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>

1 files changed, 21 insertions, 0 deletions

diff --git a/drivers/usb/host/ehci-timer.c b/drivers/usb/host/ehci-timer.c
index 0e28bae78d18..eb896a2c8f2e 100644
--- a/drivers/usb/host/ehci-timer.c
+++ b/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)