kernel/time/timekeeping.c - LeafOS-Devices/android_kernel_samsung_gta4xl - Gitiles

 /*
  *  linux/kernel/time/timekeeping.c
  *
  *  Kernel timekeeping code and accessor functions
  *
  *  This code was moved from linux/kernel/timer.c.
  *  Please see that file for copyright and history logs.
  *
  */

 #include <linux/module.h>
 #include <linux/interrupt.h>
 #include <linux/percpu.h>
 #include <linux/init.h>
 #include <linux/mm.h>
 #include <linux/sysdev.h>
 #include <linux/clocksource.h>
 #include <linux/jiffies.h>
 #include <linux/time.h>
 #include <linux/tick.h>


 /*
  * This read-write spinlock protects us from races in SMP while
  * playing with xtime and avenrun.
  */
 __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);


 /*
  * The current time
  * wall_to_monotonic is what we need to add to xtime (or xtime corrected
  * for sub jiffie times) to get to monotonic time.  Monotonic is pegged
  * at zero at system boot time, so wall_to_monotonic will be negative,
  * however, we will ALWAYS keep the tv_nsec part positive so we can use
  * the usual normalization.
  *
  * wall_to_monotonic is moved after resume from suspend for the monotonic
  * time not to jump. We need to add total_sleep_time to wall_to_monotonic
  * to get the real boot based time offset.
  *
  * - wall_to_monotonic is no longer the boot time, getboottime must be
  * used instead.
  */
 struct timespec xtime __attribute__ ((aligned (16)));
 struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
 static unsigned long total_sleep_time;		/* seconds */

 static struct timespec xtime_cache __attribute__ ((aligned (16)));
 void update_xtime_cache(u64 nsec)
 {
 	xtime_cache = xtime;
 	timespec_add_ns(&xtime_cache, nsec);
 }

 struct clocksource *clock;


 #ifdef CONFIG_GENERIC_TIME
 /**
  * clocksource_forward_now - update clock to the current time
  *
  * Forward the current clock to update its state since the last call to
  * update_wall_time(). This is useful before significant clock changes,
  * as it avoids having to deal with this time offset explicitly.
  */
 static void clocksource_forward_now(void)
 {
 	cycle_t cycle_now, cycle_delta;
 	s64 nsec;

 	cycle_now = clocksource_read(clock);
 	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
 	clock->cycle_last = cycle_now;

 	nsec = cyc2ns(clock, cycle_delta);
 	timespec_add_ns(&xtime, nsec);

 	nsec = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;
 	clock->raw_time.tv_nsec += nsec;
 }

 /**
  * getnstimeofday - Returns the time of day in a timespec
  * @ts:		pointer to the timespec to be set
  *
  * Returns the time of day in a timespec.
  */
 void getnstimeofday(struct timespec *ts)
 {
 	cycle_t cycle_now, cycle_delta;
 	unsigned long seq;
 	s64 nsecs;

 	do {
 		seq = read_seqbegin(&xtime_lock);

 		*ts = xtime;

 		/* read clocksource: */
 		cycle_now = clocksource_read(clock);

 		/* calculate the delta since the last update_wall_time: */
 		cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

 		/* convert to nanoseconds: */
 		nsecs = cyc2ns(clock, cycle_delta);

 	} while (read_seqretry(&xtime_lock, seq));

 	timespec_add_ns(ts, nsecs);
 }

 EXPORT_SYMBOL(getnstimeofday);

 /**
  * do_gettimeofday - Returns the time of day in a timeval
  * @tv:		pointer to the timeval to be set
  *
  * NOTE: Users should be converted to using getnstimeofday()
  */
 void do_gettimeofday(struct timeval *tv)
 {
 	struct timespec now;

 	getnstimeofday(&now);
 	tv->tv_sec = now.tv_sec;
 	tv->tv_usec = now.tv_nsec/1000;
 }

