USB: EHCI: use hrtimer for unlinking empty async QHs

This patch (as1583) changes ehci-hcd to use an hrtimer event for
unlinking empty (unused) async QHs instead of using a kernel timer.

The check for empty QHs is moved to a new routine, where it doesn't
require going through an entire scan of both the async and periodic
schedules.  And it can unlink multiple QHs at once, unlike the current
code.

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

1 files changed, 53 insertions, 25 deletions

diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index 1818329..bae9317 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -1205,7 +1205,7 @@ static void start_iaa_cycle(struct ehci_hcd *ehci, bool nested)
 			end_unlink_async(ehci);
 
 	/* Otherwise start a new IAA cycle */
-	} else {
+	} else if (likely(ehci->rh_state == EHCI_RH_RUNNING)) {
 		/* Make sure the unlinks are all visible to the hardware */
 		wmb();
 
@@ -1253,6 +1253,39 @@ static void end_unlink_async(struct ehci_hcd *ehci)
 	}
 }
 
+static void unlink_empty_async(struct ehci_hcd *ehci)
+{
+	struct ehci_qh		*qh, *next;
+	bool			stopped = (ehci->rh_state < EHCI_RH_RUNNING);
+	bool			check_unlinks_later = false;
+
+	/* Unlink all the async QHs that have been empty for a timer cycle */
+	next = ehci->async->qh_next.qh;
+	while (next) {
+		qh = next;
+		next = qh->qh_next.qh;
+
+		if (list_empty(&qh->qtd_list) &&
+				qh->qh_state == QH_STATE_LINKED) {
+			if (!stopped && qh->unlink_cycle ==
+					ehci->async_unlink_cycle)
+				check_unlinks_later = true;
+			else
+				single_unlink_async(ehci, qh);
+		}
+	}
+
+	/* Start a new IAA cycle if any QHs are waiting for it */
+	if (ehci->async_unlink)
+		start_iaa_cycle(ehci, false);
+
+	/* QHs that haven't been empty for long enough will be handled later */
+	if (check_unlinks_later) {
+		ehci_enable_event(ehci, EHCI_HRTIMER_ASYNC_UNLINKS, true);
+		++ehci->async_unlink_cycle;
+	}
+}
+
 /* makes sure the async qh will become idle */
 /* caller must own ehci->lock */
 
@@ -1277,12 +1310,8 @@ static void start_unlink_async(struct ehci_hcd *ehci, struct ehci_qh *qh)
 
 static void scan_async (struct ehci_hcd *ehci)
 {
-	bool			stopped;
 	struct ehci_qh		*qh;
-	enum ehci_timer_action	action = TIMER_IO_WATCHDOG;
-
-	timer_action_done (ehci, TIMER_ASYNC_SHRINK);
-	stopped = (ehci->rh_state < EHCI_RH_RUNNING);
+	bool			check_unlinks_later = false;
 
 	ehci->qh_scan_next = ehci->async->qh_next.qh;
 	while (ehci->qh_scan_next) {
@@ -1301,28 +1330,27 @@ static void scan_async (struct ehci_hcd *ehci)
 			 * in single_unlink_async().
 			 */
 			temp = qh_completions(ehci, qh);
-			if (qh->needs_rescan)
+			if (qh->needs_rescan) {
 				start_unlink_async(ehci, qh);
-			qh->unlink_time = jiffies + EHCI_SHRINK_JIFFIES;
-			if (temp != 0)
+			} else if (list_empty(&qh->qtd_list)
+					&& qh->qh_state == QH_STATE_LINKED) {
+				qh->unlink_cycle = ehci->async_unlink_cycle;
+				check_unlinks_later = true;
+			} else if (temp != 0)
 				goto rescan;
 		}
+	}
 
-		/* unlink idle entries, reducing DMA usage as well
-		 * as HCD schedule-scanning costs.  delay for any qh
-		 * we just scanned, there's a not-unusual case that it
-		 * doesn't stay idle for long.
-		 * (plus, avoids some kind of re-activation race.)
-		 */
-		if (list_empty(&qh->qtd_list)
-				&& qh->qh_state == QH_STATE_LINKED) {
-			if (!ehci->async_unlink && (stopped ||
-					time_after_eq(jiffies, qh->unlink_time)))
-				start_unlink_async(ehci, qh);
-			else
-				action = TIMER_ASYNC_SHRINK;
-		}
+	/*
+	 * Unlink empty entries, reducing DMA usage as well
+	 * as HCD schedule-scanning costs.  Delay for any qh
+	 * we just scanned, there's a not-unusual case that it
+	 * doesn't stay idle for long.
+	 */
+	if (check_unlinks_later && ehci->rh_state == EHCI_RH_RUNNING &&
+			!(ehci->enabled_hrtimer_events &
+				BIT(EHCI_HRTIMER_ASYNC_UNLINKS))) {
+		ehci_enable_event(ehci, EHCI_HRTIMER_ASYNC_UNLINKS, true);
+		++ehci->async_unlink_cycle;
 	}
-	if (action == TIMER_ASYNC_SHRINK)
-		timer_action (ehci, TIMER_ASYNC_SHRINK);
 }