kernel/time/clockevents.c - kernel/mindspeed - Git at Google

 /*
  * linux/kernel/time/clockevents.c
  *
  * This file contains functions which manage clock event devices.
  *
  * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
  * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
  * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
  *
  * This code is licenced under the GPL version 2. For details see
  * kernel-base/COPYING.
  */

 #include <linux/clockchips.h>
 #include <linux/hrtimer.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/notifier.h>
 #include <linux/smp.h>
 #include <linux/sysdev.h>

 #include "tick-internal.h"

 /* The registered clock event devices */
 static LIST_HEAD(clockevent_devices);
 static LIST_HEAD(clockevents_released);

 /* Notification for clock events */
 static RAW_NOTIFIER_HEAD(clockevents_chain);

 /* Protection for the above */
 static DEFINE_RAW_SPINLOCK(clockevents_lock);

 /**
  * clockevents_delta2ns - Convert a latch value (device ticks) to nanoseconds
  * @latch:	value to convert
  * @evt:	pointer to clock event device descriptor
  *
  * Math helper, returns latch value converted to nanoseconds (bound checked)
  */
 u64 clockevent_delta2ns(unsigned long latch, struct clock_event_device *evt)
 {
 	u64 clc = (u64) latch << evt->shift;

 	if (unlikely(!evt->mult)) {
 		evt->mult = 1;
 		WARN_ON(1);
 	}

 	do_div(clc, evt->mult);
 	if (clc < 1000)
 		clc = 1000;
 	if (clc > KTIME_MAX)
 		clc = KTIME_MAX;

 	return clc;
 }
 EXPORT_SYMBOL_GPL(clockevent_delta2ns);

 /**
  * clockevents_set_mode - set the operating mode of a clock event device
  * @dev:	device to modify
  * @mode:	new mode
  *
  * Must be called with interrupts disabled !
  */
 void clockevents_set_mode(struct clock_event_device *dev,
 				 enum clock_event_mode mode)
 {
 	if (dev->mode != mode) {
 		dev->set_mode(mode, dev);
 		dev->mode = mode;

 		/*
 		 * A nsec2cyc multiplicator of 0 is invalid and we'd crash
 		 * on it, so fix it up and emit a warning:
 		 */
 		if (mode == CLOCK_EVT_MODE_ONESHOT) {
 			if (unlikely(!dev->mult)) {
 				dev->mult = 1;
 				WARN_ON(1);
 			}
 		}
 	}
 }

 /**
  * clockevents_shutdown - shutdown the device and clear next_event
  * @dev:	device to shutdown
  */
 void clockevents_shutdown(struct clock_event_device *dev)
 {
 	clockevents_set_mode(dev, CLOCK_EVT_MODE_SHUTDOWN);
 	dev->next_event.tv64 = KTIME_MAX;
 }

 #ifdef CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST

 /* Limit min_delta to a jiffie */
 #define MIN_DELTA_LIMIT		(NSEC_PER_SEC / HZ)

 /**
  * clockevents_increase_min_delta - raise minimum delta of a clock event device
  * @dev:       device to increase the minimum delta
  *
  * Returns 0 on success, -ETIME when the minimum delta reached the limit.
  */
 static int clockevents_increase_min_delta(struct clock_event_device *dev)
 {
 	/* Nothing to do if we already reached the limit */
 	if (dev->min_delta_ns >= MIN_DELTA_LIMIT) {
 		printk(KERN_WARNING "CE: Reprogramming failure. Giving up\n");
 		dev->next_event.tv64 = KTIME_MAX;
 		return -ETIME;
 	}

 	if (dev->min_delta_ns < 5000)
 		dev->min_delta_ns = 5000;
 	else
 		dev->min_delta_ns += dev->min_delta_ns >> 1;

 	if (dev->min_delta_ns > MIN_DELTA_LIMIT)
 		dev->min_delta_ns = MIN_DELTA_LIMIT;

 	printk(KERN_WARNING "CE: %s increased min_delta_ns to %llu nsec\n",
 	       dev->name ? dev->name : "?",
 	       (unsigned long long) dev->min_delta_ns);
 	return 0;
 }

