[alsa-devel] Asynchronous audio USB chips: choppy playback since 3.8-rc7

Michael Trimarchi michael at amarulasolutions.com
Wed Apr 3 17:19:21 CEST 2013

Hi Daniel

On 03/04/13 17:00, Daniel Mack wrote:
> Hi Michael,
> On 03.04.2013 16:11, Michael Trimarchi wrote:
>> On 03/04/13 15:55, Michael Trimarchi wrote:
>>> On 03/04/13 12:23, Daniel Mack wrote:
>>>> Hi David,
>>>> On 03.04.2013 12:15, David Henningsson wrote:
>>>>> Just to get your attention here on what seems to be an USB audio 
>>>>> regression.
>>>>> The bug is described in detail here:
>>>>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1136110?comments=all
>>>>> Quoting the bug:
>>>>> "
>>>>> This bug seems to affect only a certain kind of hardware, which is 
>>>>> called "Asynchronous USB Digital Audio Codec (DAC)". It's said that such 
>>>>> a DAC hosts the clock itself (USB Device Host). An ordinary DAC, so 
>>>>> called "Synchronous USB DAC", uses the clock hosted by the mother board, 
>>>>> which is not affected by this bug.
>>>>> When this bug affects an asynchronous USB DAC, the audio played by the 
>>>>> DAC is constantly interrupted. The playback itself does not stop, but 
>>>>> the output becomes discontinous, filling with constant crackling noises, 
>>>>> destroying everything the DAC plays.
>>>>> "
>>>>> According to the bug reporter, which seems to have done quite a bit of 
>>>>> research, this started between 3.8-rc6 and 3.8-rc7 as well as stable 
>>>>> kernels and the bug also lists a few commits which could be the cause, 
>>>>> none under sound/usb though.
>>>> There were no relevant changes for snd-usb between the two versions
>>>> mentioned. The only patches that come in mind in this time window are:
>>>>  3e619d041 "USB: EHCI: fix bug in scheduling periodic split transfers"
>>>>  b09a61cc0 "USB: EHCI: fix for leaking isochronous data"
>>> This last one, doesn't give me any problem, just a memory leak and not a choppy
>>> playback (tested on 48Khz, 96Khz, 192Khz 32bit on OMAP3 device) and I don't
>>> think that it can be the reason of the problem.
> Is OMAP3 at all a platform that is affected by the bug? It seems the
> effect is only seen on some special host controller hardware anyway.

Yes, omap3 ehci and m2tech products is not affected and I'm testing a dac with internal clock.

>> Sorry the comment was for a bug that is not included in this list and recently fixed.
>> USB: EHCI: fix bug in iTD/siTD DMA pool allocation
> Sorry, you lost me. So what's the status of this issue now? Does "USB:
> EHCI: fix bug in iTD/siTD DMA pool allocation" fix it?

With or without it, I don't have any choppy audio and this is not a fix
of this bug.

> If not - and assuming you can reproduce the bug - which patches of the
> two I mentioned did you revert, and what was the effect of that? Did you
> try and remove both as well?

In my version I have the other two commits applied. I doubt that these two
commits are the reason of the choppy audio. What I can do, it test it on my
laptop tomorrow and send feedback result


> Thanks,
> Daniel

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