Hi,
On 22/08/2024 18:45, Laurent Pinchart wrote:
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.
Maybe mention this patch in the previous patch's desc to answer the
question I sent =)
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 d3196042d5c5..32ffebae4d17 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -1450,13 +1450,43 @@ 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);
- 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. */
Maybe this could elaborate a bit, and say that non-subdev drivers should
not use v4l2_subdev_link_validate, but some do (?) or might use it by
mistake, and this catches the driver bug.
+ if (WARN_ON(source->ops->link_validate == v4l2_subdev_link_validate))
+ return -EINVAL;
This might still be risky. The driver could implement its own validate,
which does some checks and then calls v4l2_subdev_link_validate(). But
I'm sure that'll get get noticed =).
Tomi
+
+ 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 bd235d325ff9..8daa0929865c 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);
