USB: EHCI: use hrtimer for the I/O watchdog

This patch (as1586) replaces the kernel timer used by ehci-hcd as an
I/O watchdog with an hrtimer event.

Unlike in the current code, the watchdog event is now always enabled
whenever any isochronous URBs are active.  This will prevent bugs
caused by the periodic schedule wrapping around with no completion
interrupts; the watchdog handler is guaranteed to scan the isochronous
transfers at least once during each iteration of the schedule.  The
extra overhead will be negligible: one timer interrupt every 100 ms.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-hcd.c

@@ -93,8 +93,6 @@ 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 */
-
 /* Initial IRQ latency:  faster than hw default */
 static int log2_irq_thresh = 0;		// 0 to 6
 module_param (log2_irq_thresh, int, S_IRUGO);
@@ -125,25 +123,6 @@ 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)
-{
-	if (!test_and_set_bit(action, &ehci->actions)) {
-		unsigned long t;
-
-		switch (action) {
-		case TIMER_IO_WATCHDOG:
-			if (!ehci->need_io_watchdog)
-				return;
-			t = EHCI_IO_JIFFIES;
-			break;
-		}
-		mod_timer(&ehci->watchdog, t + jiffies);
-	}
-}
-
-/*-------------------------------------------------------------------------*/
-
 /*
  * handshake - spin reading hc until handshake completes or fails
  * @ptr: address of hc register to be read
@@ -307,19 +286,6 @@ static void end_unlink_intr(struct ehci_hcd *ehci, struct ehci_qh *qh);
 
 /*-------------------------------------------------------------------------*/
 
-static void ehci_watchdog(unsigned long param)
-{
-	struct ehci_hcd		*ehci = (struct ehci_hcd *) param;
-	unsigned long		flags;
-
-	spin_lock_irqsave(&ehci->lock, flags);
-
-	/* ehci could run by timer, without IRQs ... */
-	ehci_work (ehci);
-
-	spin_unlock_irqrestore (&ehci->lock, flags);
-}
-
 /* On some systems, leaving remote wakeup enabled prevents system shutdown.
  * The firmware seems to think that powering off is a wakeup event!
  * This routine turns off remote wakeup and everything else, on all ports.
@@ -357,8 +323,6 @@ static void ehci_shutdown(struct usb_hcd *hcd)
 {
 	struct ehci_hcd	*ehci = hcd_to_ehci(hcd);
 
-	del_timer_sync(&ehci->watchdog);
-
 	spin_lock_irq(&ehci->lock);
 	ehci->rh_state = EHCI_RH_STOPPING;
 	ehci_silence_controller(ehci);
@@ -394,8 +358,6 @@ static void ehci_port_power (struct ehci_hcd *ehci, int is_on)
  */
 static void ehci_work (struct ehci_hcd *ehci)
 {
-	timer_action_done (ehci, TIMER_IO_WATCHDOG);
-
 	/* another CPU may drop ehci->lock during a schedule scan while
 	 * it reports urb completions.  this flag guards against bogus
 	 * attempts at re-entrant schedule scanning.
@@ -422,10 +384,7 @@ static void ehci_work (struct ehci_hcd *ehci)
 	 * misplace IRQs, and should let us run completely without IRQs.
 	 * such lossage has been observed on both VT6202 and VT8235.
 	 */
-	if (ehci->rh_state == EHCI_RH_RUNNING &&
-			(ehci->async->qh_next.ptr != NULL ||
-			 ehci->periodic_count != 0))
-		timer_action (ehci, TIMER_IO_WATCHDOG);
+	turn_on_io_watchdog(ehci);
 }
 
 /*
@@ -438,7 +397,6 @@ static void ehci_stop (struct usb_hcd *hcd)
 	ehci_dbg (ehci, "stop\n");
 
 	/* no more interrupts ... */
-	del_timer_sync (&ehci->watchdog);
 
 	spin_lock_irq(&ehci->lock);
 	ehci->enabled_hrtimer_events = 0;
@@ -490,9 +448,6 @@ static int ehci_init(struct usb_hcd *hcd)
 	 * keep io watchdog by default, those good HCDs could turn off it later
 	 */
 	ehci->need_io_watchdog = 1;
-	init_timer(&ehci->watchdog);
-	ehci->watchdog.function = ehci_watchdog;
-	ehci->watchdog.data = (unsigned long) ehci;
 
 	hrtimer_init(&ehci->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
 	ehci->hrtimer.function = ehci_hrtimer_func;

drivers/usb/host/ehci-hub.c

@@ -208,7 +208,6 @@ static int ehci_bus_suspend (struct usb_hcd *hcd)
 
 	if (time_before (jiffies, ehci->next_statechange))
 		msleep(5);
-	del_timer_sync(&ehci->watchdog);
 
 	spin_lock_irq (&ehci->lock);
 
@@ -316,10 +315,6 @@ static int ehci_bus_suspend (struct usb_hcd *hcd)
 	ehci->next_hrtimer_event = EHCI_HRTIMER_NO_EVENT;
 	spin_unlock_irq (&ehci->lock);
 
