USB: skip Set-Interface(0) if already in altsetting 0

When a driver unbinds from an interface, usbcore always sends a
Set-Interface request to reinstall altsetting 0.  Unforunately, quite
a few devices have buggy firmware that crashes when it receives this
request.

To avoid such problems, this patch (as1180) arranges to send the
Set-Interface request only when the interface is not already in
altsetting 0.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/driver.c

@@ -279,7 +279,9 @@ static int usb_unbind_interface(struct device *dev)
 	 * altsetting means creating new endpoint device entries).
 	 * When either of these happens, defer the Set-Interface.
 	 */
-	if (!error && intf->dev.power.status == DPM_ON)
+	if (intf->cur_altsetting->desc.bAlternateSetting == 0)
+		;	/* Already in altsetting 0 so skip Set-Interface */
+	else if (!error && intf->dev.power.status == DPM_ON)
 		usb_set_interface(udev, intf->altsetting[0].
 				desc.bInterfaceNumber, 0);
 	else