kernel/time/timekeeping.c

/*
 *  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/timekeeper_internal.h>
#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>
#include <linux/pvclock_gtod.h>
#include <linux/compiler.h>

#include "tick-internal.h"
#include "ntp_internal.h"
#include "timekeeping_internal.h"

#define TK_CLEAR_NTP		(1 << 0)
#define TK_MIRROR		(1 << 1)
#define TK_CLOCK_WAS_SET	(1 << 2)

/*
 * The most important data for readout fits into a single 64 byte
 * cache line.
 */
static struct {
	seqcount_t		seq;
	struct timekeeper	timekeeper;
} tk_core ____cacheline_aligned = {
	.seq = SEQCNT_ZERO(tk_core.seq),
};

static DEFINE_RAW_SPINLOCK(timekeeper_lock);
static struct timekeeper shadow_timekeeper;

/**
 * struct tk_fast - NMI safe timekeeper
 * @seq:	Sequence counter for protecting updates. The lowest bit
 *		is the index for the tk_read_base array
 * @base:	tk_read_base array. Access is indexed by the lowest bit of
 *		@seq.
 *
 * See @update_fast_timekeeper() below.
 */
struct tk_fast {
	seqcount_t		seq;
	struct tk_read_base	base[2];
};

static struct tk_fast tk_fast_mono ____cacheline_aligned;
static struct tk_fast tk_fast_raw  ____cacheline_aligned;

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

static inline void tk_normalize_xtime(struct timekeeper *tk)
{
	while (tk->tkr_mono.xtime_nsec >= ((u64)NSEC_PER_SEC << tk->tkr_mono.shift)) {
		tk->tkr_mono.xtime_nsec -= (u64)NSEC_PER_SEC << tk->tkr_mono.shift;
		tk->xtime_sec++;
	}
	while (tk->tkr_raw.xtime_nsec >= ((u64)NSEC_PER_SEC << tk->tkr_raw.shift)) {
		tk->tkr_raw.xtime_nsec -= (u64)NSEC_PER_SEC << tk->tkr_raw.shift;
		tk->raw_sec++;
	}
}

static inline struct timespec64 tk_xtime(struct timekeeper *tk)
{
	struct timespec64 ts;

	ts.tv_sec = tk->xtime_sec;
	ts.tv_nsec = (long)(tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift);
	return ts;
}

static void tk_set_xtime(struct timekeeper *tk, const struct timespec64 *ts)
{
	tk->xtime_sec = ts->tv_sec;
	tk->tkr_mono.xtime_nsec = (u64)ts->tv_nsec << tk->tkr_mono.shift;
}

static void tk_xtime_add(struct timekeeper *tk, const struct timespec64 *ts)
{
	tk->xtime_sec += ts->tv_sec;
	tk->tkr_mono.xtime_nsec += (u64)ts->tv_nsec << tk->tkr_mono.shift;
	tk_normalize_xtime(tk);
}

static void tk_set_wall_to_mono(struct timekeeper *tk, struct timespec64 wtm)
{
	struct timespec64 tmp;

	/*
	 * Verify consistency of: offset_real = -wall_to_monotonic
	 * before modifying anything
	 */
	set_normalized_timespec64(&tmp, -tk->wall_to_monotonic.tv_sec,
					-tk->wall_to_monotonic.tv_nsec);
	WARN_ON_ONCE(tk->offs_real.tv64 != timespec64_to_ktime(tmp).tv64);
	tk->wall_to_monotonic = wtm;
	set_normalized_timespec64(&tmp, -wtm.tv_sec, -wtm.tv_nsec);
	tk->offs_real = timespec64_to_ktime(tmp);
	tk->offs_tai = ktime_add(tk->offs_real, ktime_set(tk->tai_offset, 0));
}

static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta)
{
	tk->offs_boot = ktime_add(tk->offs_boot, delta);
}

/*
 * tk_clock_read - atomic clocksource read() helper
 *
 * This helper is necessary to use in the read paths because, while the
 * seqlock ensures we don't return a bad value while structures are updated,
 * it doesn't protect from potential crashes. There is the possibility that
 * the tkr's clocksource may change between the read reference, and the
 * clock reference passed to the read function.  This can cause crashes if
 * the wrong clocksource is passed to the wrong read function.
 * This isn't necessary to use when holding the timekeeper_lock or doing
 * a read of the fast-timekeeper tkrs (which is protected by its own locking
 * and update logic).
 */
static inline u64 tk_clock_read(struct tk_read_base *tkr)
{
	struct clocksource *clock = READ_ONCE(tkr->clock);

	return clock->read(clock);
}

#ifdef CONFIG_DEBUG_TIMEKEEPING
#define WARNING_FREQ (HZ*300) /* 5 minute rate-limiting */

static void timekeeping_check_update(struct timekeeper *tk, cycle_t offset)
{

	cycle_t max_cycles = tk->tkr_mono.clock->max_cycles;
	const char *name = tk->tkr_mono.clock->name;

	if (offset > max_cycles) {
		printk_deferred("WARNING: timekeeping: Cycle offset (%lld) is larger than allowed by the '%s' clock's max_cycles value (%lld): time overflow danger\n",
				offset, name, max_cycles);
		printk_deferred("         timekeeping: Your kernel is sick, but tries to cope by capping time updates\n");
	} else {
		if (offset > (max_cycles >> 1)) {
			printk_deferred("INFO: timekeeping: Cycle offset (%lld) is larger than the the '%s' clock's 50%% safety margin (%lld)\n",
					offset, name, max_cycles >> 1);
			printk_deferred("      timekeeping: Your kernel is still fine, but is feeling a bit nervous\n");
		}
	}

	if (tk->underflow_seen) {
		if (jiffies - tk->last_warning > WARNING_FREQ) {
			printk_deferred("WARNING: Underflow in clocksource '%s' observed, time update ignored.\n", name);
			printk_deferred("         Please report this, consider using a different clocksource, if possible.\n");
			printk_deferred("         Your kernel is probably still fine.\n");
			tk->last_warning = jiffies;
		}
		tk->underflow_seen = 0;
	}

	if (tk->overflow_seen) {
		if (jiffies - tk->last_warning > WARNING_FREQ) {
			printk_deferred("WARNING: Overflow in clocksource '%s' observed, time update capped.\n", name);
			printk_deferred("         Please report this, consider using a different clocksource, if possible.\n");
			printk_deferred("         Your kernel is probably still fine.\n");
			tk->last_warning = jiffies;
		}
		tk->overflow_seen = 0;
	}
}

static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	cycle_t now, last, mask, max, delta;
	unsigned int seq;

