media: v4l2-subdev: Refactor warnings in v4l2_subdev_link_validate()

The v4l2_subdev_link_validate() function prints a one-time warning if it
gets called on a link whose source or sink is not a subdev. As links get
validated in the context of their sink, a call to the helper when the
link's sink is not a subdev indicates that the driver has set its
.link_validate() handler to v4l2_subdev_link_validate() on a non-subdev
entity, which is a clear driver bug. On the other hand, the link's
source not being a subdev indicates that the helper is used for a subdev
connected to a video output device, which is a lesser issue, if only
because this is currently common practice.

There are no drivers left in the kernel that use
v4l2_subdev_link_validate() in a context where it may get called on a
non-subdev sink. Replace the pr_warn_once() with a WARN_ON_ONCE() in
this case to make sure that new offenders won't be introduced.

A subsequent change will improve the v4l2_subdev_link_validate() helper
to properly support validating video device to subdev links.

Signed-off-by: Laurent Pinchart <[email protected]>
Reviewed-by: Tomi Valkeinen <[email protected]>
Acked-by: Sakari Ailus <[email protected]>

1 files changed, 9 insertions, 5 deletions

diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index 7c5812d55315..d3196042d5c5 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -1443,11 +1443,15 @@ int v4l2_subdev_link_validate(struct media_link *link)
 	bool states_locked;
 	int ret;
 
-	if (!is_media_entity_v4l2_subdev(link->sink->entity) ||
-	    !is_media_entity_v4l2_subdev(link->source->entity)) {
-		pr_warn_once("%s of link '%s':%u->'%s':%u is not a V4L2 sub-device, driver bug!\n",
-			     !is_media_entity_v4l2_subdev(link->sink->entity) ?
-			     "sink" : "source",
+	/*
+	 * Links are validated in the context of the sink entity. Usage of this
+	 * helper on a sink that is not a subdev is a clear driver bug.
+	 */
+	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;