/*
   *  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/sched.h>

  #include <linux/syscore_ops.h>

  #include <linux/clocksource.h>
  #include <linux/jiffies.h>
  #include <linux/time.h>
  #include <linux/tick.h>

  #include <linux/stop_machine.h>

  /* Structure holding internal timekeeping values. */
  struct timekeeper {
  	/* Current clocksource used for timekeeping. */
  	struct clocksource *clock;

  	/* The shift value of the current clocksource. */
  	int	shift;

  
  	/* Number of clock cycles in one NTP interval. */
  	cycle_t cycle_interval;
  	/* Number of clock shifted nano seconds in one NTP interval. */
  	u64	xtime_interval;

  	/* shifted nano seconds left over when rounding cycle_interval */
  	s64	xtime_remainder;

  	/* Raw nano seconds accumulated per NTP interval. */
  	u32	raw_interval;
  
  	/* Clock shifted nano seconds remainder not stored in xtime.tv_nsec. */
  	u64	xtime_nsec;
  	/* Difference between accumulated time and NTP time in ntp
  	 * shifted nano seconds. */
  	s64	ntp_error;

  	/* Shift conversion between clock shifted nano seconds and
  	 * ntp shifted nano seconds. */
  	int	ntp_error_shift;

  	/* NTP adjusted clock multiplier */
  	u32	mult;

  };

  static struct timekeeper timekeeper;

  
  /**
   * timekeeper_setup_internals - Set up internals to use clocksource clock.
   *
   * @clock:		Pointer to clocksource.
   *
   * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
   * pair and interval request.
   *
   * Unless you're the timekeeping code, you should not be using this!
   */
  static void timekeeper_setup_internals(struct clocksource *clock)
  {
  	cycle_t interval;

  	u64 tmp, ntpinterval;

  
  	timekeeper.clock = clock;
  	clock->cycle_last = clock->read(clock);
  
  	/* Do the ns -> cycle conversion first, using original mult */
  	tmp = NTP_INTERVAL_LENGTH;
  	tmp <<= clock->shift;

  	ntpinterval = tmp;

  	tmp += clock->mult/2;
  	do_div(tmp, clock->mult);

  	if (tmp == 0)
  		tmp = 1;
  
  	interval = (cycle_t) tmp;
  	timekeeper.cycle_interval = interval;
  
  	/* Go back from cycles -> shifted ns */
  	timekeeper.xtime_interval = (u64) interval * clock->mult;

  	timekeeper.xtime_remainder = ntpinterval - timekeeper.xtime_interval;

  	timekeeper.raw_interval =

  		((u64) interval * clock->mult) >> clock->shift;

  
  	timekeeper.xtime_nsec = 0;

  	timekeeper.shift = clock->shift;

  
  	timekeeper.ntp_error = 0;

  	timekeeper.ntp_error_shift = NTP_SCALE_SHIFT - clock->shift;

  
  	/*
  	 * The timekeeper keeps its own mult values for the currently
  	 * active clocksource. These value will be adjusted via NTP
  	 * to counteract clock drifting.
  	 */
  	timekeeper.mult = clock->mult;

  }

  /* Timekeeper helper functions. */
  static inline s64 timekeeping_get_ns(void)
  {
  	cycle_t cycle_now, cycle_delta;
  	struct clocksource *clock;
  
  	/* read clocksource: */
  	clock = timekeeper.clock;
  	cycle_now = clock->read(clock);
  
  	/* calculate the delta since the last update_wall_time: */
  	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
  
  	/* return delta convert to nanoseconds using ntp adjusted mult. */
  	return clocksource_cyc2ns(cycle_delta, timekeeper.mult,
  				  timekeeper.shift);
  }
  
  static inline s64 timekeeping_get_ns_raw(void)
  {
  	cycle_t cycle_now, cycle_delta;
  	struct clocksource *clock;
  
  	/* read clocksource: */
  	clock = timekeeper.clock;
  	cycle_now = clock->read(clock);
  
  	/* calculate the delta since the last update_wall_time: */
  	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

  	/* return delta convert to nanoseconds. */

  	return clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);
  }

  /*
   * This read-write spinlock protects us from races in SMP while

   * playing with xtime.

