USB: EHCI: use hrtimer for the periodic schedule

This patch (as1573) adds hrtimer support for managing ehci-hcd's
periodic schedule.  There are two issues to deal with.

First, the schedule's state (on or off) must not be changed until the
hardware status has caught up with the current command.  This is
handled by an hrtimer event that polls at 1-ms intervals to see when
the Periodic Schedule Status (PSS) flag matches the Periodic Schedule
Enable (PSE) value.

Second, the schedule should not be turned off as soon as it becomes
empty.  Turning the schedule on and off takes time, so we want to wait
until the schedule has been empty for a suitable period before turning
it off.  This is handled by an hrtimer event that gets set to expire
10 ms after the periodic schedule becomes empty.

The existing code polls (for up to 1125 us and with interrupts
disabled!) to check the status, and doesn't implement a delay before
turning off the schedule.  Furthermore, if the polling fails then the
driver decides that the controller has died.  This has caused problems
for several people; some controllers can take 10 ms or more to turn
off their periodic schedules.

This patch fixes these issues.  It also makes the "broken_periodic"
workaround unnecessary; there is no longer any danger of turning off
the periodic schedule after it has been on for less than 1 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

@@ -546,7 +546,7 @@ static void ehci_work (struct ehci_hcd *ehci)
 	 */
 	if (ehci->rh_state == EHCI_RH_RUNNING &&
 			(ehci->async->qh_next.ptr != NULL ||
-			 ehci->periodic_sched != 0))
+			 ehci->periodic_count != 0))
 		timer_action (ehci, TIMER_IO_WATCHDOG);
 }
 

drivers/usb/host/ehci-pci.c

@@ -104,10 +104,6 @@ static int ehci_pci_setup(struct usb_hcd *hcd)
 		break;
 	case PCI_VENDOR_ID_INTEL:
 		ehci->fs_i_thresh = 1;
-		if (pdev->device == 0x27cc) {
-			ehci->broken_periodic = 1;
-			ehci_info(ehci, "using broken periodic workaround\n");
-		}
 		if (pdev->device == PCI_DEVICE_ID_INTEL_CE4100_USB)
 			hcd->has_tt = 1;
 		break;

drivers/usb/host/ehci-sched.c

@@ -481,67 +481,26 @@ static int tt_no_collision (
 
 static int enable_periodic (struct ehci_hcd *ehci)
 {
-	int	status;
-
-	if (ehci->periodic_sched++)
+	if (ehci->periodic_count++)
 		return 0;
 
-	/* did clearing PSE did take effect yet?
-	 * takes effect only at frame boundaries...
-	 */
-	status = handshake_on_error_set_halt(ehci, &ehci->regs->status,
-					     STS_PSS, 0, 9 * 125);
-	if (status) {
-		usb_hc_died(ehci_to_hcd(ehci));
-		return status;
-	}
-
-	ehci->command |= CMD_PSE;
-	ehci_writel(ehci, ehci->command, &ehci->regs->command);
-	/* posted write ... PSS happens later */
+	/* Stop waiting to turn off the periodic schedule */
+	ehci->enabled_hrtimer_events &= ~BIT(EHCI_HRTIMER_DISABLE_PERIODIC);
 
-	/* make sure ehci_work scans these */
-	ehci->next_uframe = ehci_read_frame_index(ehci)
-		% (ehci->periodic_size << 3);
-	if (unlikely(ehci->broken_periodic))
-		ehci->last_periodic_enable = ktime_get_real();
+	/* Don't start the schedule until PSS is 0 */
+	ehci_poll_PSS(ehci);
 	return 0;
 }
 
 static int disable_periodic (struct ehci_hcd *ehci)
 {
-	int	status;
-
-	if (--ehci->periodic_sched)
+	if (--ehci->periodic_count)
 		return 0;
 
