media: v4l2-device: Link subdevices to their parent devices if available

Currently v4l2_device_register_subdev_nodes() does not initialize the
dev_parent field of the video_device structs it creates for subdevices
being registered. This leads to __video_register_device() falling back
to the parent device of associated v4l2_device struct, which often does
not match the physical device the subdevice is registered for.

Due to the problem above, the links between real devices and v4l-subdev
nodes cannot be obtained from sysfs, which might be confusing for the
userspace trying to identify the hardware.

Fix this by initializing the dev_parent field of the video_device struct
with the value of dev field of the v4l2_subdev struct. In case of
subdevices without a parent struct device, the field will be NULL and the
old behavior will be preserved by the semantics of
__video_register_device().

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/v4l2-core/v4l2-device.c

@@ -247,6 +247,7 @@ int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
 
 		video_set_drvdata(vdev, sd);
 		strscpy(vdev->name, sd->name, sizeof(vdev->name));
+		vdev->dev_parent = sd->dev;
 		vdev->v4l2_dev = v4l2_dev;
 		vdev->fops = &v4l2_subdev_fops;
 		vdev->release = v4l2_device_release_subdev_node;