[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, 8 insertions, 3 deletions

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 39abbafad796..4e7148815a78 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -1656,6 +1656,7 @@ static void uvc_delete(struct uvc_device *dev)
 #ifdef CONFIG_MEDIA_CONTROLLER
 	if (media_devnode_is_registered(&dev->mdev.devnode))
 		media_device_unregister(&dev->mdev);
+	media_device_cleanup(&dev->mdev);
 #endif
 
 	list_for_each_safe(p, n, &dev->chains) {
@@ -1906,7 +1907,7 @@ static int uvc_probe(struct usb_interface *intf,
 			"linux-uvc-devel mailing list.\n");
 	}
 
-	/* Register the media and V4L2 devices. */
+	/* Initialize the media device and register the V4L2 device. */
 #ifdef CONFIG_MEDIA_CONTROLLER
 	dev->mdev.dev = &intf->dev;
 	strlcpy(dev->mdev.model, dev->name, sizeof(dev->mdev.model));
@@ -1916,8 +1917,7 @@ static int uvc_probe(struct usb_interface *intf,
 	strcpy(dev->mdev.bus_info, udev->devpath);
 	dev->mdev.hw_revision = le16_to_cpu(udev->descriptor.bcdDevice);
 	dev->mdev.driver_version = LINUX_VERSION_CODE;
-	if (media_device_register(&dev->mdev) < 0)
-		goto error;
+	media_device_init(&dev->mdev);
 
 	dev->vdev.mdev = &dev->mdev;
 #endif
@@ -1936,6 +1936,11 @@ static int uvc_probe(struct usb_interface *intf,
 	if (uvc_register_chains(dev) < 0)
 		goto error;
 
+#ifdef CONFIG_MEDIA_CONTROLLER
+	/* Register the media device node */
+	if (media_device_register(&dev->mdev) < 0)
+		goto error;
+#endif
 	/* Save our data pointer in the interface data. */
 	usb_set_intfdata(intf, dev);