perform a completely atomic update. The access to path_blob_ptr is protected by the caller holding a lock on the connector.

bool drm_property_replace_blob(struct drm_property_blob ** blob, struct drm_property_blob * new_blob)

replace a blob property

Parameters

struct drm_property_blob ** blob
a pointer to the member blob to be replaced
struct drm_property_blob * new_blob
the new blob to replace with

Return

true if the blob was in fact replaced.

Standard Connector Properties

DRM connectors have a few standardized properties:

EDID:
Blob property which contains the current EDID read from the sink. This is useful to parse sink identification information like vendor, model and serial. Drivers should update this property by calling drm_mode_connector_update_edid_property(), usually after having parsed the EDID using drm_add_edid_modes(). Userspace cannot change this property.
DPMS:

Legacy property for setting the power state of the connector. For atomic drivers this is only provided for backwards compatibility with existing drivers, it remaps to controlling the “ACTIVE” property on the CRTC the connector is linked to. Drivers should never set this property directly, it is handled by the DRM core by calling the drm_connector_funcs.dpms callback. For atomic drivers the remapping to the “ACTIVE” property is implemented in the DRM core. This is the only standard connector property that userspace can change.

Note that this property cannot be set through the MODE_ATOMIC ioctl, userspace must use “ACTIVE” on the CRTC instead.

WARNING:

For userspace also running on legacy drivers the “DPMS” semantics are a lot more complicated. First, userspace cannot rely on the “DPMS” value returned by the GETCONNECTOR actually reflecting reality, because many drivers fail to update it. For atomic drivers this is taken care of in drm_atomic_helper_update_legacy_modeset_state().

The second issue is that the DPMS state is only well-defined when the connector is connected to a CRTC. In atomic the DRM core enforces that “ACTIVE” is off in such a case, no such checks exists for “DPMS”.

Finally, when enabling an output using the legacy SETCONFIG ioctl then “DPMS” is forced to ON. But see above, that might not be reflected in the software value on legacy drivers.

Summarizing: Only set “DPMS” when the connector is known to be enabled, assume that a successful SETCONFIG call also sets “DPMS” to on, and never read back the value of “DPMS” because it can be incorrect.

PATH:
Connector path property to identify how this sink is physically connected. Used by DP MST. This should be set by calling drm_mode_connector_set_path_property(), in the case of DP MST with the path property the MST manager created. Userspace cannot change this property.
TILE:
Connector tile group property to indicate how a set of DRM connector compose together into one logical screen. This is used by both high-res external screens (often only using a single cable, but exposing multiple DP MST sinks), or high-res integrated panels (like dual-link DSI) which are not gen-locked. Note that for tiled panels which are genlocked, like dual-link LVDS or dual-link DSI, the driver should try to not expose the tiling and virtualize both drm_crtc and drm_plane if needed. Drivers should update this value using drm_mode_connector_set_tile_property(). Userspace cannot change this property.
link-status:
Connector link-status property to indicate the status of link. The default value of link-status is “GOOD”. If something fails during or after modeset, the kernel driver may set this to “BAD” and issue a hotplug uevent. Drivers should update this value using drm_mode_connector_set_link_status_property().
non_desktop:
Indicates the output should be ignored for purposes of displaying a standard desktop environment or console. This is most likely because the output device is not rectilinear.
Content Protection:

This property is used by userspace to request the kernel protect future content communicated over the link. When requested, kernel will apply the appropriate means of protection (most often HDCP), and use the property to tell userspace the protection is active.

Drivers can set this up by calling drm_connector_attach_content_protection_property() on initialization.

The value of this property can be one of the following:

DRM_MODE_CONTENT_PROTECTION_UNDESIRED = 0
The link is not protected, content is transmitted in the clear.
DRM_MODE_CONTENT_PROTECTION_DESIRED = 1
Userspace has requested content protection, but the link is not currently protected. When in this state, kernel should enable Content Protection as soon as possible.
DRM_MODE_CONTENT_PROTECTION_ENABLED = 2
Userspace has requested content protection, and the link is protected. Only the driver can set the property to this value. If userspace attempts to set to ENABLED, kernel will return -EINVAL.

A few guidelines:

  • DESIRED state should be preserved until userspace de-asserts it by setting the property to UNDESIRED. This means ENABLED should only transition to UNDESIRED when the user explicitly requests it.
  • If the state is DESIRED, kernel should attempt to re-authenticate the link whenever possible. This includes across disable/enable, dpms, hotplug, downstream device changes, link status failures, etc..
  • Userspace is responsible for polling the property to determine when the value transitions from ENABLED to DESIRED. This signifies the link is no longer protected and userspace should take appropriate action (whatever that might be).

Connectors also have one standardized atomic property:

CRTC_ID:
Mode object ID of the drm_crtc this connector should be connected to.

Connectors for LCD panels may also have one standardized property:

panel orientation:
On some devices the LCD panel is mounted in the casing in such a way that the up/top side of the panel does not match with the top side of the device. Userspace can use this property to check for this. Note that input coordinates from touchscreens (input devices with INPUT_PROP_DIRECT) will still map 1:1 to the actual LCD panel coordinates, so if userspace rotates the picture to adjust for the orientation it must also apply the same transformation to the touchscreen input coordinates. This property is initialized by calling drm_connector_init_panel_orientation_property().
scaling mode:

This property defines how a non-native mode is upscaled to the native mode of an LCD panel:

None:
No upscaling happens, scaling is left to the panel. Not all drivers expose this mode.
Full:
The output is upscaled to the full resolution of the panel, ignoring the aspect ratio.
Center:
No upscaling happens, the output is centered within the native resolution the panel.
Full aspect:
The output is upscaled to maximize either the width or height while retaining the aspect ratio.

This property should be set up by calling drm_connector_attach_scaling_mode_property(). Note that drivers can also expose this property to external outputs, in which case they must support “None”, which should be the default (since external screens have a built-in scaler).