	/*
	 * Since we're called holding a seqlock, the data may shift
	 * under us while we're doing the calculation. This can cause
	 * false positives, since we'd note a problem but throw the
	 * results away. So nest another seqlock here to atomically
	 * grab the points we are checking with.
	 */
	do {
		seq = read_seqcount_begin(&tk_core.seq);
		now = tk_clock_read(tkr);
		last = tkr->cycle_last;
		mask = tkr->mask;
		max = tkr->clock->max_cycles;
	} while (read_seqcount_retry(&tk_core.seq, seq));

	delta = clocksource_delta(now, last, mask);

	/*
	 * Try to catch underflows by checking if we are seeing small
	 * mask-relative negative values.
	 */
	if (unlikely((~delta & mask) < (mask >> 3))) {
		tk->underflow_seen = 1;
		delta = 0;
	}

	/* Cap delta value to the max_cycles values to avoid mult overflows */
	if (unlikely(delta > max)) {
		tk->overflow_seen = 1;
		delta = tkr->clock->max_cycles;
	}

	return delta;
}
#else
static inline void timekeeping_check_update(struct timekeeper *tk, cycle_t offset)
{
}
static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr)
{
	cycle_t cycle_now, delta;

	/* read clocksource */
	cycle_now = tk_clock_read(tkr);

	/* calculate the delta since the last update_wall_time */
	delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask);

	return delta;
}
#endif

/**
 * tk_setup_internals - Set up internals to use clocksource clock.
 *
 * @tk:		The target timekeeper to setup.
 * @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 tk_setup_internals(struct timekeeper *tk, struct clocksource *clock)
{
	cycle_t interval;
	u64 tmp, ntpinterval;
	struct clocksource *old_clock;

	old_clock = tk->tkr_mono.clock;
	tk->tkr_mono.clock = clock;
	tk->tkr_mono.mask = clock->mask;
	tk->tkr_mono.cycle_last = tk_clock_read(&tk->tkr_mono);

	tk->tkr_raw.clock = clock;
	tk->tkr_raw.mask = clock->mask;
	tk->tkr_raw.cycle_last = tk->tkr_mono.cycle_last;

	/* 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;
	tk->cycle_interval = interval;

	/* Go back from cycles -> shifted ns */
	tk->xtime_interval = (u64) interval * clock->mult;
	tk->xtime_remainder = ntpinterval - tk->xtime_interval;
	tk->raw_interval = interval * clock->mult;

	 /* if changing clocks, convert xtime_nsec shift units */
	if (old_clock) {
		int shift_change = clock->shift - old_clock->shift;
		if (shift_change < 0) {
			tk->tkr_mono.xtime_nsec >>= -shift_change;
			tk->tkr_raw.xtime_nsec >>= -shift_change;
		} else {
			tk->tkr_mono.xtime_nsec <<= shift_change;
			tk->tkr_raw.xtime_nsec <<= shift_change;
		}
	}

	tk->tkr_mono.shift = clock->shift;
	tk->tkr_raw.shift = clock->shift;

	tk->ntp_error = 0;
	tk->ntp_error_shift = NTP_SCALE_SHIFT - clock->shift;
	tk->ntp_tick = ntpinterval << tk->ntp_error_shift;

	/*
	 * The timekeeper keeps its own mult values for the currently
	 * active clocksource. These value will be adjusted via NTP
	 * to counteract clock drifting.
	 */
	tk->tkr_mono.mult = clock->mult;
	tk->tkr_raw.mult = clock->mult;
	tk->ntp_err_mult = 0;
}

/* Timekeeper helper functions. */

#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
static u32 default_arch_gettimeoffset(void) { return 0; }
u32 (*arch_gettimeoffset)(void) = default_arch_gettimeoffset;
#else
static inline u32 arch_gettimeoffset(void) { return 0; }
#endif

static inline u64 timekeeping_delta_to_ns(struct tk_read_base *tkr,
					  cycle_t delta)
{
	u64 nsec;

	nsec = delta * tkr->mult + tkr->xtime_nsec;
	nsec >>= tkr->shift;

	/* If arch requires, add in get_arch_timeoffset() */
	return nsec + arch_gettimeoffset();
}

static inline s64 timekeeping_get_ns(struct tk_read_base *tkr)
{
	cycle_t delta;

	delta = timekeeping_get_delta(tkr);
	return timekeeping_delta_to_ns(tkr, delta);
}

static inline s64 timekeeping_cycles_to_ns(struct tk_read_base *tkr,
					    cycle_t cycles)
{
	cycle_t delta;

	/* calculate the delta since the last update_wall_time */
	delta = clocksource_delta(cycles, tkr->cycle_last, tkr->mask);
	return timekeeping_delta_to_ns(tkr, delta);
}

