[media] media-device: split media initialization and registration

The media device node is registered and so made visible to user-space
before entities are registered and links created which means that the
media graph obtained by user-space could be only partially enumerated
if that happens too early before all the graph has been created.

To avoid this race condition, split the media init and registration
in separate functions and only register the media device node when
all the pending subdevices have been registered, either explicitly
by the driver or asynchronously using v4l2_async_register_subdev().

The media_device_register() had a check for drivers not filling dev
and model fields but all drivers in mainline set them and not doing
it will be a driver bug so change the function return to void and
add a BUG_ON() for dev being NULL instead.

Also, add a media_device_cleanup() function that will destroy the
graph_mutex that is initialized in media_device_init().

[mchehab@osg.samsung.com: Fix compilation if !CONFIG_MEDIA_CONTROLLER
 and remove two warnings added by this changeset]
Suggested-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/include/media/media-device.h b/include/media/media-device.h
index ebc2f3a239eb..e01bbc427fcd 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h
@@ -338,6 +338,32 @@ struct media_device {
 #define to_media_device(node) container_of(node, struct media_device, devnode)
 
 /**
+ * media_device_init() - Initializes a media device element
+ *
+ * @mdev:	pointer to struct &media_device
+ *
+ * This function initializes the media device prior to its registration.
+ * The media device initialization and registration is split in two functions
+ * to avoid race conditions and make the media device available to user-space
+ * before the media graph has been completed.
+ *
+ * So drivers need to first initialize the media device, register any entity
+ * within the media device, create pad to pad links and then finally register
+ * the media device by calling media_device_register() as a final step.
+ */
+void media_device_init(struct media_device *mdev);
+
+/**
+ * media_device_cleanup() - Cleanups a media device element
+ *
+ * @mdev:	pointer to struct &media_device
+ *
+ * This function that will destroy the graph_mutex that is
+ * initialized in media_device_init().
+ */
+void media_device_cleanup(struct media_device *mdev);
+
+/**
  * __media_device_register() - Registers a media device element
  *
  * @mdev:	pointer to struct &media_device