kernel/time/clocksource.c - maze/linux - Git at Google

 /*
  * linux/kernel/time/clocksource.c
  *
  * This file contains the functions which manage clocksource drivers.
  *
  * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
  *
  * 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.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  *
  * TODO WishList:
  *   o Allow clocksource drivers to be unregistered
  *   o get rid of clocksource_jiffies extern
  */

 #include <linux/clocksource.h>
 #include <linux/sysdev.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
 #include <linux/tick.h>

 /* XXX - Would like a better way for initializing curr_clocksource */
 extern struct clocksource clocksource_jiffies;

 /*[Clocksource internal variables]---------
  * curr_clocksource:
  *	currently selected clocksource. Initialized to clocksource_jiffies.
  * next_clocksource:
  *	pending next selected clocksource.
  * clocksource_list:
  *	linked list with the registered clocksources
  * clocksource_lock:
  *	protects manipulations to curr_clocksource and next_clocksource
  *	and the clocksource_list
  * override_name:
  *	Name of the user-specified clocksource.
  */
 static struct clocksource *curr_clocksource = &clocksource_jiffies;
 static struct clocksource *next_clocksource;
 static struct clocksource *clocksource_override;
 static LIST_HEAD(clocksource_list);
 static DEFINE_SPINLOCK(clocksource_lock);
 static char override_name[32];
 static int finished_booting;

 /* clocksource_done_booting - Called near the end of core bootup
  *
  * Hack to avoid lots of clocksource churn at boot time.
  * We use fs_initcall because we want this to start before
  * device_initcall but after subsys_initcall.
  */
 static int __init clocksource_done_booting(void)
 {
 	finished_booting = 1;
 	return 0;
 }
 fs_initcall(clocksource_done_booting);

 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
 static LIST_HEAD(watchdog_list);
 static struct clocksource *watchdog;
 static struct timer_list watchdog_timer;
 static DEFINE_SPINLOCK(watchdog_lock);
 static cycle_t watchdog_last;
 static unsigned long watchdog_resumed;

 /*
  * Interval: 0.5sec Threshold: 0.0625s
  */
 #define WATCHDOG_INTERVAL (HZ >> 1)
 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)

 static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
 {
 	if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
 		return;

 	printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
 	       cs->name, delta);
 	cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
 	clocksource_change_rating(cs, 0);
 	list_del(&cs->wd_list);
 }

 static void clocksource_watchdog(unsigned long data)
 {
 	struct clocksource *cs, *tmp;
 	cycle_t csnow, wdnow;
 	int64_t wd_nsec, cs_nsec;
 	int resumed;

 	spin_lock(&watchdog_lock);

 	resumed = test_and_clear_bit(0, &watchdog_resumed);

 	wdnow = watchdog->read();
 	wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
 	watchdog_last = wdnow;

 	list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
 		csnow = cs->read();

 		if (unlikely(resumed)) {
 			cs->wd_last = csnow;
 			continue;
 		}

 		/* Initialized ? */
 		if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
 			if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
 			    (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
 				cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 				/*
 				 * We just marked the clocksource as
 				 * highres-capable, notify the rest of the
 				 * system as well so that we transition
 				 * into high-res mode:
 				 */
 				tick_clock_notify();
 			}
 			cs->flags |= CLOCK_SOURCE_WATCHDOG;
 			cs->wd_last = csnow;
 		} else {
 			cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
 			cs->wd_last = csnow;
 			/* Check the delta. Might remove from the list ! */
 			clocksource_ratewd(cs, cs_nsec - wd_nsec);
 		}
 	}

 	if (!list_empty(&watchdog_list)) {
 		/*
 		 * Cycle through CPUs to check if the CPUs stay
 		 * synchronized to each other.
 		 */
 		int next_cpu = next_cpu_nr(raw_smp_processor_id(), cpu_online_map);

 		if (next_cpu >= nr_cpu_ids)
 			next_cpu = first_cpu(cpu_online_map);
 		watchdog_timer.expires += WATCHDOG_INTERVAL;
 		add_timer_on(&watchdog_timer, next_cpu);
 	}
 	spin_unlock(&watchdog_lock);
 }
 static void clocksource_resume_watchdog(void)
 {
 	set_bit(0, &watchdog_resumed);
 }