Plane Composition Properties

The basic plane composition model supported by standard plane properties only has a source rectangle (in logical pixels within the drm_framebuffer), with sub-pixel accuracy, which is scaled up to a pixel-aligned destination rectangle in the visible area of a drm_crtc. The visible area of a CRTC is defined by the horizontal and vertical visible pixels (stored in hdisplay and vdisplay) of the requested mode (stored in drm_crtc_state.mode). These two rectangles are both stored in the drm_plane_state.

For the atomic ioctl the following standard (atomic) properties on the plane object encode the basic plane composition model:

SRC_X:
X coordinate offset for the source rectangle within the drm_framebuffer, in 16.16 fixed point. Must be positive.
SRC_Y:
Y coordinate offset for the source rectangle within the drm_framebuffer, in 16.16 fixed point. Must be positive.
SRC_W:
Width for the source rectangle within the drm_framebuffer, in 16.16 fixed point. SRC_X plus SRC_W must be within the width of the source framebuffer. Must be positive.
SRC_H:
Height for the source rectangle within the drm_framebuffer, in 16.16 fixed point. SRC_Y plus SRC_H must be within the height of the source framebuffer. Must be positive.
CRTC_X:
X coordinate offset for the destination rectangle. Can be negative.
CRTC_Y:
Y coordinate offset for the destination rectangle. Can be negative.
CRTC_W:
Width for the destination rectangle. CRTC_X plus CRTC_W can extend past the currently visible horizontal area of the drm_crtc.
CRTC_H:
Height for the destination rectangle. CRTC_Y plus CRTC_H can extend past the currently visible vertical area of the drm_crtc.
FB_ID:
Mode object ID of the drm_framebuffer this plane should scan out.
CRTC_ID:
Mode object ID of the drm_crtc this plane should be connected to.

Note that the source rectangle must fully lie within the bounds of the drm_framebuffer. The destination rectangle can lie outside of the visible area of the current mode of the CRTC. It must be apprpriately clipped by the driver, which can be done by calling drm_plane_helper_check_update(). Drivers are also allowed to round the subpixel sampling positions appropriately, but only to the next full pixel. No pixel outside of the source rectangle may ever be sampled, which is important when applying more sophisticated filtering than just a bilinear one when scaling. The filtering mode when scaling is unspecified.

On top of this basic transformation additional properties can be exposed by the driver:

rotation:
Rotation is set up with drm_plane_create_rotation_property(). It adds a rotation and reflection step between the source and destination rectangles. Without this property the rectangle is only scaled, but not rotated or reflected.
zpos:
Z position is set up with drm_plane_create_zpos_immutable_property() and drm_plane_create_zpos_property(). It controls the visibility of overlapping planes. Without this property the primary plane is always below the cursor plane, and ordering between all other planes is undefined.

Note that all the property extensions described here apply either to the plane or the CRTC (e.g. for the background color, which currently is not exposed and assumed to be black).

int drm_plane_create_rotation_property(struct drm_plane * plane, unsigned int rotation, unsigned int supported_rotations)

create a new rotation property

Parameters

struct drm_plane * plane
drm plane
unsigned int rotation
initial value of the rotation property
unsigned int supported_rotations
bitmask of supported rotations and reflections

Description

This creates a new property with the selected support for transformations.

Since a rotation by 180° degress is the same as reflecting both along the x and the y axis the rotation property is somewhat redundant. Drivers can use drm_rotation_simplify() to normalize values of this property.

The property exposed to userspace is a bitmask property (see drm_property_create_bitmask()) called “rotation” and has the following bitmask enumaration values:

DRM_MODE_ROTATE_0:
“rotate-0”
DRM_MODE_ROTATE_90:
“rotate-90”
DRM_MODE_ROTATE_180:
“rotate-180”
DRM_MODE_ROTATE_270:
“rotate-270”
DRM_MODE_REFLECT_X:
“reflect-x”
DRM_MODE_REFLECT_Y:
“reflect-y”

Rotation is the specified amount in degrees in counter clockwise direction, the X and Y axis are within the source rectangle, i.e. the X/Y axis before rotation. After reflection, the rotation is applied to the image sampled from the source rectangle, before scaling it to fit the destination rectangle.

unsigned int drm_rotation_simplify(unsigned int rotation, unsigned int supported_rotations)

Try to simplify the rotation

Parameters

unsigned int rotation
Rotation to be simplified
unsigned int supported_rotations
Supported rotations

Description

Attempt to simplify the rotation to a form that is supported. Eg. if the hardware supports everything except DRM_MODE_REFLECT_X one could call this function like this:

drm_rotation_simplify(rotation, DRM_MODE_ROTATE_0 |
DRM_MODE_ROTATE_90 | DRM_MODE_ROTATE_180 | DRM_MODE_ROTATE_270 | DRM_MODE_REFLECT_Y);

to eliminate the DRM_MODE_ROTATE_X flag. Depending on what kind of transforms the hardware supports, this function may not be able to produce a supported transform, so the caller should check the result afterwards.

int drm_plane_create_zpos_property(struct drm_plane * plane, unsigned int zpos, unsigned int min, unsigned int max)

create mutable zpos property

Parameters

struct drm_plane * plane
drm plane
unsigned int zpos
initial value of zpos property
unsigned int min
minimal possible value of zpos property
unsigned int max
maximal possible value of zpos property

Description

This function initializes generic mutable zpos property and enables support for it in drm core. Drivers can then attach this property to planes to enable support for configurable planes arrangement during blending operation. Drivers that attach a mutable zpos property to any plane should call the drm_atomic_normalize_zpos() helper during their implementation of drm_mode_config_funcs.atomic_check(), which will update the normalized zpos values and store them in drm_plane_state.normalized_zpos. Usually min should be set to 0 and max to maximal number of planes for given crtc - 1.