 EXPORT_SYMBOL(do_gettimeofday);
 /**
  * do_settimeofday - Sets the time of day
  * @tv:		pointer to the timespec variable containing the new time
  *
  * Sets the time of day to the new time and update NTP and notify hrtimers
  */
 int do_settimeofday(struct timespec *tv)
 {
 	struct timespec ts_delta;
 	unsigned long flags;

 	if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
 		return -EINVAL;

 	write_seqlock_irqsave(&xtime_lock, flags);

 	clocksource_forward_now();

 	ts_delta.tv_sec = tv->tv_sec - xtime.tv_sec;
 	ts_delta.tv_nsec = tv->tv_nsec - xtime.tv_nsec;
 	wall_to_monotonic = timespec_sub(wall_to_monotonic, ts_delta);

 	xtime = *tv;

 	update_xtime_cache(0);

 	clock->error = 0;
 	ntp_clear();

 	update_vsyscall(&xtime, clock);

 	write_sequnlock_irqrestore(&xtime_lock, flags);

 	/* signal hrtimers about time change */
 	clock_was_set();

 	return 0;
 }

 EXPORT_SYMBOL(do_settimeofday);

 /**
  * change_clocksource - Swaps clocksources if a new one is available
  *
  * Accumulates current time interval and initializes new clocksource
  */
 static void change_clocksource(void)
 {
 	struct clocksource *new;

 	new = clocksource_get_next();

 	if (clock == new)
 		return;

 	clocksource_forward_now();

 	new->raw_time = clock->raw_time;

 	clock = new;
 	clock->cycle_last = 0;
 	clock->cycle_last = clocksource_read(new);
 	clock->error = 0;
 	clock->xtime_nsec = 0;
 	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);

 	tick_clock_notify();

 	/*
 	 * We're holding xtime lock and waking up klogd would deadlock
 	 * us on enqueue.  So no printing!
 	printk(KERN_INFO "Time: %s clocksource has been installed.\n",
 	       clock->name);
 	 */
 }
 #else
 static inline void clocksource_forward_now(void) { }
 static inline void change_clocksource(void) { }
 #endif

 /**
  * getrawmonotonic - Returns the raw monotonic time in a timespec
  * @ts:		pointer to the timespec to be set
  *
  * Returns the raw monotonic time (completely un-modified by ntp)
  */
 void getrawmonotonic(struct timespec *ts)
 {
 	unsigned long seq;
 	s64 nsecs;
 	cycle_t cycle_now, cycle_delta;

 	do {
 		seq = read_seqbegin(&xtime_lock);

 		/* read clocksource: */
 		cycle_now = clocksource_read(clock);

 		/* calculate the delta since the last update_wall_time: */
 		cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

 		/* convert to nanoseconds: */
 		nsecs = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;

 		*ts = clock->raw_time;

 	} while (read_seqretry(&xtime_lock, seq));

 	timespec_add_ns(ts, nsecs);
 }
 EXPORT_SYMBOL(getrawmonotonic);


 /**
  * timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
  */
 int timekeeping_valid_for_hres(void)
 {
 	unsigned long seq;
 	int ret;

 	do {
 		seq = read_seqbegin(&xtime_lock);

 		ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

 	} while (read_seqretry(&xtime_lock, seq));

 	return ret;
 }

 /**
  * read_persistent_clock -  Return time in seconds from the persistent clock.
  *
  * Weak dummy function for arches that do not yet support it.
  * Returns seconds from epoch using the battery backed persistent clock.
  * Returns zero if unsupported.
  *
  *  XXX - Do be sure to remove it once all arches implement it.
  */
 unsigned long __attribute__((weak)) read_persistent_clock(void)
 {
 	return 0;
 }

 /*
  * timekeeping_init - Initializes the clocksource and common timekeeping values
  */
 void __init timekeeping_init(void)
 {
 	unsigned long flags;
 	unsigned long sec = read_persistent_clock();

 	write_seqlock_irqsave(&xtime_lock, flags);

 	ntp_init();

 	clock = clocksource_get_next();
 	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
 	clock->cycle_last = clocksource_read(clock);

 	xtime.tv_sec = sec;
 	xtime.tv_nsec = 0;
 	set_normalized_timespec(&wall_to_monotonic,
 		-xtime.tv_sec, -xtime.tv_nsec);
 	update_xtime_cache(0);
 	total_sleep_time = 0;
 	write_sequnlock_irqrestore(&xtime_lock, flags);
 }

