usb-storage: handle a skipped data phase

usb-storage: handle a skipped data phase

commit 93c9bf4d1838d5851a18ca398b0ad66397f05056 upstream.

Sometimes mass-storage devices using the Bulk-only transport will
mistakenly skip the data phase of a command.  Rather than sending the
data expected by the host or sending a zero-length packet, they go
directly to the status phase and send the CSW.

This causes problems for usb-storage, for obvious reasons.  The driver
will interpret the CSW as a short data transfer and will wait to
receive a CSW.  The device won't have anything left to send, so the
command eventually times out.

The SCSI layer doesn't retry commands after they time out (this is a
relatively recent change).  Therefore we should do our best to detect
a skipped data phase and handle it promptly.

This patch adds code to do that.  If usb-storage receives a short
13-byte data transfer from the device, and if the first four bytes of
the data match the CSW signature, the driver will set the residue to
the full transfer length and interpret the data as a CSW.

This fixes Bugzilla #86611.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Tested-by: Paul Osmialowski <newchief@king.net.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: use US_DEBUGP() not usb_stor_dbg()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>