 /**
  * clockevents_program_min_delta - Set clock event device to the minimum delay.
  * @dev:	device to program
  *
  * Returns 0 on success, -ETIME when the retry loop failed.
  */
 static int clockevents_program_min_delta(struct clock_event_device *dev)
 {
 	unsigned long long clc;
 	int64_t delta;
 	int i;

 	for (i = 0;;) {
 		delta = dev->min_delta_ns;
 		dev->next_event = ktime_add_ns(ktime_get(), delta);

 		if (dev->mode == CLOCK_EVT_MODE_SHUTDOWN)
 			return 0;

 		dev->retries++;
 		clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
 		if (dev->set_next_event((unsigned long) clc, dev) == 0)
 			return 0;

 		if (++i > 2) {
 			/*
 			 * We tried 3 times to program the device with the
 			 * given min_delta_ns. Try to increase the minimum
 			 * delta, if that fails as well get out of here.
 			 */
 			if (clockevents_increase_min_delta(dev))
 				return -ETIME;
 			i = 0;
 		}
 	}
 }

 #else  /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */

 /**
  * clockevents_program_min_delta - Set clock event device to the minimum delay.
  * @dev:	device to program
  *
  * Returns 0 on success, -ETIME when the retry loop failed.
  */
 static int clockevents_program_min_delta(struct clock_event_device *dev)
 {
 	unsigned long long clc;
 	int64_t delta;

 	delta = dev->min_delta_ns;
 	dev->next_event = ktime_add_ns(ktime_get(), delta);

 	if (dev->mode == CLOCK_EVT_MODE_SHUTDOWN)
 		return 0;

 	dev->retries++;
 	clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
 	return dev->set_next_event((unsigned long) clc, dev);
 }

 #endif /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */

 /**
  * clockevents_program_event - Reprogram the clock event device.
  * @dev:	device to program
  * @expires:	absolute expiry time (monotonic clock)
  * @force:	program minimum delay if expires can not be set
  *
  * Returns 0 on success, -ETIME when the event is in the past.
  */
 int clockevents_program_event(struct clock_event_device *dev, ktime_t expires,
 			      bool force)
 {
 	unsigned long long clc;
 	int64_t delta;
 	int rc;

 	if (unlikely(expires.tv64 < 0)) {
 		WARN_ON_ONCE(1);
 		return -ETIME;
 	}

 	dev->next_event = expires;

 	if (dev->mode == CLOCK_EVT_MODE_SHUTDOWN)
 		return 0;

 	/* Shortcut for clockevent devices that can deal with ktime. */
 	if (dev->features & CLOCK_EVT_FEAT_KTIME)
 		return dev->set_next_ktime(expires, dev);

 	delta = ktime_to_ns(ktime_sub(expires, ktime_get()));
 	if (delta <= 0)
 		return force ? clockevents_program_min_delta(dev) : -ETIME;

 	delta = min(delta, (int64_t) dev->max_delta_ns);
 	delta = max(delta, (int64_t) dev->min_delta_ns);

 	clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
 	rc = dev->set_next_event((unsigned long) clc, dev);

 	return (rc && force) ? clockevents_program_min_delta(dev) : rc;
 }

 /**
  * clockevents_register_notifier - register a clock events change listener
  */
 int clockevents_register_notifier(struct notifier_block *nb)
 {
 	unsigned long flags;
 	int ret;

 	raw_spin_lock_irqsave(&clockevents_lock, flags);
 	ret = raw_notifier_chain_register(&clockevents_chain, nb);
 	raw_spin_unlock_irqrestore(&clockevents_lock, flags);

 	return ret;
 }

 /*
  * Notify about a clock event change. Called with clockevents_lock
  * held.
  */
 static void clockevents_do_notify(unsigned long reason, void *dev)
 {
 	raw_notifier_call_chain(&clockevents_chain, reason, dev);
 }

