Re: [PATCH v9 4/4] sound/usb: Use Media Controller API to share media resources

[shuah]

On 1/18/19 1:36 AM, Hans Verkuil wrote:
> On 12/18/18 6:59 PM, shuah@xxxxxxxxxx wrote:
> > From: Shuah Khan <shuah@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > ---
> >   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.

Thanks,
-- Shuah