linux-kernel - Re: [PATCH 0/3] xhci: Some improvement for Etron xHCI host

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Message-ID: <20240912091203.3ac9b88a@foxbook>
Date: Thu, 12 Sep 2024 09:12:03 +0200
From: Michał Pecio <michal.pecio@...il.com>
To: Kuangyi Chiang <ki.chiang65@...il.com>
Cc: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
 linux-usb@...r.kernel.org, mathias.nyman@...el.com
Subject: Re: [PATCH 0/3] xhci: Some improvement for Etron xHCI host

Hi,

> > I'm aware of one more bug which affects my Etron: if an error occurs
> > on an isochronous TD, two events are generated: first the error,
> > then "success", even if the error is on the final TRB (the common
> > case). Then the "success" causes "TRB DMA not part of current TD"
> > warning. I suspect that all Etron chips are the same. This should
> > be easily reproducible by unpligging an audio/video device while
> > streaming.  
> 
> Hmm, I don't encounter this problem.

OK, I know what happened. This bug only affects SuperSpeed isochronous
endpoints. If you don't have this kind of device, you will not see it.
I checked that High-speed isochronous errors are reported correctly.

My motivation to develop a workaround for this bug has just decreased
another notch.

On the other hand, I was unable to reproduce the control transfer bug.
The exact chip I have is labeled "EtronTech EJ168A", for the record.

You are right, not all transfers have the data stage and transactions
get out of sync with segment boundaries. I modified the patch to only
print a warning instead of queuing a No-Op and then did various things
which use control transactions: setting baud rate on serial, changing
the volume on audio, starting video recording on a webcam, running
ethtool on a NIC.

The warning was printed a few times, but nothing interesting happened.
Dynamic debug was enabled on handle_tx_event() - no errors reported.

Maybe a different silicon/firmware revision, or maybe it's another
SuperSpeed-only bug, or other special conditions for it to happen?

> Ok, I will use one quirk XHCI_ETRON_HOST for these workarounds in the
> next patch revision.
That was just a suggestion, you should ask Mathias Nyman, I suppose.

But, again, my impression of this hardware is that it's pretty bad
and full of bugs, and they are bizarre enough to likely be unique.

Regards,
Michal