[alsa-devel] Asynchronous audio USB chips: choppy playback since 3.8-rc7
zonque at gmail.com
Fri Apr 19 20:54:25 CEST 2013
On 03.04.2013 12:25, Takashi Iwai wrote:
> At Wed, 03 Apr 2013 12:15:25 +0200,
> David Henningsson wrote:
>> Hi ALSA developers,
>> Just to get your attention here on what seems to be an USB audio
>> The bug is described in detail here:
>> 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.
> Yes, there is no commits regarding usb-audio itself between 3.8-rc6
> and rc7, so the likely culprit is in drivers/usb (usually either
> drivers/usb/host or drivers/usb/core). There are a bunch of changes
> there, so further bisection would be appreciated.
Ok, Joseph Salisbury has build some bisection kernels, and Tyson Tan
relentlessly tested all of them, and it turns out that
3e619d0415 ("USB: EHCI: fix bug in scheduling periodic split transfers")
Is the first bad commit. Also, reverting this commit from the current
mainline head makes the problem disappear.
Alan, any idea?
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