Re: Asynchronous audio USB chips: choppy playback since 3.8-rc7

[Daniel Mack <zonque@gmail.com>]

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"

And they have both been back-ported to stable. Copied Alan for reference.

Any chance some of the bug reporters could try and revert exactly those
for testing?


Thanks,
Daniel