[media] media: Entity use count

Due to the wide differences between drivers regarding power management
needs, the media controller does not implement power management.
However, the media_entity structure includes a use_count field that
media drivers can use to track the number of users of every entity for
power management needs.

The use_count field is owned by media drivers and must not be touched by
entity drivers. Access to the field must be protected by the media
device graph_mutex lock.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/media/media-entity.h b/include/media/media-entity.h
index 28f61f6ee549..a9b31d98e3c6 100644
--- a/include/media/media-entity.h
+++ b/include/media/media-entity.h
@@ -81,6 +81,12 @@ struct media_entity {
         struct media_pad *pads;         /* Pads array (num_pads elements) */
         struct media_link *links;       /* Links array (max_links elements)*/
 
+        /* Reference counts must never be negative, but are signed integers on
+         * purpose: a simple WARN_ON(<0) check can be used to detect reference
+         * count bugs that would make them negative.
+         */
+        int use_count;                  /* Use count for the entity. */
+
         union {
                 /* Node specifications */
                 struct {
@@ -129,6 +135,9 @@ void media_entity_cleanup(struct media_entity *entity);
 int media_entity_create_link(struct media_entity *source, u16 source_pad,
                 struct media_entity *sink, u16 sink_pad, u32 flags);
 
+struct media_entity *media_entity_get(struct media_entity *entity);
+void media_entity_put(struct media_entity *entity);
+
 void media_entity_graph_walk_start(struct media_entity_graph *graph,
                 struct media_entity *entity);
 struct media_entity *