/**
 * update_fast_timekeeper - Update the fast and NMI safe monotonic timekeeper.
 * @tkr: Timekeeping readout base from which we take the update
 *
 * We want to use this from any context including NMI and tracing /
 * instrumenting the timekeeping code itself.
 *
 * Employ the latch technique; see @raw_write_seqcount_latch.
 *
 * So if a NMI hits the update of base[0] then it will use base[1]
 * which is still consistent. In the worst case this can result is a
 * slightly wrong timestamp (a few nanoseconds). See
 * @ktime_get_mono_fast_ns.
 */
static void update_fast_timekeeper(struct tk_read_base *tkr, struct tk_fast *tkf)
{
	struct tk_read_base *base = tkf->base;

	/* Force readers off to base[1] */
	raw_write_seqcount_latch(&tkf->seq);

	/* Update base[0] */
	memcpy(base, tkr, sizeof(*base));

	/* Force readers back to base[0] */
	raw_write_seqcount_latch(&tkf->seq);

	/* Update base[1] */
	memcpy(base + 1, base, sizeof(*base));
}

/**
 * ktime_get_mono_fast_ns - Fast NMI safe access to clock monotonic
 *
 * This timestamp is not guaranteed to be monotonic across an update.
 * The timestamp is calculated by:
 *
 *	now = base_mono + clock_delta * slope
 *
 * So if the update lowers the slope, readers who are forced to the
 * not yet updated second array are still using the old steeper slope.
 *
 * tmono
 * ^
 * |    o  n
 * |   o n
 * |  u
 * | o
 * |o
 * |12345678---> reader order
 *
 * o = old slope
 * u = update
 * n = new slope
 *
 * So reader 6 will observe time going backwards versus reader 5.
 *
 * While other CPUs are likely to be able observe that, the only way
 * for a CPU local observation is when an NMI hits in the middle of
 * the update. Timestamps taken from that NMI context might be ahead
 * of the following timestamps. Callers need to be aware of that and
 * deal with it.
 */
static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
{
	struct tk_read_base *tkr;
	unsigned int seq;
	u64 now;

	do {
		seq = raw_read_seqcount_latch(&tkf->seq);
		tkr = tkf->base + (seq & 0x01);
		now = ktime_to_ns(tkr->base);

		now += timekeeping_delta_to_ns(tkr,
				clocksource_delta(
					tk_clock_read(tkr),
					tkr->cycle_last,
					tkr->mask));
	} while (read_seqcount_retry(&tkf->seq, seq));

	return now;
}

u64 ktime_get_mono_fast_ns(void)
{
	return __ktime_get_fast_ns(&tk_fast_mono);
}
EXPORT_SYMBOL_GPL(ktime_get_mono_fast_ns);

u64 ktime_get_raw_fast_ns(void)
{
	return __ktime_get_fast_ns(&tk_fast_raw);
}
EXPORT_SYMBOL_GPL(ktime_get_raw_fast_ns);

/**
 * ktime_get_boot_fast_ns - NMI safe and fast access to boot clock.
 *
 * To keep it NMI safe since we're accessing from tracing, we're not using a
 * separate timekeeper with updates to monotonic clock and boot offset
 * protected with seqlocks. This has the following minor side effects:
 *
 * (1) Its possible that a timestamp be taken after the boot offset is updated
 * but before the timekeeper is updated. If this happens, the new boot offset
 * is added to the old timekeeping making the clock appear to update slightly
 * earlier:
 *    CPU 0                                        CPU 1
 *    timekeeping_inject_sleeptime64()
 *    __timekeeping_inject_sleeptime(tk, delta);
 *                                                 timestamp();
 *    timekeeping_update(tk, TK_CLEAR_NTP...);
 *
 * (2) On 32-bit systems, the 64-bit boot offset (tk->offs_boot) may be
 * partially updated.  Since the tk->offs_boot update is a rare event, this
 * should be a rare occurrence which postprocessing should be able to handle.
 */
u64 notrace ktime_get_boot_fast_ns(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;

	return (ktime_get_mono_fast_ns() + ktime_to_ns(tk->offs_boot));
}
EXPORT_SYMBOL_GPL(ktime_get_boot_fast_ns);

/* Suspend-time cycles value for halted fast timekeeper. */
static cycle_t cycles_at_suspend;

static cycle_t dummy_clock_read(struct clocksource *cs)
{
	return cycles_at_suspend;
}

static struct clocksource dummy_clock = {
	.read = dummy_clock_read,
};

/**
 * halt_fast_timekeeper - Prevent fast timekeeper from accessing clocksource.
 * @tk: Timekeeper to snapshot.
 *
 * It generally is unsafe to access the clocksource after timekeeping has been
 * suspended, so take a snapshot of the readout base of @tk and use it as the
 * fast timekeeper's readout base while suspended.  It will return the same
 * number of cycles every time until timekeeping is resumed at which time the
 * proper readout base for the fast timekeeper will be restored automatically.
 */
static void halt_fast_timekeeper(struct timekeeper *tk)
{
	static struct tk_read_base tkr_dummy;
	struct tk_read_base *tkr = &tk->tkr_mono;

	memcpy(&tkr_dummy, tkr, sizeof(tkr_dummy));
	cycles_at_suspend = tk_clock_read(tkr);
	tkr_dummy.clock = &dummy_clock;
	update_fast_timekeeper(&tkr_dummy, &tk_fast_mono);

	tkr = &tk->tkr_raw;
	memcpy(&tkr_dummy, tkr, sizeof(tkr_dummy));
	tkr_dummy.clock = &dummy_clock;
	update_fast_timekeeper(&tkr_dummy, &tk_fast_raw);
}

#ifdef CONFIG_GENERIC_TIME_VSYSCALL_OLD

static inline void update_vsyscall(struct timekeeper *tk)
{
	struct timespec xt, wm;

	xt = timespec64_to_timespec(tk_xtime(tk));
	wm = timespec64_to_timespec(tk->wall_to_monotonic);
	update_vsyscall_old(&xt, &wm, tk->tkr_mono.clock, tk->tkr_mono.mult,
			    tk->tkr_mono.cycle_last);
}

static inline void old_vsyscall_fixup(struct timekeeper *tk)
{
	s64 remainder;