If zpos of some planes cannot be changed (like fixed background or cursor/topmost planes), driver should adjust min/max values and assign those planes immutable zpos property with lower or higher values (for more information, see drm_plane_create_zpos_immutable_property() function). In such case driver should also assign proper initial zpos values for all planes in its plane_reset() callback, so the planes will be always sorted properly.

See also drm_atomic_normalize_zpos().

The property exposed to userspace is called “zpos”.

Return

Zero on success, negative errno on failure.

int drm_plane_create_zpos_immutable_property(struct drm_plane * plane, unsigned int zpos)

create immuttable zpos property

Parameters

struct drm_plane * plane
drm plane
unsigned int zpos
value of zpos property

Description

This function initializes generic immutable zpos property and enables support for it in drm core. Using this property driver lets userspace to get the arrangement of the planes for blending operation and notifies it that the hardware (or driver) doesn’t support changing of the planes’ order. For mutable zpos see drm_plane_create_zpos_property().

The property exposed to userspace is called “zpos”.

Return

Zero on success, negative errno on failure.

int drm_atomic_normalize_zpos(struct drm_device * dev, struct drm_atomic_state * state)

calculate normalized zpos values for all crtcs

Parameters

struct drm_device * dev
DRM device
struct drm_atomic_state * state
atomic state of DRM device

Description

This function calculates normalized zpos value for all modified planes in the provided atomic state of DRM device.

For every CRTC this function checks new states of all planes assigned to it and calculates normalized zpos value for these planes. Planes are compared first by their zpos values, then by plane id (if zpos is equal). The plane with lowest zpos value is at the bottom. The drm_plane_state.normalized_zpos is then filled with unique values from 0 to number of active planes in crtc minus one.

RETURNS Zero for success or -errno

Color Management Properties

Color management or color space adjustments is supported through a set of 5 properties on the drm_crtc object. They are set up by calling drm_crtc_enable_color_mgmt().

“DEGAMMA_LUT”:

Blob property to set the degamma lookup table (LUT) mapping pixel data from the framebuffer before it is given to the transformation matrix. The data is interpreted as an array of struct drm_color_lut elements. Hardware might choose not to use the full precision of the LUT elements nor use all the elements of the LUT (for example the hardware might choose to interpolate between LUT[0] and LUT[4]).

Setting this to NULL (blob property value set to 0) means a linear/pass-thru gamma table should be used. This is generally the driver boot-up state too. Drivers can access this blob through drm_crtc_state.degamma_lut.

“DEGAMMA_LUT_SIZE”:
Unsinged range property to give the size of the lookup table to be set on the DEGAMMA_LUT property (the size depends on the underlying hardware). If drivers support multiple LUT sizes then they should publish the largest size, and sub-sample smaller sized LUTs (e.g. for split-gamma modes) appropriately.
“CTM”:

Blob property to set the current transformation matrix (CTM) apply to pixel data after the lookup through the degamma LUT and before the lookup through the gamma LUT. The data is interpreted as a struct drm_color_ctm.

Setting this to NULL (blob property value set to 0) means a unit/pass-thru matrix should be used. This is generally the driver boot-up state too. Drivers can access the blob for the color conversion matrix through drm_crtc_state.ctm.

“GAMMA_LUT”:

Blob property to set the gamma lookup table (LUT) mapping pixel data after the transformation matrix to data sent to the connector. The data is interpreted as an array of struct drm_color_lut elements. Hardware might choose not to use the full precision of the LUT elements nor use all the elements of the LUT (for example the hardware might choose to interpolate between LUT[0] and LUT[4]).

Setting this to NULL (blob property value set to 0) means a linear/pass-thru gamma table should be used. This is generally the driver boot-up state too. Drivers can access this blob through drm_crtc_state.gamma_lut.

“GAMMA_LUT_SIZE”:
Unsigned range property to give the size of the lookup table to be set on the GAMMA_LUT property (the size depends on the underlying hardware). If drivers support multiple LUT sizes then they should publish the largest size, and sub-sample smaller sized LUTs (e.g. for split-gamma modes) appropriately.

There is also support for a legacy gamma table, which is set up by calling drm_mode_crtc_set_gamma_size(). Drivers which support both should use drm_atomic_helper_legacy_gamma_set() to alias the legacy gamma ramp with the “GAMMA_LUT” property above.

Support for different non RGB color encodings is controlled through drm_plane specific COLOR_ENCODING and COLOR_RANGE properties. They are set up by calling drm_plane_create_color_properties().

“COLOR_ENCODING”
Optional plane enum property to support different non RGB color encodings. The driver can provide a subset of standard enum values supported by the DRM plane.
“COLOR_RANGE”
Optional plane enum property to support different non RGB color parameter ranges. The driver can provide a subset of standard enum values supported by the DRM plane.
uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision)

clamp and round LUT entries

Parameters

uint32_t user_input
input value
uint32_t bit_precision
number of bits the hw LUT supports

Description

Extract a degamma/gamma LUT value provided by user (in the form of drm_color_lut entries) and round it to the precision supported by the hardware.

void drm_crtc_enable_color_mgmt(struct drm_crtc * crtc, uint degamma_lut_size, bool has_ctm, uint gamma_lut_size)

enable color management properties

Parameters

struct drm_crtc * crtc
DRM CRTC
uint degamma_lut_size
the size of the degamma lut (before CSC)
bool has_ctm
whether to attach ctm_property for CSC matrix
uint gamma_lut_size
the size of the gamma lut (after CSC)

Description

This function lets the driver enable the color correction properties on a CRTC. This includes 3 degamma, csc and gamma properties that userspace can set and 2 size properties to inform the userspace of the lut sizes. Each of the properties are optional. The gamma and degamma properties are only attached if their size is not 0 and ctm_property is only attached if has_ctm is true.