 /*
  * Called after a notify add to make devices available which were
  * released from the notifier call.
  */
 static void clockevents_notify_released(void)
 {
 	struct clock_event_device *dev;

 	while (!list_empty(&clockevents_released)) {
 		dev = list_entry(clockevents_released.next,
 				 struct clock_event_device, list);
 		list_del(&dev->list);
 		list_add(&dev->list, &clockevent_devices);
 		clockevents_do_notify(CLOCK_EVT_NOTIFY_ADD, dev);
 	}
 }

 /**
  * clockevents_register_device - register a clock event device
  * @dev:	device to register
  */
 void clockevents_register_device(struct clock_event_device *dev)
 {
 	unsigned long flags;

 	BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
 	if (!dev->cpumask) {
 		WARN_ON(num_possible_cpus() > 1);
 		dev->cpumask = cpumask_of(smp_processor_id());
 	}

 	raw_spin_lock_irqsave(&clockevents_lock, flags);

 	list_add(&dev->list, &clockevent_devices);
 	clockevents_do_notify(CLOCK_EVT_NOTIFY_ADD, dev);
 	clockevents_notify_released();

 	raw_spin_unlock_irqrestore(&clockevents_lock, flags);
 }
 EXPORT_SYMBOL_GPL(clockevents_register_device);

 static void clockevents_config(struct clock_event_device *dev,
 			       u32 freq)
 {
 	u64 sec;

 	if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT))
 		return;

 	/*
 	 * Calculate the maximum number of seconds we can sleep. Limit
 	 * to 10 minutes for hardware which can program more than
 	 * 32bit ticks so we still get reasonable conversion values.
 	 */
 	sec = dev->max_delta_ticks;
 	do_div(sec, freq);
 	if (!sec)
 		sec = 1;
 	else if (sec > 600 && dev->max_delta_ticks > UINT_MAX)
 		sec = 600;

 	clockevents_calc_mult_shift(dev, freq, sec);
 	dev->min_delta_ns = clockevent_delta2ns(dev->min_delta_ticks, dev);
 	dev->max_delta_ns = clockevent_delta2ns(dev->max_delta_ticks, dev);
 }

 /**
  * clockevents_config_and_register - Configure and register a clock event device
  * @dev:	device to register
  * @freq:	The clock frequency
  * @min_delta:	The minimum clock ticks to program in oneshot mode
  * @max_delta:	The maximum clock ticks to program in oneshot mode
  *
  * min/max_delta can be 0 for devices which do not support oneshot mode.
  */
 void clockevents_config_and_register(struct clock_event_device *dev,
 				     u32 freq, unsigned long min_delta,
 				     unsigned long max_delta)
 {
 	dev->min_delta_ticks = min_delta;
 	dev->max_delta_ticks = max_delta;
 	clockevents_config(dev, freq);
 	clockevents_register_device(dev);
 }

 /**
  * clockevents_update_freq - Update frequency and reprogram a clock event device.
  * @dev:	device to modify
  * @freq:	new device frequency
  *
  * Reconfigure and reprogram a clock event device in oneshot
  * mode. Must be called on the cpu for which the device delivers per
  * cpu timer events with interrupts disabled!  Returns 0 on success,
  * -ETIME when the event is in the past.
  */
 int clockevents_update_freq(struct clock_event_device *dev, u32 freq)
 {
 	clockevents_config(dev, freq);

 	if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
 		return 0;

 	return clockevents_program_event(dev, dev->next_event, false);
 }

 /*
  * Noop handler when we shut down an event device
  */
 void clockevents_handle_noop(struct clock_event_device *dev)
 {
 }

