[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>

2 files changed, 13 insertions, 0 deletions

diff --git a/include/media/media-device.h b/include/media/media-device.h
index a8390fe87e83..5d2bff4fc9e0 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h
@@ -25,6 +25,7 @@
 
 #include <linux/device.h>
 #include <linux/list.h>
+#include <linux/mutex.h>
 #include <linux/spinlock.h>
 
 #include <media/media-devnode.h>
@@ -42,6 +43,7 @@
  * @entity_id:  ID of the next entity to be registered
  * @entities:   List of registered entities
  * @lock:       Entities list lock
+ * @graph_mutex: Entities graph operation lock
  *
  * This structure represents an abstract high-level media device. It allows easy
  * access to entities and provides basic media device-level support. The
@@ -69,6 +71,8 @@ struct media_device {
 
         /* Protects the entities list */
         spinlock_t lock;
+        /* Serializes graph operations. */
+        struct mutex graph_mutex;
 };
 
 /* media_devnode to media_device */
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 *