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>

2 files changed, 8 insertions, 5 deletions

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 38c3dd2a44e0..63d47946e3db 100644
--- a/drivers/usb/core/driver.c
+++ b/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) {
diff --git a/drivers/usb/core/generic.c b/drivers/usb/core/generic.c
index 9bbcb20e2d94..e7ec9b6b7a93 100644
--- a/drivers/usb/core/generic.c
+++ b/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);
 }