 static void clocksource_check_watchdog(struct clocksource *cs)
 {
 	struct clocksource *cse;
 	unsigned long flags;

 	spin_lock_irqsave(&watchdog_lock, flags);
 	if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
 		int started = !list_empty(&watchdog_list);

 		list_add(&cs->wd_list, &watchdog_list);
 		if (!started && watchdog) {
 			watchdog_last = watchdog->read();
 			watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
 			add_timer_on(&watchdog_timer,
 				     first_cpu(cpu_online_map));
 		}
 	} else {
 		if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;

 		if (!watchdog || cs->rating > watchdog->rating) {
 			if (watchdog)
 				del_timer(&watchdog_timer);
 			watchdog = cs;
 			init_timer(&watchdog_timer);
 			watchdog_timer.function = clocksource_watchdog;

 			/* Reset watchdog cycles */
 			list_for_each_entry(cse, &watchdog_list, wd_list)
 				cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
 			/* Start if list is not empty */
 			if (!list_empty(&watchdog_list)) {
 				watchdog_last = watchdog->read();
 				watchdog_timer.expires =
 					jiffies + WATCHDOG_INTERVAL;
 				add_timer_on(&watchdog_timer,
 					     first_cpu(cpu_online_map));
 			}
 		}
 	}
 	spin_unlock_irqrestore(&watchdog_lock, flags);
 }
 #else
 static void clocksource_check_watchdog(struct clocksource *cs)
 {
 	if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 		cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 }

 static inline void clocksource_resume_watchdog(void) { }
 #endif

 /**
  * clocksource_resume - resume the clocksource(s)
  */
 void clocksource_resume(void)
 {
 	struct clocksource *cs;
 	unsigned long flags;

 	spin_lock_irqsave(&clocksource_lock, flags);

 	list_for_each_entry(cs, &clocksource_list, list) {
 		if (cs->resume)
 			cs->resume();
 	}

 	clocksource_resume_watchdog();

 	spin_unlock_irqrestore(&clocksource_lock, flags);
 }

 /**
  * clocksource_touch_watchdog - Update watchdog
  *
  * Update the watchdog after exception contexts such as kgdb so as not
  * to incorrectly trip the watchdog.
  *
  */
 void clocksource_touch_watchdog(void)
 {
 	clocksource_resume_watchdog();
 }

 /**
  * clocksource_get_next - Returns the selected clocksource
  *
  */
 struct clocksource *clocksource_get_next(void)
 {
 	unsigned long flags;

 	spin_lock_irqsave(&clocksource_lock, flags);
 	if (next_clocksource && finished_booting) {
 		curr_clocksource = next_clocksource;
 		next_clocksource = NULL;
 	}
 	spin_unlock_irqrestore(&clocksource_lock, flags);

 	return curr_clocksource;
 }

 /**
  * select_clocksource - Selects the best registered clocksource.
  *
  * Private function. Must hold clocksource_lock when called.
  *
  * Select the clocksource with the best rating, or the clocksource,
  * which is selected by userspace override.
  */
 static struct clocksource *select_clocksource(void)
 {
 	struct clocksource *next;

 	if (list_empty(&clocksource_list))
 		return NULL;

 	if (clocksource_override)
 		next = clocksource_override;
 	else
 		next = list_entry(clocksource_list.next, struct clocksource,
 				  list);

 	if (next == curr_clocksource)
 		return NULL;

 	return next;
 }

 /*
  * Enqueue the clocksource sorted by rating
  */
 static int clocksource_enqueue(struct clocksource *c)
 {
 	struct list_head *tmp, *entry = &clocksource_list;

 	list_for_each(tmp, &clocksource_list) {
 		struct clocksource *cs;

 		cs = list_entry(tmp, struct clocksource, list);
 		if (cs == c)
 			return -EBUSY;
 		/* Keep track of the place, where to insert */
 		if (cs->rating >= c->rating)
 			entry = tmp;
 	}
 	list_add(&c->list, entry);

 	if (strlen(c->name) == strlen(override_name) &&
 	    !strcmp(c->name, override_name))
 		clocksource_override = c;

 	return 0;
 }

 /**
  * clocksource_register - Used to install new clocksources
  * @t:		clocksource to be registered
  *
  * Returns -EBUSY if registration fails, zero otherwise.
  */
 int clocksource_register(struct clocksource *c)
 {
 	unsigned long flags;
 	int ret;

