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

The media_entity_remote_pad_first() helper function returns the first
remote pad it finds connected to a given pad. Beside being possibly
non-deterministic (as it stops at the first enabled link), the fact that
it returns the first match makes it unsuitable for drivers that need to
guarantee that a single link is enabled, for instance when an entity can
process data from one of multiple sources at a time.

For those use cases, add a new helper function,
media_entity_remote_pad_unique(), that operates on an entity and returns
a remote pad, with a guarantee that only one link is enabled. To ease
its use in drivers, also add an inline wrapper that locates source pads
specifically. A wrapper that locates sink pads can easily be added when
needed.

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, 46 insertions, 0 deletions

diff --git a/include/media/media-entity.h b/include/media/media-entity.h
index 5e272a0a9895..c5618f7c1408 100644
--- a/include/media/media-entity.h
+++ b/include/media/media-entity.h
@@ -860,6 +860,52 @@ 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_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)
+ *
+ * Search for and return a remote pad of @type connected to @entity through an
+ * enabled link. If multiple (or no) remote pads match these criteria, an error
+ * is returned.
+ *
+ * The uniqueness constraint makes this helper function suitable for entities
+ * that support a single active source or sink at a time.
+ *
+ * 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_entity_remote_pad_unique(const struct media_entity *entity,
+			       unsigned int type);
+
+/**
+ * media_entity_remote_source_pad_unique - Find a remote source pad connected to
+ *	an entity
+ * @entity: The entity
+ *
+ * Search for and return a remote source pad connected to @entity through an
+ * enabled link. If multiple (or no) remote pads match these criteria, an error
+ * is returned.
+ *
+ * The uniqueness constraint makes this helper function suitable for entities
+ * that support a single active source at a time.
+ *
+ * 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
+ */
+static inline struct media_pad *
+media_entity_remote_source_pad_unique(const struct media_entity *entity)
+{
+	return media_entity_remote_pad_unique(entity, MEDIA_PAD_FL_SOURCE);
+}
+
+/**
  * media_entity_is_streaming - Test if an entity is part of a streaming pipeline
  * @entity: The entity
  *