@@ -275,8 +275,13 @@ system the .unbind() method is called. All three callbacks are optional.
V4L2 sub-device userspace API
-----------------------------
-Beside exposing a kernel API through the :c:type:`v4l2_subdev_ops` structure,
-V4L2 sub-devices can also be controlled directly by userspace applications.
+Bridge drivers traditionally expose one or multiple video nodes to userspace,
+and control subdevices through the :c:type:`v4l2_subdev_ops` operations in
+response to video node operations. This hides the complexity of the underlying
+hardware from applications. For complex devices, finer-grained control of the
+device than what the video nodes offer may be required. In those cases, bridge
+drivers that implement :ref:`the media controller API <media_controller>` may
+opt for making the subdevice operations directly accessible from userpace.
Device nodes named ``v4l-subdev``\ *X* can be created in ``/dev`` to access
sub-devices directly. If a sub-device supports direct userspace configuration