results in bogus kernel messages

[thomas001]

On recent ArchLinux (Linux 3.17.4, libusb 1.0.19) the driver works from time to time (sometimes fprintd just hangs in a futex lock). The following messages are generated by fprint-enroll, maybe they are helpful:

[Nov29 17:32] usb 1-7: reset full-speed USB device number 8 using xhci_hcd
[  +0,000027] xhci_hcd 0000:00:14.0: Setup ERROR: setup context command for slot 7.
[  +0,000003] usb 1-7: hub failed to enable device, error -22
[  +0,159876] usb 1-7: reset full-speed USB device number 8 using xhci_hcd
[  +0,000026] xhci_hcd 0000:00:14.0: Setup ERROR: setup context command for slot 7.
[  +0,000003] usb 1-7: hub failed to enable device, error -22
[  +0,160062] usb 1-7: reset full-speed USB device number 8 using xhci_hcd
[  +0,015624] xhci_hcd 0000:00:14.0: xHCI xhci_drop_endpoint called with disabled ep ffff8803f967d400
[  +0,000004] xhci_hcd 0000:00:14.0: xHCI xhci_drop_endpoint called with disabled ep ffff8803f967d448
[  +0,000002] xhci_hcd 0000:00:14.0: xHCI xhci_drop_endpoint called with disabled ep ffff8803f967d490
[  +0,000001] xhci_hcd 0000:00:14.0: xHCI xhci_drop_endpoint called with disabled ep ffff8803f967d4d8
[  +0,562259] xhci_hcd 0000:00:14.0: WARN Event TRB for slot 7 ep 4 with no TDs queued?
[  +6,001693] xhci_hcd 0000:00:14.0: WARN Event TRB for slot 7 ep 4 with no TDs queued?