Drivers should use drm_atomic_helper_legacy_gamma_set() to implement the legacy drm_crtc_funcs.gamma_set callback.

int drm_mode_crtc_set_gamma_size(struct drm_crtc * crtc, int gamma_size)

set the gamma table size

Parameters

struct drm_crtc * crtc
CRTC to set the gamma table size for
int gamma_size
size of the gamma table

Description

Drivers which support gamma tables should set this to the supported gamma table size when initializing the CRTC. Currently the drm core only supports a fixed gamma table size.

Return

Zero on success, negative errno on failure.

int drm_plane_create_color_properties(struct drm_plane * plane, u32 supported_encodings, u32 supported_ranges, enum drm_color_encoding default_encoding, enum drm_color_range default_range)

color encoding related plane properties

Parameters

struct drm_plane * plane
plane object
u32 supported_encodings
bitfield indicating supported color encodings
u32 supported_ranges
bitfileld indicating supported color ranges
enum drm_color_encoding default_encoding
default color encoding
enum drm_color_range default_range
default color range

Description

Create and attach plane specific COLOR_ENCODING and COLOR_RANGE properties to plane. The supported encodings and ranges should be provided in supported_encodings and supported_ranges bitmasks. Each bit set in the bitmask indicates that its number as enum value is supported.

Tile Group Property

Tile groups are used to represent tiled monitors with a unique integer identifier. Tiled monitors using DisplayID v1.3 have a unique 8-byte handle, we store this in a tile group, so we have a common identifier for all tiles in a monitor group. The property is called “TILE”. Drivers can manage tile groups using drm_mode_create_tile_group(), drm_mode_put_tile_group() and drm_mode_get_tile_group(). But this is only needed for internal panels where the tile group information is exposed through a non-standard way.

Explicit Fencing Properties

Explicit fencing allows userspace to control the buffer synchronization between devices. A Fence or a group of fences are transfered to/from userspace using Sync File fds and there are two DRM properties for that. IN_FENCE_FD on each DRM Plane to send fences to the kernel and OUT_FENCE_PTR on each DRM CRTC to receive fences from the kernel.

As a contrast, with implicit fencing the kernel keeps track of any ongoing rendering, and automatically ensures that the atomic update waits for any pending rendering to complete. For shared buffers represented with a struct dma_buf this is tracked in struct reservation_object. Implicit syncing is how Linux traditionally worked (e.g. DRI2/3 on X.org), whereas explicit fencing is what Android wants.

“IN_FENCE_FD”:

Use this property to pass a fence that DRM should wait on before proceeding with the Atomic Commit request and show the framebuffer for the plane on the screen. The fence can be either a normal fence or a merged one, the sync_file framework will handle both cases and use a fence_array if a merged fence is received. Passing -1 here means no fences to wait on.

If the Atomic Commit request has the DRM_MODE_ATOMIC_TEST_ONLY flag it will only check if the Sync File is a valid one.

On the driver side the fence is stored on the fence parameter of struct drm_plane_state. Drivers which also support implicit fencing should set the implicit fence using drm_atomic_set_fence_for_plane(), to make sure there’s consistent behaviour between drivers in precedence of implicit vs. explicit fencing.

“OUT_FENCE_PTR”:

Use this property to pass a file descriptor pointer to DRM. Once the Atomic Commit request call returns OUT_FENCE_PTR will be filled with the file descriptor number of a Sync File. This Sync File contains the CRTC fence that will be signaled when all framebuffers present on the Atomic Commit * request for that given CRTC are scanned out on the screen.

The Atomic Commit request fails if a invalid pointer is passed. If the Atomic Commit request fails for any other reason the out fence fd returned will be -1. On a Atomic Commit with the DRM_MODE_ATOMIC_TEST_ONLY flag the out fence will also be set to -1.

Note that out-fences don’t have a special interface to drivers and are internally represented by a struct drm_pending_vblank_event in struct drm_crtc_state, which is also used by the nonblocking atomic commit helpers and for the DRM event handling for existing userspace.

Existing KMS Properties

The following table gives description of drm properties exposed by various modules/drivers. Because this table is very unwieldy, do not add any new properties here. Instead document them in a section above.

