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

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Message-ID: <s5hy4sgumjo.wl-tiwai@suse.de>
Date:	Thu, 16 Oct 2014 16:16:59 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Shuah Khan <shuahkh@....samsung.com>
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

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...?


Takashi
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