When an endpoint stalls, the xHCI driver must move the endpoint ring's
dequeue pointer past the stalled transfer.  To do that, the driver issues
a Set TR Dequeue Pointer command, which will complete some time later.

Takashi was having issues with USB 1.1 audio devices that stalled, and his
analysis of the code was that the old code would not update the xHCI
driver's ring dequeue pointer after the command completes.  However, the
dequeue pointer is set in xhci_find_new_dequeue_state(), just before the
set command is issued to the hardware.

Setting the dequeue pointer before the Set TR Dequeue Pointer command
completes is a dangerous thing to do, since the xHCI hardware can fail the
command.  Instead, store the new dequeue pointer in the xhci_virt_ep
structure, and update the ring's dequeue pointer when the Set TR dequeue
pointer command completes.

While we're at it, make sure we can't queue another Set TR Dequeue Command
while the first one is still being processed.  This just won't work with
the internal xHCI state code.  I'm still not sure if this is the right
thing to do, since we might have a case where a driver queues multiple
URBs to a control ring, one of the URBs Stalls, and then the driver tries
to cancel the second URB.  There may be a race condition there where the
xHCI driver might try to issue multiple Set TR Dequeue Pointer commands,
but I would have to think very hard about how the Stop Endpoint and
cancellation code works.  Keep the fix simple until when/if we run into
that case.

This patch should be queued to kernels all the way back to 2.6.31.
Signed-off-by: NSarah Sharp <sarah.a.sharp@linux.intel.com>
Tested-by: NTakashi Iwai <tiwai@suse.de>
Cc: stable@kernel.org