This patch introduces a new call to be able to do a USB reset from an
atomic contect. This is quite helpful in USB callbacks to handle
errors (when the only thing that can be done is to do a device
reset).

It is done queuing a work struct that will do the actual reset. The
struct is "attached" to an interface so pending requests from an
interface are removed when said interface is unbound from the driver.

The call flow then becomes:

usb_queue_reset_device()
  __usb_queue_reset_device() [workqueue]
    usb_reset_device()

usb_probe_interface()
  usb_cancel_queue_reset()      [error path]

usb_unbind_interface()
  usb_cancel_queue_reset()

usb_driver_release_interface()
  usb_cancel_queue_reset()

Note usb_cancel_queue_reset() needs smarts to try not to unqueue when
it is actually being executed. This happens when we run the reset from
the workqueue: usb_reset_device() is called and on interface unbind
time, usb_cancel_queue_reset() would be called. That would deadlock on
cancel_work_sync(). To avoid that, we set (before running
usb_reset_device()) usb_intf->reset_running and clear it inmediately
after returning.

Patch is against 2.6.28-rc2 and depends on
http://marc.info/?l=linux-usb&m=122581634925308&w=2 (as submitted by
Alan Stern).
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>