high cpu load on omap3 using musb

[Adam Wozniak <awozniak@irobot.com>]

[-- Attachment #1: Type: text/plain, Size: 1232 bytes --]

With a USB 2.0 webcam attached to the OTG port on an OMAP3 (applies to 
overo gumstix, beagleboard, probably others) we see a high CPU load in a 
kworker thread.

Between 2.6.33 and 2.6.34 musb_core.c changed.

IRQ handlers changed with the result that a worker in musb_core.c got 
scheduled far more frequently than needed.

I've included a patch below against 3.7, but i think it'll apply against 
mainline.
[I apologize for any whitespace mangling.  I've also attached the patch.]

I'd like more eyeballs to tell me if this is right.  I'd also like to 
know who I need to talk to to get this pushed into mainline.

--Adam

# The MUSB IRQ schedules work on every interrupt.
# This is unnecessary, and causes excessive CPU load.
#
# Here we only schedule work if there is something for
# the worker to do.

Index: git/drivers/usb/musb/musb_core.c
===================================================================
--- git.orig/drivers/usb/musb/musb_core.c
+++ git/drivers/usb/musb/musb_core.c
@@ -925,7 +925,9 @@ b_host:
         }
  #endif

-       schedule_work(&musb->irq_work);
+       if (musb->xceiv->state != musb->xceiv_old_state) {
+               schedule_work(&musb->irq_work);
+       }

         return handled;
  }


[-- Attachment #2: musb_smartwork.patch --]
[-- Type: text/x-patch, Size: 560 bytes --]

# The MUSB IRQ schedules work on every interrupt.
# This is unnecessary, and causes excessive CPU load.
#
# Here we only schedule work if there is something for
# the worker to do.

Index: git/drivers/usb/musb/musb_core.c
===================================================================
--- git.orig/drivers/usb/musb/musb_core.c
+++ git/drivers/usb/musb/musb_core.c
@@ -925,7 +925,9 @@ b_host:
 	}
 #endif
 
-	schedule_work(&musb->irq_work);
+	if (musb->xceiv->state != musb->xceiv_old_state) {
+		schedule_work(&musb->irq_work);
+	}
 
 	return handled;
 }