Re: Misbehaving Alder Lake-N PCH USB 3.2 xHCI Host Controller

["Michał Pecio" <michal.pecio@gmail.com>]

Hi,


I can offer a few quick suggestions:

1. When kernel bugs are suspected, try other kernels offered by your
distribution. See if there is any chance that -rt paches are causing
issues.

2. Does any of that go away when ALSA buffer size is increased or is it
always there on this machine?

3. When posting wall of text errors, start at the beginning because it
may offer clues about what originally went wrong ('dmesg -W' helps).

4. Playing a tiny file with 'aplay --period-size=48 --buffer-size=96'
is a simpler way to reproduce the problem and generates a shorter log.


> I have to note that these "WARN Event TRB for slot 18 ep 1 with no TDs
> queued?" were there before enabling this dynamic debug feature, I just
> forgot to mention them in my original mail.

This particular part is probably caused by our failure to properly
handle the preceding condition ("underrun event still with TDs queued").
I can't know for sure, but assuming no hardware bugs, it appears that a
new transfer descriptor is queued after the hardware reports a ring
underrun but before we actually process the report. While processing
the underrun we are surprised by this unexpected TD, then we see that
skip flag is set so we erronously report all TDs (most likely including
the new one) as failed to the audio driver. Meanwhile the hardware may
execute this transfer and report its completion later, at which point
we have already forgotten about it.

*Maybe* this creates enough chaos that some sort of infinite loop of
cascading errors is established as a result of one recoverable error.
Or maybe your problem is elsewhere and this bug is only a side effect.

Are you able to test kernel patches?


Mathias may have other ideas to try.

Regards,
Michal