   */

  __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.

   */

  static struct timespec xtime __attribute__ ((aligned (16)));
  static struct timespec wall_to_monotonic __attribute__ ((aligned (16)));

  static struct timespec total_sleep_time;

  /*
   * The raw monotonic time for the CLOCK_MONOTONIC_RAW posix clock.
   */

  static struct timespec raw_time;

  /* flag for if timekeeping is suspended */
  int __read_mostly timekeeping_suspended;

  /* must hold xtime_lock */
  void timekeeping_leap_insert(int leapsecond)
  {
  	xtime.tv_sec += leapsecond;
  	wall_to_monotonic.tv_sec -= leapsecond;

  	update_vsyscall(&xtime, &wall_to_monotonic, timekeeper.clock,
  			timekeeper.mult);

  }

  /**

   * timekeeping_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 timekeeping_forward_now(void)

  {
  	cycle_t cycle_now, cycle_delta;

  	struct clocksource *clock;

  	s64 nsec;

  	clock = timekeeper.clock;

  	cycle_now = clock->read(clock);

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

  	clock->cycle_last = cycle_now;

  	nsec = clocksource_cyc2ns(cycle_delta, timekeeper.mult,
  				  timekeeper.shift);

  
  	/* If arch requires, add in gettimeoffset() */
  	nsec += arch_gettimeoffset();

  	timespec_add_ns(&xtime, nsec);

  	nsec = clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);

  	timespec_add_ns(&raw_time, 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)

  {
  	unsigned long seq;
  	s64 nsecs;

  	WARN_ON(timekeeping_suspended);

  	do {
  		seq = read_seqbegin(&xtime_lock);
  
  		*ts = xtime;

  		nsecs = timekeeping_get_ns();

  		/* If arch requires, add in gettimeoffset() */
  		nsecs += arch_gettimeoffset();

  	} while (read_seqretry(&xtime_lock, seq));
  
  	timespec_add_ns(ts, nsecs);
  }

  EXPORT_SYMBOL(getnstimeofday);

  ktime_t ktime_get(void)
  {

  	unsigned int seq;
  	s64 secs, nsecs;
  
  	WARN_ON(timekeeping_suspended);
  
  	do {
  		seq = read_seqbegin(&xtime_lock);
  		secs = xtime.tv_sec + wall_to_monotonic.tv_sec;
  		nsecs = xtime.tv_nsec + wall_to_monotonic.tv_nsec;

  		nsecs += timekeeping_get_ns();

  		/* If arch requires, add in gettimeoffset() */
  		nsecs += arch_gettimeoffset();

  
  	} while (read_seqretry(&xtime_lock, seq));
  	/*
  	 * Use ktime_set/ktime_add_ns to create a proper ktime on
  	 * 32-bit architectures without CONFIG_KTIME_SCALAR.
  	 */
  	return ktime_add_ns(ktime_set(secs, 0), nsecs);
  }
  EXPORT_SYMBOL_GPL(ktime_get);
  
  /**
   * ktime_get_ts - get the monotonic clock in timespec format
   * @ts:		pointer to timespec variable
   *
   * The function calculates the monotonic clock from the realtime
   * clock and the wall_to_monotonic offset and stores the result
   * in normalized timespec format in the variable pointed to by @ts.
   */
  void ktime_get_ts(struct timespec *ts)
  {

  	struct timespec tomono;
  	unsigned int seq;
  	s64 nsecs;
  
  	WARN_ON(timekeeping_suspended);
  
  	do {
  		seq = read_seqbegin(&xtime_lock);
  		*ts = xtime;
  		tomono = wall_to_monotonic;

  		nsecs = timekeeping_get_ns();

  		/* If arch requires, add in gettimeoffset() */
  		nsecs += arch_gettimeoffset();

  
  	} while (read_seqretry(&xtime_lock, seq));
  
  	set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec,
  				ts->tv_nsec + tomono.tv_nsec + nsecs);
  }
  EXPORT_SYMBOL_GPL(ktime_get_ts);

  #ifdef CONFIG_NTP_PPS
  
  /**
   * getnstime_raw_and_real - get day and raw monotonic time in timespec format
   * @ts_raw:	pointer to the timespec to be set to raw monotonic time
   * @ts_real:	pointer to the timespec to be set to the time of day
   *
   * This function reads both the time of day and raw monotonic time at the
   * same time atomically and stores the resulting timestamps in timespec
   * format.
   */
  void getnstime_raw_and_real(struct timespec *ts_raw, struct timespec *ts_real)
  {
  	unsigned long seq;
  	s64 nsecs_raw, nsecs_real;
  
  	WARN_ON_ONCE(timekeeping_suspended);
  
  	do {
  		u32 arch_offset;
  
  		seq = read_seqbegin(&xtime_lock);
  