 /* flag for if timekeeping is suspended */
 static int timekeeping_suspended;
 /* time in seconds when suspend began */
 static unsigned long timekeeping_suspend_time;

 /**
  * timekeeping_resume - Resumes the generic timekeeping subsystem.
  * @dev:	unused
  *
  * This is for the generic clocksource timekeeping.
  * xtime/wall_to_monotonic/jiffies/etc are
  * still managed by arch specific suspend/resume code.
  */
 static int timekeeping_resume(struct sys_device *dev)
 {
 	unsigned long flags;
 	unsigned long now = read_persistent_clock();

 	clocksource_resume();

 	write_seqlock_irqsave(&xtime_lock, flags);

 	if (now && (now > timekeeping_suspend_time)) {
 		unsigned long sleep_length = now - timekeeping_suspend_time;

 		xtime.tv_sec += sleep_length;
 		wall_to_monotonic.tv_sec -= sleep_length;
 		total_sleep_time += sleep_length;
 	}
 	update_xtime_cache(0);
 	/* re-base the last cycle value */
 	clock->cycle_last = 0;
 	clock->cycle_last = clocksource_read(clock);
 	clock->error = 0;
 	timekeeping_suspended = 0;
 	write_sequnlock_irqrestore(&xtime_lock, flags);

 	touch_softlockup_watchdog();

 	clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);

 	/* Resume hrtimers */
 	hres_timers_resume();

 	return 0;
 }

 static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
 {
 	unsigned long flags;

 	timekeeping_suspend_time = read_persistent_clock();

 	write_seqlock_irqsave(&xtime_lock, flags);
 	clocksource_forward_now();
 	timekeeping_suspended = 1;
 	write_sequnlock_irqrestore(&xtime_lock, flags);

 	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);

 	return 0;
 }

 /* sysfs resume/suspend bits for timekeeping */
 static struct sysdev_class timekeeping_sysclass = {
 	.name		= "timekeeping",
 	.resume		= timekeeping_resume,
 	.suspend	= timekeeping_suspend,
 };

 static struct sys_device device_timer = {
 	.id		= 0,
 	.cls		= &timekeeping_sysclass,
 };

 static int __init timekeeping_init_device(void)
 {
 	int error = sysdev_class_register(&timekeeping_sysclass);
 	if (!error)
 		error = sysdev_register(&device_timer);
 	return error;
 }

 device_initcall(timekeeping_init_device);

 /*
  * If the error is already larger, we look ahead even further
  * to compensate for late or lost adjustments.
  */
 static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
 						 s64 *offset)
 {
 	s64 tick_error, i;
 	u32 look_ahead, adj;
 	s32 error2, mult;

 	/*
 	 * Use the current error value to determine how much to look ahead.
 	 * The larger the error the slower we adjust for it to avoid problems
 	 * with losing too many ticks, otherwise we would overadjust and
 	 * produce an even larger error.  The smaller the adjustment the
 	 * faster we try to adjust for it, as lost ticks can do less harm
 	 * here.  This is tuned so that an error of about 1 msec is adjusted
 	 * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
 	 */
 	error2 = clock->error >> (NTP_SCALE_SHIFT + 22 - 2 * SHIFT_HZ);
 	error2 = abs(error2);
 	for (look_ahead = 0; error2 > 0; look_ahead++)
 		error2 >>= 2;

 	/*
 	 * Now calculate the error in (1 << look_ahead) ticks, but first
 	 * remove the single look ahead already included in the error.
 	 */
 	tick_error = tick_length >> (NTP_SCALE_SHIFT - clock->shift + 1);
 	tick_error -= clock->xtime_interval >> 1;
 	error = ((error - tick_error) >> look_ahead) + tick_error;

 	/* Finally calculate the adjustment shift value.  */
 	i = *interval;
 	mult = 1;
 	if (error < 0) {
 		error = -error;
 		*interval = -*interval;
 		*offset = -*offset;
 		mult = -1;
 	}
 	for (adj = 0; error > i; adj++)
 		error >>= 1;

