The default control endpoint ep0 can return a STALL indicating the
device does not support the control transfer requests. This is called
a protocol stall and does not halt the endpoint.

xHC behaves a bit different. Its internal endpoint state will always
be halted on any stall, even if the device side of the endpiont is not
halted. So we do need to issue the reset endpoint command to clear the
xHC host intenal endpoint halt state, but should not request the HS hub
to clear the TT buffer unless device side of endpoint is halted.

Clearing the hub TT buffer at protocol stall caused ep0 to become
unresponsive for some FS/LS devices behind HS hubs, and class drivers
failed to set the interface due to timeout:

usb 1-2.1: 1:1: usb_set_interface failed (-110)

Fixes: ef513be0 ("usb: xhci: Add Clear_TT_Buffer")
Cc: <stable@vger.kernel.org> # v5.3
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200421140822.28233-4-mathias.nyman@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>