[PATCH 0/1] usb: xhci: Don't trust the EP Context cycle bit when moving HW dequeue

[Michal Pecio <michal.pecio@gmail.com>]

Hi,

I ran into an annoying bug in VIA hardware, where Endpoint Context
state is not updated when it's supposed to and Set TR Dequeue issued
by the driver sets wrong cycle state and the endpoint stops working.

This can be triggered by stalls, which are relatively common:
- some card readers without a card inserted
- disk I/O errors
- failing SMART commands, possibly issued by daemons like udisks2

I knew immediately what to do, because it's a known bug and Raspberry
Pi has a fix for it, which they submitted upstream but it got reverted
later. The revert is puzzling, because it was a boot issue, happening
before the changed code is supposed to run.

If the problem wasn't misdiagnozed and blamed on a wrong patch, I can
imagine the workaround could put the chip in a bad state which caused
problems after rebooting. The commit surely had a blatant endian bug
and VL805 is prone to locking up hard under some unclear conditions.

This is my attempt at a simpler, and hopefully correct, solution.
I tried to come up with something stable-friendly, but the patch is
not marked for stable becasue it wouldn't compile anyway. If there
is interest in having this in stable, we can trivially backport it
(a matter of end_trb/last_trb rename) and submit later.

Regards,
Michal