usb-serial: ftdi_sio: fix oops during autosuspend

This patch (as1550) fixes a bug in the usb-serial core that affects
the ftdi_sio driver and most likely others as well.  The core
implements suspend and resume routines, but it doesn't store pointers
to those routines in the usb_driver structures that it registers,
even though it does set those drivers' supports_autosuspend flag.  The
end result is that when one of these devices is autosuspended, we try
to call through a NULL pointer.

The patch fixes the problem by setting the suspend and resume method
pointers to the appropriate routines in the USB serial core, along
with the supports_autosuspend field, in each driver as it is
registered.

This should be back-ported to all the stable kernels that have the new
usb_serial_register_drivers() interface.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: Frank Schäfer <schaefer.frank@gmx.net>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/usb-serial.c

@@ -1336,7 +1336,6 @@ static int usb_serial_register(struct usb_serial_driver *driver)
 				driver->description);
 		return -EINVAL;
 	}
-	driver->usb_driver->supports_autosuspend = 1;
 
 	/* Add this device to our list of devices */
 	mutex_lock(&table_lock);
@@ -1371,7 +1370,7 @@ static void usb_serial_deregister(struct usb_serial_driver *device)
  * @serial_drivers: NULL-terminated array of pointers to drivers to be registered
  *
  * Registers @udriver and all the drivers in the @serial_drivers array.
- * Automatically fills in the .no_dynamic_id field in @udriver and
+ * Automatically fills in the .no_dynamic_id and PM fields in @udriver and
  * the .usb_driver field in each serial driver.
  */
 int usb_serial_register_drivers(struct usb_driver *udriver,
@@ -1390,11 +1389,17 @@ int usb_serial_register_drivers(struct usb_driver *udriver,
 	 * the serial drivers are registered, because the probe would
 	 * simply fail for lack of a matching serial driver.
 	 * Therefore save off udriver's id_table until we are all set.
+	 *
+	 * Suspend/resume support is implemented in the usb-serial core,
+	 * so fill in the PM-related fields in udriver.
 	 */
 	saved_id_table = udriver->id_table;
 	udriver->id_table = NULL;
 
 	udriver->no_dynamic_id = 1;
+	udriver->supports_autosuspend = 1;
+	udriver->suspend = usb_serial_suspend;
+	udriver->resume = usb_serial_resume;
 	rc = usb_register(udriver);
 	if (rc)
 		return rc;