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

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Message-ID: <s5hegbyk30q.wl-tiwai@suse.de>
Date:	Sat, 27 Feb 2016 08:48:05 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Shuah Khan <shuahkh@....samsung.com>
Cc:	hans.verkuil@...co.com, laurent.pinchart@...asonboard.com,
	clemens@...isch.de, sakari.ailus@...ux.intel.com,
	javier@....samsung.com, mchehab@....samsung.com,
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	sw0312.kim@...sung.com, elfring@...rs.sourceforge.net,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
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	daniel@...que.org
Subject: Re: [PATCH v3 22/22] sound/usb: Use Media Controller API to share media resources

On Sat, 27 Feb 2016 03:55:39 +0100,
Shuah Khan wrote:
> 
> On 02/26/2016 01:50 PM, Takashi Iwai wrote:
> > 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@....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?
> 
> Sorry my mistake. I misspoke. My config had:
> CONFIG_MEDIA_SUPPORT=m
> CONFIG_MEDIA_CONTROLLER=y
> CONFIG_SND_USB_AUDIO=m
> 
> The following doesn't work as you pointed out.
> 
> CONFIG_MEDIA_SUPPORT=m
> CONFIG_MEDIA_CONTROLLER=y
> CONFIG_SND_USB_AUDIO=y
> 
> okay here is what will work for all of the possible
> combinations of CONFIG_MEDIA_SUPPORT and CONFIG_SND_USB_AUDIO
> 
> select SND_USB_AUDIO_USE_MEDIA_CONTROLLER \
>        if MEDIA_CONTROLLER && ((MEDIA_SUPPORT=y) || (MEDIA_SUPPORT=m && SND_USB_AUDIO=m))
> 
> The above will cover the cases when
> 
> 1. CONFIG_MEDIA_SUPPORT and CONFIG_SND_USB_AUDIO are
>    both modules
>    CONFIG_SND_USB_AUDIO_USE_MEDIA_CONTROLLER is selected
> 
> 2. CONFIG_MEDIA_SUPPORT=y and CONFIG_SND_USB_AUDIO=m
>    CONFIG_SND_USB_AUDIO_USE_MEDIA_CONTROLLER is selected
> 
> 3. CONFIG_MEDIA_SUPPORT=y and CONFIG_SND_USB_AUDIO=y
>    CONFIG_SND_USB_AUDIO_USE_MEDIA_CONTROLLER is selected
> 
> 4. CONFIG_MEDIA_SUPPORT=m and CONFIG_SND_USB_AUDIO=y
>    This is when we don't want
>    CONFIG_SND_USB_AUDIO_USE_MEDIA_CONTROLLER selected
> 
> I verified all of the above combinations to make sure
> the logic works.
> 
> If you think of a better way to do this please let me
> know. I will go ahead and send patch v4 with the above
> change and you can decide if that is acceptable.

I'm not 100% sure whether CONFIG_SND_USB_AUDIO=m can be put there as
conditional inside CONFIG_SND_USB_AUDIO definition.  Maybe a safer
form would be like:

config SND_USB_AUDIO_USE_MEDIA_CONTROLLER
	bool
	default y
	depends on SND_USB_AUDIO
	depends on MEDIA_CONTROLLER
	depends on (MEDIA_SUPPORT=y || MEDIA_SUPPORT=SND_USB_AUDIO)

and drop select from SND_USB_AUDIO.


> >>> 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?
> > 
> 
> There is a known problem with device removal when
> media device file is open and ioctl is in progress.
> This isn't specific to this patch series, a general
> problem that is related to media device removal in
> general.
> 
> I am working on a fix for this problem. As you said,
> earlier, I can work on fixing issues after the merge.

OK, understood.


Takashi