  		*ts_raw = raw_time;
  		*ts_real = xtime;
  
  		nsecs_raw = timekeeping_get_ns_raw();
  		nsecs_real = timekeeping_get_ns();
  
  		/* If arch requires, add in gettimeoffset() */
  		arch_offset = arch_gettimeoffset();
  		nsecs_raw += arch_offset;
  		nsecs_real += arch_offset;
  
  	} while (read_seqretry(&xtime_lock, seq));
  
  	timespec_add_ns(ts_raw, nsecs_raw);
  	timespec_add_ns(ts_real, nsecs_real);
  }
  EXPORT_SYMBOL(getnstime_raw_and_real);
  
  #endif /* CONFIG_NTP_PPS */

  /**
   * 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(const 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);

  	timekeeping_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;

  	timekeeper.ntp_error = 0;

  	ntp_clear();

  	update_vsyscall(&xtime, &wall_to_monotonic, timekeeper.clock,
  				timekeeper.mult);

  
  	write_sequnlock_irqrestore(&xtime_lock, flags);
  
  	/* signal hrtimers about time change */
  	clock_was_set();
  
  	return 0;
  }
  
  EXPORT_SYMBOL(do_settimeofday);

  
  /**
   * timekeeping_inject_offset - Adds or subtracts from the current time.
   * @tv:		pointer to the timespec variable containing the offset
   *
   * Adds or subtracts an offset value from the current time.
   */
  int timekeeping_inject_offset(struct timespec *ts)
  {
  	unsigned long flags;
  
  	if ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC)
  		return -EINVAL;
  
  	write_seqlock_irqsave(&xtime_lock, flags);
  
  	timekeeping_forward_now();
  
  	xtime = timespec_add(xtime, *ts);
  	wall_to_monotonic = timespec_sub(wall_to_monotonic, *ts);
  
  	timekeeper.ntp_error = 0;
  	ntp_clear();
  
  	update_vsyscall(&xtime, &wall_to_monotonic, timekeeper.clock,
  				timekeeper.mult);
  
  	write_sequnlock_irqrestore(&xtime_lock, flags);
  
  	/* signal hrtimers about time change */
  	clock_was_set();
  
  	return 0;
  }
  EXPORT_SYMBOL(timekeeping_inject_offset);

  /**
   * change_clocksource - Swaps clocksources if a new one is available
   *
   * Accumulates current time interval and initializes new clocksource
   */

  static int change_clocksource(void *data)

  {

  	struct clocksource *new, *old;

  	new = (struct clocksource *) data;

  	timekeeping_forward_now();

  	if (!new->enable || new->enable(new) == 0) {
  		old = timekeeper.clock;
  		timekeeper_setup_internals(new);
  		if (old->disable)
  			old->disable(old);
  	}
  	return 0;
  }

  /**
   * timekeeping_notify - Install a new clock source
   * @clock:		pointer to the clock source
   *
   * This function is called from clocksource.c after a new, better clock
   * source has been registered. The caller holds the clocksource_mutex.
   */
  void timekeeping_notify(struct clocksource *clock)
  {
  	if (timekeeper.clock == clock)

  		return;

  	stop_machine(change_clocksource, clock, NULL);

  	tick_clock_notify();

  }

  /**
   * ktime_get_real - get the real (wall-) time in ktime_t format
   *
   * returns the time in ktime_t format
   */
  ktime_t ktime_get_real(void)
  {
  	struct timespec now;
  
  	getnstimeofday(&now);
  
  	return timespec_to_ktime(now);
  }
  EXPORT_SYMBOL_GPL(ktime_get_real);

  
  /**

   * 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;

  
  	do {
  		seq = read_seqbegin(&xtime_lock);

  		nsecs = timekeeping_get_ns_raw();

  		*ts = 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 = timekeeper.clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

  
  	} while (read_seqretry(&xtime_lock, seq));
  
  	return ret;
  }
  
  /**

   * timekeeping_max_deferment - Returns max time the clocksource can be deferred
   *
   * Caller must observe xtime_lock via read_seqbegin/read_seqretry to
   * ensure that the clocksource does not change!
   */
  u64 timekeeping_max_deferment(void)
  {
  	return timekeeper.clock->max_idle_ns;
  }
  
  /**

   * read_persistent_clock -  Return time from the persistent clock.

   *
   * Weak dummy function for arches that do not yet support it.

   * Reads the time from the battery backed persistent clock.
   * Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.

