Messages in this thread | | | Subject | Re: [PATCH v9 4/4] sound/usb: Use Media Controller API to share media resources | From | shuah <> | Date | Sun, 20 Jan 2019 12:32:44 -0700 |
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On 1/19/19 3:30 AM, Hans Verkuil wrote: > On 01/19/2019 02:03 AM, shuah wrote: >> On 1/18/19 2:54 PM, shuah wrote: >>> On 1/18/19 1:36 AM, Hans Verkuil wrote: >>>> On 12/18/18 6:59 PM, shuah@kernel.org wrote: >>>>> From: Shuah Khan <shuah@kernel.org> >>>>> >>>>> 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. >>>>> >>>>> Change the ALSA driver to use the Media Controller API to share media >>>>> resources with DVB, and V4L2 drivers on a AU0828 media device. >>>>> >>>>> The Media Controller specific initialization is done after sound card is >>>>> registered. ALSA creates Media interface and entity function graph nodes >>>>> for Control, Mixer, PCM Playback, and PCM Capture devices. >>>>> >>>>> snd_usb_hw_params() will call Media Controller enable source handler >>>>> interface to request the media resource. If resource request is granted, >>>>> it will release it from snd_usb_hw_free(). If resource is busy, >>>>> -EBUSY is >>>>> returned. >>>>> >>>>> Media specific cleanup is done in usb_audio_disconnect(). >>>>> >>>>> Signed-off-by: Shuah Khan <shuah@kernel.org> >>>>> --- >>>>> sound/usb/Kconfig | 4 + >>>>> sound/usb/Makefile | 2 + >>>>> sound/usb/card.c | 14 ++ >>>>> sound/usb/card.h | 3 + >>>>> sound/usb/media.c | 321 +++++++++++++++++++++++++++++++++++++++ >>>>> sound/usb/media.h | 74 +++++++++ >>>>> sound/usb/mixer.h | 3 + >>>>> sound/usb/pcm.c | 29 +++- >>>>> sound/usb/quirks-table.h | 1 + >>>>> sound/usb/stream.c | 2 + >>>>> sound/usb/usbaudio.h | 6 + >>>>> 11 files changed, 455 insertions(+), 4 deletions(-) >>>>> create mode 100644 sound/usb/media.c >>>>> create mode 100644 sound/usb/media.h >>>>> >>>> >>>> <snip> >>>> >>>>> +int snd_media_device_create(struct snd_usb_audio *chip, >>>>> + struct usb_interface *iface) >>>>> +{ >>>>> + struct media_device *mdev; >>>>> + struct usb_device *usbdev = interface_to_usbdev(iface); >>>>> + int ret; >>>>> + >>>>> + /* usb-audio driver is probed for each usb interface, and >>>>> + * there are multiple interfaces per device. Avoid calling >>>>> + * media_device_usb_allocate() each time usb_audio_probe() >>>>> + * is called. Do it only once. >>>>> + */ >>>>> + if (chip->media_dev) >>>>> + goto snd_mixer_init; >>>>> + >>>>> + mdev = media_device_usb_allocate(usbdev, KBUILD_MODNAME); >>>>> + if (!mdev) >>>>> + return -ENOMEM; >>>>> + >>>>> + if (!media_devnode_is_registered(mdev->devnode)) { >>>> >>>> It looks like you missed my comment for v8: >>>> >>>> "You should first configure the media device before registering it." >>>> >>>> In other words, first create the media entities, and only then do you >>>> register the media device. Otherwise it will come up without any alsa >>>> entities, which are then added. So an application that immediately >>>> opens the media device upon creation will see a topology that is still >>>> in flux. >>> >>> Yes. You are right. I saw your comment and thought I got it addressed. >>> I will fix it. I have the logic correct in au0828, but not here. >>> >> >> One thing to mention here is some ALSA entities get created dynamically >> during PCM open when stream is initialized. This happens after media >> device is registered. These get deleted when pcm close happens. There is >> no way to avoid creating entities after media device register. > > That's OK. We're missing some infrastructure (media events) to inform the > application about topology changes. > > But when registering the media device for the first time it is good practice > to do that after creating all the entities that you can. >
Great. We have the same understanding. I think at least one mixer controller entries can be created prior to registering the media device. I am working on v10 to do that. Sorry I misread init sequence in this patch the flow the first time around for v9.
thanks, -- Shuah
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