Owner Module/Drivers Group Property Name Type Property Values Object attached Description/Restrictions
  DVI-I “subconnector” ENUM { “Unknown”, “DVI-D”, “DVI-A” } Connector TBD
    “select subconnector” ENUM { “Automatic”, “DVI-D”, “DVI-A” } Connector TBD
  TV “subconnector” ENUM { “Unknown”, “Composite”, “SVIDEO”, “Component”, “SCART” } Connector TBD
    “select subconnector” ENUM { “Automatic”, “Composite”, “SVIDEO”, “Component”, “SCART” } Connector TBD
    “mode” ENUM { “NTSC_M”, “NTSC_J”, “NTSC_443”, “PAL_B” } etc. Connector TBD
    “left margin” RANGE Min=0, Max=100 Connector TBD
    “right margin” RANGE Min=0, Max=100 Connector TBD
    “top margin” RANGE Min=0, Max=100 Connector TBD
    “bottom margin” RANGE Min=0, Max=100 Connector TBD
    “brightness” RANGE Min=0, Max=100 Connector TBD
    “contrast” RANGE Min=0, Max=100 Connector TBD
    “flicker reduction” RANGE Min=0, Max=100 Connector TBD
    “overscan” RANGE Min=0, Max=100 Connector TBD
    “saturation” RANGE Min=0, Max=100 Connector TBD
    “hue” RANGE Min=0, Max=100 Connector TBD
  Virtual GPU “suggested X” RANGE Min=0, Max=0xffffffff Connector property to suggest an X offset for a connector
    “suggested Y” RANGE Min=0, Max=0xffffffff Connector property to suggest an Y offset for a connector
  Optional “aspect ratio” ENUM { “None”, “4:3”, “16:9” } Connector TDB
i915 Generic “Broadcast RGB” ENUM { “Automatic”, “Full”, “Limited 16:235” } Connector When this property is set to Limited 16:235 and CTM is set, the hardware will be programmed with the result of the multiplication of CTM by the limited range matrix to ensure the pixels normaly in the range 0..1.0 are remapped to the range 16/255..235/255.
    “audio” ENUM { “force-dvi”, “off”, “auto”, “on” } Connector TBD
  SDVO-TV “mode” ENUM { “NTSC_M”, “NTSC_J”, “NTSC_443”, “PAL_B” } etc. Connector TBD
    “left_margin” RANGE Min=0, Max= SDVO dependent Connector TBD
    “right_margin” RANGE Min=0, Max= SDVO dependent Connector TBD
    “top_margin” RANGE Min=0, Max= SDVO dependent Connector TBD
    “bottom_margin” RANGE Min=0, Max= SDVO dependent Connector TBD
    “hpos” RANGE Min=0, Max= SDVO dependent Connector TBD
    “vpos” RANGE Min=0, Max= SDVO dependent Connector TBD
    “contrast” RANGE Min=0, Max= SDVO dependent Connector TBD
    “saturation” RANGE Min=0, Max= SDVO dependent Connector TBD
    “hue” RANGE Min=0, Max= SDVO dependent Connector TBD
    “sharpness” RANGE Min=0, Max= SDVO dependent Connector TBD
    “flicker_filter” RANGE Min=0, Max= SDVO dependent Connector TBD
    “flicker_filter_adaptive” RANGE Min=0, Max= SDVO dependent Connector TBD
    “flicker_filter_2d” RANGE Min=0, Max= SDVO dependent Connector TBD
    “tv_chroma_filter” RANGE Min=0, Max= SDVO dependent Connector TBD
    “tv_luma_filter” RANGE Min=0, Max= SDVO dependent Connector TBD
    “dot_crawl” RANGE Min=0, Max=1 Connector TBD
  SDVO-TV/LVDS “brightness” RANGE Min=0, Max= SDVO dependent Connector TBD
CDV gma-500 Generic “Broadcast RGB” ENUM { “Full”, “Limited 16:235” } Connector TBD
    “Broadcast RGB” ENUM { “off”, “auto”, “on” } Connector TBD
Poulsbo Generic “backlight” RANGE Min=0, Max=100 Connector TBD
  SDVO-TV “mode” ENUM { “NTSC_M”, “NTSC_J”, “NTSC_443”, “PAL_B” } etc. Connector TBD
    “left_margin” RANGE Min=0, Max= SDVO dependent Connector TBD
    “right_margin” RANGE Min=0, Max= SDVO dependent Connector TBD
    “top_margin” RANGE Min=0, Max= SDVO dependent Connector TBD
    “bottom_margin” RANGE Min=0, Max= SDVO dependent Connector TBD
    “hpos” RANGE Min=0, Max= SDVO dependent Connector TBD
    “vpos” RANGE Min=0, Max= SDVO dependent Connector TBD
    “contrast” RANGE Min=0, Max= SDVO dependent Connector TBD
    “saturation” RANGE Min=0, Max= SDVO dependent Connector TBD
    “hue” RANGE Min=0, Max= SDVO dependent Connector TBD
    “sharpness” RANGE Min=0, Max= SDVO dependent Connector TBD
    “flicker_filter” RANGE Min=0, Max= SDVO dependent Connector TBD
    “flicker_filter_adaptive” RANGE Min=0, Max= SDVO dependent Connector TBD
    “flicker_filter_2d” RANGE Min=0, Max= SDVO dependent Connector TBD
    “tv_chroma_filter” RANGE Min=0, Max= SDVO dependent Connector TBD
    “tv_luma_filter” RANGE Min=0, Max= SDVO dependent Connector TBD
    “dot_crawl” RANGE Min=0, Max=1 Connector TBD
  SDVO-TV/LVDS “brightness” RANGE Min=0, Max= SDVO dependent Connector TBD
armada CRTC “CSC_YUV” ENUM { “Auto” , “CCIR601”, “CCIR709” } CRTC TBD
    “CSC_RGB” ENUM { “Auto”, “Computer system”, “Studio” } CRTC TBD
  Overlay “colorkey” RANGE Min=0, Max=0xffffff Plane TBD
    “colorkey_min” RANGE Min=0, Max=0xffffff Plane TBD
    “colorkey_max” RANGE Min=0, Max=0xffffff Plane TBD
    “colorkey_val” RANGE Min=0, Max=0xffffff Plane TBD
    “colorkey_alpha” RANGE Min=0, Max=0xffffff Plane TBD
    “colorkey_mode” ENUM { “disabled”, “Y component”, “U component” , “V component”, “RGB”, “R component”, “G component”, “B component” } Plane TBD
    “brightness” RANGE Min=0, Max=256 + 255 Plane TBD
    “contrast” RANGE Min=0, Max=0x7fff Plane TBD
    “saturation” RANGE Min=0, Max=0x7fff Plane TBD
exynos CRTC “mode” ENUM { “normal”, “blank” } CRTC TBD
i2c/ch7006_drv Generic “scale” RANGE Min=0, Max=2 Connector TBD
  TV “mode” ENUM { “PAL”, “PAL-M”,”PAL-N”}, ”PAL-Nc” , “PAL-60”, “NTSC-M”, “NTSC-J” } Connector TBD
nouveau NV10 Overlay “colorkey” RANGE Min=0, Max=0x01ffffff Plane TBD
    “contrast” RANGE Min=0, Max=8192-1 Plane TBD
    “brightness” RANGE Min=0, Max=1024 Plane TBD
    “hue” RANGE Min=0, Max=359 Plane TBD
    “saturation” RANGE Min=0, Max=8192-1 Plane TBD
    “iturbt_709” RANGE Min=0, Max=1 Plane TBD
  Nv04 Overlay “colorkey” RANGE Min=0, Max=0x01ffffff Plane TBD
    “brightness” RANGE Min=0, Max=1024 Plane TBD
  Display “dithering mode” ENUM { “auto”, “off”, “on” } Connector TBD
    “dithering depth” ENUM { “auto”, “off”, “on”, “static 2x2”, “dynamic 2x2”, “temporal” } Connector TBD
    “underscan” ENUM { “auto”, “6 bpc”, “8 bpc” } Connector TBD
    “underscan hborder” RANGE Min=0, Max=128 Connector TBD
    “underscan vborder” RANGE Min=0, Max=128 Connector TBD
    “vibrant hue” RANGE Min=0, Max=180 Connector TBD
    “color vibrance” RANGE Min=0, Max=200 Connector TBD
omap Generic “zorder” RANGE Min=0, Max=3 CRTC, Plane TBD
qxl Generic “hotplug_mode_update” RANGE Min=0, Max=1 Connector TBD
radeon DVI-I “coherent” RANGE Min=0, Max=1 Connector TBD
  DAC enable load detect “load detection” RANGE Min=0, Max=1 Connector TBD
  TV Standard “tv standard” ENUM { “ntsc”, “pal”, “pal-m”, “pal-60”, “ntsc-j” , “scart-pal”, “pal-cn”, “secam” } Connector TBD
  legacy TMDS PLL detect “tmds_pll” ENUM { “driver”, “bios” }
TBD
  Underscan “underscan” ENUM { “off”, “on”, “auto” } Connector TBD
    “underscan hborder” RANGE Min=0, Max=128 Connector TBD
    “underscan vborder” RANGE Min=0, Max=128 Connector TBD
  Audio “audio” ENUM { “off”, “on”, “auto” } Connector TBD
  FMT Dithering “dither” ENUM { “off”, “on” } Connector TBD
rcar-du Generic “alpha” RANGE Min=0, Max=255 Plane TBD
    “colorkey” RANGE Min=0, Max=0x01ffffff Plane TBD