   *
   *  XXX - Do be sure to remove it once all arches implement it.
   */

  void __attribute__((weak)) read_persistent_clock(struct timespec *ts)

  {

  	ts->tv_sec = 0;
  	ts->tv_nsec = 0;

  }

  /**
   * read_boot_clock -  Return time of the system start.
   *
   * Weak dummy function for arches that do not yet support it.
   * Function to read the exact time the system has been started.
   * Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
   *
   *  XXX - Do be sure to remove it once all arches implement it.
   */
  void __attribute__((weak)) read_boot_clock(struct timespec *ts)
  {
  	ts->tv_sec = 0;
  	ts->tv_nsec = 0;
  }

  /*
   * timekeeping_init - Initializes the clocksource and common timekeeping values
   */
  void __init timekeeping_init(void)
  {

  	struct clocksource *clock;

  	unsigned long flags;

  	struct timespec now, boot;

  
  	read_persistent_clock(&now);

  	read_boot_clock(&boot);

  
  	write_seqlock_irqsave(&xtime_lock, flags);

  	ntp_init();

  	clock = clocksource_default_clock();

  	if (clock->enable)
  		clock->enable(clock);

  	timekeeper_setup_internals(clock);

  	xtime.tv_sec = now.tv_sec;
  	xtime.tv_nsec = now.tv_nsec;

  	raw_time.tv_sec = 0;
  	raw_time.tv_nsec = 0;

  	if (boot.tv_sec == 0 && boot.tv_nsec == 0) {
  		boot.tv_sec = xtime.tv_sec;
  		boot.tv_nsec = xtime.tv_nsec;
  	}

  	set_normalized_timespec(&wall_to_monotonic,

  				-boot.tv_sec, -boot.tv_nsec);

  	total_sleep_time.tv_sec = 0;
  	total_sleep_time.tv_nsec = 0;

  	write_sequnlock_irqrestore(&xtime_lock, flags);
  }

  /* time in seconds when suspend began */

  static struct timespec timekeeping_suspend_time;

  
  /**

   * __timekeeping_inject_sleeptime - Internal function to add sleep interval
   * @delta: pointer to a timespec delta value
   *
   * Takes a timespec offset measuring a suspend interval and properly
   * adds the sleep offset to the timekeeping variables.
   */
  static void __timekeeping_inject_sleeptime(struct timespec *delta)
  {

  	if (!timespec_valid(delta)) {

  		printk(KERN_WARNING "__timekeeping_inject_sleeptime: Invalid "

  					"sleep delta value!
  ");
  		return;
  	}

  	xtime = timespec_add(xtime, *delta);
  	wall_to_monotonic = timespec_sub(wall_to_monotonic, *delta);
  	total_sleep_time = timespec_add(total_sleep_time, *delta);
  }
  
  
  /**
   * timekeeping_inject_sleeptime - Adds suspend interval to timeekeeping values
   * @delta: pointer to a timespec delta value
   *
   * This hook is for architectures that cannot support read_persistent_clock
   * because their RTC/persistent clock is only accessible when irqs are enabled.
   *
   * This function should only be called by rtc_resume(), and allows
   * a suspend offset to be injected into the timekeeping values.
   */
  void timekeeping_inject_sleeptime(struct timespec *delta)
  {
  	unsigned long flags;
  	struct timespec ts;
  
  	/* Make sure we don't set the clock twice */
  	read_persistent_clock(&ts);
  	if (!(ts.tv_sec == 0 && ts.tv_nsec == 0))
  		return;
  
  	write_seqlock_irqsave(&xtime_lock, flags);
  	timekeeping_forward_now();
  
  	__timekeeping_inject_sleeptime(delta);
  
  	timekeeper.ntp_error = 0;
  	ntp_clear();
  	update_vsyscall(&xtime, &wall_to_monotonic, timekeeper.clock,
  				timekeeper.mult);
  
  	write_sequnlock_irqrestore(&xtime_lock, flags);
  
  	/* signal hrtimers about time change */
  	clock_was_set();
  }
  
  
  /**

   * timekeeping_resume - Resumes the generic timekeeping subsystem.

