USB: EHCI: use hrtimer for async schedule

This patch (as1576) adds hrtimer support for managing ehci-hcd's
async schedule.  Just as with the earlier change to the periodic
schedule management, two new hrtimer events take care of everything.

One event polls at 1-ms intervals to see when the Asynchronous
Schedule Status (ASS) flag matches the Asynchronous Schedule Enable
(ASE) value; the schedule's state must not be changed until it does.
The other event delays for 15 ms after the async schedule becomes
empty before turning it off.

The new events replace a busy-wait poll and a kernel timer usage.
They also replace the rather illogical method currently used for
indicating the async schedule should be turned off: attempting to
unlink the dedicated QH at the head of the async list.

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

drivers/usb/host/ehci-hcd.c

@@ -95,7 +95,6 @@ static const char	hcd_name [] = "ehci_hcd";
 
 #define EHCI_IAA_MSECS		10		/* arbitrary */
 #define EHCI_IO_JIFFIES		(HZ/10)		/* io watchdog > irq_thresh */
-#define EHCI_ASYNC_JIFFIES	(HZ/20)		/* async idle timeout */
 #define EHCI_SHRINK_JIFFIES	(DIV_ROUND_UP(HZ, 200) + 1)
 						/* 5-ms async qh unlink delay */
 
@@ -137,7 +136,7 @@ timer_action(struct ehci_hcd *ehci, enum ehci_timer_action action)
 	 * SHRINK were pending, OFF would never be requested.
 	 */
 	if (timer_pending(&ehci->watchdog)
-			&& ((BIT(TIMER_ASYNC_SHRINK) | BIT(TIMER_ASYNC_OFF))
+			&& (BIT(TIMER_ASYNC_SHRINK)
 				& ehci->actions))
 		return;
 
@@ -150,9 +149,6 @@ timer_action(struct ehci_hcd *ehci, enum ehci_timer_action action)
 				return;
 			t = EHCI_IO_JIFFIES;
 			break;
-		case TIMER_ASYNC_OFF:
-			t = EHCI_ASYNC_JIFFIES;
-			break;
 		/* case TIMER_ASYNC_SHRINK: */
 		default:
 			t = EHCI_SHRINK_JIFFIES;
@@ -376,10 +372,6 @@ static void ehci_watchdog(unsigned long param)
 
 	spin_lock_irqsave(&ehci->lock, flags);
 
-	/* stop async processing after it's idled a bit */
-	if (test_bit (TIMER_ASYNC_OFF, &ehci->actions))
-		start_unlink_async (ehci, ehci->async);
-
 	/* ehci could run by timer, without IRQs ... */
 	ehci_work (ehci);
 
@@ -470,7 +462,8 @@ static void ehci_work (struct ehci_hcd *ehci)
 	if (ehci->scanning)
 		return;
 	ehci->scanning = 1;
-	scan_async (ehci);
+	if (ehci->async_count)
+		scan_async(ehci);
 	if (ehci->next_uframe != -1)
 		scan_periodic (ehci);
 	ehci->scanning = 0;

drivers/usb/host/ehci-q.c

@@ -964,6 +964,30 @@ done:
 
 /*-------------------------------------------------------------------------*/
 
+static void enable_async(struct ehci_hcd *ehci)
+{
+	if (ehci->async_count++)
+		return;
+
+	/* Stop waiting to turn off the async schedule */
+	ehci->enabled_hrtimer_events &= ~BIT(EHCI_HRTIMER_DISABLE_ASYNC);
+
+	/* Don't start the schedule until ASS is 0 */
+	ehci_poll_ASS(ehci);
+}
+
+static void disable_async(struct ehci_hcd *ehci)
+{
+	if (--ehci->async_count)
+		return;
+
+	/* The async schedule and async_unlink list are supposed to be empty */
+	WARN_ON(ehci->async->qh_next.qh || ehci->async_unlink);
+
+	/* Don't turn off the schedule until ASS is 1 */
+	ehci_poll_ASS(ehci);
+}
+
 /* move qh (and its qtds) onto async queue; maybe enable queue.  */
 
 static void qh_link_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
@@ -977,24 +1001,11 @@ static void qh_link_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
 
