Re: [PATCH 2/2] usb: xhci: Warn about suspected "start-stop" bugs in HCs

Michał Pecio
2024-10-15T18:52:36Z

Hi,

> + if (!(xhci->quirks & XHCI_NEC_HOST)) {
> > + xhci_warn(xhci, "Unhandled Stop Endpoint failure on slot %d ep_index %d\n",
> > + slot_id, ep_index);
>
> If a user sees this, what are they supposed to do? This is a hardware
> bug, but with this we are going to get reports of "something broke in
> the kernel", right? Why not make it just more informative, like:
> xhci_info(xhci, "hardware can not deal with...
>
> or something like that so that people know we know about the bug, and
> are working around it, but that it's not our issue, but rather the
> hardware that is at fault?

Yes, the point is that ideally some users would report when they see it.
This is not a warning for a bug we know about and work around, it's for
hypothetical bugs that aren't known. If I'm adding code to handle a bug
of my HC, I might as well use it to sanity check other HCs for free.

Ideally they are OK and no one will ever see it. I tested several HCs
in January and found no similar issues. Maybe I will test them again.

I specifically worded it as something the kernel could do better rather
than the kernel just whining about something incomprehensibly. For the
latter, we already have the absolute classic "ERROR Transfer event TRB
DMA ptr not part of current TD", which would often follow this one, but
offer little clue about the root cause. It's kinda too late by then.

Regards,
Michal