 	*interval <<= adj;
 	*offset <<= adj;
 	return mult << adj;
 }

 /*
  * Adjust the multiplier to reduce the error value,
  * this is optimized for the most common adjustments of -1,0,1,
  * for other values we can do a bit more work.
  */
 static void clocksource_adjust(s64 offset)
 {
 	s64 error, interval = clock->cycle_interval;
 	int adj;

 	error = clock->error >> (NTP_SCALE_SHIFT - clock->shift - 1);
 	if (error > interval) {
 		error >>= 2;
 		if (likely(error <= interval))
 			adj = 1;
 		else
 			adj = clocksource_bigadjust(error, &interval, &offset);
 	} else if (error < -interval) {
 		error >>= 2;
 		if (likely(error >= -interval)) {
 			adj = -1;
 			interval = -interval;
 			offset = -offset;
 		} else
 			adj = clocksource_bigadjust(error, &interval, &offset);
 	} else
 		return;

 	clock->mult += adj;
 	clock->xtime_interval += interval;
 	clock->xtime_nsec -= offset;
 	clock->error -= (interval - offset) <<
 			(NTP_SCALE_SHIFT - clock->shift);
 }

 /**
  * update_wall_time - Uses the current clocksource to increment the wall time
  *
  * Called from the timer interrupt, must hold a write on xtime_lock.
  */
 void update_wall_time(void)
 {
 	cycle_t offset;

 	/* Make sure we're fully resumed: */
 	if (unlikely(timekeeping_suspended))
 		return;

 #ifdef CONFIG_GENERIC_TIME
 	offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask;
 #else
 	offset = clock->cycle_interval;
 #endif
 	clock->xtime_nsec = (s64)xtime.tv_nsec << clock->shift;

 	/* normally this loop will run just once, however in the
 	 * case of lost or late ticks, it will accumulate correctly.
 	 */
 	while (offset >= clock->cycle_interval) {
 		/* accumulate one interval */
 		offset -= clock->cycle_interval;
 		clock->cycle_last += clock->cycle_interval;

 		clock->xtime_nsec += clock->xtime_interval;
 		if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
 			clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
 			xtime.tv_sec++;
 			second_overflow();
 		}

 		clock->raw_time.tv_nsec += clock->raw_interval;
 		if (clock->raw_time.tv_nsec >= NSEC_PER_SEC) {
 			clock->raw_time.tv_nsec -= NSEC_PER_SEC;
 			clock->raw_time.tv_sec++;
 		}

 		/* accumulate error between NTP and clock interval */
 		clock->error += tick_length;
 		clock->error -= clock->xtime_interval << (NTP_SCALE_SHIFT - clock->shift);
 	}

 	/* correct the clock when NTP error is too big */
 	clocksource_adjust(offset);

 	/* store full nanoseconds into xtime after rounding it up and
 	 * add the remainder to the error difference.
 	 */
 	xtime.tv_nsec = ((s64)clock->xtime_nsec >> clock->shift) + 1;
 	clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
 	clock->error += clock->xtime_nsec << (NTP_SCALE_SHIFT - clock->shift);

 	update_xtime_cache(cyc2ns(clock, offset));

 	/* check to see if there is a new clocksource to use */
 	change_clocksource();
 	update_vsyscall(&xtime, clock);
 }

 /**
  * getboottime - Return the real time of system boot.
  * @ts:		pointer to the timespec to be set
  *
  * Returns the time of day in a timespec.
  *
  * This is based on the wall_to_monotonic offset and the total suspend
  * time. Calls to settimeofday will affect the value returned (which
  * basically means that however wrong your real time clock is at boot time,
  * you get the right time here).
  */
 void getboottime(struct timespec *ts)
 {
 	set_normalized_timespec(ts,
 		- (wall_to_monotonic.tv_sec + total_sleep_time),
 		- wall_to_monotonic.tv_nsec);
 }

