1 files changed, 45 insertions, 8 deletions

diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index 7c5812d55315..3a4ba08810d2 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -1443,16 +1443,53 @@ 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",
-			     link->source->entity->name, link->source->index,
-			     link->sink->entity->name, link->sink->index);
-		return 0;
+	/*
+	 * 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 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);