On Fri, May 25, 2012 at 04:54:01PM -0400, Alan Stern wrote: > On Fri, 25 May 2012, Hans de Goede wrote: > > Here is what I believe is happening, at 2 libusb splits the > > bulk in transfer into 2 packets, 1 of 16k and 1 of 4k, setting the > > USBDEVFS_URB_SHORT_NOT_OK flag on both and the > > USBDEVFS_URB_BULK_CONTINUATION flag on the second. > > > > With the EHCI controller all then works as intended, the first packet > > transfers 36 bytes and returns a status of EREMOTEIO, the second > > packet gets cancelled by drivers/usb/core/devio.c, transferring 0 bytes > > and returns a status of ECONNRESET and we all live happily ever after :) > > That's the expected result. > > > With the XHCI controller however, the first packet transfers 36 bytes > > and returns a status of EREMOTEIO, as it should, but the second > > packet transfers the 13 next bytes and returns a status of ECONNRESET. > > However that is wrong. > > > IOW the second packet of the split bulk transfer reads more data > > despite the first packet returning an error status and the > > USBDEVFS_URB_BULK_CONTINUATION flag being set. > > > > Thus the second packets has consumed the data the device had ready > > which should have been read by the next bulk transfer from the guest > > pov. > > > > All in all it seems that the cancel of further packets done by > > drivers/usb/core/devio.c: cancel_bulk_urbs() > > comes too late when the device is on an XHCI controller, it seems that > > the controller is already "executing" the next bulk transfer *before* > > the completion handler of the previous one has completed. > > No, the cancellation doesn't come too late. Rather, the endpoint queue > did not get stopped as it should when the EREMOTEIO error occurred.
Why would the xHCI endpoint queue get stopped after an EREMOTEIO error? The upper layers never clear a halt on a short bulk packet, so the xHCI driver has to restart the ring itself after a short packet. Sarah Sharp ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ libusbx-devel mailing list libusbx-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libusbx-devel