	/*
	* Store only full nanoseconds into xtime_nsec after rounding
	* it up and add the remainder to the error difference.
	* XXX - This is necessary to avoid small 1ns inconsistnecies caused
	* by truncating the remainder in vsyscalls. However, it causes
	* additional work to be done in timekeeping_adjust(). Once
	* the vsyscall implementations are converted to use xtime_nsec
	* (shifted nanoseconds), and CONFIG_GENERIC_TIME_VSYSCALL_OLD
	* users are removed, this can be killed.
	*/
	remainder = tk->tkr_mono.xtime_nsec & ((1ULL << tk->tkr_mono.shift) - 1);
	tk->tkr_mono.xtime_nsec -= remainder;
	tk->tkr_mono.xtime_nsec += 1ULL << tk->tkr_mono.shift;
	tk->ntp_error += remainder << tk->ntp_error_shift;
	tk->ntp_error -= (1ULL << tk->tkr_mono.shift) << tk->ntp_error_shift;
}
#else
#define old_vsyscall_fixup(tk)
#endif

static RAW_NOTIFIER_HEAD(pvclock_gtod_chain);

static void update_pvclock_gtod(struct timekeeper *tk, bool was_set)
{
	raw_notifier_call_chain(&pvclock_gtod_chain, was_set, tk);
}

/**
 * pvclock_gtod_register_notifier - register a pvclock timedata update listener
 */
int pvclock_gtod_register_notifier(struct notifier_block *nb)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long flags;
	int ret;

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	ret = raw_notifier_chain_register(&pvclock_gtod_chain, nb);
	update_pvclock_gtod(tk, true);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

	return ret;
}
EXPORT_SYMBOL_GPL(pvclock_gtod_register_notifier);

/**
 * pvclock_gtod_unregister_notifier - unregister a pvclock
 * timedata update listener
 */
int pvclock_gtod_unregister_notifier(struct notifier_block *nb)
{
	unsigned long flags;
	int ret;

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	ret = raw_notifier_chain_unregister(&pvclock_gtod_chain, nb);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

	return ret;
}
EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier);

/*
 * tk_update_leap_state - helper to update the next_leap_ktime
 */
static inline void tk_update_leap_state(struct timekeeper *tk)
{
	tk->next_leap_ktime = ntp_get_next_leap();
	if (tk->next_leap_ktime.tv64 != KTIME_MAX)
		/* Convert to monotonic time */
		tk->next_leap_ktime = ktime_sub(tk->next_leap_ktime, tk->offs_real);
}

/*
 * Update the ktime_t based scalar nsec members of the timekeeper
 */
static inline void tk_update_ktime_data(struct timekeeper *tk)
{
	u64 seconds;
	u32 nsec;

	/*
	 * The xtime based monotonic readout is:
	 *	nsec = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec + now();
	 * The ktime based monotonic readout is:
	 *	nsec = base_mono + now();
	 * ==> base_mono = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec
	 */
	seconds = (u64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec);
	nsec = (u32) tk->wall_to_monotonic.tv_nsec;
	tk->tkr_mono.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec);

	/*
	 * The sum of the nanoseconds portions of xtime and
	 * wall_to_monotonic can be greater/equal one second. Take
	 * this into account before updating tk->ktime_sec.
	 */
	nsec += (u32)(tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift);
	if (nsec >= NSEC_PER_SEC)
		seconds++;
	tk->ktime_sec = seconds;

	/* Update the monotonic raw base */
	tk->tkr_raw.base = ns_to_ktime(tk->raw_sec * NSEC_PER_SEC);
}

/* must hold timekeeper_lock */
static void timekeeping_update(struct timekeeper *tk, unsigned int action)
{
	if (action & TK_CLEAR_NTP) {
		tk->ntp_error = 0;
		ntp_clear();
	}

	tk_update_leap_state(tk);
	tk_update_ktime_data(tk);

	update_vsyscall(tk);
	update_pvclock_gtod(tk, action & TK_CLOCK_WAS_SET);

	update_fast_timekeeper(&tk->tkr_mono, &tk_fast_mono);
	update_fast_timekeeper(&tk->tkr_raw,  &tk_fast_raw);

	if (action & TK_CLOCK_WAS_SET)
		tk->clock_was_set_seq++;
	/*
	 * The mirroring of the data to the shadow-timekeeper needs
	 * to happen last here to ensure we don't over-write the
	 * timekeeper structure on the next update with stale data
	 */
	if (action & TK_MIRROR)
		memcpy(&shadow_timekeeper, &tk_core.timekeeper,
		       sizeof(tk_core.timekeeper));
}

/**
 * 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(struct timekeeper *tk)
{
	cycle_t cycle_now, delta;

	cycle_now = tk_clock_read(&tk->tkr_mono);
	delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last, tk->tkr_mono.mask);
	tk->tkr_mono.cycle_last = cycle_now;
	tk->tkr_raw.cycle_last  = cycle_now;

	tk->tkr_mono.xtime_nsec += delta * tk->tkr_mono.mult;

	/* If arch requires, add in get_arch_timeoffset() */
	tk->tkr_mono.xtime_nsec += (u64)arch_gettimeoffset() << tk->tkr_mono.shift;


	tk->tkr_raw.xtime_nsec += delta * tk->tkr_raw.mult;