 /**
  * clockevents_exchange_device - release and request clock devices
  * @old:	device to release (can be NULL)
  * @new:	device to request (can be NULL)
  *
  * Called from the notifier chain. clockevents_lock is held already
  */
 void clockevents_exchange_device(struct clock_event_device *old,
 				 struct clock_event_device *new)
 {
 	unsigned long flags;

 	local_irq_save(flags);
 	/*
 	 * Caller releases a clock event device. We queue it into the
 	 * released list and do a notify add later.
 	 */
 	if (old) {
 		clockevents_set_mode(old, CLOCK_EVT_MODE_UNUSED);
 		list_del(&old->list);
 		list_add(&old->list, &clockevents_released);
 	}

 	if (new) {
 		BUG_ON(new->mode != CLOCK_EVT_MODE_UNUSED);
 		clockevents_shutdown(new);
 	}
 	local_irq_restore(flags);
 }

 #ifdef CONFIG_GENERIC_CLOCKEVENTS
 /**
  * clockevents_notify - notification about relevant events
  */
 void clockevents_notify(unsigned long reason, void *arg)
 {
 	struct clock_event_device *dev, *tmp;
 	unsigned long flags;
 	int cpu;

 	raw_spin_lock_irqsave(&clockevents_lock, flags);
 	clockevents_do_notify(reason, arg);

 	switch (reason) {
 	case CLOCK_EVT_NOTIFY_CPU_DEAD:
 		/*
 		 * Unregister the clock event devices which were
 		 * released from the users in the notify chain.
 		 */
 		list_for_each_entry_safe(dev, tmp, &clockevents_released, list)
 			list_del(&dev->list);
 		/*
 		 * Now check whether the CPU has left unused per cpu devices
 		 */
 		cpu = *((int *)arg);
 		list_for_each_entry_safe(dev, tmp, &clockevent_devices, list) {
 			if (cpumask_test_cpu(cpu, dev->cpumask) &&
 			    cpumask_weight(dev->cpumask) == 1 &&
 			    !tick_is_broadcast_device(dev)) {
 				BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
 				list_del(&dev->list);
 			}
 		}
 		break;
 	default:
 		break;
 	}
 	raw_spin_unlock_irqrestore(&clockevents_lock, flags);
 }
 EXPORT_SYMBOL_GPL(clockevents_notify);
 #endif
	/*
	* linux/kernel/time/clockevents.c
	*
	* This file contains functions which manage clock event devices.
	*
	* Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
	* Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
	* Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
	*
	* This code is licenced under the GPL version 2. For details see
	* kernel-base/COPYING.
	*/

	#include <linux/clockchips.h>
	#include <linux/hrtimer.h>
	#include <linux/init.h>
	#include <linux/module.h>
	#include <linux/notifier.h>
	#include <linux/smp.h>
	#include <linux/sysdev.h>

	#include "tick-internal.h"

	/* The registered clock event devices */
	static LIST_HEAD(clockevent_devices);
	static LIST_HEAD(clockevents_released);

	/* Notification for clock events */
	static RAW_NOTIFIER_HEAD(clockevents_chain);

	/* Protection for the above */
	static DEFINE_RAW_SPINLOCK(clockevents_lock);

	/**
	* clockevents_delta2ns - Convert a latch value (device ticks) to nanoseconds
	* @latch: value to convert
	* @evt: pointer to clock event device descriptor
	*
	* Math helper, returns latch value converted to nanoseconds (bound checked)
	*/
	u64 clockevent_delta2ns(unsigned long latch, struct clock_event_device *evt)
	{
	u64 clc = (u64) latch << evt->shift;

	if (unlikely(!evt->mult)) {
	evt->mult = 1;
	WARN_ON(1);
	}

	do_div(clc, evt->mult);
	if (clc < 1000)
	clc = 1000;
	if (clc > KTIME_MAX)
	clc = KTIME_MAX;

	return clc;
	}
	EXPORT_SYMBOL_GPL(clockevent_delta2ns);

