USB: EHCI: change deschedule logic for interrupt QHs

This patch (as1281) changes the way ehci-hcd deschedules interrupt
QHs, copying the approach used for async QHs.  The caller is no longer
responsible for rescheduling the QH if its queue is non-empty; instead
the reschedule is done directly by intr_deschedule(), after calling
qh_completions().  This is exactly the same as how end_unlink_async()
works.

ehci_urb_dequeue() and intr_deschedule() now correctly handle the case
where they are called while another interrupt URB for the same QH is
being given back.  This was a surprisingly large blind spot.  And
scan_periodic() now respects the new needs_rescan flag.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/host/ehci-hcd.c

@@ -934,8 +934,9 @@ static int ehci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
 			break;
 		switch (qh->qh_state) {
 		case QH_STATE_LINKED:
+		case QH_STATE_COMPLETING:
 			intr_deschedule (ehci, qh);
-			/* FALL THROUGH */
+			break;
 		case QH_STATE_IDLE:
 			qh_completions (ehci, qh);
 			break;
@@ -944,23 +945,6 @@ static int ehci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
 					qh, qh->qh_state);
 			goto done;
 		}
-
-		/* reschedule QH iff another request is queued */
-		if (!list_empty (&qh->qtd_list)
-				&& HC_IS_RUNNING (hcd->state)) {
-			rc = qh_schedule(ehci, qh);
-
-			/* An error here likely indicates handshake failure
-			 * or no space left in the schedule.  Neither fault
-			 * should happen often ...
-			 *
-			 * FIXME kill the now-dysfunctional queued urbs
-			 */
-			if (rc != 0)
-				ehci_err(ehci,
-					"can't reschedule qh %p, err %d",
-					qh, rc);
-		}
 		break;
 
 	case PIPE_ISOCHRONOUS:
@@ -1079,12 +1063,10 @@ ehci_endpoint_reset(struct usb_hcd *hcd, struct usb_host_endpoint *ep)
 			 * while the QH is active.  Unlink it now;
 			 * re-linking will call qh_refresh().
 			 */
-			if (eptype == USB_ENDPOINT_XFER_BULK) {
+			if (eptype == USB_ENDPOINT_XFER_BULK)
 				unlink_async(ehci, qh);
-			} else {
+			else
 				intr_deschedule(ehci, qh);
-				(void) qh_schedule(ehci, qh);
-			}
 		}
 	}
 	spin_unlock_irqrestore(&ehci->lock, flags);

drivers/usb/host/ehci-q.c

@@ -299,7 +299,6 @@ __acquires(ehci->lock)
 static void start_unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh);
 static void unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh);
 
-static void intr_deschedule (struct ehci_hcd *ehci, struct ehci_qh *qh);
 static int qh_schedule (struct ehci_hcd *ehci, struct ehci_qh *qh);
 
 /*
@@ -555,14 +554,9 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh)
 			 * That should be rare for interrupt transfers,
 			 * except maybe high bandwidth ...
 			 */
-			if ((cpu_to_hc32(ehci, QH_SMASK)
-					& hw->hw_info2) != 0) {
-				intr_deschedule (ehci, qh);
-				(void) qh_schedule (ehci, qh);
-			} else {
-				/* Tell the caller to start an unlink */
-				qh->needs_rescan = 1;
-			}
+
+			/* Tell the caller to start an unlink */
+			qh->needs_rescan = 1;
 			break;
 		/* otherwise, unlink already started */
 		}

drivers/usb/host/ehci-sched.c

@@ -615,8 +615,19 @@ static int qh_unlink_periodic(struct ehci_hcd *ehci, struct ehci_qh *qh)
 
 static void intr_deschedule (struct ehci_hcd *ehci, struct ehci_qh *qh)
 {
-	unsigned	wait;
-	struct ehci_qh_hw *hw = qh->hw;
+	unsigned		wait;
+	struct ehci_qh_hw	*hw = qh->hw;
+	int			rc;
+
+	/* If the QH isn't linked then there's nothing we can do
+	 * unless we were called during a giveback, in which case
+	 * qh_completions() has to deal with it.
+	 */
+	if (qh->qh_state != QH_STATE_LINKED) {
+		if (qh->qh_state == QH_STATE_COMPLETING)
+			qh->needs_rescan = 1;
+		return;
+	}
 
 	qh_unlink_periodic (ehci, qh);
 
@@ -636,6 +647,24 @@ static void intr_deschedule (struct ehci_hcd *ehci, struct ehci_qh *qh)
 	qh->qh_state = QH_STATE_IDLE;
 	hw->hw_next = EHCI_LIST_END(ehci);
 	wmb ();
+
+	qh_completions(ehci, qh);
+
+	/* reschedule QH iff another request is queued */
+	if (!list_empty(&qh->qtd_list) &&
+			HC_IS_RUNNING(ehci_to_hcd(ehci)->state)) {
+		rc = qh_schedule(ehci, qh);
+
+		/* An error here likely indicates handshake failure
+		 * or no space left in the schedule.  Neither fault
+		 * should happen often ...
+		 *
+		 * FIXME kill the now-dysfunctional queued urbs
+		 */
+		if (rc != 0)
+			ehci_err(ehci, "can't reschedule qh %p, err %d\n",
+					qh, rc);
+	}
 }
 
 /*-------------------------------------------------------------------------*/
@@ -2213,7 +2242,8 @@ scan_periodic (struct ehci_hcd *ehci)
 				type = Q_NEXT_TYPE(ehci, q.qh->hw->hw_next);
 				q = q.qh->qh_next;
 				modified = qh_completions (ehci, temp.qh);
-				if (unlikely (list_empty (&temp.qh->qtd_list)))
+				if (unlikely(list_empty(&temp.qh->qtd_list) ||
+						temp.qh->needs_rescan))
 					intr_deschedule (ehci, temp.qh);
 				qh_put (temp.qh);
 				break;