media: Fix Media Controller API config checks

2021-06-24T12:26:00+00:00

Smatch static checker warns that "mdev" can be null: sound/usb/media.c:287 snd_media_device_create() warn: 'mdev' can also be NULL If CONFIG_MEDIA_CONTROLLER is disabled, this file should not be included in the build. The below conditions in the sound/usb/Makefile are in place to ensure that media.c isn't included in the build. sound/usb/Makefile: snd-usb-audio-$(CONFIG_SND_USB_AUDIO_USE_MEDIA_CONTROLLER) += media.o select SND_USB_AUDIO_USE_MEDIA_CONTROLLER if MEDIA_CONTROLLER && (MEDIA_SUPPORT=y || MEDIA_SUPPORT=SND_USB_AUDIO) The following config check in include/media/media-dev-allocator.h is in place to enable the API only when CONFIG_MEDIA_CONTROLLER and CONFIG_USB are enabled. #if defined(CONFIG_MEDIA_CONTROLLER) && defined(CONFIG_USB) This check doesn't work as intended when CONFIG_USB=m. When CONFIG_USB=m, CONFIG_USB_MODULE is defined and CONFIG_USB is not. The above config check doesn't catch that CONFIG_USB is defined as a module and disables the API. This results in sound/usb enabling Media Controller specific ALSA driver code, while Media disables the Media Controller API. Fix the problem requires two changes: 1. Change the check to use IS_ENABLED to detect when CONFIG_USB is enabled as a module or static. Since CONFIG_MEDIA_CONTROLLER is a bool, leave the check unchanged to be consistent with drivers/media/Makefile. 2. Change the drivers/media/mc/Makefile to include mc-dev-allocator.o in mc-objs when CONFIG_USB is enabled. Link: https://lore.kernel.org/alsa-devel/YLeAvT+R22FQ%2FEyw@mwanda/ Reported-by: Dan Carpenter Signed-off-by: Shuah Khan Signed-off-by: Hans Verkuil Signed-off-by: Mauro Carvalho Chehab

media: Media Device Allocator API

2019-04-22T15:18:26+00:00

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 Signed-off-by: Hans Verkuil Signed-off-by: Mauro Carvalho Chehab

kernel/linux.git/include/media/media-dev-allocator.h, branch v6.6.132

media: Fix Media Controller API config checks

media: Media Device Allocator API