[media] media: Media Controller register/unregister entity_notify API

Add new interfaces to register and unregister entity_notify
hook to media device. These interfaces allow drivers to add
hooks to take appropriate actions when new entities get added
to a shared media device. For example, au0828 bridge driver
registers an entity_notify hook to create links as needed
between media graph nodes.

[mchehab@osg.samsung.com: simple comments should be /* and not /**]

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

include/media/media-device.h

@@ -264,6 +264,22 @@
 struct ida;
 struct device;
 
+/**
+ * struct media_entity_notify - Media Entity Notify
+ *
+ * @list: List head
+ * @notify_data: Input data to invoke the callback
+ * @notify: Callback function pointer
+ *
+ * Drivers may register a callback to take action when
+ * new entities get registered with the media device.
+ */
+struct media_entity_notify {
+	struct list_head list;
+	void *notify_data;
+	void (*notify)(struct media_entity *entity, void *notify_data);
+};
+
 /**
  * struct media_device - Media device
  * @dev:	Parent device
@@ -287,6 +303,7 @@ struct device;
  * @interfaces:	List of registered interfaces
  * @pads:	List of registered pads
  * @links:	List of registered links
+ * @entity_notify: List of registered entity_notify callbacks
  * @lock:	Entities list lock
  * @graph_mutex: Entities graph operation lock
  * @link_notify: Link state change notification callback
@@ -324,6 +341,9 @@ struct media_device {
 	struct list_head pads;
 	struct list_head links;
 
+	/* notify callback list invoked when a new entity is registered */
+	struct list_head entity_notify;
+
 	/* Protects the graph objects creation/removal */
 	spinlock_t lock;
 	/* Serializes graph operations. */
@@ -506,6 +526,31 @@ int __must_check media_device_register_entity(struct media_device *mdev,
  */
 void media_device_unregister_entity(struct media_entity *entity);
 
+/**
+ * media_device_register_entity_notify() - Registers a media entity_notify
+ *					   callback
+ *
+ * @mdev:      The media device
+ * @nptr:      The media_entity_notify
+ *
+ * Note: When a new entity is registered, all the registered
+ * media_entity_notify callbacks are invoked.
+ */
+
+int __must_check media_device_register_entity_notify(struct media_device *mdev,
+					struct media_entity_notify *nptr);
+
+/**
+ * media_device_unregister_entity_notify() - Unregister a media entity notify
+ *					     callback
+ *
+ * @mdev:      The media device
+ * @nptr:      The media_entity_notify
+ *
+ */
+void media_device_unregister_entity_notify(struct media_device *mdev,
+					struct media_entity_notify *nptr);
+
 /**
  * media_device_get_devres() -	get media device as device resource
  *				creates if one doesn't exist
@@ -594,6 +639,17 @@ static inline int media_device_register_entity(struct media_device *mdev,
 static inline void media_device_unregister_entity(struct media_entity *entity)
 {
 }
+static inline int media_device_register_entity_notify(
+					struct media_device *mdev,
+					struct media_entity_notify *nptr)
+{
+	return 0;
+}
+static inline void media_device_unregister_entity_notify(
+					struct media_device *mdev,
+					struct media_entity_notify *nptr)
+{
+}
 static inline struct media_device *media_device_get_devres(struct device *dev)
 {
 	return NULL;