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media: Media Device Allocator API

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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 <[email protected]>
Signed-off-by: Hans Verkuil <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>
This commit is contained in:
Shuah Khan 2019-04-01 20:40:19 -04:00 • committed by Mauro Carvalho Chehab
commit 6e1d824e7a
4 changed files with 245 additions and 0 deletions
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63
include/media/media-dev-allocator.h Normal file
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/* SPDX-License-Identifier: GPL-2.0+ */
/*
* media-dev-allocator.h - Media Controller Device Allocator API
*
* Copyright (c) 2019 Shuah Khan <shuah@kernel.org>
*
* Credits: Suggested by Laurent Pinchart <laurent.pinchart@ideasonboard.com>
*/
/*
* This file adds a global ref-counted Media Controller Device Instance API.
* A system wide global media device list is managed and each media device
* includes a kref count. The last put on the media device releases the media
* device instance.
*/
#ifndef _MEDIA_DEV_ALLOCATOR_H
#define _MEDIA_DEV_ALLOCATOR_H
struct usb_device;
#if defined(CONFIG_MEDIA_CONTROLLER) && defined(CONFIG_USB)
/**
* media_device_usb_allocate() - Allocate and return struct &media device
*
* @udev: struct &usb_device pointer
* @module_name: should be filled with %KBUILD_MODNAME
* @owner: struct module pointer %THIS_MODULE for the driver.
* %THIS_MODULE is null for a built-in driver.
* It is safe even when %THIS_MODULE is null.
*
* This interface should be called to allocate a Media Device when multiple
* drivers share usb_device and the media device. This interface allocates
* &media_device structure and calls media_device_usb_init() to initialize
* it.
*
*/
struct media_device *media_device_usb_allocate(struct usb_device *udev,
const char *module_name,
struct module *owner);
/**
* media_device_delete() - Release media device. Calls kref_put().
*
* @mdev: struct &media_device pointer
* @module_name: should be filled with %KBUILD_MODNAME
* @owner: struct module pointer %THIS_MODULE for the driver.
* %THIS_MODULE is null for a built-in driver.
* It is safe even when %THIS_MODULE is null.
*
* This interface should be called to put Media Device Instance kref.
*/
void media_device_delete(struct media_device *mdev, const char *module_name,
struct module *owner);
#else
static inline struct media_device *media_device_usb_allocate(
struct usb_device *udev, const char *module_name,
struct module *owner)
{ return NULL; }
static inline void media_device_delete(
struct media_device *mdev, const char *module_name,
struct module *owner) { }
#endif /* CONFIG_MEDIA_CONTROLLER && CONFIG_USB */
#endif /* _MEDIA_DEV_ALLOCATOR_H */