[0/5] xHCI: Isochronous error handling fixes and improvements

Message

Michal Pecio Feb. 10, 2025, 7:37 a.m. UTC

These patches reduce latency of error reporting in some cases related
to 'error mid TD' and Missed Service events and sometimes fix a failure
to give back such TDs altogether until they are cancelled.

Also included are fixes for potential packet loss or memory corruption
due to an obscure race. Whether it causes problems IRL is not known and
the worst case would be hard to reproduce, but exactly for this reason
if the worst case actually happens, it could be hard to debug too.

2/5 is a cleanup which makes 3/5 implementation shorter and simpler.

The first three should be safe. The fourth should also be safe, but it
relies on HC functionality Linux never relied on before, so I placed it
towards the end in case it would need some tweaks. I tested it on all
hardware I have and it worked just fine.

The last one is perhaps the most controversial, though it should be
OK with typical "complete -> resubmit" drivers. It's the only one here
which increases latency in some severe error cases. The intent is to
avoid potentially giving back URBs not yet executed by hardware.

Michal Pecio (5):
  usb: xhci: Complete 'error mid TD' transfers when handling Missed
    Service
  usb: xhci: Clean up the TD skipping loop
  usb: xhci: Fix isochronous Ring Underrun/Overrun event handling
  usb: xhci: Expedite skipping missed isoch TDs on modern HCs
  usb: xhci: Skip only one TD on Ring Underrun/Overrun

 drivers/usb/host/xhci-ring.c | 110 +++++++++++++++++++++--------------
 1 file changed, 67 insertions(+), 43 deletions(-)