USB: EHCI: split needs_rescan into two flags

This patch (as1662) does some more QH-related cleanup in ehci-hcd.
The qh->needs_rescan flag is currently used for two different
purposes; the patch replaces it with two separate flags for greater
clarity: qh->dequeue_during_giveback indicates that a completion
handler dequeued an URB (implying that a rescan is needed), and
qh->exception indicates that the QH is in an exceptional state
requiring an unlink (either it encountered an I/O error or an unlink
was requested).

The new flags get set where the dequeue, exception, or unlink request
occurred, rather than where the unlink is started.  This is so that in
the future, if we need to, we will be able to tell apart unlinks that
truly were required from those that were carried out merely because
the QH wasn't being used.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 22 insertions, 40 deletions

diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index c95f60d43b1a..fca741dbf9df 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -322,7 +322,7 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh)
  rescan:
 	last = NULL;
 	last_status = -EINPROGRESS;
-	qh->needs_rescan = 0;
+	qh->dequeue_during_giveback = 0;
 
 	/* remove de-activated QTDs from front of queue.
 	 * after faults (including short reads), cleanup this urb
@@ -518,18 +518,12 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh)
 	}
 
 	/* Do we need to rescan for URBs dequeued during a giveback? */
-	if (unlikely(qh->needs_rescan)) {
+	if (unlikely(qh->dequeue_during_giveback)) {
 		/* If the QH is already unlinked, do the rescan now. */
 		if (state == QH_STATE_IDLE)
 			goto rescan;
 
-		/* Otherwise we have to wait until the QH is fully unlinked.
-		 * Our caller will start an unlink if qh->needs_rescan is
-		 * set.  But if an unlink has already started, nothing needs
-		 * to be done.
-		 */
-		if (state != QH_STATE_LINKED)
-			qh->needs_rescan = 0;
+		/* Otherwise the caller must unlink the QH. */
 	}
 
 	/* restore original state; caller must unlink or relink */
@@ -538,29 +532,23 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh)
 	/* be sure the hardware's done with the qh before refreshing
 	 * it after fault cleanup, or recovering from silicon wrongly
 	 * overlaying the dummy qtd (which reduces DMA chatter).
+	 *
+	 * We won't refresh a QH that's linked (after the HC
+	 * stopped the queue).  That avoids a race:
+	 *  - HC reads first part of QH;
+	 *  - CPU updates that first part and the token;
+	 *  - HC reads rest of that QH, including token
+	 * Result:  HC gets an inconsistent image, and then
+	 * DMAs to/from the wrong memory (corrupting it).
+	 *
+	 * That should be rare for interrupt transfers,
+	 * except maybe high bandwidth ...
 	 */
-	if (stopped != 0 || hw->hw_qtd_next == EHCI_LIST_END(ehci)) {
-		if (state == QH_STATE_LINKED) {
-			/*
-			 * We won't refresh a QH that's linked (after the HC
-			 * stopped the queue).  That avoids a race:
-			 *  - HC reads first part of QH;
-			 *  - CPU updates that first part and the token;
-			 *  - HC reads rest of that QH, including token
-			 * Result:  HC gets an inconsistent image, and then
-			 * DMAs to/from the wrong memory (corrupting it).
-			 *
-			 * That should be rare for interrupt transfers,
-			 * except maybe high bandwidth ...
-			 *
-			 * Therefore tell the caller to start an unlink.
-			 */
-			qh->needs_rescan = 1;
-		}
-		/* otherwise, unlink already started */
-	}
+	if (stopped != 0 || hw->hw_qtd_next == EHCI_LIST_END(ehci))
+		qh->exception = 1;
 
-	return qh->needs_rescan;
+	/* Let the caller know if the QH needs to be unlinked. */
+	return qh->exception;
 }
 
 /*-------------------------------------------------------------------------*/
@@ -1002,8 +990,9 @@ static void qh_link_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
 	head->qh_next.qh = qh;
 	head->hw->hw_next = dma;
 
-	qh->xacterrs = 0;
 	qh->qh_state = QH_STATE_LINKED;
+	qh->xacterrs = 0;
+	qh->exception = 0;
 	/* qtd completions reported later by interrupt */
 
 	enable_async(ehci);
@@ -1317,16 +1306,9 @@ static void unlink_empty_async_suspended(struct ehci_hcd *ehci)
 
 static void start_unlink_async(struct ehci_hcd *ehci, struct ehci_qh *qh)
 {
-	/*
-	 * 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;
+	/* If the QH isn't linked then there's nothing we can do. */
+	if (qh->qh_state != QH_STATE_LINKED)
 		return;
-	}
 
 	single_unlink_async(ehci, qh);
 	start_iaa_cycle(ehci, false);