	/* If arch requires, add in get_arch_timeoffset() */
	tk->tkr_raw.xtime_nsec += (u64)arch_gettimeoffset() << tk->tkr_raw.shift;

	tk_normalize_xtime(tk);
}

/**
 * __getnstimeofday64 - Returns the time of day in a timespec64.
 * @ts:		pointer to the timespec to be set
 *
 * Updates the time of day in the timespec.
 * Returns 0 on success, or -ve when suspended (timespec will be undefined).
 */
int __getnstimeofday64(struct timespec64 *ts)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long seq;
	s64 nsecs = 0;

	do {
		seq = read_seqcount_begin(&tk_core.seq);

		ts->tv_sec = tk->xtime_sec;
		nsecs = timekeeping_get_ns(&tk->tkr_mono);

	} while (read_seqcount_retry(&tk_core.seq, seq));

	ts->tv_nsec = 0;
	timespec64_add_ns(ts, nsecs);

	/*
	 * Do not bail out early, in case there were callers still using
	 * the value, even in the face of the WARN_ON.
	 */
	if (unlikely(timekeeping_suspended))
		return -EAGAIN;
	return 0;
}
EXPORT_SYMBOL(__getnstimeofday64);

/**
 * getnstimeofday64 - Returns the time of day in a timespec64.
 * @ts:		pointer to the timespec64 to be set
 *
 * Returns the time of day in a timespec64 (WARN if suspended).
 */
void getnstimeofday64(struct timespec64 *ts)
{
	WARN_ON(__getnstimeofday64(ts));
}
EXPORT_SYMBOL(getnstimeofday64);

ktime_t ktime_get(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned int seq;
	ktime_t base;
	s64 nsecs;

	WARN_ON(timekeeping_suspended);

	do {
		seq = read_seqcount_begin(&tk_core.seq);
		base = tk->tkr_mono.base;
		nsecs = timekeeping_get_ns(&tk->tkr_mono);

	} while (read_seqcount_retry(&tk_core.seq, seq));

	return ktime_add_ns(base, nsecs);
}
EXPORT_SYMBOL_GPL(ktime_get);

u32 ktime_get_resolution_ns(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned int seq;
	u32 nsecs;

	WARN_ON(timekeeping_suspended);

	do {
		seq = read_seqcount_begin(&tk_core.seq);
		nsecs = tk->tkr_mono.mult >> tk->tkr_mono.shift;
	} while (read_seqcount_retry(&tk_core.seq, seq));

	return nsecs;
}
EXPORT_SYMBOL_GPL(ktime_get_resolution_ns);

static ktime_t *offsets[TK_OFFS_MAX] = {
	[TK_OFFS_REAL]	= &tk_core.timekeeper.offs_real,
	[TK_OFFS_BOOT]	= &tk_core.timekeeper.offs_boot,
	[TK_OFFS_TAI]	= &tk_core.timekeeper.offs_tai,
};

ktime_t ktime_get_with_offset(enum tk_offsets offs)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned int seq;
	ktime_t base, *offset = offsets[offs];
	s64 nsecs;

	WARN_ON(timekeeping_suspended);

	do {
		seq = read_seqcount_begin(&tk_core.seq);
		base = ktime_add(tk->tkr_mono.base, *offset);
		nsecs = timekeeping_get_ns(&tk->tkr_mono);

	} while (read_seqcount_retry(&tk_core.seq, seq));

	return ktime_add_ns(base, nsecs);

}
EXPORT_SYMBOL_GPL(ktime_get_with_offset);

/**
 * ktime_mono_to_any() - convert mononotic time to any other time
 * @tmono:	time to convert.
 * @offs:	which offset to use
 */
ktime_t ktime_mono_to_any(ktime_t tmono, enum tk_offsets offs)
{
	ktime_t *offset = offsets[offs];
	unsigned long seq;
	ktime_t tconv;

	do {
		seq = read_seqcount_begin(&tk_core.seq);
		tconv = ktime_add(tmono, *offset);
	} while (read_seqcount_retry(&tk_core.seq, seq));

	return tconv;
}
EXPORT_SYMBOL_GPL(ktime_mono_to_any);

/**
 * ktime_get_raw - Returns the raw monotonic time in ktime_t format
 */
ktime_t ktime_get_raw(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned int seq;
	ktime_t base;
	s64 nsecs;

	do {
		seq = read_seqcount_begin(&tk_core.seq);
		base = tk->tkr_raw.base;
		nsecs = timekeeping_get_ns(&tk->tkr_raw);

	} while (read_seqcount_retry(&tk_core.seq, seq));

	return ktime_add_ns(base, nsecs);
}
EXPORT_SYMBOL_GPL(ktime_get_raw);

/**
 * ktime_get_ts64 - get the monotonic clock in timespec64 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 timespec64 format in the variable pointed to by @ts.
 */
void ktime_get_ts64(struct timespec64 *ts)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	struct timespec64 tomono;
	s64 nsec;
	unsigned int seq;

	WARN_ON(timekeeping_suspended);

	do {
		seq = read_seqcount_begin(&tk_core.seq);
		ts->tv_sec = tk->xtime_sec;
		nsec = timekeeping_get_ns(&tk->tkr_mono);
		tomono = tk->wall_to_monotonic;

	} while (read_seqcount_retry(&tk_core.seq, seq));

	ts->tv_sec += tomono.tv_sec;
	ts->tv_nsec = 0;
	timespec64_add_ns(ts, nsec + tomono.tv_nsec);
}
EXPORT_SYMBOL_GPL(ktime_get_ts64);

/**
 * ktime_get_seconds - Get the seconds portion of CLOCK_MONOTONIC
 *
 * Returns the seconds portion of CLOCK_MONOTONIC with a single non
 * serialized read. tk->ktime_sec is of type 'unsigned long' so this
 * works on both 32 and 64 bit systems. On 32 bit systems the readout
 * covers ~136 years of uptime which should be enough to prevent
 * premature wrap arounds.
 */
time64_t ktime_get_seconds(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;

	WARN_ON(timekeeping_suspended);
	return tk->ktime_sec;
}
EXPORT_SYMBOL_GPL(ktime_get_seconds);