-	if (unlikely(ehci->broken_periodic)) {
-		/* delay experimentally determined */
-		ktime_t safe = ktime_add_us(ehci->last_periodic_enable, 1000);
-		ktime_t now = ktime_get_real();
-		s64 delay = ktime_us_delta(safe, now);
-
-		if (unlikely(delay > 0))
-			udelay(delay);
-	}
-
-	/* did setting PSE not take effect yet?
-	 * takes effect only at frame boundaries...
-	 */
-	status = handshake_on_error_set_halt(ehci, &ehci->regs->status,
-					     STS_PSS, STS_PSS, 9 * 125);
-	if (status) {
-		usb_hc_died(ehci_to_hcd(ehci));
-		return status;
-	}
-
-	ehci->command &= ~CMD_PSE;
-	ehci_writel(ehci, ehci->command, &ehci->regs->command);
-	/* posted write ... */
-
-	free_cached_lists(ehci);
+	ehci->next_uframe = -1;		/* the periodic schedule is empty */
 
-	ehci->next_uframe = -1;
+	/* Don't turn off the schedule until PSS is 1 */
+	ehci_poll_PSS(ehci);
 	return 0;
 }
 
@@ -650,8 +609,7 @@ static int qh_unlink_periodic(struct ehci_hcd *ehci, struct ehci_qh *qh)
 	qh->qh_state = QH_STATE_UNLINK;
 	qh->qh_next.ptr = NULL;
 
-	/* maybe turn off periodic schedule */
-	return disable_periodic(ehci);
+	return 0;
 }
 
 static void intr_deschedule (struct ehci_hcd *ehci, struct ehci_qh *qh)
@@ -706,6 +664,9 @@ static void intr_deschedule (struct ehci_hcd *ehci, struct ehci_qh *qh)
 			ehci_err(ehci, "can't reschedule qh %p, err %d\n",
 					qh, rc);
 	}
+
+	/* maybe turn off periodic schedule */
+	disable_periodic(ehci);
 }
 
 /*-------------------------------------------------------------------------*/
@@ -2447,7 +2408,7 @@ scan_periodic (struct ehci_hcd *ehci)
 
 			/* assume completion callbacks modify the queue */
 			if (unlikely (modified)) {
-				if (likely(ehci->periodic_sched > 0))
+				if (likely(ehci->periodic_count > 0))
 					goto restart;
 				/* short-circuit this scan */
 				now_uframe = clock;
@@ -2476,7 +2437,7 @@ scan_periodic (struct ehci_hcd *ehci)
 			unsigned	now;
 
 			if (ehci->rh_state < EHCI_RH_RUNNING
-					|| ehci->periodic_sched == 0)
+					|| ehci->periodic_count == 0)
 				break;
 			ehci->next_uframe = now_uframe;
 			now = ehci_read_frame_index(ehci) & (mod - 1);

drivers/usb/host/ehci-timer.c

@@ -16,6 +16,28 @@
 
 /*-------------------------------------------------------------------------*/
 
+/* Set a bit in the USBCMD register */
+static void ehci_set_command_bit(struct ehci_hcd *ehci, u32 bit)
+{
+	ehci->command |= bit;
+	ehci_writel(ehci, ehci->command, &ehci->regs->command);
+
+	/* unblock posted write */
+	ehci_readl(ehci, &ehci->regs->command);
+}
+
+/* Clear a bit in the USBCMD register */
+static void ehci_clear_command_bit(struct ehci_hcd *ehci, u32 bit)
+{
+	ehci->command &= ~bit;
+	ehci_writel(ehci, ehci->command, &ehci->regs->command);
+
+	/* unblock posted write */
+	ehci_readl(ehci, &ehci->regs->command);
+}
+
+/*-------------------------------------------------------------------------*/
+
 /*
  * EHCI timer support...  Now using hrtimers.
  *
@@ -45,6 +67,8 @@
  * the event types indexed by enum ehci_hrtimer_event in ehci.h.
  */
 static unsigned event_delays_ns[] = {
+	1 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_POLL_PSS */
+	10 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_DISABLE_PERIODIC */
 };
 
 /* Enable a pending hrtimer event */
@@ -67,12 +91,68 @@ static void ehci_enable_event(struct ehci_hcd *ehci, unsigned event,
 }
 