	/**
	* clockevents_set_mode - set the operating mode of a clock event device
	* @dev: device to modify
	* @mode: new mode
	*
	* Must be called with interrupts disabled !
	*/
	void clockevents_set_mode(struct clock_event_device *dev,
	enum clock_event_mode mode)
	{
	if (dev->mode != mode) {
	dev->set_mode(mode, dev);
	dev->mode = mode;

	/*
	* A nsec2cyc multiplicator of 0 is invalid and we'd crash
	* on it, so fix it up and emit a warning:
	*/
	if (mode == CLOCK_EVT_MODE_ONESHOT) {
	if (unlikely(!dev->mult)) {
	dev->mult = 1;
	WARN_ON(1);
	}
	}
	}
	}

	/**
	* clockevents_shutdown - shutdown the device and clear next_event
	* @dev: device to shutdown
	*/
	void clockevents_shutdown(struct clock_event_device *dev)
	{
	clockevents_set_mode(dev, CLOCK_EVT_MODE_SHUTDOWN);
	dev->next_event.tv64 = KTIME_MAX;
	}

	#ifdef CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST

	/* Limit min_delta to a jiffie */
	#define MIN_DELTA_LIMIT (NSEC_PER_SEC / HZ)

	/**
	* clockevents_increase_min_delta - raise minimum delta of a clock event device
	* @dev: device to increase the minimum delta
	*
	* Returns 0 on success, -ETIME when the minimum delta reached the limit.
	*/
	static int clockevents_increase_min_delta(struct clock_event_device *dev)
	{
	/* Nothing to do if we already reached the limit */
	if (dev->min_delta_ns >= MIN_DELTA_LIMIT) {
	printk(KERN_WARNING "CE: Reprogramming failure. Giving up\n");
	dev->next_event.tv64 = KTIME_MAX;
	return -ETIME;
	}

	if (dev->min_delta_ns < 5000)
	dev->min_delta_ns = 5000;
	else
	dev->min_delta_ns += dev->min_delta_ns >> 1;

	if (dev->min_delta_ns > MIN_DELTA_LIMIT)
	dev->min_delta_ns = MIN_DELTA_LIMIT;

	printk(KERN_WARNING "CE: %s increased min_delta_ns to %llu nsec\n",
	dev->name ? dev->name : "?",
	(unsigned long long) dev->min_delta_ns);
	return 0;
	}

	/**
	* clockevents_program_min_delta - Set clock event device to the minimum delay.
	* @dev: device to program
	*
	* Returns 0 on success, -ETIME when the retry loop failed.
	*/
	static int clockevents_program_min_delta(struct clock_event_device *dev)
	{
	unsigned long long clc;
	int64_t delta;
	int i;

	for (i = 0;;) {
	delta = dev->min_delta_ns;
	dev->next_event = ktime_add_ns(ktime_get(), delta);

	if (dev->mode == CLOCK_EVT_MODE_SHUTDOWN)
	return 0;

	dev->retries++;
	clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
	if (dev->set_next_event((unsigned long) clc, dev) == 0)
	return 0;

	if (++i > 2) {
	/*
	* We tried 3 times to program the device with the
	* given min_delta_ns. Try to increase the minimum
	* delta, if that fails as well get out of here.
	*/
	if (clockevents_increase_min_delta(dev))
	return -ETIME;
	i = 0;
	}
	}
	}

	#else /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */

	/**
	* clockevents_program_min_delta - Set clock event device to the minimum delay.
	* @dev: device to program
	*
	* Returns 0 on success, -ETIME when the retry loop failed.
	*/
	static int clockevents_program_min_delta(struct clock_event_device *dev)
	{
	unsigned long long clc;
	int64_t delta;

	delta = dev->min_delta_ns;
	dev->next_event = ktime_add_ns(ktime_get(), delta);

	if (dev->mode == CLOCK_EVT_MODE_SHUTDOWN)
	return 0;

	dev->retries++;
	clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
	return dev->set_next_event((unsigned long) clc, dev);
	}