   *
   * This is for the generic clocksource timekeeping.
   * xtime/wall_to_monotonic/jiffies/etc are
   * still managed by arch specific suspend/resume code.
   */

  static void timekeeping_resume(void)

  {
  	unsigned long flags;

  	struct timespec ts;
  
  	read_persistent_clock(&ts);

  	clocksource_resume();

  	write_seqlock_irqsave(&xtime_lock, flags);

  	if (timespec_compare(&ts, &timekeeping_suspend_time) > 0) {
  		ts = timespec_sub(ts, timekeeping_suspend_time);

  		__timekeeping_inject_sleeptime(&ts);

  	}
  	/* re-base the last cycle value */

  	timekeeper.clock->cycle_last = timekeeper.clock->read(timekeeper.clock);
  	timekeeper.ntp_error = 0;

  	timekeeping_suspended = 0;
  	write_sequnlock_irqrestore(&xtime_lock, flags);
  
  	touch_softlockup_watchdog();
  
  	clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);
  
  	/* Resume hrtimers */

  	hrtimers_resume();

  }

  static int timekeeping_suspend(void)

  {
  	unsigned long flags;

  	struct timespec		delta, delta_delta;
  	static struct timespec	old_delta;

  	read_persistent_clock(&timekeeping_suspend_time);

  	write_seqlock_irqsave(&xtime_lock, flags);

  	timekeeping_forward_now();

  	timekeeping_suspended = 1;

  
  	/*
  	 * To avoid drift caused by repeated suspend/resumes,
  	 * which each can add ~1 second drift error,
  	 * try to compensate so the difference in system time
  	 * and persistent_clock time stays close to constant.
  	 */
  	delta = timespec_sub(xtime, timekeeping_suspend_time);
  	delta_delta = timespec_sub(delta, old_delta);
  	if (abs(delta_delta.tv_sec)  >= 2) {
  		/*
  		 * if delta_delta is too large, assume time correction
  		 * has occured and set old_delta to the current delta.
  		 */
  		old_delta = delta;
  	} else {
  		/* Otherwise try to adjust old_system to compensate */
  		timekeeping_suspend_time =
  			timespec_add(timekeeping_suspend_time, delta_delta);
  	}

  	write_sequnlock_irqrestore(&xtime_lock, flags);
  
  	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);

  	clocksource_suspend();

  
  	return 0;
  }
  
  /* sysfs resume/suspend bits for timekeeping */

  static struct syscore_ops timekeeping_syscore_ops = {

  	.resume		= timekeeping_resume,
  	.suspend	= timekeeping_suspend,

  };

  static int __init timekeeping_init_ops(void)

  {

  	register_syscore_ops(&timekeeping_syscore_ops);
  	return 0;

  }

  device_initcall(timekeeping_init_ops);

  
  /*
   * If the error is already larger, we look ahead even further
   * to compensate for late or lost adjustments.
   */

  static __always_inline int timekeeping_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 = timekeeper.ntp_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 >> (timekeeper.ntp_error_shift + 1);

  	tick_error -= timekeeper.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 timekeeping_adjust(s64 offset)

  {

  	s64 error, interval = timekeeper.cycle_interval;

  	int adj;

  	/*
  	 * The point of this is to check if the error is greater then half
  	 * an interval.
  	 *
  	 * First we shift it down from NTP_SHIFT to clocksource->shifted nsecs.
  	 *
  	 * Note we subtract one in the shift, so that error is really error*2.

  	 * This "saves" dividing(shifting) interval twice, but keeps the
  	 * (error > interval) comparison as still measuring if error is

  	 * larger then half an interval.
  	 *

  	 * Note: It does not "save" on aggravation when reading the code.

  	 */

  	error = timekeeper.ntp_error >> (timekeeper.ntp_error_shift - 1);

  	if (error > interval) {

  		/*
  		 * We now divide error by 4(via shift), which checks if
  		 * the error is greater then twice the interval.
  		 * If it is greater, we need a bigadjust, if its smaller,
  		 * we can adjust by 1.
  		 */

  		error >>= 2;

  		/*
  		 * XXX - In update_wall_time, we round up to the next
  		 * nanosecond, and store the amount rounded up into
  		 * the error. This causes the likely below to be unlikely.
  		 *

  		 * The proper fix is to avoid rounding up by using

  		 * the high precision timekeeper.xtime_nsec instead of
  		 * xtime.tv_nsec everywhere. Fixing this will take some
  		 * time.
  		 */

  		if (likely(error <= interval))
  			adj = 1;
  		else

  			adj = timekeeping_bigadjust(error, &interval, &offset);

  	} else if (error < -interval) {

  		/* See comment above, this is just switched for the negative */

  		error >>= 2;
  		if (likely(error >= -interval)) {
  			adj = -1;
  			interval = -interval;
  			offset = -offset;
  		} else

  			adj = timekeeping_bigadjust(error, &interval, &offset);

  	} else /* No adjustment needed */

  		return;