/**
 * ktime_get_real_seconds - Get the seconds portion of CLOCK_REALTIME
 *
 * Returns the wall clock seconds since 1970. This replaces the
 * get_seconds() interface which is not y2038 safe on 32bit systems.
 *
 * For 64bit systems the fast access to tk->xtime_sec is preserved. On
 * 32bit systems the access must be protected with the sequence
 * counter to provide "atomic" access to the 64bit tk->xtime_sec
 * value.
 */
time64_t ktime_get_real_seconds(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	time64_t seconds;
	unsigned int seq;

	if (IS_ENABLED(CONFIG_64BIT))
		return tk->xtime_sec;

	do {
		seq = read_seqcount_begin(&tk_core.seq);
		seconds = tk->xtime_sec;

	} while (read_seqcount_retry(&tk_core.seq, seq));

	return seconds;
}
EXPORT_SYMBOL_GPL(ktime_get_real_seconds);

#ifdef CONFIG_NTP_PPS

/**
 * ktime_get_raw_and_real_ts64 - 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 ktime_get_raw_and_real_ts64(struct timespec64 *ts_raw, struct timespec64 *ts_real)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long seq;
	s64 nsecs_raw, nsecs_real;

	WARN_ON_ONCE(timekeeping_suspended);

	do {
		seq = read_seqcount_begin(&tk_core.seq);

		*ts_raw = tk->raw_time;
		ts_real->tv_sec = tk->xtime_sec;
		ts_real->tv_nsec = 0;

		nsecs_raw  = timekeeping_get_ns(&tk->tkr_raw);
		nsecs_real = timekeeping_get_ns(&tk->tkr_mono);

	} while (read_seqcount_retry(&tk_core.seq, seq));

	timespec64_add_ns(ts_raw, nsecs_raw);
	timespec64_add_ns(ts_real, nsecs_real);
}
EXPORT_SYMBOL(ktime_get_raw_and_real_ts64);

#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 timespec64 now;

	getnstimeofday64(&now);
	tv->tv_sec = now.tv_sec;
	tv->tv_usec = now.tv_nsec/1000;
}
EXPORT_SYMBOL(do_gettimeofday);

/**
 * do_settimeofday64 - Sets the time of day.
 * @ts:     pointer to the timespec64 variable containing the new time
 *
 * Sets the time of day to the new time and update NTP and notify hrtimers
 */
int do_settimeofday64(const struct timespec64 *ts)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	struct timespec64 ts_delta, xt;
	unsigned long flags;
	int ret = 0;

	if (!timespec64_valid_strict(ts))
		return -EINVAL;

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	write_seqcount_begin(&tk_core.seq);

	timekeeping_forward_now(tk);

	xt = tk_xtime(tk);
	ts_delta.tv_sec = ts->tv_sec - xt.tv_sec;
	ts_delta.tv_nsec = ts->tv_nsec - xt.tv_nsec;

	if (timespec64_compare(&tk->wall_to_monotonic, &ts_delta) > 0) {
		ret = -EINVAL;
		goto out;
	}

	tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, ts_delta));

	tk_set_xtime(tk, ts);
out:
	timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);

	write_seqcount_end(&tk_core.seq);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

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

	return ret;
}
EXPORT_SYMBOL(do_settimeofday64);

/**
 * 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)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long flags;
	struct timespec64 ts64, tmp;
	int ret = 0;

	if (!timespec_inject_offset_valid(ts))
		return -EINVAL;

	ts64 = timespec_to_timespec64(*ts);

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	write_seqcount_begin(&tk_core.seq);

	timekeeping_forward_now(tk);

	/* Make sure the proposed value is valid */
	tmp = timespec64_add(tk_xtime(tk),  ts64);
	if (timespec64_compare(&tk->wall_to_monotonic, &ts64) > 0 ||
	    !timespec64_valid_strict(&tmp)) {
		ret = -EINVAL;
		goto error;
	}

	tk_xtime_add(tk, &ts64);
	tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, ts64));

error: /* even if we error out, we forwarded the time, so call update */
	timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);

	write_seqcount_end(&tk_core.seq);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

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

	return ret;
}
EXPORT_SYMBOL(timekeeping_inject_offset);


/**
 * timekeeping_get_tai_offset - Returns current TAI offset from UTC
 *
 */
s32 timekeeping_get_tai_offset(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned int seq;
	s32 ret;

	do {
		seq = read_seqcount_begin(&tk_core.seq);
		ret = tk->tai_offset;
	} while (read_seqcount_retry(&tk_core.seq, seq));

	return ret;
}

/**
 * __timekeeping_set_tai_offset - Lock free worker function
 *
 */
static void __timekeeping_set_tai_offset(struct timekeeper *tk, s32 tai_offset)
{
	tk->tai_offset = tai_offset;
	tk->offs_tai = ktime_add(tk->offs_real, ktime_set(tai_offset, 0));
}

/**
 * timekeeping_set_tai_offset - Sets the current TAI offset from UTC
 *
 */
void timekeeping_set_tai_offset(s32 tai_offset)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long flags;

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	write_seqcount_begin(&tk_core.seq);
	__timekeeping_set_tai_offset(tk, tai_offset);
	timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
	write_seqcount_end(&tk_core.seq);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
	clock_was_set();
}

/**
 * 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 timekeeper *tk = &tk_core.timekeeper;
	struct clocksource *new, *old;
	unsigned long flags;

	new = (struct clocksource *) data;

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	write_seqcount_begin(&tk_core.seq);

	timekeeping_forward_now(tk);
	/*
	 * If the cs is in module, get a module reference. Succeeds
	 * for built-in code (owner == NULL) as well.
	 */
	if (try_module_get(new->owner)) {
		if (!new->enable || new->enable(new) == 0) {
			old = tk->tkr_mono.clock;
			tk_setup_internals(tk, new);
			if (old->disable)
				old->disable(old);
			module_put(old->owner);
		} else {
			module_put(new->owner);
		}
	}
	timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);

	write_seqcount_end(&tk_core.seq);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

