[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, 47 insertions, 0 deletions

diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
index a36509a1df09..d2bc809d7a2a 100644
--- a/drivers/media/media-device.c
+++ b/drivers/media/media-device.c
@@ -73,6 +73,7 @@ int __must_check media_device_register(struct media_device *mdev)
         mdev->entity_id = 1;
         INIT_LIST_HEAD(&mdev->entities);
         spin_lock_init(&mdev->lock);
+        mutex_init(&mdev->graph_mutex);
 
         /* Register the device node. */
         mdev->devnode.fops = &media_device_fops;
diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
index 166f2b5505ce..3e7e2d569cec 100644
--- a/drivers/media/media-entity.c
+++ b/drivers/media/media-entity.c
@@ -23,6 +23,7 @@
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <media/media-entity.h>
+#include <media/media-device.h>
 
 /**
  * media_entity_init - Initialize a media entity
@@ -196,6 +197,51 @@ media_entity_graph_walk_next(struct media_entity_graph *graph)
 EXPORT_SYMBOL_GPL(media_entity_graph_walk_next);
 
 /* -----------------------------------------------------------------------------
+ * Module use count
+ */
+
+/*
+ * media_entity_get - Get a reference to the parent module
+ * @entity: The entity
+ *
+ * Get a reference to the parent media device module.
+ *
+ * The function will return immediately if @entity is NULL.
+ *
+ * Return a pointer to the entity on success or NULL on failure.
+ */
+struct media_entity *media_entity_get(struct media_entity *entity)
+{
+        if (entity == NULL)
+                return NULL;
+
+        if (entity->parent->dev &&
+            !try_module_get(entity->parent->dev->driver->owner))
+                return NULL;
+
+        return entity;
+}
+EXPORT_SYMBOL_GPL(media_entity_get);
+
+/*
+ * media_entity_put - Release the reference to the parent module
+ * @entity: The entity
+ *
+ * Release the reference count acquired by media_entity_get().
+ *
+ * The function will return immediately if @entity is NULL.
+ */
+void media_entity_put(struct media_entity *entity)
+{
+        if (entity == NULL)
+                return;
+
+        if (entity->parent->dev)
+                module_put(entity->parent->dev->driver->owner);
+}
+EXPORT_SYMBOL_GPL(media_entity_put);
+
+/* -----------------------------------------------------------------------------
  * Links management
  */