On 14.12.2016 12:58, Michal Necasek wrote:Thanks for confirming that.
prior to the endpoint reset. SetFeature(CLEAR_HALT) resets the toggle
on the device, but not on the host. But we know for a fact that the
device sends a packet (with data toggle 0) which the host USB stack
never sees, and a data toggle mismatch explains that quite well.
We are using USBFS to talk to the printer, but that shouldn't matter
much. I will note that the available documentation<1> explicitly says
that USBDEVFS_RESETEP and USBDEVFS_CLEAR_HALT both reset the data
toggle. That is indeed the case for the Linux EHCI driver but not
xHCI. Both of the USBFS IOCTLs call into xhci_reset_endpoint() which
does nothing.
This is very likely the case.
xhci can not reset the host side of the endpoint unless it really isRight, the Reset Endpoint is limited to halted endpoints, not even stopped ones. It's really only useful for error cleanup.
halted.
xhci 4.6.8:
"If the endpoint is not in the Halted state when an Reset Endpoint Command
is executed -The xHC shall reject the command and generate a Command
Completion Event with the Completion Code set to Context State Error."
Normal halt/stall case is that xhci receives a STALL from the device,OK, that's what I thought was happening.
and immediately resets the endpoint (clears toggle, host side) then
propagates the HALT status to usb core.
USB core then sends SetFeature(CLEAR_HALT) to the device which will
reset the
toggle for the device side of the endpoint, and host and device toggles
will be in sync.
After this xhci_endpoint_reset() is called by usb core to inform xhci
that the
endpoint was reset, but currently we don't do anything in it.
If SetFeature(CLEAR_HALT) is called without endpoint actually beingAh, that's interesting. I'm not surprised that we weren't the first ones running into this. The scenario is a bit obscure but not very device specific.
HALTED we can not
reset it from xhci. we should issue a config endpoint command to reset
the host side
toggle, as mentioned in xhci 1.0 120814 as a last note:
"Note: The Reset Endpoint Command may only be issued to endpoints in the
Halted state.
If software wishes reset the Data Toggle or Sequence Number of an
endpoint that isn't
in the Halted state, then software may issue a Configure Endpoint
Command with the Drop
and Add bits set for the target endpoint. that is in the Stopped state."
There was a case with a scanner we believed had the same issue, and we
tried to
resolve it by issuing the configure endpoint command in
xhci_endpoint_reset() but
if I remember correctly It did not resolve the case and code never got
anywhere.
I might have some really old implementation somewhere for this, at leastThanks, we'll have to try it out. It looks like the right approach to me.
there is
a really old and outdated hack at
git://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git
ep_reset_halt_test
https://git.kernel.org/cgit/linux/kernel/git/mnyman/xhci.git/log/?h=ep_reset_halt_test
which really is quite a hack, and based on 3.19 kernel so it's probably
only useful
as an Idea to base a real solution on.