  	WARN_ONCE(timekeeper.clock->maxadj &&
  			(timekeeper.mult + adj > timekeeper.clock->mult +
  						timekeeper.clock->maxadj),
  			"Adjusting %s more then 11%% (%ld vs %ld)
  ",
  			timekeeper.clock->name, (long)timekeeper.mult + adj,
  			(long)timekeeper.clock->mult +
  				timekeeper.clock->maxadj);

  	/*
  	 * So the following can be confusing.
  	 *
  	 * To keep things simple, lets assume adj == 1 for now.
  	 *
  	 * When adj != 1, remember that the interval and offset values
  	 * have been appropriately scaled so the math is the same.
  	 *
  	 * The basic idea here is that we're increasing the multiplier
  	 * by one, this causes the xtime_interval to be incremented by
  	 * one cycle_interval. This is because:
  	 *	xtime_interval = cycle_interval * mult
  	 * So if mult is being incremented by one:
  	 *	xtime_interval = cycle_interval * (mult + 1)
  	 * Its the same as:
  	 *	xtime_interval = (cycle_interval * mult) + cycle_interval
  	 * Which can be shortened to:
  	 *	xtime_interval += cycle_interval
  	 *
  	 * So offset stores the non-accumulated cycles. Thus the current
  	 * time (in shifted nanoseconds) is:
  	 *	now = (offset * adj) + xtime_nsec
  	 * Now, even though we're adjusting the clock frequency, we have
  	 * to keep time consistent. In other words, we can't jump back
  	 * in time, and we also want to avoid jumping forward in time.
  	 *
  	 * So given the same offset value, we need the time to be the same
  	 * both before and after the freq adjustment.
  	 *	now = (offset * adj_1) + xtime_nsec_1
  	 *	now = (offset * adj_2) + xtime_nsec_2
  	 * So:
  	 *	(offset * adj_1) + xtime_nsec_1 =
  	 *		(offset * adj_2) + xtime_nsec_2
  	 * And we know:
  	 *	adj_2 = adj_1 + 1
  	 * So:
  	 *	(offset * adj_1) + xtime_nsec_1 =
  	 *		(offset * (adj_1+1)) + xtime_nsec_2
  	 *	(offset * adj_1) + xtime_nsec_1 =
  	 *		(offset * adj_1) + offset + xtime_nsec_2
  	 * Canceling the sides:
  	 *	xtime_nsec_1 = offset + xtime_nsec_2
  	 * Which gives us:
  	 *	xtime_nsec_2 = xtime_nsec_1 - offset
  	 * Which simplfies to:
  	 *	xtime_nsec -= offset
  	 *
  	 * XXX - TODO: Doc ntp_error calculation.
  	 */

  	timekeeper.mult += adj;

  	timekeeper.xtime_interval += interval;
  	timekeeper.xtime_nsec -= offset;
  	timekeeper.ntp_error -= (interval - offset) <<

  				timekeeper.ntp_error_shift;

  }

  /**

   * logarithmic_accumulation - shifted accumulation of cycles
   *
   * This functions accumulates a shifted interval of cycles into
   * into a shifted interval nanoseconds. Allows for O(log) accumulation
   * loop.
   *
   * Returns the unconsumed cycles.
   */
  static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
  {
  	u64 nsecps = (u64)NSEC_PER_SEC << timekeeper.shift;

  	u64 raw_nsecs;

  
  	/* If the offset is smaller then a shifted interval, do nothing */
  	if (offset < timekeeper.cycle_interval<<shift)
  		return offset;
  
  	/* Accumulate one shifted interval */
  	offset -= timekeeper.cycle_interval << shift;
  	timekeeper.clock->cycle_last += timekeeper.cycle_interval << shift;
  
  	timekeeper.xtime_nsec += timekeeper.xtime_interval << shift;
  	while (timekeeper.xtime_nsec >= nsecps) {
  		timekeeper.xtime_nsec -= nsecps;
  		xtime.tv_sec++;
  		second_overflow();
  	}

  	/* Accumulate raw time */
  	raw_nsecs = timekeeper.raw_interval << shift;
  	raw_nsecs += raw_time.tv_nsec;

  	if (raw_nsecs >= NSEC_PER_SEC) {
  		u64 raw_secs = raw_nsecs;
  		raw_nsecs = do_div(raw_secs, NSEC_PER_SEC);
  		raw_time.tv_sec += raw_secs;

  	}

  	raw_time.tv_nsec = raw_nsecs;