 	/* save mult_orig on registration */
 	c->mult_orig = c->mult;

 	spin_lock_irqsave(&clocksource_lock, flags);
 	ret = clocksource_enqueue(c);
 	if (!ret)
 		next_clocksource = select_clocksource();
 	spin_unlock_irqrestore(&clocksource_lock, flags);
 	if (!ret)
 		clocksource_check_watchdog(c);
 	return ret;
 }
 EXPORT_SYMBOL(clocksource_register);

 /**
  * clocksource_change_rating - Change the rating of a registered clocksource
  *
  */
 void clocksource_change_rating(struct clocksource *cs, int rating)
 {
 	unsigned long flags;

 	spin_lock_irqsave(&clocksource_lock, flags);
 	list_del(&cs->list);
 	cs->rating = rating;
 	clocksource_enqueue(cs);
 	next_clocksource = select_clocksource();
 	spin_unlock_irqrestore(&clocksource_lock, flags);
 }

 /**
  * clocksource_unregister - remove a registered clocksource
  */
 void clocksource_unregister(struct clocksource *cs)
 {
 	unsigned long flags;

 	spin_lock_irqsave(&clocksource_lock, flags);
 	list_del(&cs->list);
 	if (clocksource_override == cs)
 		clocksource_override = NULL;
 	next_clocksource = select_clocksource();
 	spin_unlock_irqrestore(&clocksource_lock, flags);
 }

 #ifdef CONFIG_SYSFS
 /**
  * sysfs_show_current_clocksources - sysfs interface for current clocksource
  * @dev:	unused
  * @buf:	char buffer to be filled with clocksource list
  *
  * Provides sysfs interface for listing current clocksource.
  */
 static ssize_t
 sysfs_show_current_clocksources(struct sys_device *dev,
 				struct sysdev_attribute *attr, char *buf)
 {
 	ssize_t count = 0;

 	spin_lock_irq(&clocksource_lock);
 	count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
 	spin_unlock_irq(&clocksource_lock);

 	return count;
 }

 /**
  * sysfs_override_clocksource - interface for manually overriding clocksource
  * @dev:	unused
  * @buf:	name of override clocksource
  * @count:	length of buffer
  *
  * Takes input from sysfs interface for manually overriding the default
  * clocksource selction.
  */
 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
 					  struct sysdev_attribute *attr,
 					  const char *buf, size_t count)
 {
 	struct clocksource *ovr = NULL;
 	size_t ret = count;
 	int len;

 	/* strings from sysfs write are not 0 terminated! */
 	if (count >= sizeof(override_name))
 		return -EINVAL;

 	/* strip of \n: */
 	if (buf[count-1] == '\n')
 		count--;

 	spin_lock_irq(&clocksource_lock);

 	if (count > 0)
 		memcpy(override_name, buf, count);
 	override_name[count] = 0;

 	len = strlen(override_name);
 	if (len) {
 		struct clocksource *cs;

 		ovr = clocksource_override;
 		/* try to select it: */
 		list_for_each_entry(cs, &clocksource_list, list) {
 			if (strlen(cs->name) == len &&
 			    !strcmp(cs->name, override_name))
 				ovr = cs;
 		}
 	}

 	/* Reselect, when the override name has changed */
 	if (ovr != clocksource_override) {
 		clocksource_override = ovr;
 		next_clocksource = select_clocksource();
 	}

 	spin_unlock_irq(&clocksource_lock);

 	return ret;
 }

 /**
  * sysfs_show_available_clocksources - sysfs interface for listing clocksource
  * @dev:	unused
  * @buf:	char buffer to be filled with clocksource list
  *
  * Provides sysfs interface for listing registered clocksources
  */
 static ssize_t
 sysfs_show_available_clocksources(struct sys_device *dev,
 				  struct sysdev_attribute *attr,
 				  char *buf)
 {
 	struct clocksource *src;
 	ssize_t count = 0;

 	spin_lock_irq(&clocksource_lock);
 	list_for_each_entry(src, &clocksource_list, list) {
 		count += snprintf(buf + count,
 				  max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
 				  "%s ", src->name);
 	}
 	spin_unlock_irq(&clocksource_lock);

