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, 39 insertions, 0 deletions

diff --git a/drivers/media/mc/mc-entity.c b/drivers/media/mc/mc-entity.c
index 66ba0629c4ce..767846b216c5 100644
--- a/drivers/media/mc/mc-entity.c
+++ b/drivers/media/mc/mc-entity.c
@@ -921,6 +921,45 @@ struct media_pad *media_pad_remote_pad_first(const struct media_pad *pad)
 }
 EXPORT_SYMBOL_GPL(media_pad_remote_pad_first);
 
+struct media_pad *
+media_entity_remote_pad_unique(const struct media_entity *entity,
+			       unsigned int type)
+{
+	struct media_pad *pad = NULL;
+	struct media_link *link;
+
+	list_for_each_entry(link, &entity->links, list) {
+		struct media_pad *local_pad;
+		struct media_pad *remote_pad;
+
+		if (((link->flags & MEDIA_LNK_FL_LINK_TYPE) !=
+		     MEDIA_LNK_FL_DATA_LINK) ||
+		    !(link->flags & MEDIA_LNK_FL_ENABLED))
+			continue;
+
+		if (type == MEDIA_PAD_FL_SOURCE) {
+			local_pad = link->sink;
+			remote_pad = link->source;
+		} else {
+			local_pad = link->source;
+			remote_pad = link->sink;
+		}
+
+		if (local_pad->entity == entity) {
+			if (pad)
+				return ERR_PTR(-ENOTUNIQ);
+
+			pad = remote_pad;
+		}
+	}
+
+	if (!pad)
+		return ERR_PTR(-ENOLINK);
+
+	return pad;
+}
+EXPORT_SYMBOL_GPL(media_entity_remote_pad_unique);
+
 static void media_interface_init(struct media_device *mdev,
 				 struct media_interface *intf,
 				 u32 gobj_type,