  
  	/* Accumulate error between NTP and clock interval */
  	timekeeper.ntp_error += tick_length << shift;

  	timekeeper.ntp_error -=
  	    (timekeeper.xtime_interval + timekeeper.xtime_remainder) <<

  				(timekeeper.ntp_error_shift + shift);
  
  	return offset;
  }

  /**
   * update_wall_time - Uses the current clocksource to increment the wall time
   *
   * Called from the timer interrupt, must hold a write on xtime_lock.
   */

  static void update_wall_time(void)

  {

  	struct clocksource *clock;

  	cycle_t offset;

  	int shift = 0, maxshift;

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

  	clock = timekeeper.clock;

  
  #ifdef CONFIG_ARCH_USES_GETTIMEOFFSET

  	offset = timekeeper.cycle_interval;

  #else
  	offset = (clock->read(clock) - clock->cycle_last) & clock->mask;

  #endif

  	timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift;

  	/*
  	 * With NO_HZ we may have to accumulate many cycle_intervals
  	 * (think "ticks") worth of time at once. To do this efficiently,
  	 * we calculate the largest doubling multiple of cycle_intervals
  	 * that is smaller then the offset. We then accumulate that
  	 * chunk in one go, and then try to consume the next smaller
  	 * doubled multiple.

  	 */

  	shift = ilog2(offset) - ilog2(timekeeper.cycle_interval);
  	shift = max(0, shift);
  	/* Bound shift to one less then what overflows tick_length */
  	maxshift = (8*sizeof(tick_length) - (ilog2(tick_length)+1)) - 1;
  	shift = min(shift, maxshift);

  	while (offset >= timekeeper.cycle_interval) {

  		offset = logarithmic_accumulation(offset, shift);

  		if(offset < timekeeper.cycle_interval<<shift)
  			shift--;

  	}
  
  	/* correct the clock when NTP error is too big */

  	timekeeping_adjust(offset);

  	/*
  	 * Since in the loop above, we accumulate any amount of time
  	 * in xtime_nsec over a second into xtime.tv_sec, its possible for
  	 * xtime_nsec to be fairly small after the loop. Further, if we're

  	 * slightly speeding the clocksource up in timekeeping_adjust(),

  	 * its possible the required corrective factor to xtime_nsec could
  	 * cause it to underflow.
  	 *
  	 * Now, we cannot simply roll the accumulated second back, since
  	 * the NTP subsystem has been notified via second_overflow. So
  	 * instead we push xtime_nsec forward by the amount we underflowed,
  	 * and add that amount into the error.
  	 *
  	 * We'll correct this error next time through this function, when
  	 * xtime_nsec is not as small.
  	 */

  	if (unlikely((s64)timekeeper.xtime_nsec < 0)) {
  		s64 neg = -(s64)timekeeper.xtime_nsec;
  		timekeeper.xtime_nsec = 0;

  		timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;

  	}

  
  	/*
  	 * Store full nanoseconds into xtime after rounding it up and

  	 * add the remainder to the error difference.
  	 */

  	xtime.tv_nsec =	((s64) timekeeper.xtime_nsec >> timekeeper.shift) + 1;
  	timekeeper.xtime_nsec -= (s64) xtime.tv_nsec << timekeeper.shift;
  	timekeeper.ntp_error +=	timekeeper.xtime_nsec <<
  				timekeeper.ntp_error_shift;

  	/*
  	 * Finally, make sure that after the rounding
  	 * xtime.tv_nsec isn't larger then NSEC_PER_SEC
  	 */
  	if (unlikely(xtime.tv_nsec >= NSEC_PER_SEC)) {
  		xtime.tv_nsec -= NSEC_PER_SEC;
  		xtime.tv_sec++;
  		second_overflow();
  	}

  	/* check to see if there is a new clocksource to use */

  	update_vsyscall(&xtime, &wall_to_monotonic, timekeeper.clock,
  				timekeeper.mult);

  }

  
  /**
   * getboottime - Return the real time of system boot.
   * @ts:		pointer to the timespec to be set
   *

   * Returns the wall-time of boot 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)
  {

  	struct timespec boottime = {
  		.tv_sec = wall_to_monotonic.tv_sec + total_sleep_time.tv_sec,
  		.tv_nsec = wall_to_monotonic.tv_nsec + total_sleep_time.tv_nsec
  	};

  	set_normalized_timespec(ts, -boottime.tv_sec, -boottime.tv_nsec);

  }

  EXPORT_SYMBOL_GPL(getboottime);

