2.19. V4L2 Media Controller functions and data structures

int v4l2_mc_create_media_graph(struct media_device *mdev)

create Media Controller links at the graph.

Parameters

struct media_device *mdev

pointer to the media_device struct.

Description

Add links between the entities commonly found on PC customer’s hardware at the V4L2 side: camera sensors, audio and video PLL-IF decoders, tuners, analog TV decoder and I/O entities (video, VBI and Software Defined Radio).

Note

Webcams are modelled on a very simple way: the sensor is connected directly to the I/O entity. All dirty details, like scaler and crop HW are hidden. While such mapping is enough for v4l2 interface centric PC-consumer’s hardware, V4L2 subdev centric camera hardware should not use this routine, as it will not build the right graph.

int v4l_enable_media_source(struct video_device *vdev)

Hold media source for exclusive use if free

Parameters

struct video_device *vdev

pointer to struct video_device

Description

This interface calls enable_source handler to determine if media source is free for use. The enable_source handler is responsible for checking is the media source is free and start a pipeline between the media source and the media entity associated with the video device. This interface should be called from v4l2-core and dvb-core interfaces that change the source configuration.

Return

returns zero on success or a negative error code.

void v4l_disable_media_source(struct video_device *vdev)

Release media source

Parameters

struct video_device *vdev

pointer to struct video_device

Description

This interface calls disable_source handler to release the media source. The disable_source handler stops the active media pipeline between the media source and the media entity associated with the video device.

Return

returns zero on success or a negative error code.

Create fwnode-based links from a source subdev to a sink pad.

Parameters

struct v4l2_subdev *src_sd

pointer to a source subdev

struct media_pad *sink

pointer to a sink pad

u32 flags

the link flags

Description

This function searches for fwnode endpoint connections from a source subdevice to a single sink pad, and if suitable connections are found, translates them into media links to that pad. The function can be called by the sink, in its v4l2-async notifier bound callback, to create links from a bound source subdevice.

The flags argument specifies the link flags. The caller shall ensure that the flags are valid regardless of the number of links that may be created. For instance, setting the MEDIA_LNK_FL_ENABLED flag will cause all created links to be enabled, which isn’t valid if more than one link is created.

Note

Any sink subdevice that calls this function must implement the .get_fwnode_pad media operation in order to verify endpoints passed to the sink are owned by the sink.

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

Create fwnode-based links from a source subdev to a sink subdev.

Parameters

struct v4l2_subdev *src_sd

pointer to a source subdevice

struct v4l2_subdev *sink_sd

pointer to a sink subdevice

Description

This function searches for any and all fwnode endpoint connections between source and sink subdevices, and translates them into media links. The function can be called by the sink subdevice, in its v4l2-async notifier subdev bound callback, to create all links from a bound source subdevice.

Note

Any sink subdevice that calls this function must implement the .get_fwnode_pad media operation in order to verify endpoints passed to the sink are owned by the sink.

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

int v4l2_pipeline_pm_get(struct media_entity *entity)

Increase the use count of a pipeline

Parameters

struct media_entity *entity

The root entity of a pipeline

Description

THIS FUNCTION IS DEPRECATED. DO NOT USE IN NEW DRIVERS. USE RUNTIME PM ON SUB-DEVICE DRIVERS INSTEAD.

Update the use count of all entities in the pipeline and power entities on.

This function is intended to be called in video node open. It uses struct media_entity.use_count to track the power status. The use of this function should be paired with v4l2_pipeline_link_notify().

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

void v4l2_pipeline_pm_put(struct media_entity *entity)

Decrease the use count of a pipeline

Parameters

struct media_entity *entity

The root entity of a pipeline

Description

THIS FUNCTION IS DEPRECATED. DO NOT USE IN NEW DRIVERS. USE RUNTIME PM ON SUB-DEVICE DRIVERS INSTEAD.

Update the use count of all entities in the pipeline and power entities off.

This function is intended to be called in video node release. It uses struct media_entity.use_count to track the power status. The use of this function should be paired with v4l2_pipeline_link_notify().

Link management notification callback

Parameters

struct media_link *link

The link

u32 flags

New link flags that will be applied

unsigned int notification

The link’s state change notification type (MEDIA_DEV_NOTIFY_*)

Description

THIS FUNCTION IS DEPRECATED. DO NOT USE IN NEW DRIVERS. USE RUNTIME PM ON SUB-DEVICE DRIVERS INSTEAD.

React to link management on powered pipelines by updating the use count of all entities in the source and sink sides of the link. Entities are powered on or off accordingly. The use of this function should be paired with v4l2_pipeline_pm_{get,put}().

Return 0 on success or a negative error code on failure. Powering entities off is assumed to never fail. This function will not fail for disconnection events.

int v4l2_mc_pipeline_enabled(struct video_device *vdev, bool (*func)(struct video_device *vdev), struct media_pad **__sink_pad, u64 *__sink_streams)

Tell when to start streaming

Parameters

struct video_device *vdev

The video device

bool (*func)(struct video_device *vdev)

Caller-provided function to tell a video device’s streaming state

struct media_pad **__sink_pad

sink pad at the root of the local pipeline

u64 *__sink_streams

streams to start

Description

Use to tell whether streaming should start on a video node. func returns true if streaming has been started on a given video node. __sink_pad and __sink_streams are filled with pad and streams on the sub-device closest to the video nodes, to be used for calling v4l2_subdev_enable_streams() and v4l2_subdev_disable_streams().

Using v4l2_mc_pipeline_enabled() has a few limitations currently (consider it a to-do list):

  • only unbranched streams can be supported albeit adding support for downstream branches would be fairly trivial,

  • streams within a single source sub-device are considered to start at the same time, more control could be added in two ways: 1) for sources to determine stream starting, a control could be added to UAPI and 2) sources could tell which streams start at the same time using a sub-device operation,

  • CSI-2 VC framing is ignored currently, but VC-based stream starting could be implemented by letting the caller to provide a function to determine which streams are of interest and

  • routes leading to nowhere are ignored, on some hardware this is a problem, but this can also be rather trivially addressed.

Return

  • 0: Success, but don’t start streaming yet

  • 1: Success, now it’s time to start streaming

  • -ENXIO: Route traversal encountered a non-video device/sub-device entity

  • -ENOTUNIQ: No unique remote pad

  • -ENOLINK: No remote pad found

  • -ENOENT: Enabled upstream route not found

  • -EMLINK: No unique downstream route found

  • -EINVAL: Stream could not be followed to source or was not produced by

    the source