 	WARN_ON(qh->qh_state != QH_STATE_IDLE);
 
-	/* (re)start the async schedule? */
-	head = ehci->async;
-	timer_action_done (ehci, TIMER_ASYNC_OFF);
-	if (!head->qh_next.qh) {
-		if (!(ehci->command & CMD_ASE)) {
-			/* in case a clear of CMD_ASE didn't take yet */
-			(void)handshake(ehci, &ehci->regs->status,
-					STS_ASS, 0, 150);
-			ehci->command |= CMD_ASE;
-			ehci_writel(ehci, ehci->command, &ehci->regs->command);
-			/* posted write need not be known to HC yet ... */
-		}
-	}
-
 	/* clear halt and/or toggle; and maybe recover from silicon quirk */
 	qh_refresh(ehci, qh);
 
 	/* splice right after start */
+	head = ehci->async;
 	qh->qh_next = head->qh_next;
 	qh->hw->hw_next = head->hw->hw_next;
 	wmb ();
@@ -1005,6 +1016,8 @@ static void qh_link_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
 	qh->xacterrs = 0;
 	qh->qh_state = QH_STATE_LINKED;
 	/* qtd completions reported later by interrupt */
+
+	enable_async(ehci);
 }
 
 /*-------------------------------------------------------------------------*/
@@ -1173,16 +1186,10 @@ static void end_unlink_async (struct ehci_hcd *ehci)
 
 	qh_completions (ehci, qh);
 
-	if (!list_empty(&qh->qtd_list) && ehci->rh_state == EHCI_RH_RUNNING) {
+	if (!list_empty(&qh->qtd_list) && ehci->rh_state == EHCI_RH_RUNNING)
 		qh_link_async (ehci, qh);
-	} else {
-		/* it's not free to turn the async schedule on/off; leave it
-		 * active but idle for a while once it empties.
-		 */
-		if (ehci->rh_state == EHCI_RH_RUNNING
-				&& ehci->async->qh_next.qh == NULL)
-			timer_action (ehci, TIMER_ASYNC_OFF);
-	}
+
+	disable_async(ehci);
 
 	if (next) {
 		ehci->async_unlink = NULL;
@@ -1210,21 +1217,6 @@ static void start_unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
 		BUG ();
 #endif
 
-	/* stop async schedule right now? */
-	if (unlikely (qh == ehci->async)) {
-		/* can't get here without STS_ASS set */
-		if (ehci->rh_state != EHCI_RH_HALTED
-				&& !ehci->async_unlink) {
-			/* ... and CMD_IAAD clear */
-			ehci->command &= ~CMD_ASE;
-			ehci_writel(ehci, ehci->command, &ehci->regs->command);
-			wmb ();
-			// handshake later, if we need to
-			timer_action_done (ehci, TIMER_ASYNC_OFF);
-		}
-		return;
-	}
-
 	qh->qh_state = QH_STATE_UNLINK;
 	ehci->async_unlink = qh;
 	if (!qh->unlink_next)

drivers/usb/host/ehci-timer.c

@@ -67,8 +67,10 @@ static void ehci_clear_command_bit(struct ehci_hcd *ehci, u32 bit)
  * the event types indexed by enum ehci_hrtimer_event in ehci.h.
  */
 static unsigned event_delays_ns[] = {
+	1 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_POLL_ASS */
 	1 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_POLL_PSS */
 	10 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_DISABLE_PERIODIC */
+	15 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_DISABLE_ASYNC */
 };
 
 /* Enable a pending hrtimer event */
@@ -91,6 +93,51 @@ static void ehci_enable_event(struct ehci_hcd *ehci, unsigned event,
 }
 
