USB: EHCI: introduce high-res timer

This patch (as1572) begins the conversion of ehci-hcd over to using
high-resolution timers rather than old-fashioned low-resolution kernel
timers.  This reduces overhead caused by timer roundoff on systems
where HZ is smaller than 1000.  Also, the new timer framework
introduced here is much more logical and easily extended than the
ad-hoc approach ehci-hcd currently uses for timers.

An hrtimer structure is added to ehci_hcd, along with a bitflag array
and an array of ktime_t values, to keep track of which timing events
are pending and what their expiration times are.

Only the infrastructure for the timing operations is added in this
patch.  Later patches will add routines for handling each of the
various timing events the driver needs.  In some cases the new hrtimer
handlers will replace the existing handlers for ehci-hcd's kernel
timers; as this happens the old timers will be removed.  In other
cases the new timing events will replace busy-wait loops.

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

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index 9e8e82ecce58..070be83028d5 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -73,7 +73,23 @@ enum ehci_rh_state {
         EHCI_RH_STOPPING
 };
 
+/*
+ * Timer events, ordered by increasing delay length.
+ * Always update event_delays_ns[] and event_handlers[] (defined in
+ * ehci-timer.c) in parallel with this list.
+ */
+enum ehci_hrtimer_event {
+        EHCI_HRTIMER_NUM_EVENTS         /* Must come last */
+};
+#define EHCI_HRTIMER_NO_EVENT   99
+
 struct ehci_hcd {                       /* one per controller */
+        /* timing support */
+        enum ehci_hrtimer_event next_hrtimer_event;
+        unsigned                enabled_hrtimer_events;
+        ktime_t                 hr_timeouts[EHCI_HRTIMER_NUM_EVENTS];
+        struct hrtimer          hrtimer;
+
         /* glue to PCI and HCD framework */
         struct ehci_caps __iomem *caps;
         struct ehci_regs __iomem *regs;