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>

drivers/usb/host/ehci-hcd.c

@@ -30,8 +30,7 @@
 #include <linux/vmalloc.h>
 #include <linux/errno.h>
 #include <linux/init.h>
-#include <linux/timer.h>
-#include <linux/ktime.h>
+#include <linux/hrtimer.h>
 #include <linux/list.h>
 #include <linux/interrupt.h>
 #include <linux/usb.h>
@@ -380,6 +379,7 @@ static void ehci_quiesce (struct ehci_hcd *ehci)
 static void end_unlink_async(struct ehci_hcd *ehci);
 static void ehci_work(struct ehci_hcd *ehci);
 
+#include "ehci-timer.c"
 #include "ehci-hub.c"
 #include "ehci-lpm.c"
 #include "ehci-mem.c"
@@ -494,7 +494,10 @@ static void ehci_shutdown(struct usb_hcd *hcd)
 	spin_lock_irq(&ehci->lock);
 	ehci->rh_state = EHCI_RH_STOPPING;
 	ehci_silence_controller(ehci);
+	ehci->enabled_hrtimer_events = 0;
 	spin_unlock_irq(&ehci->lock);
+
+	hrtimer_cancel(&ehci->hrtimer);
 }
 
 static void ehci_port_power (struct ehci_hcd *ehci, int is_on)
@@ -561,12 +564,14 @@ static void ehci_stop (struct usb_hcd *hcd)
 	del_timer_sync(&ehci->iaa_watchdog);
 
 	spin_lock_irq(&ehci->lock);
+	ehci->enabled_hrtimer_events = 0;
 	ehci_quiesce(ehci);
 
 	ehci_silence_controller(ehci);
 	ehci_reset (ehci);
 	spin_unlock_irq(&ehci->lock);
 
+	hrtimer_cancel(&ehci->hrtimer);
 	remove_sysfs_files(ehci);
 	remove_debug_files (ehci);
 
@@ -615,6 +620,10 @@ static int ehci_init(struct usb_hcd *hcd)
 	ehci->iaa_watchdog.function = ehci_iaa_watchdog;
 	ehci->iaa_watchdog.data = (unsigned long) ehci;
 
+	hrtimer_init(&ehci->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+	ehci->hrtimer.function = ehci_hrtimer_func;
+	ehci->next_hrtimer_event = EHCI_HRTIMER_NO_EVENT;
+
 	hcc_params = ehci_readl(ehci, &ehci->caps->hcc_params);
 
 	/*
@@ -954,6 +963,8 @@ static irqreturn_t ehci_irq (struct usb_hcd *hcd)
 		dbg_status(ehci, "fatal", status);
 		ehci_halt(ehci);
 dead:
+		ehci->enabled_hrtimer_events = 0;
+		hrtimer_try_to_cancel(&ehci->hrtimer);
 		ehci_reset(ehci);
 		ehci_writel(ehci, 0, &ehci->regs->configured_flag);
 		usb_hc_died(hcd);

drivers/usb/host/ehci-hub.c

@@ -311,12 +311,15 @@ static int ehci_bus_suspend (struct usb_hcd *hcd)
 	ehci_readl(ehci, &ehci->regs->intr_enable);
 
 	ehci->next_statechange = jiffies + msecs_to_jiffies(10);
+	ehci->enabled_hrtimer_events = 0;
+	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-timer.c

@@ -0,0 +1,106 @@
+/*
+ * Copyright (C) 2012 by Alan Stern
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+
+/* This file is part of ehci-hcd.c */
+
+/*-------------------------------------------------------------------------*/
+
+/*
+ * EHCI timer support...  Now using hrtimers.
+ *
+ * Lots of different events are triggered from ehci->hrtimer.  Whenever
+ * the timer routine runs, it checks each possible event; events that are
+ * currently enabled and whose expiration time has passed get handled.
+ * The set of enabled events is stored as a collection of bitflags in
+ * ehci->enabled_hrtimer_events, and they are numbered in order of
+ * increasing delay values (ranging between 1 ms and 100 ms).
+ *
+ * Rather than implementing a sorted list or tree of all pending events,
+ * we keep track only of the lowest-numbered pending event, in
+ * ehci->next_hrtimer_event.  Whenever ehci->hrtimer gets restarted, its
+ * expiration time is set to the timeout value for this event.
+ *
+ * As a result, events might not get handled right away; the actual delay
+ * could be anywhere up to twice the requested delay.  This doesn't
+ * matter, because none of the events are especially time-critical.  The
+ * ones that matter most all have a delay of 1 ms, so they will be
+ * handled after 2 ms at most, which is okay.  In addition to this, we
+ * allow for an expiration range of 1 ms.
+ */
+
+/*
+ * Delay lengths for the hrtimer event types.
+ * Keep this list sorted by delay length, in the same order as
+ * the event types indexed by enum ehci_hrtimer_event in ehci.h.
+ */
+static unsigned event_delays_ns[] = {
+};
+
+/* Enable a pending hrtimer event */
+static void ehci_enable_event(struct ehci_hcd *ehci, unsigned event,
+		bool resched)
+{
+	ktime_t		*timeout = &ehci->hr_timeouts[event];
+
+	if (resched)
+		*timeout = ktime_add(ktime_get(),
+				ktime_set(0, event_delays_ns[event]));
+	ehci->enabled_hrtimer_events |= (1 << event);
+
+	/* Track only the lowest-numbered pending event */
+	if (event < ehci->next_hrtimer_event) {
+		ehci->next_hrtimer_event = event;
+		hrtimer_start_range_ns(&ehci->hrtimer, *timeout,
+				NSEC_PER_MSEC, HRTIMER_MODE_ABS);
+	}
+}
+
+
+/*
+ * 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 *) = {
+};
+
+static enum hrtimer_restart ehci_hrtimer_func(struct hrtimer *t)
+{
+	struct ehci_hcd	*ehci = container_of(t, struct ehci_hcd, hrtimer);
+	ktime_t		now;
+	unsigned long	events;
+	unsigned long	flags;
+	unsigned	e;
+
+	spin_lock_irqsave(&ehci->lock, flags);
+
+	events = ehci->enabled_hrtimer_events;
+	ehci->enabled_hrtimer_events = 0;
+	ehci->next_hrtimer_event = EHCI_HRTIMER_NO_EVENT;
+
+	/*
+	 * Check each pending event.  If its time has expired, handle
+	 * the event; otherwise re-enable it.
+	 */
+	now = ktime_get();
+	for_each_set_bit(e, &events, EHCI_HRTIMER_NUM_EVENTS) {
+		if (now.tv64 >= ehci->hr_timeouts[e].tv64)
+			event_handlers[e](ehci);
+		else
+			ehci_enable_event(ehci, e, false);
+	}
+
+	spin_unlock_irqrestore(&ehci->lock, flags);
+	return HRTIMER_NORESTART;
+}

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;