Vertical Blanking

Vertical blanking plays a major role in graphics rendering. To achieve tear-free display, users must synchronize page flips and/or rendering to vertical blanking. The DRM API offers ioctls to perform page flips synchronized to vertical blanking and wait for vertical blanking.

The DRM core handles most of the vertical blanking management logic, which involves filtering out spurious interrupts, keeping race-free blanking counters, coping with counter wrap-around and resets and keeping use counts. It relies on the driver to generate vertical blanking interrupts and optionally provide a hardware vertical blanking counter.

Drivers must initialize the vertical blanking handling core with a call to drm_vblank_init(). Minimally, a driver needs to implement drm_crtc_funcs.enable_vblank and drm_crtc_funcs.disable_vblank plus call drm_crtc_handle_vblank() in it’s vblank interrupt handler for working vblank support.

Vertical blanking interrupts can be enabled by the DRM core or by drivers themselves (for instance to handle page flipping operations). The DRM core maintains a vertical blanking use count to ensure that the interrupts are not disabled while a user still needs them. To increment the use count, drivers call drm_crtc_vblank_get() and release the vblank reference again with drm_crtc_vblank_put(). In between these two calls vblank interrupts are guaranteed to be enabled.

On many hardware disabling the vblank interrupt cannot be done in a race-free manner, see drm_driver.vblank_disable_immediate and drm_driver.max_vblank_count. In that case the vblank core only disables the vblanks after a timer has expired, which can be configured through the vblankoffdelay module parameter.

Vertical Blanking and Interrupt Handling Functions Reference

struct drm_pending_vblank_event

pending vblank event tracking

Definition

struct drm_pending_vblank_event {
  struct drm_pending_event base;
  unsigned int pipe;
  u64 sequence;
  union {
    struct drm_event base;
    struct drm_event_vblank vbl;
    struct drm_event_crtc_sequence seq;
  } event;
};

Members

base
Base structure for tracking pending DRM events.
pipe
drm_crtc_index() of the drm_crtc this event is for.
sequence
frame event should be triggered at
event
Actual event which will be sent to userspace.
event.base
DRM event base class.
event.vbl
Event payload for vblank events, requested through either the MODE_PAGE_FLIP or MODE_ATOMIC IOCTL. Also generated by the legacy WAIT_VBLANK IOCTL, but new userspace should use MODE_QUEUE_SEQUENCE and event.seq instead.
event.seq
Event payload for the MODE_QUEUEU_SEQUENCE IOCTL.
struct drm_vblank_crtc

vblank tracking for a CRTC

Definition

struct drm_vblank_crtc {
  struct drm_device *dev;
  wait_queue_head_t queue;
  struct timer_list disable_timer;
  seqlock_t seqlock;
  u64 count;
  ktime_t time;
  atomic_t refcount;
  u32 last;
  unsigned int inmodeset;
  unsigned int pipe;
  int framedur_ns;
  int linedur_ns;
  struct drm_display_mode hwmode;
  bool enabled;
};

Members

dev
Pointer to the drm_device.
queue
Wait queue for vblank waiters.
disable_timer
Disable timer for the delayed vblank disabling hysteresis logic. Vblank disabling is controlled through the drm_vblank_offdelay module option and the setting of the drm_device.max_vblank_count value.
seqlock
Protect vblank count and time.
count
Current software vblank counter.
time
Vblank timestamp corresponding to count.
refcount
Number of users/waiters of the vblank interrupt. Only when this refcount reaches 0 can the hardware interrupt be disabled using disable_timer.
last
Protected by drm_device.vbl_lock, used for wraparound handling.
inmodeset
Tracks whether the vblank is disabled due to a modeset. For legacy driver bit 2 additionally tracks whether an additional temporary vblank reference has been acquired to paper over the hardware counter resetting/jumping. KMS drivers should instead just call drm_crtc_vblank_off() and drm_crtc_vblank_on(), which explicitly save and restore the vblank count.
pipe
drm_crtc_index() of the drm_crtc corresponding to this structure.
framedur_ns
Frame/Field duration in ns, used by drm_calc_vbltimestamp_from_scanoutpos() and computed by drm_calc_timestamping_constants().
linedur_ns
Line duration in ns, used by drm_calc_vbltimestamp_from_scanoutpos() and computed by drm_calc_timestamping_constants().
hwmode
Cache of the current hardware display mode. Only valid when enabled is set. This is used by helpers like drm_calc_vbltimestamp_from_scanoutpos(). We can’t just access the hardware mode by e.g. looking at drm_crtc_state.adjusted_mode, because that one is really hard to get from interrupt context.
enabled
Tracks the enabling state of the corresponding drm_crtc to avoid double-disabling and hence corrupting saved state. Needed by drivers not using atomic KMS, since those might go through their CRTC disabling functions multiple times.

