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

[Daniel Mack]

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.

> 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?

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?


Thanks,
Daniel