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>

1 files changed, 80 insertions, 0 deletions

diff --git a/drivers/usb/host/ehci-timer.c b/drivers/usb/host/ehci-timer.c
index f6279e2..ecd3296 100644
--- a/drivers/usb/host/ehci-timer.c
+++ b/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)