 	count += snprintf(buf + count,
 			  max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");

 	return count;
 }

 /*
  * Sysfs setup bits:
  */
 static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
 		   sysfs_override_clocksource);

 static SYSDEV_ATTR(available_clocksource, 0444,
 		   sysfs_show_available_clocksources, NULL);

 static struct sysdev_class clocksource_sysclass = {
 	.name = "clocksource",
 };

 static struct sys_device device_clocksource = {
 	.id	= 0,
 	.cls	= &clocksource_sysclass,
 };

 static int __init init_clocksource_sysfs(void)
 {
 	int error = sysdev_class_register(&clocksource_sysclass);

 	if (!error)
 		error = sysdev_register(&device_clocksource);
 	if (!error)
 		error = sysdev_create_file(
 				&device_clocksource,
 				&attr_current_clocksource);
 	if (!error)
 		error = sysdev_create_file(
 				&device_clocksource,
 				&attr_available_clocksource);
 	return error;
 }

 device_initcall(init_clocksource_sysfs);
 #endif /* CONFIG_SYSFS */

 /**
  * boot_override_clocksource - boot clock override
  * @str:	override name
  *
  * Takes a clocksource= boot argument and uses it
  * as the clocksource override name.
  */
 static int __init boot_override_clocksource(char* str)
 {
 	unsigned long flags;
 	spin_lock_irqsave(&clocksource_lock, flags);
 	if (str)
 		strlcpy(override_name, str, sizeof(override_name));
 	spin_unlock_irqrestore(&clocksource_lock, flags);
 	return 1;
 }

 __setup("clocksource=", boot_override_clocksource);

 /**
  * boot_override_clock - Compatibility layer for deprecated boot option
  * @str:	override name
  *
  * DEPRECATED! Takes a clock= boot argument and uses it
  * as the clocksource override name
  */
 static int __init boot_override_clock(char* str)
 {
 	if (!strcmp(str, "pmtmr")) {
 		printk("Warning: clock=pmtmr is deprecated. "
 			"Use clocksource=acpi_pm.\n");
 		return boot_override_clocksource("acpi_pm");
 	}
 	printk("Warning! clock= boot option is deprecated. "
 		"Use clocksource=xyz\n");
 	return boot_override_clocksource(str);
 }

 __setup("clock=", boot_override_clock);
	/*
	* linux/kernel/time/clocksource.c
	*
	* This file contains the functions which manage clocksource drivers.
	*
	* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
	*
	* 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.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
	*
	* TODO WishList:
	* o Allow clocksource drivers to be unregistered
	* o get rid of clocksource_jiffies extern
	*/

	#include <linux/clocksource.h>
	#include <linux/sysdev.h>
	#include <linux/init.h>
	#include <linux/module.h>
	#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
	#include <linux/tick.h>

	/* XXX - Would like a better way for initializing curr_clocksource */
	extern struct clocksource clocksource_jiffies;

	/*[Clocksource internal variables]---------
	* curr_clocksource:
	* currently selected clocksource. Initialized to clocksource_jiffies.
	* next_clocksource:
	* pending next selected clocksource.
	* clocksource_list:
	* linked list with the registered clocksources
	* clocksource_lock:
	* protects manipulations to curr_clocksource and next_clocksource
	* and the clocksource_list
	* override_name:
	* Name of the user-specified clocksource.
	*/
	static struct clocksource *curr_clocksource = &clocksource_jiffies;
	static struct clocksource *next_clocksource;
	static struct clocksource *clocksource_override;
	static LIST_HEAD(clocksource_list);
	static DEFINE_SPINLOCK(clocksource_lock);
	static char override_name[32];
	static int finished_booting;

	/* clocksource_done_booting - Called near the end of core bootup
	*
	* Hack to avoid lots of clocksource churn at boot time.
	* We use fs_initcall because we want this to start before
	* device_initcall but after subsys_initcall.
	*/
	static int __init clocksource_done_booting(void)
	{
	finished_booting = 1;
	return 0;
	}
	fs_initcall(clocksource_done_booting);

	#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
	static LIST_HEAD(watchdog_list);
	static struct clocksource *watchdog;
	static struct timer_list watchdog_timer;
	static DEFINE_SPINLOCK(watchdog_lock);
	static cycle_t watchdog_last;
	static unsigned long watchdog_resumed;

