[PATCH v4 20/26] media: Documentation: Document how Media device resources are released

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Document that after unregistering, Media device memory resources are
released by the release() callback rather than by calling
media_device_cleanup().

Also add that driver memory resources should be bound to the Media device,
not V4L2 device.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
---
 Documentation/driver-api/media/mc-core.rst | 18 ++++++++++++++++--
 include/media/media-device.h               |  6 ++++--
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/Documentation/driver-api/media/mc-core.rst b/Documentation/driver-api/media/mc-core.rst
index 2456950ce8ff..f9108f14d1ed 100644
--- a/Documentation/driver-api/media/mc-core.rst
+++ b/Documentation/driver-api/media/mc-core.rst
@@ -46,13 +46,27 @@ 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()`.
+:c:func:`media_device_unregister()`. The resources of a newly unregistered media
+device will be released by the ``release()`` callback of :c:type:`media_device`
+ops, which will be called when the last user of the media device has released it
+calling :c:func:`media_device_put()`.
+
+The ``release()`` callback is the way all the resources of the media device are
+released once :c:func:`media_device_init()` has been called. This is also
+relevant during device driver's probe function as the ``release()`` callback
+will also have to be able to safely release the resources related to a partially
+initialised media device.
 
 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.
 
+Media device and driver's per-device context
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Drivers should use the struct media_device_ops ``release()`` callback to release
+their own resources and not e.g. that of the struct v4l2_device.
+
 Entities
 ^^^^^^^^
 
diff --git a/include/media/media-device.h b/include/media/media-device.h
index f1afbfc4dca2..fe4625f3f62b 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h
@@ -252,8 +252,10 @@ static inline void media_device_put(struct media_device *mdev)
  *
  * @mdev:	pointer to struct &media_device
  *
- * This function that will destroy the graph_mutex that is
- * initialized in media_device_init().
+ * This function that will destroy the graph_mutex that is initialized in
+ * media_device_init(). Note that *only* drivers that do not manage releasing
+ * the memory of th media device itself call this function. This function is
+ * thus effectively DEPRECATED.
  */
 void media_device_cleanup(struct media_device *mdev);
 
-- 
2.39.2