 /**
  * monotonic_to_bootbased - Convert the monotonic time to boot based.
  * @ts:		pointer to the timespec to be converted
  */
 void monotonic_to_bootbased(struct timespec *ts)
 {
 	ts->tv_sec += total_sleep_time;
 }

 unsigned long get_seconds(void)
 {
 	return xtime_cache.tv_sec;
 }
 EXPORT_SYMBOL(get_seconds);


 struct timespec current_kernel_time(void)
 {
 	struct timespec now;
 	unsigned long seq;

 	do {
 		seq = read_seqbegin(&xtime_lock);

 		now = xtime_cache;
 	} while (read_seqretry(&xtime_lock, seq));

 	return now;
 }
 EXPORT_SYMBOL(current_kernel_time);
	/*
	* linux/kernel/time/timekeeping.c
	*
	* Kernel timekeeping code and accessor functions
	*
	* This code was moved from linux/kernel/timer.c.
	* Please see that file for copyright and history logs.
	*
	*/

	#include <linux/module.h>
	#include <linux/interrupt.h>
	#include <linux/percpu.h>
	#include <linux/init.h>
	#include <linux/mm.h>
	#include <linux/sysdev.h>
	#include <linux/clocksource.h>
	#include <linux/jiffies.h>
	#include <linux/time.h>
	#include <linux/tick.h>


	/*
	* This read-write spinlock protects us from races in SMP while
	* playing with xtime and avenrun.
	*/
	__cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);


	/*
	* The current time
	* wall_to_monotonic is what we need to add to xtime (or xtime corrected
	* for sub jiffie times) to get to monotonic time. Monotonic is pegged
	* at zero at system boot time, so wall_to_monotonic will be negative,
	* however, we will ALWAYS keep the tv_nsec part positive so we can use
	* the usual normalization.
	*
	* wall_to_monotonic is moved after resume from suspend for the monotonic
	* time not to jump. We need to add total_sleep_time to wall_to_monotonic
	* to get the real boot based time offset.
	*
	* - wall_to_monotonic is no longer the boot time, getboottime must be
	* used instead.
	*/
	struct timespec xtime __attribute__ ((aligned (16)));
	struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
	static unsigned long total_sleep_time; /* seconds */

	static struct timespec xtime_cache __attribute__ ((aligned (16)));
	void update_xtime_cache(u64 nsec)
	{
	xtime_cache = xtime;
	timespec_add_ns(&xtime_cache, nsec);
	}

	struct clocksource *clock;


	#ifdef CONFIG_GENERIC_TIME
	/**
	* clocksource_forward_now - update clock to the current time
	*
	* Forward the current clock to update its state since the last call to
	* update_wall_time(). This is useful before significant clock changes,
	* as it avoids having to deal with this time offset explicitly.
	*/
	static void clocksource_forward_now(void)
	{
	cycle_t cycle_now, cycle_delta;
	s64 nsec;

	cycle_now = clocksource_read(clock);
	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
	clock->cycle_last = cycle_now;

	nsec = cyc2ns(clock, cycle_delta);
	timespec_add_ns(&xtime, nsec);

	nsec = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;
	clock->raw_time.tv_nsec += nsec;
	}

	/**
	* getnstimeofday - Returns the time of day in a timespec
	* @ts: pointer to the timespec to be set
	*
	* Returns the time of day in a timespec.
	*/
	void getnstimeofday(struct timespec *ts)
	{
	cycle_t cycle_now, cycle_delta;
	unsigned long seq;
	s64 nsecs;

	do {
	seq = read_seqbegin(&xtime_lock);

	*ts = xtime;

	/* read clocksource: */
	cycle_now = clocksource_read(clock);

	/* calculate the delta since the last update_wall_time: */
	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

	/* convert to nanoseconds: */
	nsecs = cyc2ns(clock, cycle_delta);

	} while (read_seqretry(&xtime_lock, seq));

	timespec_add_ns(ts, nsecs);
	}

	EXPORT_SYMBOL(getnstimeofday);

	/**
	* do_gettimeofday - Returns the time of day in a timeval
	* @tv: pointer to the timeval to be set
	*
	* NOTE: Users should be converted to using getnstimeofday()
	*/
	void do_gettimeofday(struct timeval *tv)
	{
	struct timespec now;

	getnstimeofday(&now);
	tv->tv_sec = now.tv_sec;
	tv->tv_usec = now.tv_nsec/1000;
	}

