.complete() callback is called. When a subdevice is removed from the
system the .unbind() method is called. All three callbacks are optional.
+Drivers can store any type of custom data in their driver-specific
+:c:type:`v4l2_async_subdev` wrapper. If any of that data requires special
+handling when the structure is freed, drivers must implement the ``.destroy()``
+notifier callback. The framework will call it right before freeing the
+:c:type:`v4l2_async_subdev`.
+
Calling subdev operations
~~~~~~~~~~~~~~~~~~~~~~~~~