	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.
 */
int timekeeping_notify(struct clocksource *clock)
{
	struct timekeeper *tk = &tk_core.timekeeper;

	if (tk->tkr_mono.clock == clock)
		return 0;
	stop_machine(change_clocksource, clock, NULL);
	tick_clock_notify();
	return tk->tkr_mono.clock == clock ? 0 : -1;
}

/**
 * getrawmonotonic64 - Returns the raw monotonic time in a timespec
 * @ts:		pointer to the timespec64 to be set
 *
 * Returns the raw monotonic time (completely un-modified by ntp)
 */
void getrawmonotonic64(struct timespec64 *ts)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long seq;
	s64 nsecs;

	do {
		seq = read_seqcount_begin(&tk_core.seq);
		ts->tv_sec = tk->raw_sec;
		nsecs = timekeeping_get_ns(&tk->tkr_raw);

	} while (read_seqcount_retry(&tk_core.seq, seq));

	ts->tv_nsec = 0;
	timespec64_add_ns(ts, nsecs);
}
EXPORT_SYMBOL(getrawmonotonic64);


/**
 * timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
 */
int timekeeping_valid_for_hres(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long seq;
	int ret;

	do {
		seq = read_seqcount_begin(&tk_core.seq);

		ret = tk->tkr_mono.clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

	} while (read_seqcount_retry(&tk_core.seq, seq));

	return ret;
}

/**
 * timekeeping_max_deferment - Returns max time the clocksource can be deferred
 */
u64 timekeeping_max_deferment(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long seq;
	u64 ret;

	do {
		seq = read_seqcount_begin(&tk_core.seq);

		ret = tk->tkr_mono.clock->max_idle_ns;

	} while (read_seqcount_retry(&tk_core.seq, seq));

	return ret;
}

/**
 * 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 __weak read_persistent_clock(struct timespec *ts)
{
	ts->tv_sec = 0;
	ts->tv_nsec = 0;
}

void __weak read_persistent_clock64(struct timespec64 *ts64)
{
	struct timespec ts;

	read_persistent_clock(&ts);
	*ts64 = timespec_to_timespec64(ts);
}

/**
 * read_boot_clock64 -  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 timespec64 with tv_sec=0 and tv_nsec=0 if unsupported.
 *
 *  XXX - Do be sure to remove it once all arches implement it.
 */
void __weak read_boot_clock64(struct timespec64 *ts)
{
	ts->tv_sec = 0;
	ts->tv_nsec = 0;
}

/* Flag for if timekeeping_resume() has injected sleeptime */
static bool sleeptime_injected;

/* Flag for if there is a persistent clock on this platform */
static bool persistent_clock_exists;

/*
 * timekeeping_init - Initializes the clocksource and common timekeeping values
 */
void __init timekeeping_init(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	struct clocksource *clock;
	unsigned long flags;
	struct timespec64 now, boot, tmp;

	read_persistent_clock64(&now);
	if (!timespec64_valid_strict(&now)) {
		pr_warn("WARNING: Persistent clock returned invalid value!\n"
			"         Check your CMOS/BIOS settings.\n");
		now.tv_sec = 0;
		now.tv_nsec = 0;
	} else if (now.tv_sec || now.tv_nsec)
		persistent_clock_exists = true;

	read_boot_clock64(&boot);
	if (!timespec64_valid_strict(&boot)) {
		pr_warn("WARNING: Boot clock returned invalid value!\n"
			"         Check your CMOS/BIOS settings.\n");
		boot.tv_sec = 0;
		boot.tv_nsec = 0;
	}

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	write_seqcount_begin(&tk_core.seq);
	ntp_init();

	clock = clocksource_default_clock();
	if (clock->enable)
		clock->enable(clock);
	tk_setup_internals(tk, clock);

	tk_set_xtime(tk, &now);
	tk->raw_sec = 0;
	if (boot.tv_sec == 0 && boot.tv_nsec == 0)
		boot = tk_xtime(tk);

	set_normalized_timespec64(&tmp, -boot.tv_sec, -boot.tv_nsec);
	tk_set_wall_to_mono(tk, tmp);

	timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);

	write_seqcount_end(&tk_core.seq);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
}

/* time in seconds when suspend began for persistent clock */
static struct timespec64 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 timekeeper *tk,
					   struct timespec64 *delta)
{
	if (!timespec64_valid_strict(delta)) {
		printk_deferred(KERN_WARNING
				"__timekeeping_inject_sleeptime: Invalid "
				"sleep delta value!\n");
		return;
	}
	tk_xtime_add(tk, delta);
	tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, *delta));
	tk_update_sleep_time(tk, timespec64_to_ktime(*delta));
	tk_debug_account_sleep_time(delta);
}

#if defined(CONFIG_PM_SLEEP) && defined(CONFIG_RTC_HCTOSYS_DEVICE)
/**
 * We have three kinds of time sources to use for sleep time
 * injection, the preference order is:
 * 1) non-stop clocksource
 * 2) persistent clock (ie: RTC accessible when irqs are off)
 * 3) RTC
 *
 * 1) and 2) are used by timekeeping, 3) by RTC subsystem.
 * If system has neither 1) nor 2), 3) will be used finally.
 *
 *
 * If timekeeping has injected sleeptime via either 1) or 2),
 * 3) becomes needless, so in this case we don't need to call
 * rtc_resume(), and this is what timekeeping_rtc_skipresume()
 * means.
 */
bool timekeeping_rtc_skipresume(void)
{
	return sleeptime_injected;
}