	EXPORT_SYMBOL(do_gettimeofday);
	/**
	* do_settimeofday - Sets the time of day
	* @tv: pointer to the timespec variable containing the new time
	*
	* Sets the time of day to the new time and update NTP and notify hrtimers
	*/
	int do_settimeofday(struct timespec *tv)
	{
	struct timespec ts_delta;
	unsigned long flags;

	if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
	return -EINVAL;

	write_seqlock_irqsave(&xtime_lock, flags);

	clocksource_forward_now();

	ts_delta.tv_sec = tv->tv_sec - xtime.tv_sec;
	ts_delta.tv_nsec = tv->tv_nsec - xtime.tv_nsec;
	wall_to_monotonic = timespec_sub(wall_to_monotonic, ts_delta);

	xtime = *tv;

	update_xtime_cache(0);

	clock->error = 0;
	ntp_clear();

	update_vsyscall(&xtime, clock);

	write_sequnlock_irqrestore(&xtime_lock, flags);

	/* signal hrtimers about time change */
	clock_was_set();

	return 0;
	}

	EXPORT_SYMBOL(do_settimeofday);

	/**
	* change_clocksource - Swaps clocksources if a new one is available
	*
	* Accumulates current time interval and initializes new clocksource
	*/
	static void change_clocksource(void)
	{
	struct clocksource *new;

	new = clocksource_get_next();

	if (clock == new)
	return;

	clocksource_forward_now();

	new->raw_time = clock->raw_time;

	clock = new;
	clock->cycle_last = 0;
	clock->cycle_last = clocksource_read(new);
	clock->error = 0;
	clock->xtime_nsec = 0;
	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);

	tick_clock_notify();

	/*
	* We're holding xtime lock and waking up klogd would deadlock
	* us on enqueue. So no printing!
	printk(KERN_INFO "Time: %s clocksource has been installed.\n",
	clock->name);
	*/
	}
	#else
	static inline void clocksource_forward_now(void) { }
	static inline void change_clocksource(void) { }
	#endif

	/**
	* getrawmonotonic - Returns the raw monotonic time in a timespec
	* @ts: pointer to the timespec to be set
	*
	* Returns the raw monotonic time (completely un-modified by ntp)
	*/
	void getrawmonotonic(struct timespec *ts)
	{
	unsigned long seq;
	s64 nsecs;
	cycle_t cycle_now, cycle_delta;

	do {
	seq = read_seqbegin(&xtime_lock);

	/* read clocksource: */
	cycle_now = clocksource_read(clock);

	/* calculate the delta since the last update_wall_time: */
	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

	/* convert to nanoseconds: */
	nsecs = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;

	*ts = clock->raw_time;

	} while (read_seqretry(&xtime_lock, seq));

	timespec_add_ns(ts, nsecs);
	}
	EXPORT_SYMBOL(getrawmonotonic);


	/**
	* timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
	*/
	int timekeeping_valid_for_hres(void)
	{
	unsigned long seq;
	int ret;

	do {
	seq = read_seqbegin(&xtime_lock);

	ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

	} while (read_seqretry(&xtime_lock, seq));

	return ret;
	}

	/**
	* read_persistent_clock - Return time in seconds from the persistent clock.
	*
	* Weak dummy function for arches that do not yet support it.
	* Returns seconds from epoch using the battery backed persistent clock.
	* Returns zero if unsupported.
	*
	* XXX - Do be sure to remove it once all arches implement it.
	*/
	unsigned long __attribute__((weak)) read_persistent_clock(void)
	{
	return 0;
	}

	/*
	* timekeeping_init - Initializes the clocksource and common timekeeping values
	*/
	void __init timekeeping_init(void)
	{
	unsigned long flags;
	unsigned long sec = read_persistent_clock();

	write_seqlock_irqsave(&xtime_lock, flags);

	ntp_init();

	clock = clocksource_get_next();
	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
	clock->cycle_last = clocksource_read(clock);

	xtime.tv_sec = sec;
	xtime.tv_nsec = 0;
	set_normalized_timespec(&wall_to_monotonic,
	-xtime.tv_sec, -xtime.tv_nsec);
	update_xtime_cache(0);
	total_sleep_time = 0;
	write_sequnlock_irqrestore(&xtime_lock, flags);
	}

