summaryrefslogtreecommitdiffstats
path: root/Documentation/media
diff options
context:
space:
mode:
authorShuah Khan <shuah@kernel.org>2019-04-01 20:40:19 -0400
committerMauro Carvalho Chehab <mchehab+samsung@kernel.org>2019-04-22 11:18:26 -0400
commit6e1d824e7a1d324f7fdd276fb7133013109d3764 (patch)
treedd135d8fd4f43d2375e1716eb0b6cb0dfc055ee7 /Documentation/media
parent33dfeb62e23c31619d2197850f7e8b50e8cc5466 (diff)
downloadlinux-6e1d824e7a1d324f7fdd276fb7133013109d3764.tar.bz2
media: Media Device Allocator API
Media Device Allocator API to allows multiple drivers share a media device. This API solves a very common use-case for media devices where one physical device (an USB stick) provides both audio and video. When such media device exposes a standard USB Audio class, a proprietary Video class, two or more independent drivers will share a single physical USB bridge. In such cases, it is necessary to coordinate access to the shared resource. Using this API, drivers can allocate a media device with the shared struct device as the key. Once the media device is allocated by a driver, other drivers can get a reference to it. The media device is released when all the references are released. Signed-off-by: Shuah Khan <shuah@kernel.org> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Diffstat (limited to 'Documentation/media')
-rw-r--r--Documentation/media/kapi/mc-core.rst41
1 files changed, 41 insertions, 0 deletions
diff --git a/Documentation/media/kapi/mc-core.rst b/Documentation/media/kapi/mc-core.rst
index f930725e0d6b..05bba0b61748 100644
--- a/Documentation/media/kapi/mc-core.rst
+++ b/Documentation/media/kapi/mc-core.rst
@@ -259,6 +259,45 @@ Subsystems should facilitate link validation by providing subsystem specific
helper functions to provide easy access for commonly needed information, and
in the end provide a way to use driver-specific callbacks.
+Media Controller Device Allocator API
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When the media device belongs to more than one driver, the shared media
+device is allocated with the shared struct device as the key for look ups.
+
+The shared media device should stay in registered state until the last
+driver unregisters it. In addition, the media device should be released when
+all the references are released. Each driver gets a reference to the media
+device during probe, when it allocates the media device. If media device is
+already allocated, the allocate API bumps up the refcount and returns the
+existing media device. The driver puts the reference back in its disconnect
+routine when it calls :c:func:`media_device_delete()`.
+
+The media device is unregistered and cleaned up from the kref put handler to
+ensure that the media device stays in registered state until the last driver
+unregisters the media device.
+
+**Driver Usage**
+
+Drivers should use the appropriate media-core routines to manage the shared
+media device life-time handling the two states:
+1. allocate -> register -> delete
+2. get reference to already registered device -> delete
+
+call :c:func:`media_device_delete()` routine to make sure the shared media
+device delete is handled correctly.
+
+**driver probe:**
+Call :c:func:`media_device_usb_allocate()` to allocate or get a reference
+Call :c:func:`media_device_register()`, if media devnode isn't registered
+
+**driver disconnect:**
+Call :c:func:`media_device_delete()` to free the media_device. Freeing is
+handled by the kref put handler.
+
+API Definitions
+^^^^^^^^^^^^^^^
+
.. kernel-doc:: include/media/media-device.h
.. kernel-doc:: include/media/media-devnode.h
@@ -266,3 +305,5 @@ in the end provide a way to use driver-specific callbacks.
.. kernel-doc:: include/media/media-entity.h
.. kernel-doc:: include/media/media-request.h
+
+.. kernel-doc:: include/media/media-dev-allocator.h