	/*
	* Interval: 0.5sec Threshold: 0.0625s
	*/
	#define WATCHDOG_INTERVAL (HZ >> 1)
	#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)

	static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
	{
	if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
	return;

	printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
	cs->name, delta);
	cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES \| CLOCK_SOURCE_WATCHDOG);
	clocksource_change_rating(cs, 0);
	list_del(&cs->wd_list);
	}

	static void clocksource_watchdog(unsigned long data)
	{
	struct clocksource cs, tmp;
	cycle_t csnow, wdnow;
	int64_t wd_nsec, cs_nsec;
	int resumed;

	spin_lock(&watchdog_lock);

	resumed = test_and_clear_bit(0, &watchdog_resumed);

	wdnow = watchdog->read();
	wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
	watchdog_last = wdnow;

	list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
	csnow = cs->read();

	if (unlikely(resumed)) {
	cs->wd_last = csnow;
	continue;
	}

	/* Initialized ? */
	if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
	if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
	(watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
	cs->flags \|= CLOCK_SOURCE_VALID_FOR_HRES;
	/*
	* We just marked the clocksource as
	* highres-capable, notify the rest of the
	* system as well so that we transition
	* into high-res mode:
	*/
	tick_clock_notify();
	}
	cs->flags \|= CLOCK_SOURCE_WATCHDOG;
	cs->wd_last = csnow;
	} else {
	cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
	cs->wd_last = csnow;
	/* Check the delta. Might remove from the list ! */
	clocksource_ratewd(cs, cs_nsec - wd_nsec);
	}
	}

	if (!list_empty(&watchdog_list)) {
	/*
	* Cycle through CPUs to check if the CPUs stay
	* synchronized to each other.
	*/
	int next_cpu = next_cpu_nr(raw_smp_processor_id(), cpu_online_map);

	if (next_cpu >= nr_cpu_ids)
	next_cpu = first_cpu(cpu_online_map);
	watchdog_timer.expires += WATCHDOG_INTERVAL;
	add_timer_on(&watchdog_timer, next_cpu);
	}
	spin_unlock(&watchdog_lock);
	}
	static void clocksource_resume_watchdog(void)
	{
	set_bit(0, &watchdog_resumed);
	}

	static void clocksource_check_watchdog(struct clocksource *cs)
	{
	struct clocksource *cse;
	unsigned long flags;

	spin_lock_irqsave(&watchdog_lock, flags);
	if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
	int started = !list_empty(&watchdog_list);

	list_add(&cs->wd_list, &watchdog_list);
	if (!started && watchdog) {
	watchdog_last = watchdog->read();
	watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
	add_timer_on(&watchdog_timer,
	first_cpu(cpu_online_map));
	}
	} else {
	if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
	cs->flags \|= CLOCK_SOURCE_VALID_FOR_HRES;

	if (!watchdog \|\| cs->rating > watchdog->rating) {
	if (watchdog)
	del_timer(&watchdog_timer);
	watchdog = cs;
	init_timer(&watchdog_timer);
	watchdog_timer.function = clocksource_watchdog;

	/* Reset watchdog cycles */
	list_for_each_entry(cse, &watchdog_list, wd_list)
	cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
	/* Start if list is not empty */
	if (!list_empty(&watchdog_list)) {
	watchdog_last = watchdog->read();
	watchdog_timer.expires =
	jiffies + WATCHDOG_INTERVAL;
	add_timer_on(&watchdog_timer,
	first_cpu(cpu_online_map));
	}
	}
	}
	spin_unlock_irqrestore(&watchdog_lock, flags);
	}
	#else
	static void clocksource_check_watchdog(struct clocksource *cs)
	{
	if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
	cs->flags \|= CLOCK_SOURCE_VALID_FOR_HRES;
	}

	static inline void clocksource_resume_watchdog(void) { }
	#endif

	/**
	* clocksource_resume - resume the clocksource(s)
	*/
	void clocksource_resume(void)
	{
	struct clocksource *cs;
	unsigned long flags;

	spin_lock_irqsave(&clocksource_lock, flags);

	list_for_each_entry(cs, &clocksource_list, list) {
	if (cs->resume)
	cs->resume();
	}

	clocksource_resume_watchdog();

	spin_unlock_irqrestore(&clocksource_lock, flags);
	}

	/**
	* clocksource_touch_watchdog - Update watchdog
	*
	* Update the watchdog after exception contexts such as kgdb so as not
	* to incorrectly trip the watchdog.
	*
	*/
	void clocksource_touch_watchdog(void)
	{
	clocksource_resume_watchdog();
	}