Description

This structure tracks the vblank state for one CRTC.

Note that for historical reasons - the vblank handling code is still shared with legacy/non-kms drivers - this is a free-standing structure not directly connected to struct drm_crtc. But all public interface functions are taking a struct drm_crtc to hide this implementation detail.

u64 drm_crtc_accurate_vblank_count(struct drm_crtc * crtc)

retrieve the master vblank counter

Parameters

struct drm_crtc * crtc
which counter to retrieve

Description

This function is similar to drm_crtc_vblank_count() but this function interpolates to handle a race with vblank interrupts using the high precision timestamping support.

This is mostly useful for hardware that can obtain the scanout position, but doesn’t have a hardware frame counter.

int drm_vblank_init(struct drm_device * dev, unsigned int num_crtcs)

initialize vblank support

Parameters

struct drm_device * dev
DRM device
unsigned int num_crtcs
number of CRTCs supported by dev

Description

This function initializes vblank support for num_crtcs display pipelines. Cleanup is handled by the DRM core, or through calling drm_dev_fini() for drivers with a drm_driver.release callback.

Return

Zero on success or a negative error code on failure.

wait_queue_head_t * drm_crtc_vblank_waitqueue(struct drm_crtc * crtc)

get vblank waitqueue for the CRTC

Parameters

struct drm_crtc * crtc
which CRTC’s vblank waitqueue to retrieve

Description

This function returns a pointer to the vblank waitqueue for the CRTC. Drivers can use this to implement vblank waits using wait_event() and related functions.

void drm_calc_timestamping_constants(struct drm_crtc * crtc, const struct drm_display_mode * mode)

calculate vblank timestamp constants

Parameters

struct drm_crtc * crtc
drm_crtc whose timestamp constants should be updated.
const struct drm_display_mode * mode
display mode containing the scanout timings

Description

Calculate and store various constants which are later needed by vblank and swap-completion timestamping, e.g, by drm_calc_vbltimestamp_from_scanoutpos(). They are derived from CRTC’s true scanout timing, so they take things like panel scaling or other adjustments into account.

bool drm_calc_vbltimestamp_from_scanoutpos(struct drm_device * dev, unsigned int pipe, int * max_error, ktime_t * vblank_time, bool in_vblank_irq)

precise vblank timestamp helper

Parameters

struct drm_device * dev
DRM device
unsigned int pipe
index of CRTC whose vblank timestamp to retrieve
int * max_error
Desired maximum allowable error in timestamps (nanosecs) On return contains true maximum error of timestamp
ktime_t * vblank_time
Pointer to time which should receive the timestamp
bool in_vblank_irq
True when called from drm_crtc_handle_vblank(). Some drivers need to apply some workarounds for gpu-specific vblank irq quirks if flag is set.

Description

Implements calculation of exact vblank timestamps from given drm_display_mode timings and current video scanout position of a CRTC. This can be directly used as the drm_driver.get_vblank_timestamp implementation of a kms driver if drm_driver.get_scanout_position is implemented.

The current implementation only handles standard video modes. For double scan and interlaced modes the driver is supposed to adjust the hardware mode (taken from drm_crtc_state.adjusted mode for atomic modeset drivers) to match the scanout position reported.

Note that atomic drivers must call drm_calc_timestamping_constants() before enabling a CRTC. The atomic helpers already take care of that in drm_atomic_helper_update_legacy_modeset_state().

Return

Returns true on success, and false on failure, i.e. when no accurate timestamp could be acquired.

u64 drm_crtc_vblank_count(struct drm_crtc * crtc)

retrieve “cooked” vblank counter value

Parameters

struct drm_crtc * crtc
which counter to retrieve

Description

Fetches the “cooked” vblank count value that represents the number of vblank events since the system was booted, including lost events due to modesetting activity. Note that this timer isn’t correct against a racing vblank interrupt (since it only reports the software vblank counter), see drm_crtc_accurate_vblank_count() for such use-cases.

Return

The software vblank counter.

u64 drm_crtc_vblank_count_and_time(struct drm_crtc * crtc, ktime_t * vblanktime)

retrieve “cooked” vblank counter value and the system timestamp corresponding to that vblank counter value

Parameters

struct drm_crtc * crtc
which counter to retrieve
ktime_t * vblanktime
Pointer to time to receive the vblank timestamp.

Description

Fetches the “cooked” vblank count value that represents the number of vblank events since the system was booted, including lost events due to modesetting activity. Returns corresponding system timestamp of the time of the vblank interval that corresponds to the current vblank counter value.

void drm_crtc_arm_vblank_event(struct drm_crtc * crtc, struct drm_pending_vblank_event * e)

arm vblank event after pageflip

Parameters

struct drm_crtc * crtc
the source CRTC of the vblank event
struct drm_pending_vblank_event * e
the event to send

Description

A lot of drivers need to generate vblank events for the very next vblank interrupt. For example when the page flip interrupt happens when the page flip gets armed, but not when it actually executes within the next vblank period. This helper function implements exactly the required vblank arming behaviour.

NOTE

Drivers using this to send out the drm_crtc_state.event as part of an atomic commit must ensure that the next vblank happens at exactly the same time as the atomic commit is committed to the hardware. This function itself does not protect against the next vblank interrupt racing with either this function call or the atomic commit operation. A possible sequence could be:

  1. Driver commits new hardware state into vblank-synchronized registers.
  2. A vblank happens, committing the hardware state. Also the corresponding vblank interrupt is fired off and fully processed by the interrupt handler.
  3. The atomic commit operation proceeds to call drm_crtc_arm_vblank_event().
  4. The event is only send out for the next vblank, which is wrong.

