Re: [PATCH v3 22/22] sound/usb: Use Media Controller API to share media resources

Takashi Iwai
2016-02-26T20:50:22Z

On Fri, 26 Feb 2016 21:08:43 +0100,
Shuah Khan wrote:
>
> On 02/26/2016 12:55 PM, Takashi Iwai wrote:
> > On Fri, 12 Feb 2016 00:41:38 +0100,
> > Shuah Khan wrote:
> >>
> >> Change ALSA driver to use Media Controller API to
> >> share media resources with DVB and V4L2 drivers
> >> on a AU0828 media device. 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 <shuahkh@osg.samsung.com>
> >> ---
> >> sound/usb/Kconfig | 4 +
> >> sound/usb/Makefile | 2 +
> >> sound/usb/card.c | 14 +++
> >> sound/usb/card.h | 3 +
> >> sound/usb/media.c | 318 +++++++++++++++++++++++++++++++++++++++++++++++
> >> sound/usb/media.h | 72 +++++++++++
> >> sound/usb/mixer.h | 3 +
> >> sound/usb/pcm.c | 28 ++++-
> >> sound/usb/quirks-table.h | 1 +
> >> sound/usb/stream.c | 2 +
> >> sound/usb/usbaudio.h | 6 +
> >> 11 files changed, 448 insertions(+), 5 deletions(-)
> >> create mode 100644 sound/usb/media.c
> >> create mode 100644 sound/usb/media.h
> >>
> >> diff --git a/sound/usb/Kconfig b/sound/usb/Kconfig
> >> index a452ad7..ba117f5 100644
> >> --- a/sound/usb/Kconfig
> >> +++ b/sound/usb/Kconfig
> >> @@ -15,6 +15,7 @@ config SND_USB_AUDIO
> >> select SND_RAWMIDI
> >> select SND_PCM
> >> select BITREVERSE
> >> + select SND_USB_AUDIO_USE_MEDIA_CONTROLLER if MEDIA_CONTROLLER && MEDIA_SUPPORT
> >
> > Looking at the media Kconfig again, this would be broken if
> > MEDIA_SUPPORT=m and SND_USB_AUDIO=y. The ugly workaround is something
> > like:
> > select SND_USB_AUDIO_USE_MEDIA_CONTROLLER \
> > if MEDIA_CONTROLLER && (MEDIA_SUPPORT=y || MEDIA_SUPPORT=SND)
>
> My current config is MEDIA_SUPPORT=m and SND_USB_AUDIO=y
> It is working and I didn't see any issues so far.

Hmm, how does it be? In drivers/media/Makefile:

ifeq ($(CONFIG_MEDIA_CONTROLLER),y)
obj-$(CONFIG_MEDIA_SUPPORT) += media.o
endif

So it's a module. Meanwhile you have reference from usb-audio driver
that is built-in kernel. How is the symbol resolved?

> Maybe
> the current change is good. I am hoping kbuild-bot can
> find issues (if any) once it gets merged.
>
> >
> > Other than that, it looks more or less OK to me.
> > The way how media_stream_init() gets called is a bit worrisome, but it
> > should work practically. Another concern is about the disconnection.
> > Can all function calls in media_device_delete() be safe even if it's
> > called while the application still opens the MC device?
>
> Right. I have been looking into device removal path when
> ioctls are active and I can resolve any issues that might
> surface while an audio app is active when device is removed.

So, it's 100% safe to call all these media_*() functions while the
device is being accessed before closing?

Takashi