linux-kernel - Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api

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Message-ID: <543FD892.6010209@osg.samsung.com>
Date:	Thu, 16 Oct 2014 08:39:14 -0600
From:	Shuah Khan <shuahkh@....samsung.com>
To:	Takashi Iwai <tiwai@...e.de>
CC:	Lars-Peter Clausen <lars@...afoo.de>, m.chehab@...sung.com,
	akpm@...ux-foundation.org, gregkh@...uxfoundation.org,
	crope@....fi, olebowle@....com, dheitmueller@...nellabs.com,
	hverkuil@...all.nl, ramakrmu@...co.com,
	sakari.ailus@...ux.intel.com, laurent.pinchart@...asonboard.com,
	perex@...ex.cz, prabhakar.csengg@...il.com,
	tim.gardner@...onical.com, linux@...elenboom.it,
	linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
	linux-media@...r.kernel.org
Subject: Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media
 token api

On 10/16/2014 08:16 AM, Takashi Iwai wrote:
> At Thu, 16 Oct 2014 08:10:52 -0600,
> Shuah Khan wrote:
>>
>> On 10/16/2014 08:01 AM, Takashi Iwai wrote:
>>> At Thu, 16 Oct 2014 07:10:37 -0600,
>>> Shuah Khan wrote:
>>>>
>>>> On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
>>>>> On 10/14/2014 04:58 PM, Shuah Khan wrote:
>>>>> [...]
>>>>>>       switch (cmd) {
>>>>>>       case SNDRV_PCM_TRIGGER_START:
>>>>>> +        err = media_get_audio_tkn(&subs->dev->dev);
>>>>>> +        if (err == -EBUSY) {
>>>>>> +            dev_info(&subs->dev->dev, "%s device is busy\n",
>>>>>> +                    __func__);
>>>>>
>>>>> In my opinion this should not dev_info() as this is out of band error
>>>>> signaling and also as the potential to spam the log. The userspace
>>>>> application is already properly notified by the return code.
>>>>>
>>>>
>>>> Yes it has the potential to flood the dmesg especially with alsa,
>>>> I will remove the dev_info().
>>>
>>> Yes.  And, I think doing this in the trigger isn't the best.
>>> Why not in open & close?
>>
>> My first cut of this change was in open and close. I saw pulseaudio
>> application go into this loop trying to open the device. To avoid
>> such problems, I went with trigger stat and stop. That made all the
>> pulseaudio continues attempts to open problems go away.
> 
> But now starting the stream gives the error, and PA would loop it
> again, no?
> 
> 
>>> Also, is this token restriction needed only for PCM?  No mixer or
>>> other controls?
>>
>> snd_pcm_ops are the only ones media drivers implement and use. So
>> I don't think mixer is needed. If it is needed, it is not to hard
>> to add for that case.
> 
> Well, then I wonder what resource does actually conflict with
> usb-audio and media drivers at all...?
> 

audio for dvb/v4l apps gets disrupted when audio app starts. For
example, dvb or v4l app tuned to a channel, and when an audio app
starts. audio path needs protected to avoid conflicts between
digital and analog applications as well.

-- Shuah


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