linux-kernel - Re: snd-usb: "delay: estimated 0, actual 352"

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Message-ID: <s5h627rioxt.wl%tiwai@suse.de>
Date:	Thu, 06 Sep 2012 09:35:26 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>
Cc:	Daniel Mack <zonque@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
	Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Subject: Re: snd-usb: "delay: estimated 0, actual 352"

At Thu, 6 Sep 2012 09:17:57 +0200,
Markus Trippelsdorf wrote:
> 
> On 2012.09.06 at 09:08 +0200, Daniel Mack wrote:
> > On 06.09.2012 08:53, Markus Trippelsdorf wrote:
> > > On 2012.09.06 at 08:48 +0200, Takashi Iwai wrote:
> > >> At Thu, 06 Sep 2012 08:33:30 +0200,
> > >> Daniel Mack wrote:
> > >>>
> > >>> On 06.09.2012 08:02, Markus Trippelsdorf wrote:
> > >>>> On 2012.09.04 at 16:40 +0200, Takashi Iwai wrote:
> > >>>>> ----------------------------------------------------------------
> > >>>>> Sound fixes for 3.6-rc5
> > >>>>>
> > >>>>> There are nothing scaring, contains only small fixes for HD-audio and
> > >>>>> USB-audio:
> > >>>>> - EPSS regression fix and GPIO fix for HD-audio IDT codecs
> > >>>>> - A series of USB-audio regression fixes that are found since 3.5 kernel
> > >>>>>
> > >>>>> ----------------------------------------------------------------
> > >>>>> Daniel Mack (4):
> > >>>>>       ALSA: snd-usb: Fix URB cancellation at stream start
> > >>>>>       ALSA: snd-usb: restore delay information
> > >>>>         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
> > >>>> The commit fbcfbf5f above causes the following lines to be printed
> > >>>> whenever I start a new song:
> > >>>
> > >>> Copied Pierre-Louis Bossart - he wrote the code in 294c4fb8 which this
> > >>> patch (fbcfbf5f) brings back now.
> > >>>
> > >>>> delay: estimated 0, actual 352
> > >>>> delay: estimated 353, actual 705
> > >>>>
> > >>>> (44.1 * 8 = 352.8)
> > >>>>
> > >>>> This happens with an USB-DAC that identifies itself as "C-Media USB
> > >>>> Headphone Set".
> > >>>
> > >>> And you didn't you see these lines with 3.4?
> > >>
> > >> Maybe the difference of start condition?
> > >>
> > >> Markus, does the patch below fix anything?
> > > 
> > > Unfortunately no.
> > > However reverting the following fixes the problem:
> > > 
> > > commit 245baf983cc39524cce39c24d01b276e6e653c9e
> > > Author: Daniel Mack <zonque@...il.com>
> > > Date:   Thu Aug 30 18:52:30 2012 +0200
> > > 
> > >     ALSA: snd-usb: fix calls to next_packet_size
> > > 
> > 
> > No, this one certainly fixes a problem and does the right thing by
> > restoring the original code.
> > 
> > If you wouldn't state that you didn't see the same effect with 3.4(!),
> > before the refactoring done in 3.5, I would believe the device is simply
> > slightly off in its feedback rate and the tighter delay code complains
> > about it while compensating, just as it did before.
> > 
> > Are there any more than these two lines? And is audio working at all? Is
> > it distorted in any way?
> 
> There are only these two lines (printed whenever sound starts). Audio is
> working just fine with no distortions.
> 
> I did see similar lines before when the system load was very high
> (happend during "make check" when building glibc).
> 
> Here is what Pierre-Louis wrote in November 2011:
> 
> Â»This was supposed to be an informational message, I thought it was only
> enabled for debug. Regular users don't really need to know.Â«

I guess the problem is that the new endpoint scheme doesn't count the
last_delay update unless the stream is triggered.  In the old code,
retire_playback_urb is always called even before the trigger(START) is
set.  And, there retire_playback_urb() does nothing but updating the
delay information.

In the new code, retire_playback_urb is set only at
snd_usb_substream_playback_trigger().  Thus at the very first shot,
the delay account got confused.


Takashi
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