	#endif /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */

	/**
	* clockevents_program_event - Reprogram the clock event device.
	* @dev: device to program
	* @expires: absolute expiry time (monotonic clock)
	* @force: program minimum delay if expires can not be set
	*
	* Returns 0 on success, -ETIME when the event is in the past.
	*/
	int clockevents_program_event(struct clock_event_device *dev, ktime_t expires,
	bool force)
	{
	unsigned long long clc;
	int64_t delta;
	int rc;

	if (unlikely(expires.tv64 < 0)) {
	WARN_ON_ONCE(1);
	return -ETIME;
	}

	dev->next_event = expires;

	if (dev->mode == CLOCK_EVT_MODE_SHUTDOWN)
	return 0;

	/* Shortcut for clockevent devices that can deal with ktime. */
	if (dev->features & CLOCK_EVT_FEAT_KTIME)
	return dev->set_next_ktime(expires, dev);

	delta = ktime_to_ns(ktime_sub(expires, ktime_get()));
	if (delta <= 0)
	return force ? clockevents_program_min_delta(dev) : -ETIME;

	delta = min(delta, (int64_t) dev->max_delta_ns);
	delta = max(delta, (int64_t) dev->min_delta_ns);

	clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
	rc = dev->set_next_event((unsigned long) clc, dev);

	return (rc && force) ? clockevents_program_min_delta(dev) : rc;
	}

	/**
	* clockevents_register_notifier - register a clock events change listener
	*/
	int clockevents_register_notifier(struct notifier_block *nb)
	{
	unsigned long flags;
	int ret;

	raw_spin_lock_irqsave(&clockevents_lock, flags);
	ret = raw_notifier_chain_register(&clockevents_chain, nb);
	raw_spin_unlock_irqrestore(&clockevents_lock, flags);

	return ret;
	}

	/*
	* Notify about a clock event change. Called with clockevents_lock
	* held.
	*/
	static void clockevents_do_notify(unsigned long reason, void *dev)
	{
	raw_notifier_call_chain(&clockevents_chain, reason, dev);
	}

	/*
	* Called after a notify add to make devices available which were
	* released from the notifier call.
	*/
	static void clockevents_notify_released(void)
	{
	struct clock_event_device *dev;

	while (!list_empty(&clockevents_released)) {
	dev = list_entry(clockevents_released.next,
	struct clock_event_device, list);
	list_del(&dev->list);
	list_add(&dev->list, &clockevent_devices);
	clockevents_do_notify(CLOCK_EVT_NOTIFY_ADD, dev);
	}
	}

	/**
	* clockevents_register_device - register a clock event device
	* @dev: device to register
	*/
	void clockevents_register_device(struct clock_event_device *dev)
	{
	unsigned long flags;

	BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
	if (!dev->cpumask) {
	WARN_ON(num_possible_cpus() > 1);
	dev->cpumask = cpumask_of(smp_processor_id());
	}

	raw_spin_lock_irqsave(&clockevents_lock, flags);

	list_add(&dev->list, &clockevent_devices);
	clockevents_do_notify(CLOCK_EVT_NOTIFY_ADD, dev);
	clockevents_notify_released();

	raw_spin_unlock_irqrestore(&clockevents_lock, flags);
	}
	EXPORT_SYMBOL_GPL(clockevents_register_device);

	static void clockevents_config(struct clock_event_device *dev,
	u32 freq)
	{
	u64 sec;

	if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT))
	return;

	/*
	* Calculate the maximum number of seconds we can sleep. Limit
	* to 10 minutes for hardware which can program more than
	* 32bit ticks so we still get reasonable conversion values.
	*/
	sec = dev->max_delta_ticks;
	do_div(sec, freq);
	if (!sec)
	sec = 1;
	else if (sec > 600 && dev->max_delta_ticks > UINT_MAX)
	sec = 600;

	clockevents_calc_mult_shift(dev, freq, sec);
	dev->min_delta_ns = clockevent_delta2ns(dev->min_delta_ticks, dev);
	dev->max_delta_ns = clockevent_delta2ns(dev->max_delta_ticks, dev);
	}

