Re: [PATCH 0/3] ASoC: SOF: pcm/Intel: Handle IPC dependent sequencing correctly

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 6/30/23 08:33, Sam Edwards wrote:
> Hi folks,
> 
> When I upgraded my system to 6.4.0, I encountered a regression in audio
> output. In regression testing, I found that patch 1/3 here was the
> culprit, and the regression goes away entirely (on 6.4.0 final) when
> applying a patch that reverts this whole patchset. The problem is
> currently still unresolved even in broonie/sound.git.
> 
> The regression is an intermittent (few minutes on, few minutes off)
> distortion in audio output on my Tigerlake->ALC298 path. When playing a
> 440 Hz test tone, the output spectrum is distorted into 440 Hz, 560 Hz,
> 1440 Hz, 1560 Hz, 2440 Hz, 2560 Hz, and so on. Since this is the exact
> spectrum one would get if the output were modulated with a 1000 Hz Dirac
> comb, I interpret this to mean that the audio subsystem is dropping
> (zeroing) 1 sample every 1ms.
> 
> There seem to be conditions for this problem to come and go
> spontaneously -- in particular, it won't happen if my nvidia driver is
> unloaded. However, I can make it occur (even with no out-of-tree modules
> loaded) by sending several SIGSTOP->10ms->SIGCONT sequences to my
> pipewire daemon while it's playing audio. The distortion then continues
> until I send several more signals of that same sequence.
> 
> Now, aside from having some DSP background, I'm a total outsider to the
> ALSA and SOF world, so what follows is mere speculation on my part: I
> believe the problem has some probability of being "toggled" by a buffer
> underrun, which happens either deliberately by briefly interrupting
> pipewire, or accidentally due to bus contention from having my GPU
> active. Something (userspace? ALSA?) tries to restart the stream in
> response to that underrun, but this patchset makes stream stop+start
> more of a "warm reset," in that it doesn't clean up DMA. As a result, an
> off-by-one error somehow creeps into the DMA size, thus omitting the
> final sample of every 1ms transfer.
> 
> I am not sure if this is a regression introduced with this patchset, or
> merely a different bug that became apparent now that DMA isn't being
> reset when underruns happen. If it's the latter case, I'm happy to open
> an issue on Bugzilla instead. In either case, let me know if I can
> provide any additional troubleshooting information.

please file an issue here: https://github.com/thesofproject/linux/issues

It would help if you clarified a bit more what the issue is, it's not
clear to me if the problem happens during a long continuous playback or
when starting/stopping the stream.

Also try to disable SOF with the instructions in
https://thesofproject.github.io/latest/getting_started/intel_debug/suggestions.html
to make sure it's not an HDaudio codec issue.

Thanks!