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

From: Takashi Iwai <tiwai@suse.de>
To: Shuah Khan <shuahkh@osg.samsung.com>
Cc: hans.verkuil@cisco.com, laurent.pinchart@ideasonboard.com,
	clemens@ladisch.de, sakari.ailus@linux.intel.com,
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	sw0312.kim@samsung.com, elfring@users.sourceforge.net,
	linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
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Subject: Re: [PATCH v3 22/22] sound/usb: Use Media Controller API to share media resources
Date: Fri, 26 Feb 2016 21:50:11 +0100	[thread overview]
Message-ID: <s5hio1bjiws.wl-tiwai@suse.de> (raw)
In-Reply-To: <56D0B0CB.8060709@osg.samsung.com>

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