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>

drivers/usb/host/ehci-hcd.c

@@ -94,8 +94,6 @@ static const char	hcd_name [] = "ehci_hcd";
 #define	EHCI_TUNE_FLS		1	/* (medium) 512-frame schedule */
 
 #define EHCI_IO_JIFFIES		(HZ/10)		/* io watchdog > irq_thresh */
-#define EHCI_SHRINK_JIFFIES	(DIV_ROUND_UP(HZ, 200) + 1)
-						/* 5-ms async qh unlink delay */
 
 /* Initial IRQ latency:  faster than hw default */
 static int log2_irq_thresh = 0;		// 0 to 6
@@ -130,15 +128,6 @@ MODULE_PARM_DESC(hird, "host initiated resume duration, +1 for each 75us");
 static void
 timer_action(struct ehci_hcd *ehci, enum ehci_timer_action action)
 {
-	/* Don't override timeouts which shrink or (later) disable
-	 * the async ring; just the I/O watchdog.  Note that if a
-	 * SHRINK were pending, OFF would never be requested.
-	 */
-	if (timer_pending(&ehci->watchdog)
-			&& (BIT(TIMER_ASYNC_SHRINK)
-				& ehci->actions))
-		return;
-
 	if (!test_and_set_bit(action, &ehci->actions)) {
 		unsigned long t;
 
@@ -148,10 +137,6 @@ timer_action(struct ehci_hcd *ehci, enum ehci_timer_action action)
 				return;
 			t = EHCI_IO_JIFFIES;
 			break;
-		/* case TIMER_ASYNC_SHRINK: */
-		default:
-			t = EHCI_SHRINK_JIFFIES;
-			break;
 		}
 		mod_timer(&ehci->watchdog, t + jiffies);
 	}
@@ -307,6 +292,7 @@ static void ehci_quiesce (struct ehci_hcd *ehci)
 /*-------------------------------------------------------------------------*/
 
 static void end_unlink_async(struct ehci_hcd *ehci);
+static void unlink_empty_async(struct ehci_hcd *ehci);
 static void ehci_work(struct ehci_hcd *ehci);
 static void start_unlink_intr(struct ehci_hcd *ehci, struct ehci_qh *qh);
 static void end_unlink_intr(struct ehci_hcd *ehci, struct ehci_qh *qh);

drivers/usb/host/ehci-hub.c

@@ -300,6 +300,7 @@ static int ehci_bus_suspend (struct usb_hcd *hcd)
 	ehci->rh_state = EHCI_RH_SUSPENDED;
 
 	end_unlink_async(ehci);
+	unlink_empty_async(ehci);
 	ehci_handle_intr_unlinks(ehci);
 	end_free_itds(ehci);
 

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);
 }

drivers/usb/host/ehci-timer.c

@@ -72,6 +72,7 @@ static unsigned event_delays_ns[] = {
 	1 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_POLL_DEAD */
 	1125 * NSEC_PER_USEC,	/* EHCI_HRTIMER_UNLINK_INTR */
 	2 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_FREE_ITDS */
+	6 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_ASYNC_UNLINKS */
 	10 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_IAA_WATCHDOG */
 	10 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_DISABLE_PERIODIC */
 	15 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_DISABLE_ASYNC */
@@ -347,6 +348,7 @@ static void (*event_handlers[])(struct ehci_hcd *) = {
 	ehci_handle_controller_death,	/* EHCI_HRTIMER_POLL_DEAD */
 	ehci_handle_intr_unlinks,	/* EHCI_HRTIMER_UNLINK_INTR */
 	end_free_itds,			/* EHCI_HRTIMER_FREE_ITDS */
+	unlink_empty_async,		/* EHCI_HRTIMER_ASYNC_UNLINKS */
 	ehci_iaa_watchdog,		/* EHCI_HRTIMER_IAA_WATCHDOG */
 	ehci_disable_PSE,		/* EHCI_HRTIMER_DISABLE_PERIODIC */
 	ehci_disable_ASE,		/* EHCI_HRTIMER_DISABLE_ASYNC */

drivers/usb/host/ehci.h

@@ -84,6 +84,7 @@ enum ehci_hrtimer_event {
 	EHCI_HRTIMER_POLL_DEAD,		/* Wait for dead controller to stop */
 	EHCI_HRTIMER_UNLINK_INTR,	/* Wait for interrupt QH unlink */
 	EHCI_HRTIMER_FREE_ITDS,		/* Wait for unused iTDs and siTDs */
+	EHCI_HRTIMER_ASYNC_UNLINKS,	/* Unlink empty async QHs */
 	EHCI_HRTIMER_IAA_WATCHDOG,	/* Handle lost IAA interrupts */
 	EHCI_HRTIMER_DISABLE_PERIODIC,	/* Wait to disable periodic sched */
 	EHCI_HRTIMER_DISABLE_ASYNC,	/* Wait to disable async sched */
@@ -123,6 +124,7 @@ struct ehci_hcd {			/* one per controller */
 	struct ehci_qh		*async_unlink_last;
 	struct ehci_qh		*async_iaa;
 	struct ehci_qh		*qh_scan_next;
+	unsigned		async_unlink_cycle;
 	unsigned		async_count;	/* async activity count */
 
 	/* periodic schedule support */
@@ -232,7 +234,6 @@ static inline struct usb_hcd *ehci_to_hcd (struct ehci_hcd *ehci)
 
 enum ehci_timer_action {
 	TIMER_IO_WATCHDOG,
-	TIMER_ASYNC_SHRINK,
 };
 
 static inline void
@@ -382,7 +383,6 @@ struct ehci_qh {
 	struct ehci_qtd		*dummy;
 	struct ehci_qh		*unlink_next;	/* next on unlink list */
 
-	unsigned long		unlink_time;
 	unsigned		unlink_cycle;
 	unsigned		stamp;