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!
