> > Updating hw_ptr_jiffies at that code path looks correct, but it still leaves the > question why this condition happens. It means that the actual hwptr isn't > changed and yet only jiffies increase significantly; it means that the hardware > can't report proper pointer, and it should have set > SNDRV_PCM_INFO_BATCH flag, then the jiffies check is skipped. > > With which hardware and under which situation did it happen (and the patch > fixed)? > > > thanks, > > Takashi > >From time to time we got questions from google about why sometimes the snd_pcm_avail() returns a value larger than buffer size. Recently we finally found reliable reproduce steps: it's on Intel GLK Chromebook Fleex with SOF firmware. There is a 1/20 chance the audio playback to HDMI fails. >From the FW side we observe a buffer runderrun, the FW is not able to recover it for some reason and stops the pipe. >From the Linux side we see the pos does not increase because the FW stops receiving data but suddenly the hw_prt is increased by buffer_size (16368). It could make snd_pcm_avail() reporting a false underrun to the caller like following log: 2020-05-09T16:08:32.712042+08:00 DEBUG kernel: [ 418.510086] sound pcmC0D5p: pos 96 hw_ptr 96 appl_ptr 4096 avail 12368 2020-05-09T16:08:32.712043+08:00 DEBUG kernel: [ 418.510149] sound pcmC0D5p: pos 96 hw_ptr 96 appl_ptr 6910 avail 9554 ... 2020-05-09T16:08:32.883095+08:00 DEBUG kernel: [ 418.680868] sound pcmC0D5p: pos 96 hw_ptr 96 appl_ptr 15102 avail 1362 2020-05-09T16:08:32.883104+08:00 DEBUG kernel: [ 418.681052] sound pcmC0D5p: pos 96 hw_ptr 96 appl_ptr 15102 avail 1362 2020-05-09T16:08:32.883109+08:00 DEBUG kernel: [ 418.681130] sound pcmC0D5p: pos 96 hw_ptr 96 appl_ptr 16464 avail 0 2020-05-09T16:08:32.929330+08:00 DEBUG kernel: [ 418.726515] sound pcmC0D5p: pos 96 hw_ptr 16464 appl_ptr 16464 avail 16368 2020-05-09T16:08:32.929512+08:00 DEBUG kernel: [ 418.727041] sound pcmC0D5p: pos 96 hw_ptr 16464 appl_ptr 16464 avail 16368 Or it could make snd_pcm_avail() returns an invalid number and confuses the Caller like following log: 2020-05-09T16:08:33.054039+08:00 DEBUG kernel: [ 418.851755] sound pcmC0D5p: pos 96 hw_ptr 16464 appl_ptr 27390 avail 5442 2020-05-09T16:08:33.129552+08:00 DEBUG kernel: [ 418.926491] sound pcmC0D5p: pos 96 hw_ptr 32832 appl_ptr 27390 avail 21810 2020-05-09T16:08:33.131746+08:00 ERR cras_server[1907]: pcm_avail returned frames larger than buf_size: sof-glkda7219max: :0,5: 21810 > 16368 I've submitted a patch to fix the issue in SOF side. However, I think it's also good to fix the incorrect hw_base increasement in Linux side. https://github.com/thesofproject/sof/pull/2926 Regards, Brent
