media: mc-entity: Add a new helper function to get a remote pad for a pad

The newly added media_entity_remote_source_pad_unique() helper function
handles use cases where the entity has a link enabled uniqueness
constraint covering all pads. There are use cases where the constraint
covers a specific pad only. Add a new media_pad_remote_pad_unique()
function to handle this. It operates as
media_entity_remote_source_pad_unique(), but on a given pad instead of
on the entity.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/include/media/media-entity.h b/include/media/media-entity.h
index c5618f7c1408..f16ffe70f7a6 100644
--- a/include/media/media-entity.h
+++ b/include/media/media-entity.h
@@ -860,6 +860,24 @@ struct media_link *media_entity_find_link(struct media_pad *source,
 struct media_pad *media_pad_remote_pad_first(const struct media_pad *pad);
 
 /**
+ * media_pad_remote_pad_unique - Find a remote pad connected to a pad
+ * @pad: The pad
+ *
+ * Search for and return a remote pad connected to @pad through an enabled
+ * link. If multiple (or no) remote pads are found, an error is returned.
+ *
+ * The uniqueness constraint makes this helper function suitable for entities
+ * that support a single active source at a time on a given pad.
+ *
+ * Return: A pointer to the remote pad, or one of the following error pointers
+ * if an error occurs:
+ *
+ * * -ENOTUNIQ - Multiple links are enabled
+ * * -ENOLINK - No connected pad found
+ */
+struct media_pad *media_pad_remote_pad_unique(const struct media_pad *pad);
+
+/**
  * media_entity_remote_pad_unique - Find a remote pad connected to an entity
  * @entity: The entity
  * @type: The type of pad to find (MEDIA_PAD_FL_SINK or MEDIA_PAD_FL_SOURCE)