	/**
	* clocksource_get_next - Returns the selected clocksource
	*
	*/
	struct clocksource *clocksource_get_next(void)
	{
	unsigned long flags;

	spin_lock_irqsave(&clocksource_lock, flags);
	if (next_clocksource && finished_booting) {
	curr_clocksource = next_clocksource;
	next_clocksource = NULL;
	}
	spin_unlock_irqrestore(&clocksource_lock, flags);

	return curr_clocksource;
	}

	/**
	* select_clocksource - Selects the best registered clocksource.
	*
	* Private function. Must hold clocksource_lock when called.
	*
	* Select the clocksource with the best rating, or the clocksource,
	* which is selected by userspace override.
	*/
	static struct clocksource *select_clocksource(void)
	{
	struct clocksource *next;

	if (list_empty(&clocksource_list))
	return NULL;

	if (clocksource_override)
	next = clocksource_override;
	else
	next = list_entry(clocksource_list.next, struct clocksource,
	list);

	if (next == curr_clocksource)
	return NULL;

	return next;
	}

	/*
	* Enqueue the clocksource sorted by rating
	*/
	static int clocksource_enqueue(struct clocksource *c)
	{
	struct list_head tmp, entry = &clocksource_list;

	list_for_each(tmp, &clocksource_list) {
	struct clocksource *cs;

	cs = list_entry(tmp, struct clocksource, list);
	if (cs == c)
	return -EBUSY;
	/* Keep track of the place, where to insert */
	if (cs->rating >= c->rating)
	entry = tmp;
	}
	list_add(&c->list, entry);

	if (strlen(c->name) == strlen(override_name) &&
	!strcmp(c->name, override_name))
	clocksource_override = c;

	return 0;
	}

	/**
	* clocksource_register - Used to install new clocksources
	* @t: clocksource to be registered
	*
	* Returns -EBUSY if registration fails, zero otherwise.
	*/
	int clocksource_register(struct clocksource *c)
	{
	unsigned long flags;
	int ret;

	/* save mult_orig on registration */
	c->mult_orig = c->mult;

	spin_lock_irqsave(&clocksource_lock, flags);
	ret = clocksource_enqueue(c);
	if (!ret)
	next_clocksource = select_clocksource();
	spin_unlock_irqrestore(&clocksource_lock, flags);
	if (!ret)
	clocksource_check_watchdog(c);
	return ret;
	}
	EXPORT_SYMBOL(clocksource_register);

	/**
	* clocksource_change_rating - Change the rating of a registered clocksource
	*
	*/
	void clocksource_change_rating(struct clocksource *cs, int rating)
	{
	unsigned long flags;

	spin_lock_irqsave(&clocksource_lock, flags);
	list_del(&cs->list);
	cs->rating = rating;
	clocksource_enqueue(cs);
	next_clocksource = select_clocksource();
	spin_unlock_irqrestore(&clocksource_lock, flags);
	}

	/**
	* clocksource_unregister - remove a registered clocksource
	*/
	void clocksource_unregister(struct clocksource *cs)
	{
	unsigned long flags;

	spin_lock_irqsave(&clocksource_lock, flags);
	list_del(&cs->list);
	if (clocksource_override == cs)
	clocksource_override = NULL;
	next_clocksource = select_clocksource();
	spin_unlock_irqrestore(&clocksource_lock, flags);
	}

	#ifdef CONFIG_SYSFS
	/**
	* sysfs_show_current_clocksources - sysfs interface for current clocksource
	* @dev: unused
	* @buf: char buffer to be filled with clocksource list
	*
	* Provides sysfs interface for listing current clocksource.
	*/
	static ssize_t
	sysfs_show_current_clocksources(struct sys_device *dev,
	struct sysdev_attribute attr, char buf)
	{
	ssize_t count = 0;

	spin_lock_irq(&clocksource_lock);
	count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
	spin_unlock_irq(&clocksource_lock);

	return count;
	}

	/**
	* sysfs_override_clocksource - interface for manually overriding clocksource
	* @dev: unused
	* @buf: name of override clocksource
	* @count: length of buffer
	*
	* Takes input from sysfs interface for manually overriding the default
	* clocksource selction.
	*/
	static ssize_t sysfs_override_clocksource(struct sys_device *dev,
	struct sysdev_attribute *attr,
	const char *buf, size_t count)
	{
	struct clocksource *ovr = NULL;
	size_t ret = count;
	int len;

