media: Documentation: mc: Add media_device_{init,cleanup}

Document that drivers must first initialise a media device before
registering it, and clean up once the media device is unregistered.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Documentation/driver-api/media/mc-core.rst

@@ -42,9 +42,16 @@ Allocation of the structure is handled by the media device driver, usually by
 embedding the :c:type:`media_device` instance in a larger driver-specific
 structure.
 
-Drivers register media device instances by calling
-:c:func:`__media_device_register()` via the macro ``media_device_register()``
-and unregistered by calling :c:func:`media_device_unregister()`.
+Drivers initialise media device instances by calling
+:c:func:`media_device_init()`. After initialising a media device instance, it is
+registered by calling :c:func:`__media_device_register()` via the macro
+``media_device_register()`` and unregistered by calling
+:c:func:`media_device_unregister()`. An initialised media device must be
+eventually cleaned up by calling :c:func:`media_device_cleanup()`.
+
+Note that it is not allowed to unregister a media device instance that was not
+previously registered, or clean up a media device instance that was not
+previously initialised.
 
 Entities
 ^^^^^^^^