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

[Shuah Khan <shuahkh@osg.samsung.com>]

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@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?

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.

>>>
>>> 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.

thanks,
-- Shuah


-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@osg.samsung.com | (970) 217-8978