	/* flag for if timekeeping is suspended */
	static int timekeeping_suspended;
	/* time in seconds when suspend began */
	static unsigned long timekeeping_suspend_time;

	/**
	* timekeeping_resume - Resumes the generic timekeeping subsystem.
	* @dev: unused
	*
	* This is for the generic clocksource timekeeping.
	* xtime/wall_to_monotonic/jiffies/etc are
	* still managed by arch specific suspend/resume code.
	*/
	static int timekeeping_resume(struct sys_device *dev)
	{
	unsigned long flags;
	unsigned long now = read_persistent_clock();

	clocksource_resume();

	write_seqlock_irqsave(&xtime_lock, flags);

	if (now && (now > timekeeping_suspend_time)) {
	unsigned long sleep_length = now - timekeeping_suspend_time;

	xtime.tv_sec += sleep_length;
	wall_to_monotonic.tv_sec -= sleep_length;
	total_sleep_time += sleep_length;
	}
	update_xtime_cache(0);
	/* re-base the last cycle value */
	clock->cycle_last = 0;
	clock->cycle_last = clocksource_read(clock);
	clock->error = 0;
	timekeeping_suspended = 0;
	write_sequnlock_irqrestore(&xtime_lock, flags);

	touch_softlockup_watchdog();

	clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);

	/* Resume hrtimers */
	hres_timers_resume();

	return 0;
	}

	static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
	{
	unsigned long flags;

	timekeeping_suspend_time = read_persistent_clock();

	write_seqlock_irqsave(&xtime_lock, flags);
	clocksource_forward_now();
	timekeeping_suspended = 1;
	write_sequnlock_irqrestore(&xtime_lock, flags);

	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);

	return 0;
	}

	/* sysfs resume/suspend bits for timekeeping */
	static struct sysdev_class timekeeping_sysclass = {
	.name = "timekeeping",
	.resume = timekeeping_resume,
	.suspend = timekeeping_suspend,
	};

	static struct sys_device device_timer = {
	.id = 0,
	.cls = &timekeeping_sysclass,
	};

	static int __init timekeeping_init_device(void)
	{
	int error = sysdev_class_register(&timekeeping_sysclass);
	if (!error)
	error = sysdev_register(&device_timer);
	return error;
	}

	device_initcall(timekeeping_init_device);

	/*
	* If the error is already larger, we look ahead even further
	* to compensate for late or lost adjustments.
	*/
	static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
	s64 *offset)
	{
	s64 tick_error, i;
	u32 look_ahead, adj;
	s32 error2, mult;

	/*
	* Use the current error value to determine how much to look ahead.
	* The larger the error the slower we adjust for it to avoid problems
	* with losing too many ticks, otherwise we would overadjust and
	* produce an even larger error. The smaller the adjustment the
	* faster we try to adjust for it, as lost ticks can do less harm
	* here. This is tuned so that an error of about 1 msec is adjusted
	* within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
	*/
	error2 = clock->error >> (NTP_SCALE_SHIFT + 22 - 2 * SHIFT_HZ);
	error2 = abs(error2);
	for (look_ahead = 0; error2 > 0; look_ahead++)
	error2 >>= 2;

	/*
	* Now calculate the error in (1 << look_ahead) ticks, but first
	* remove the single look ahead already included in the error.
	*/
	tick_error = tick_length >> (NTP_SCALE_SHIFT - clock->shift + 1);
	tick_error -= clock->xtime_interval >> 1;
	error = ((error - tick_error) >> look_ahead) + tick_error;

	/* Finally calculate the adjustment shift value. */
	i = *interval;
	mult = 1;
	if (error < 0) {
	error = -error;
	interval = -interval;
	offset = -offset;
	mult = -1;
	}
	for (adj = 0; error > i; adj++)
	error >>= 1;

