USB: Implement PM FREEZE and PRETHAW

This patch (as884) finally implements the time-saving semantics
possible with the Power Management FREEZE and PRETHAW events.  Their
proper handling requires only that devices be quiesced, with
interrupts and DMA turned off; non-root USB devices don't actually
need to be put in a suspended state.  The patch checks and avoids
doing the suspend call when possible.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/driver.c

@@ -1050,8 +1050,15 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
 				break;
 		}
 	}
-	if (status == 0)
+	if (status == 0) {
+
+		/* Non-root devices don't need to do anything for FREEZE
+		 * or PRETHAW. */
+		if (udev->parent && (msg.event == PM_EVENT_FREEZE ||
+				msg.event == PM_EVENT_PRETHAW))
+			goto done;
 		status = usb_suspend_device(udev, msg);
+	}
 
 	/* If the suspend failed, resume interfaces that did get suspended */
 	if (status != 0) {

drivers/usb/core/generic.c

@@ -193,10 +193,6 @@ static void generic_disconnect(struct usb_device *udev)
 
 static int generic_suspend(struct usb_device *udev, pm_message_t msg)
 {
-	/* USB devices enter SUSPEND state through their hubs, but can be
-	 * marked for FREEZE as soon as their children are already idled.
-	 * But those semantics are useless, so we equate the two (sigh).
-	 */
 	return usb_port_suspend(udev);
 }