[PATCH] USB: Only process ports with change events pending

This patch adds a bit-array to the hub driver's private data structure,
used for storing the contents of the hub's interrupt status message.  That
message indicates which ports have events pending (and whether the hub
itself has events pending).  By only polling the status of the ports
listed in the bit-array we can save a fair amount of overhead in hub
communication.

(The #error test added to hub.h is a little awkward, but it's purely
precautionary -- it won't matter until someone decides to support hubs
with more than 31 ports!)

Also included in the patch, since this seemed the perfect opportunity for
it, is Byron's suggestion for handling hub events in the order in which
they were received.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/usb/core/hub.c

@@ -231,6 +231,8 @@ static void hub_irq(struct urb *urb, struct pt_regs *regs)
 {
 	struct usb_hub *hub = (struct usb_hub *)urb->context;
 	int status;
+	int i;
+	unsigned long bits;
 
 	spin_lock(&hub_event_lock);
 	hub->urb_active = 0;
@@ -255,6 +257,11 @@ static void hub_irq(struct urb *urb, struct pt_regs *regs)
 	
 	/* let khubd handle things */
 	case 0:			/* we got data:  port status changed */
+		bits = 0;
+		for (i = 0; i < urb->actual_length; ++i)
+			bits |= ((unsigned long) ((*hub->buffer)[i]))
+					<< (i*8);
+		hub->event_bits[0] = bits;
 		break;
 	}
 
@@ -262,7 +269,7 @@ static void hub_irq(struct urb *urb, struct pt_regs *regs)
 
 	/* Something happened, let khubd figure it out */
 	if (list_empty(&hub->event_list)) {
-		list_add(&hub->event_list, &hub_event_list);
+		list_add_tail(&hub->event_list, &hub_event_list);
 		wake_up(&khubd_wait);
 	}
 
@@ -1776,7 +1783,10 @@ static void hub_events(void)
 			hub->error = 0;
 		}
 
+		/* deal with port status changes */
 		for (i = 0; i < hub->descriptor->bNbrPorts; i++) {
+			if (!test_and_clear_bit(i+1, hub->event_bits))
+				continue;
 			ret = hub_port_status(hdev, i, &portstatus, &portchange);
 			if (ret < 0)
 				continue;
@@ -1846,7 +1856,9 @@ static void hub_events(void)
 		} /* end for i */
 
 		/* deal with hub status changes */
-		if (hub_hub_status(hub, &hubstatus, &hubchange) < 0)
+		if (test_and_clear_bit(0, hub->event_bits) == 0)
+			;	/* do nothing */
+		else if (hub_hub_status(hub, &hubstatus, &hubchange) < 0)
 			dev_err (hub_dev, "get_hub_status failed\n");
 		else {
 			if (hubchange & HUB_CHANGE_LOCAL_POWER) {

drivers/usb/core/hub.h

@@ -203,6 +203,10 @@ struct usb_hub {
 	int			nerrors;	/* track consecutive errors */
 
 	struct list_head	event_list;	/* hubs w/data or errs ready */
+	unsigned long		event_bits[1];	/* status change bitmask */
+#if USB_MAXCHILDREN > 31 /* 8*sizeof(unsigned long) - 1 */
+#error event_bits[] is too short!
+#endif
 
 	struct usb_hub_descriptor *descriptor;	/* class descriptor */
 	struct usb_tt		tt;		/* Transaction Translator */