	*interval <<= adj;
	*offset <<= adj;
	return mult << adj;
	}

	/*
	* Adjust the multiplier to reduce the error value,
	* this is optimized for the most common adjustments of -1,0,1,
	* for other values we can do a bit more work.
	*/
	static void clocksource_adjust(s64 offset)
	{
	s64 error, interval = clock->cycle_interval;
	int adj;

	error = clock->error >> (NTP_SCALE_SHIFT - clock->shift - 1);
	if (error > interval) {
	error >>= 2;
	if (likely(error <= interval))
	adj = 1;
	else
	adj = clocksource_bigadjust(error, &interval, &offset);
	} else if (error < -interval) {
	error >>= 2;
	if (likely(error >= -interval)) {
	adj = -1;
	interval = -interval;
	offset = -offset;
	} else
	adj = clocksource_bigadjust(error, &interval, &offset);
	} else
	return;

	clock->mult += adj;
	clock->xtime_interval += interval;
	clock->xtime_nsec -= offset;
	clock->error -= (interval - offset) <<
	(NTP_SCALE_SHIFT - clock->shift);
	}

	/**
	* update_wall_time - Uses the current clocksource to increment the wall time
	*
	* Called from the timer interrupt, must hold a write on xtime_lock.
	*/
	void update_wall_time(void)
	{
	cycle_t offset;

	/* Make sure we're fully resumed: */
	if (unlikely(timekeeping_suspended))
	return;

	#ifdef CONFIG_GENERIC_TIME
	offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask;
	#else
	offset = clock->cycle_interval;
	#endif
	clock->xtime_nsec = (s64)xtime.tv_nsec << clock->shift;

	/* normally this loop will run just once, however in the
	* case of lost or late ticks, it will accumulate correctly.
	*/
	while (offset >= clock->cycle_interval) {
	/* accumulate one interval */
	offset -= clock->cycle_interval;
	clock->cycle_last += clock->cycle_interval;

	clock->xtime_nsec += clock->xtime_interval;
	if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
	clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
	xtime.tv_sec++;
	second_overflow();
	}

	clock->raw_time.tv_nsec += clock->raw_interval;
	if (clock->raw_time.tv_nsec >= NSEC_PER_SEC) {
	clock->raw_time.tv_nsec -= NSEC_PER_SEC;
	clock->raw_time.tv_sec++;
	}

	/* accumulate error between NTP and clock interval */
	clock->error += tick_length;
	clock->error -= clock->xtime_interval << (NTP_SCALE_SHIFT - clock->shift);
	}

	/* correct the clock when NTP error is too big */
	clocksource_adjust(offset);

	/* store full nanoseconds into xtime after rounding it up and
	* add the remainder to the error difference.
	*/
	xtime.tv_nsec = ((s64)clock->xtime_nsec >> clock->shift) + 1;
	clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
	clock->error += clock->xtime_nsec << (NTP_SCALE_SHIFT - clock->shift);

	update_xtime_cache(cyc2ns(clock, offset));

	/* check to see if there is a new clocksource to use */
	change_clocksource();
	update_vsyscall(&xtime, clock);
	}

	/**
	* getboottime - Return the real time of system boot.
	* @ts: pointer to the timespec to be set
	*
	* Returns the time of day in a timespec.
	*
	* This is based on the wall_to_monotonic offset and the total suspend
	* time. Calls to settimeofday will affect the value returned (which
	* basically means that however wrong your real time clock is at boot time,
	* you get the right time here).
	*/
	void getboottime(struct timespec *ts)
	{
	set_normalized_timespec(ts,
	- (wall_to_monotonic.tv_sec + total_sleep_time),
	- wall_to_monotonic.tv_nsec);
	}

	/**
	* monotonic_to_bootbased - Convert the monotonic time to boot based.
	* @ts: pointer to the timespec to be converted
	*/
	void monotonic_to_bootbased(struct timespec *ts)
	{
	ts->tv_sec += total_sleep_time;
	}

	unsigned long get_seconds(void)
	{
	return xtime_cache.tv_sec;
	}
	EXPORT_SYMBOL(get_seconds);


	struct timespec current_kernel_time(void)
	{
	struct timespec now;
	unsigned long seq;

	do {
	seq = read_seqbegin(&xtime_lock);

	now = xtime_cache;
	} while (read_seqretry(&xtime_lock, seq));

	return now;
	}
	EXPORT_SYMBOL(current_kernel_time);