 
+/* Poll the STS_PSS status bit; see when it agrees with CMD_PSE */
+static void ehci_poll_PSS(struct ehci_hcd *ehci)
+{
+	unsigned	actual, want;
+
+	/* Don't do anything if the controller isn't running (e.g., died) */
+	if (ehci->rh_state != EHCI_RH_RUNNING)
+		return;
+
+	want = (ehci->command & CMD_PSE) ? STS_PSS : 0;
+	actual = ehci_readl(ehci, &ehci->regs->status) & STS_PSS;
+
+	if (want != actual) {
+
+		/* Poll again later, but give up after about 20 ms */
+		if (ehci->PSS_poll_count++ < 20) {
+			ehci_enable_event(ehci, EHCI_HRTIMER_POLL_PSS, true);
+			return;
+		}
+		ehci_warn(ehci, "Waited too long for the periodic schedule status, giving up\n");
+	}
+	ehci->PSS_poll_count = 0;
+
+	/* The status is up-to-date; restart or stop the schedule as needed */
+	if (want == 0) {	/* Stopped */
+		free_cached_lists(ehci);
+		if (ehci->periodic_count > 0) {
+
+			/* make sure ehci_work scans these */
+			ehci->next_uframe = ehci_read_frame_index(ehci)
+					& ((ehci->periodic_size << 3) - 1);
+			ehci_set_command_bit(ehci, CMD_PSE);
+		}
+
+	} else {		/* Running */
+		if (ehci->periodic_count == 0) {
+
+			/* Turn off the schedule after a while */
+			ehci_enable_event(ehci, EHCI_HRTIMER_DISABLE_PERIODIC,
+					true);
+		}
+	}
+}
+
+/* Turn off the periodic schedule after a brief delay */
+static void ehci_disable_PSE(struct ehci_hcd *ehci)
+{
+	ehci_clear_command_bit(ehci, CMD_PSE);
+
+	/* Poll to see when it actually stops */
+	ehci_enable_event(ehci, EHCI_HRTIMER_POLL_PSS, true);
+}
+
+
 /*
  * Handler functions for the hrtimer event types.
  * Keep this array in the same order as the event types indexed by
  * enum ehci_hrtimer_event in ehci.h.
  */
 static void (*event_handlers[])(struct ehci_hcd *) = {
+	ehci_poll_PSS,			/* EHCI_HRTIMER_POLL_PSS */
+	ehci_disable_PSE,		/* EHCI_HRTIMER_DISABLE_PERIODIC */
 };
 
 static enum hrtimer_restart ehci_hrtimer_func(struct hrtimer *t)

drivers/usb/host/ehci.h

@@ -79,6 +79,8 @@ enum ehci_rh_state {
  * ehci-timer.c) in parallel with this list.
  */
 enum ehci_hrtimer_event {
+	EHCI_HRTIMER_POLL_PSS,		/* Poll for periodic schedule off */
+	EHCI_HRTIMER_DISABLE_PERIODIC,	/* Wait to disable periodic sched */
 	EHCI_HRTIMER_NUM_EVENTS		/* Must come last */
 };
 #define EHCI_HRTIMER_NO_EVENT	99
@@ -90,6 +92,8 @@ struct ehci_hcd {			/* one per controller */
 	ktime_t			hr_timeouts[EHCI_HRTIMER_NUM_EVENTS];
 	struct hrtimer		hrtimer;
 
+	int			PSS_poll_count;
+
 	/* glue to PCI and HCD framework */
 	struct ehci_caps __iomem *caps;
 	struct ehci_regs __iomem *regs;
@@ -116,7 +120,7 @@ struct ehci_hcd {			/* one per controller */
 
 	union ehci_shadow	*pshadow;	/* mirror hw periodic table */
 	int			next_uframe;	/* scan periodic, start here */
-	unsigned		periodic_sched;	/* periodic activity count */
+	unsigned		periodic_count;	/* periodic activity count */
 	unsigned		uframe_periodic_max; /* max periodic time per uframe */
 
 
@@ -165,7 +169,6 @@ struct ehci_hcd {			/* one per controller */
 	unsigned		big_endian_capbase:1;
 	unsigned		has_amcc_usb23:1;
 	unsigned		need_io_watchdog:1;
-	unsigned		broken_periodic:1;
 	unsigned		amd_pll_fix:1;
 	unsigned		fs_i_thresh:1;	/* Intel iso scheduling */
 	unsigned		use_dummy_qh:1;	/* AMD Frame List table quirk*/