	/* strings from sysfs write are not 0 terminated! */
	if (count >= sizeof(override_name))
	return -EINVAL;

	/* strip of \n: */
	if (buf[count-1] == '\n')
	count--;

	spin_lock_irq(&clocksource_lock);

	if (count > 0)
	memcpy(override_name, buf, count);
	override_name[count] = 0;

	len = strlen(override_name);
	if (len) {
	struct clocksource *cs;

	ovr = clocksource_override;
	/* try to select it: */
	list_for_each_entry(cs, &clocksource_list, list) {
	if (strlen(cs->name) == len &&
	!strcmp(cs->name, override_name))
	ovr = cs;
	}
	}

	/* Reselect, when the override name has changed */
	if (ovr != clocksource_override) {
	clocksource_override = ovr;
	next_clocksource = select_clocksource();
	}

	spin_unlock_irq(&clocksource_lock);

	return ret;
	}

	/**
	* sysfs_show_available_clocksources - sysfs interface for listing clocksource
	* @dev: unused
	* @buf: char buffer to be filled with clocksource list
	*
	* Provides sysfs interface for listing registered clocksources
	*/
	static ssize_t
	sysfs_show_available_clocksources(struct sys_device *dev,
	struct sysdev_attribute *attr,
	char *buf)
	{
	struct clocksource *src;
	ssize_t count = 0;

	spin_lock_irq(&clocksource_lock);
	list_for_each_entry(src, &clocksource_list, list) {
	count += snprintf(buf + count,
	max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
	"%s ", src->name);
	}
	spin_unlock_irq(&clocksource_lock);

	count += snprintf(buf + count,
	max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");

	return count;
	}

	/*
	* Sysfs setup bits:
	*/
	static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
	sysfs_override_clocksource);

	static SYSDEV_ATTR(available_clocksource, 0444,
	sysfs_show_available_clocksources, NULL);

	static struct sysdev_class clocksource_sysclass = {
	.name = "clocksource",
	};

	static struct sys_device device_clocksource = {
	.id = 0,
	.cls = &clocksource_sysclass,
	};

	static int __init init_clocksource_sysfs(void)
	{
	int error = sysdev_class_register(&clocksource_sysclass);

	if (!error)
	error = sysdev_register(&device_clocksource);
	if (!error)
	error = sysdev_create_file(
	&device_clocksource,
	&attr_current_clocksource);
	if (!error)
	error = sysdev_create_file(
	&device_clocksource,
	&attr_available_clocksource);
	return error;
	}

	device_initcall(init_clocksource_sysfs);
	#endif /* CONFIG_SYSFS */

	/**
	* boot_override_clocksource - boot clock override
	* @str: override name
	*
	* Takes a clocksource= boot argument and uses it
	* as the clocksource override name.
	*/
	static int __init boot_override_clocksource(char* str)
	{
	unsigned long flags;
	spin_lock_irqsave(&clocksource_lock, flags);
	if (str)
	strlcpy(override_name, str, sizeof(override_name));
	spin_unlock_irqrestore(&clocksource_lock, flags);
	return 1;
	}

	__setup("clocksource=", boot_override_clocksource);

	/**
	* boot_override_clock - Compatibility layer for deprecated boot option
	* @str: override name
	*
	* DEPRECATED! Takes a clock= boot argument and uses it
	* as the clocksource override name
	*/
	static int __init boot_override_clock(char* str)
	{
	if (!strcmp(str, "pmtmr")) {
	printk("Warning: clock=pmtmr is deprecated. "
	"Use clocksource=acpi_pm.\n");
	return boot_override_clocksource("acpi_pm");
	}
	printk("Warning! clock= boot option is deprecated. "
	"Use clocksource=xyz\n");
	return boot_override_clocksource(str);
	}

	__setup("clock=", boot_override_clock);