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@xxxxxxxxxxxxxxxx> --- drivers/media/v4l2-core/v4l2-subdev.c | 40 +++++++++++++++++++++++---- include/media/v4l2-subdev.h | 6 ++++ 2 files changed, 41 insertions(+), 5 deletions(-) diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c index 2d5e39c79620..e1e1333cfb0a 100644 --- a/drivers/media/v4l2-core/v4l2-subdev.c +++ b/drivers/media/v4l2-core/v4l2-subdev.c @@ -1458,13 +1458,43 @@ int v4l2_subdev_link_validate(struct media_link *link) if (WARN_ON(!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); - return 0; + /* + * 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. */ + 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); diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h index 1b74e037e440..731be85a7af1 100644 --- a/include/media/v4l2-subdev.h +++ b/include/media/v4l2-subdev.h @@ -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); -- Regards, Laurent Pinchart