-	/* ehci_work() may have re-enabled the watchdog timer, which we do not
-	 * want, and so we must delete any pending watchdog timer events.
-	 */
-	del_timer_sync(&ehci->watchdog);
 	hrtimer_cancel(&ehci->hrtimer);
 	return 0;
 }

drivers/usb/host/ehci-q.c

@@ -970,6 +970,7 @@ static void enable_async(struct ehci_hcd *ehci)
 
 	/* Don't start the schedule until ASS is 0 */
 	ehci_poll_ASS(ehci);
+	turn_on_io_watchdog(ehci);
 }
 
 static void disable_async(struct ehci_hcd *ehci)

drivers/usb/host/ehci-sched.c

@@ -489,6 +489,7 @@ static void enable_periodic(struct ehci_hcd *ehci)
 
 	/* Don't start the schedule until PSS is 0 */
 	ehci_poll_PSS(ehci);
+	turn_on_io_watchdog(ehci);
 }
 
 static void disable_periodic(struct ehci_hcd *ehci)
@@ -1649,7 +1650,6 @@ static void itd_link_urb(
 	iso_sched_free (stream, iso_sched);
 	urb->hcpriv = NULL;
 
-	timer_action (ehci, TIMER_IO_WATCHDOG);
 	++ehci->isoc_count;
 	enable_periodic(ehci);
 }
@@ -2052,7 +2052,6 @@ static void sitd_link_urb(
 	iso_sched_free (stream, sched);
 	urb->hcpriv = NULL;
 
-	timer_action (ehci, TIMER_IO_WATCHDOG);
 	++ehci->isoc_count;
 	enable_periodic(ehci);
 }

drivers/usb/host/ehci-timer.c

@@ -76,6 +76,7 @@ static unsigned event_delays_ns[] = {
 	10 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_IAA_WATCHDOG */
 	10 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_DISABLE_PERIODIC */
 	15 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_DISABLE_ASYNC */
+	100 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_IO_WATCHDOG */
 };
 
 /* Enable a pending hrtimer event */
@@ -332,6 +333,25 @@ static void ehci_iaa_watchdog(struct ehci_hcd *ehci)
 }
 
 
+/* Enable the I/O watchdog, if appropriate */
+static void turn_on_io_watchdog(struct ehci_hcd *ehci)
+{
+	/* Not needed if the controller isn't running or it's already enabled */
+	if (ehci->rh_state != EHCI_RH_RUNNING ||
+			(ehci->enabled_hrtimer_events &
+				BIT(EHCI_HRTIMER_IO_WATCHDOG)))
+		return;
+
+	/*
+	 * Isochronous transfers always need the watchdog.
+	 * For other sorts we use it only if the flag is set.
+	 */
+	if (ehci->isoc_count > 0 || (ehci->need_io_watchdog &&
+			ehci->async_count + ehci->intr_count > 0))
+		ehci_enable_event(ehci, EHCI_HRTIMER_IO_WATCHDOG, true);
+}
+
+
 /*
  * Handler functions for the hrtimer event types.
  * Keep this array in the same order as the event types indexed by
@@ -347,6 +367,7 @@ static void (*event_handlers[])(struct ehci_hcd *) = {
 	ehci_iaa_watchdog,		/* EHCI_HRTIMER_IAA_WATCHDOG */
 	ehci_disable_PSE,		/* EHCI_HRTIMER_DISABLE_PERIODIC */
 	ehci_disable_ASE,		/* EHCI_HRTIMER_DISABLE_ASYNC */
+	ehci_work,			/* EHCI_HRTIMER_IO_WATCHDOG */
 };
 
 static enum hrtimer_restart ehci_hrtimer_func(struct hrtimer *t)

drivers/usb/host/ehci.h

@@ -88,6 +88,7 @@ enum ehci_hrtimer_event {
 	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 */
+	EHCI_HRTIMER_IO_WATCHDOG,	/* Check for missing IRQs */
 	EHCI_HRTIMER_NUM_EVENTS		/* Must come last */
 };
 #define EHCI_HRTIMER_NO_EVENT	99
@@ -177,8 +178,6 @@ struct ehci_hcd {			/* one per controller */
 	struct dma_pool		*itd_pool;	/* itd per iso urb */
 	struct dma_pool		*sitd_pool;	/* sitd per split iso urb */
 
-	struct timer_list	watchdog;
-	unsigned long		actions;
 	unsigned		random_frame;
 	unsigned long		next_statechange;
 	ktime_t			last_periodic_enable;
@@ -235,16 +234,6 @@ static inline struct usb_hcd *ehci_to_hcd (struct ehci_hcd *ehci)
 	return container_of ((void *) ehci, struct usb_hcd, hcd_priv);
 }
 
-enum ehci_timer_action {
-	TIMER_IO_WATCHDOG,
-};
-
-static inline void
-timer_action_done (struct ehci_hcd *ehci, enum ehci_timer_action action)
-{
-	clear_bit (action, &ehci->actions);
-}
-
 /*-------------------------------------------------------------------------*/
 
 #include <linux/usb/ehci_def.h>