  
  /**
   * get_monotonic_boottime - Returns monotonic time since boot
   * @ts:		pointer to the timespec to be set
   *
   * Returns the monotonic time since boot in a timespec.
   *
   * This is similar to CLOCK_MONTONIC/ktime_get_ts, but also
   * includes the time spent in suspend.
   */
  void get_monotonic_boottime(struct timespec *ts)
  {
  	struct timespec tomono, sleep;
  	unsigned int seq;
  	s64 nsecs;
  
  	WARN_ON(timekeeping_suspended);
  
  	do {
  		seq = read_seqbegin(&xtime_lock);
  		*ts = xtime;
  		tomono = wall_to_monotonic;
  		sleep = total_sleep_time;
  		nsecs = timekeeping_get_ns();
  
  	} while (read_seqretry(&xtime_lock, seq));
  
  	set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec + sleep.tv_sec,
  			ts->tv_nsec + tomono.tv_nsec + sleep.tv_nsec + nsecs);
  }
  EXPORT_SYMBOL_GPL(get_monotonic_boottime);
  
  /**
   * ktime_get_boottime - Returns monotonic time since boot in a ktime
   *
   * Returns the monotonic time since boot in a ktime
   *
   * This is similar to CLOCK_MONTONIC/ktime_get, but also
   * includes the time spent in suspend.
   */
  ktime_t ktime_get_boottime(void)
  {
  	struct timespec ts;
  
  	get_monotonic_boottime(&ts);
  	return timespec_to_ktime(ts);
  }
  EXPORT_SYMBOL_GPL(ktime_get_boottime);

  /**
   * 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 = timespec_add(*ts, total_sleep_time);

  }

  EXPORT_SYMBOL_GPL(monotonic_to_bootbased);

  unsigned long get_seconds(void)
  {

  	return xtime.tv_sec;

  }
  EXPORT_SYMBOL(get_seconds);

  struct timespec __current_kernel_time(void)
  {

  	return xtime;

  }

  struct timespec current_kernel_time(void)
  {
  	struct timespec now;
  	unsigned long seq;
  
  	do {
  		seq = read_seqbegin(&xtime_lock);

  		now = xtime;

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

  EXPORT_SYMBOL(current_kernel_time);

  
  struct timespec get_monotonic_coarse(void)
  {
  	struct timespec now, mono;
  	unsigned long seq;
  
  	do {
  		seq = read_seqbegin(&xtime_lock);

  		now = xtime;

  		mono = wall_to_monotonic;
  	} while (read_seqretry(&xtime_lock, seq));
  
  	set_normalized_timespec(&now, now.tv_sec + mono.tv_sec,
  				now.tv_nsec + mono.tv_nsec);
  	return now;
  }

  
  /*
   * The 64-bit jiffies value is not atomic - you MUST NOT read it
   * without sampling the sequence number in xtime_lock.
   * jiffies is defined in the linker script...
   */
  void do_timer(unsigned long ticks)
  {
  	jiffies_64 += ticks;
  	update_wall_time();
  	calc_global_load(ticks);
  }

  
  /**

   * get_xtime_and_monotonic_and_sleep_offset() - get xtime, wall_to_monotonic,
   *    and sleep offsets.

   * @xtim:	pointer to timespec to be set with xtime
   * @wtom:	pointer to timespec to be set with wall_to_monotonic

   * @sleep:	pointer to timespec to be set with time in suspend

   */

  void get_xtime_and_monotonic_and_sleep_offset(struct timespec *xtim,
  				struct timespec *wtom, struct timespec *sleep)

  {
  	unsigned long seq;
  
  	do {
  		seq = read_seqbegin(&xtime_lock);
  		*xtim = xtime;
  		*wtom = wall_to_monotonic;

  		*sleep = total_sleep_time;

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

  
  /**

   * ktime_get_monotonic_offset() - get wall_to_monotonic in ktime_t format
   */
  ktime_t ktime_get_monotonic_offset(void)
  {
  	unsigned long seq;
  	struct timespec wtom;
  
  	do {
  		seq = read_seqbegin(&xtime_lock);
  		wtom = wall_to_monotonic;
  	} while (read_seqretry(&xtime_lock, seq));
  	return timespec_to_ktime(wtom);
  }
  
  /**

   * xtime_update() - advances the timekeeping infrastructure
   * @ticks:	number of ticks, that have elapsed since the last call.
   *
   * Must be called with interrupts disabled.
   */
  void xtime_update(unsigned long ticks)
  {
  	write_seqlock(&xtime_lock);
  	do_timer(ticks);
  	write_sequnlock(&xtime_lock);
  }