 
+/* Poll the STS_ASS status bit; see when it agrees with CMD_ASE */
+static void ehci_poll_ASS(struct ehci_hcd *ehci)
+{
+	unsigned	actual, want;
+
+	/* Don't enable anything if the controller isn't running (e.g., died) */
+	if (ehci->rh_state != EHCI_RH_RUNNING)
+		return;
+
+	want = (ehci->command & CMD_ASE) ? STS_ASS : 0;
+	actual = ehci_readl(ehci, &ehci->regs->status) & STS_ASS;
+
+	if (want != actual) {
+
+		/* Poll again later, but give up after about 20 ms */
+		if (ehci->ASS_poll_count++ < 20) {
+			ehci_enable_event(ehci, EHCI_HRTIMER_POLL_ASS, true);
+			return;
+		}
+		ehci_warn(ehci, "Waited too long for the async schedule status, giving up\n");
+	}
+	ehci->ASS_poll_count = 0;
+
+	/* The status is up-to-date; restart or stop the schedule as needed */
+	if (want == 0) {	/* Stopped */
+		if (ehci->async_count > 0)
+			ehci_set_command_bit(ehci, CMD_ASE);
+
+	} else {		/* Running */
+		if (ehci->async_count == 0) {
+
+			/* Turn off the schedule after a while */
+			ehci_enable_event(ehci, EHCI_HRTIMER_DISABLE_ASYNC,
+					true);
+		}
+	}
+}
+
+/* Turn off the async schedule after a brief delay */
+static void ehci_disable_ASE(struct ehci_hcd *ehci)
+{
+	ehci_clear_command_bit(ehci, CMD_ASE);
+}
+
+
 /* Poll the STS_PSS status bit; see when it agrees with CMD_PSE */
 static void ehci_poll_PSS(struct ehci_hcd *ehci)
 {
@@ -151,8 +198,10 @@ static void ehci_disable_PSE(struct ehci_hcd *ehci)
  * enum ehci_hrtimer_event in ehci.h.
  */
 static void (*event_handlers[])(struct ehci_hcd *) = {
+	ehci_poll_ASS,			/* EHCI_HRTIMER_POLL_ASS */
 	ehci_poll_PSS,			/* EHCI_HRTIMER_POLL_PSS */
 	ehci_disable_PSE,		/* EHCI_HRTIMER_DISABLE_PERIODIC */
+	ehci_disable_ASE,		/* EHCI_HRTIMER_DISABLE_ASYNC */
 };
 
 static enum hrtimer_restart ehci_hrtimer_func(struct hrtimer *t)

drivers/usb/host/ehci.h

@@ -79,8 +79,10 @@ enum ehci_rh_state {
  * ehci-timer.c) in parallel with this list.
  */
 enum ehci_hrtimer_event {
+	EHCI_HRTIMER_POLL_ASS,		/* Poll for async schedule off */
 	EHCI_HRTIMER_POLL_PSS,		/* Poll for periodic schedule off */
 	EHCI_HRTIMER_DISABLE_PERIODIC,	/* Wait to disable periodic sched */
+	EHCI_HRTIMER_DISABLE_ASYNC,	/* Wait to disable async sched */
 	EHCI_HRTIMER_NUM_EVENTS		/* Must come last */
 };
 #define EHCI_HRTIMER_NO_EVENT	99
@@ -93,6 +95,7 @@ struct ehci_hcd {			/* one per controller */
 	struct hrtimer		hrtimer;
 
 	int			PSS_poll_count;
+	int			ASS_poll_count;
 
 	/* glue to PCI and HCD framework */
 	struct ehci_caps __iomem *caps;
@@ -110,6 +113,7 @@ struct ehci_hcd {			/* one per controller */
 	struct ehci_qh		*async_unlink_last;
 	struct ehci_qh		*qh_scan_next;
 	unsigned		scanning : 1;
+	unsigned		async_count;	/* async activity count */
 
 	/* periodic schedule support */
 #define	DEFAULT_I_TDPS		1024		/* some HCs can do less */
@@ -229,7 +233,6 @@ static inline void iaa_watchdog_done(struct ehci_hcd *ehci)
 enum ehci_timer_action {
 	TIMER_IO_WATCHDOG,
 	TIMER_ASYNC_SHRINK,
-	TIMER_ASYNC_OFF,
 };
 
 static inline void