	/**
	* clockevents_config_and_register - Configure and register a clock event device
	* @dev: device to register
	* @freq: The clock frequency
	* @min_delta: The minimum clock ticks to program in oneshot mode
	* @max_delta: The maximum clock ticks to program in oneshot mode
	*
	* min/max_delta can be 0 for devices which do not support oneshot mode.
	*/
	void clockevents_config_and_register(struct clock_event_device *dev,
	u32 freq, unsigned long min_delta,
	unsigned long max_delta)
	{
	dev->min_delta_ticks = min_delta;
	dev->max_delta_ticks = max_delta;
	clockevents_config(dev, freq);
	clockevents_register_device(dev);
	}

	/**
	* clockevents_update_freq - Update frequency and reprogram a clock event device.
	* @dev: device to modify
	* @freq: new device frequency
	*
	* Reconfigure and reprogram a clock event device in oneshot
	* mode. Must be called on the cpu for which the device delivers per
	* cpu timer events with interrupts disabled! Returns 0 on success,
	* -ETIME when the event is in the past.
	*/
	int clockevents_update_freq(struct clock_event_device *dev, u32 freq)
	{
	clockevents_config(dev, freq);

	if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
	return 0;

	return clockevents_program_event(dev, dev->next_event, false);
	}

	/*
	* Noop handler when we shut down an event device
	*/
	void clockevents_handle_noop(struct clock_event_device *dev)
	{
	}

	/**
	* clockevents_exchange_device - release and request clock devices
	* @old: device to release (can be NULL)
	* @new: device to request (can be NULL)
	*
	* Called from the notifier chain. clockevents_lock is held already
	*/
	void clockevents_exchange_device(struct clock_event_device *old,
	struct clock_event_device *new)
	{
	unsigned long flags;

	local_irq_save(flags);
	/*
	* Caller releases a clock event device. We queue it into the
	* released list and do a notify add later.
	*/
	if (old) {
	clockevents_set_mode(old, CLOCK_EVT_MODE_UNUSED);
	list_del(&old->list);
	list_add(&old->list, &clockevents_released);
	}

	if (new) {
	BUG_ON(new->mode != CLOCK_EVT_MODE_UNUSED);
	clockevents_shutdown(new);
	}
	local_irq_restore(flags);
	}

	#ifdef CONFIG_GENERIC_CLOCKEVENTS
	/**
	* clockevents_notify - notification about relevant events
	*/
	void clockevents_notify(unsigned long reason, void *arg)
	{
	struct clock_event_device dev, tmp;
	unsigned long flags;
	int cpu;

	raw_spin_lock_irqsave(&clockevents_lock, flags);
	clockevents_do_notify(reason, arg);

	switch (reason) {
	case CLOCK_EVT_NOTIFY_CPU_DEAD:
	/*
	* Unregister the clock event devices which were
	* released from the users in the notify chain.
	*/
	list_for_each_entry_safe(dev, tmp, &clockevents_released, list)
	list_del(&dev->list);
	/*
	* Now check whether the CPU has left unused per cpu devices
	*/
	cpu = ((int )arg);
	list_for_each_entry_safe(dev, tmp, &clockevent_devices, list) {
	if (cpumask_test_cpu(cpu, dev->cpumask) &&
	cpumask_weight(dev->cpumask) == 1 &&
	!tick_is_broadcast_device(dev)) {
	BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
	list_del(&dev->list);
	}
	}
	break;
	default:
	break;
	}
	raw_spin_unlock_irqrestore(&clockevents_lock, flags);
	}
	EXPORT_SYMBOL_GPL(clockevents_notify);
	#endif