An equivalent race can happen when the driver calls drm_crtc_arm_vblank_event() before writing out the new hardware state.

The only way to make this work safely is to prevent the vblank from firing (and the hardware from committing anything else) until the entire atomic commit sequence has run to completion. If the hardware does not have such a feature (e.g. using a “go” bit), then it is unsafe to use this functions. Instead drivers need to manually send out the event from their interrupt handler by calling drm_crtc_send_vblank_event() and make sure that there’s no possible race with the hardware committing the atomic update.

Caller must hold a vblank reference for the event e, which will be dropped when the next vblank arrives.

void drm_crtc_send_vblank_event(struct drm_crtc * crtc, struct drm_pending_vblank_event * e)

helper to send vblank event after pageflip

Parameters

struct drm_crtc * crtc
the source CRTC of the vblank event
struct drm_pending_vblank_event * e
the event to send

Description

Updates sequence # and timestamp on event for the most recently processed vblank, and sends it to userspace. Caller must hold event lock.

See drm_crtc_arm_vblank_event() for a helper which can be used in certain situation, especially to send out events for atomic commit operations.

int drm_crtc_vblank_get(struct drm_crtc * crtc)

get a reference count on vblank events

Parameters

struct drm_crtc * crtc
which CRTC to own

Description

Acquire a reference count on vblank events to avoid having them disabled while in use.

Return

Zero on success or a negative error code on failure.

void drm_crtc_vblank_put(struct drm_crtc * crtc)

give up ownership of vblank events

Parameters

struct drm_crtc * crtc
which counter to give up

Description

Release ownership of a given vblank counter, turning off interrupts if possible. Disable interrupts after drm_vblank_offdelay milliseconds.

void drm_wait_one_vblank(struct drm_device * dev, unsigned int pipe)

wait for one vblank

Parameters

struct drm_device * dev
DRM device
unsigned int pipe
CRTC index

Description

This waits for one vblank to pass on pipe, using the irq driver interfaces. It is a failure to call this when the vblank irq for pipe is disabled, e.g. due to lack of driver support or because the crtc is off.

This is the legacy version of drm_crtc_wait_one_vblank().

void drm_crtc_wait_one_vblank(struct drm_crtc * crtc)

wait for one vblank

Parameters

struct drm_crtc * crtc
DRM crtc

Description

This waits for one vblank to pass on crtc, using the irq driver interfaces. It is a failure to call this when the vblank irq for crtc is disabled, e.g. due to lack of driver support or because the crtc is off.

void drm_crtc_vblank_off(struct drm_crtc * crtc)

disable vblank events on a CRTC

Parameters

struct drm_crtc * crtc
CRTC in question

Description

Drivers can use this function to shut down the vblank interrupt handling when disabling a crtc. This function ensures that the latest vblank frame count is stored so that drm_vblank_on can restore it again.

Drivers must use this function when the hardware vblank counter can get reset, e.g. when suspending or disabling the crtc in general.

void drm_crtc_vblank_reset(struct drm_crtc * crtc)

reset vblank state to off on a CRTC

Parameters

struct drm_crtc * crtc
CRTC in question

Description

Drivers can use this function to reset the vblank state to off at load time. Drivers should use this together with the drm_crtc_vblank_off() and drm_crtc_vblank_on() functions. The difference compared to drm_crtc_vblank_off() is that this function doesn’t save the vblank counter and hence doesn’t need to call any driver hooks.

This is useful for recovering driver state e.g. on driver load, or on resume.

void drm_crtc_vblank_on(struct drm_crtc * crtc)

enable vblank events on a CRTC

Parameters

struct drm_crtc * crtc
CRTC in question

Description

This functions restores the vblank interrupt state captured with drm_crtc_vblank_off() again and is generally called when enabling crtc. Note that calls to drm_crtc_vblank_on() and drm_crtc_vblank_off() can be unbalanced and so can also be unconditionally called in driver load code to reflect the current hardware state of the crtc.

void drm_vblank_restore(struct drm_device * dev, unsigned int pipe)

estimate missed vblanks and update vblank count.

Parameters

struct drm_device * dev
DRM device
unsigned int pipe
CRTC index

Description

Power manamement features can cause frame counter resets between vblank disable and enable. Drivers can use this function in their drm_crtc_funcs.enable_vblank implementation to estimate missed vblanks since the last drm_crtc_funcs.disable_vblank using timestamps and update the vblank counter.

This function is the legacy version of drm_crtc_vblank_restore().

void drm_crtc_vblank_restore(struct drm_crtc * crtc)

estimate missed vblanks and update vblank count.

Parameters

struct drm_crtc * crtc
CRTC in question

Description

Power manamement features can cause frame counter resets between vblank disable and enable. Drivers can use this function in their drm_crtc_funcs.enable_vblank implementation to estimate missed vblanks since the last drm_crtc_funcs.disable_vblank using timestamps and update the vblank counter.

bool drm_handle_vblank(struct drm_device * dev, unsigned int pipe)

handle a vblank event

Parameters

struct drm_device * dev
DRM device
unsigned int pipe
index of CRTC where this event occurred

Description

Drivers should call this routine in their vblank interrupt handlers to update the vblank counter and send any signals that may be pending.

This is the legacy version of drm_crtc_handle_vblank().

bool drm_crtc_handle_vblank(struct drm_crtc * crtc)

handle a vblank event

Parameters

struct drm_crtc * crtc
where this event occurred

Description

Drivers should call this routine in their vblank interrupt handlers to update the vblank counter and send any signals that may be pending.

This is the native KMS version of drm_handle_vblank().

Return

True if the event was successfully handled, false on failure.