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media: v4l2-subdev: Support hybrid links in v4l2_subdev_link_validate()

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The v4l2_subdev_link_validate() helper function is meant to be used as a
drop-in implementation of a V4L2 subdev entity .link_validate() handler.
It supports subdev-to-subdev links only, and complains if one end of the
link is not a subdev. This forces drivers that have video output devices
connected to subdevs to implement a custom .link_validate() handler,
calling v4l2_subdev_link_validate() for the subdev-to-subdev links, and
performing manual link validation for the video-to-subdev links.

Video devices embed a media entity, and therefore also have a
.link_validate() operation. For video capture devices, the operation
should be manually implemented by drivers for validate the
subdev-to-video links. For video output devices, on the other hand, that
operation is never called, as link validation is performed in the
context of the sink entity.

As a result, we end up forcing drivers to implement a custom
.link_validate() handler for subdevs connected to video output devices,
when the video devices provide an operation that could be used for that
purpose.

To improve that situation, make v4l2_subdev_link_validate() delegate
link validation to the source's .link_validate() operation when the link
source is a video device and the link sink is a subdev. This allows
broader usage of v4l2_subdev_link_validate(), and simplifies drivers by
making video device link validation easy to implement in the video
device .link_validate(), regardless of whether the video device is an
output device or a capture device.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
This commit is contained in:
Laurent Pinchart 2024-06-19 03:02:42 +03:00
parent d1307671e5
commit 5fd3e2412a
2 changed files with 44 additions and 5 deletions
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41
drivers/media/v4l2-core/v4l2-subdev.c
View File

@ -1450,13 +1450,46 @@ int v4l2_subdev_link_validate(struct media_link *link)
if (WARN_ON_ONCE(!is_media_entity_v4l2_subdev(link->sink->entity)))
return -EINVAL;
if (!is_media_entity_v4l2_subdev(link->source->entity)) {
pr_warn_once("source of link '%s':%u->'%s':%u is not a V4L2 sub-device, driver bug!\n",
link->source->entity->name, link->source->index,
link->sink->entity->name, link->sink->index);
/*
* If the source is a video device, delegate link validation to it. This
* allows usage of this helper for subdev connected to a video output
* device, provided that the driver implement the video output device's
* .link_validate() operation.
*/
if (is_media_entity_v4l2_video_device(link->source->entity)) {
struct media_entity *source = link->source->entity;
if (!source->ops || !source->ops->link_validate) {
/*
* Many existing drivers do not implement the required
* .link_validate() operation for their video devices.
* Print a warning to get the drivers fixed, and return
* 0 to avoid breaking userspace. This should
* eventually be turned into a WARN_ON() when all
* drivers will have been fixed.
*/
pr_warn_once("video device '%s' does not implement .link_validate(), driver bug!\n",
source->name);
return 0;
}
/*
* Avoid infinite loops in case a video device incorrectly uses
* this helper function as its .link_validate() handler.
*/
if (WARN_ON(source->ops->link_validate == v4l2_subdev_link_validate))
return -EINVAL;
return source->ops->link_validate(link);
}
/*
* If the source is still not a subdev, usage of this helper is a clear
* driver bug.
*/
if (WARN_ON(!is_media_entity_v4l2_subdev(link->source->entity)))
return -EINVAL;
sink_sd = media_entity_to_v4l2_subdev(link->sink->entity);
source_sd = media_entity_to_v4l2_subdev(link->source->entity);

6
include/media/v4l2-subdev.h
View File

@ -1250,6 +1250,12 @@ int v4l2_subdev_link_validate_default(struct v4l2_subdev *sd,
* calls v4l2_subdev_link_validate_default() to ensure that
* width, height and the media bus pixel code are equal on both
* source and sink of the link.
*
* The function can be used as a drop-in &media_entity_ops.link_validate
* implementation for v4l2_subdev instances. It supports all links between
* subdevs, as well as links between subdevs and video devices, provided that
* the video devices also implement their &media_entity_ops.link_validate
* operation.
*/
int v4l2_subdev_link_validate(struct media_link *link);