/**
 * 1) can be determined whether to use or not only when doing
 * timekeeping_resume() which is invoked after rtc_suspend(),
 * so we can't skip rtc_suspend() surely if system has 1).
 *
 * But if system has 2), 2) will definitely be used, so in this
 * case we don't need to call rtc_suspend(), and this is what
 * timekeeping_rtc_skipsuspend() means.
 */
bool timekeeping_rtc_skipsuspend(void)
{
	return persistent_clock_exists;
}

/**
 * timekeeping_inject_sleeptime64 - Adds suspend interval to timeekeeping values
 * @delta: pointer to a timespec64 delta value
 *
 * This hook is for architectures that cannot support read_persistent_clock64
 * because their RTC/persistent clock is only accessible when irqs are enabled.
 * and also don't have an effective nonstop clocksource.
 *
 * This function should only be called by rtc_resume(), and allows
 * a suspend offset to be injected into the timekeeping values.
 */
void timekeeping_inject_sleeptime64(struct timespec64 *delta)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long flags;

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	write_seqcount_begin(&tk_core.seq);

	timekeeping_forward_now(tk);

	__timekeeping_inject_sleeptime(tk, delta);

	timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);

	write_seqcount_end(&tk_core.seq);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

	/* signal hrtimers about time change */
	clock_was_set();
}
#endif

/**
 * timekeeping_resume - Resumes the generic timekeeping subsystem.
 */
void timekeeping_resume(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	struct clocksource *clock = tk->tkr_mono.clock;
	unsigned long flags;
	struct timespec64 ts_new, ts_delta;
	cycle_t cycle_now, cycle_delta;

	sleeptime_injected = false;
	read_persistent_clock64(&ts_new);

	clockevents_resume();
	clocksource_resume();

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	write_seqcount_begin(&tk_core.seq);

	/*
	 * After system resumes, we need to calculate the suspended time and
	 * compensate it for the OS time. There are 3 sources that could be
	 * used: Nonstop clocksource during suspend, persistent clock and rtc
	 * device.
	 *
	 * One specific platform may have 1 or 2 or all of them, and the
	 * preference will be:
	 *	suspend-nonstop clocksource -> persistent clock -> rtc
	 * The less preferred source will only be tried if there is no better
	 * usable source. The rtc part is handled separately in rtc core code.
	 */
	cycle_now = tk_clock_read(&tk->tkr_mono);
	if ((clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&
		cycle_now > tk->tkr_mono.cycle_last) {
		u64 num, max = ULLONG_MAX;
		u32 mult = clock->mult;
		u32 shift = clock->shift;
		s64 nsec = 0;

		cycle_delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last,
						tk->tkr_mono.mask);

		/*
		 * "cycle_delta * mutl" may cause 64 bits overflow, if the
		 * suspended time is too long. In that case we need do the
		 * 64 bits math carefully
		 */
		do_div(max, mult);
		if (cycle_delta > max) {
			num = div64_u64(cycle_delta, max);
			nsec = (((u64) max * mult) >> shift) * num;
			cycle_delta -= num * max;
		}
		nsec += ((u64) cycle_delta * mult) >> shift;

		ts_delta = ns_to_timespec64(nsec);
		sleeptime_injected = true;
	} else if (timespec64_compare(&ts_new, &timekeeping_suspend_time) > 0) {
		ts_delta = timespec64_sub(ts_new, timekeeping_suspend_time);
		sleeptime_injected = true;
	}

	if (sleeptime_injected)
		__timekeeping_inject_sleeptime(tk, &ts_delta);

	/* Re-base the last cycle value */
	tk->tkr_mono.cycle_last = cycle_now;
	tk->tkr_raw.cycle_last  = cycle_now;

	tk->ntp_error = 0;
	timekeeping_suspended = 0;
	timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
	write_seqcount_end(&tk_core.seq);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

	touch_softlockup_watchdog();

	tick_resume();
	hrtimers_resume();
}

int timekeeping_suspend(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long flags;
	struct timespec64		delta, delta_delta;
	static struct timespec64	old_delta;

	read_persistent_clock64(&timekeeping_suspend_time);

	/*
	 * On some systems the persistent_clock can not be detected at
	 * timekeeping_init by its return value, so if we see a valid
	 * value returned, update the persistent_clock_exists flag.
	 */
	if (timekeeping_suspend_time.tv_sec || timekeeping_suspend_time.tv_nsec)
		persistent_clock_exists = true;

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	write_seqcount_begin(&tk_core.seq);
	timekeeping_forward_now(tk);
	timekeeping_suspended = 1;

	if (persistent_clock_exists) {
		/*
		 * 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 = timespec64_sub(tk_xtime(tk), timekeeping_suspend_time);
		delta_delta = timespec64_sub(delta, old_delta);
		if (abs(delta_delta.tv_sec) >= 2) {
			/*
			 * if delta_delta is too large, assume time correction
			 * has occurred and set old_delta to the current delta.
			 */
			old_delta = delta;
		} else {
			/* Otherwise try to adjust old_system to compensate */
			timekeeping_suspend_time =
				timespec64_add(timekeeping_suspend_time, delta_delta);
		}
	}

	timekeeping_update(tk, TK_MIRROR);
	halt_fast_timekeeper(tk);
	write_seqcount_end(&tk_core.seq);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

	tick_suspend();
	clocksource_suspend();
	clockevents_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);

/*
 * Apply a multiplier adjustment to the timekeeper
 */
static __always_inline void timekeeping_apply_adjustment(struct timekeeper *tk,
							 s64 offset,
							 bool negative,
							 int adj_scale)
{
	s64 interval = tk->cycle_interval;
	s32 mult_adj = 1;

	if (negative) {
		mult_adj = -mult_adj;
		interval = -interval;
		offset  = -offset;
	}
	mult_adj <<= adj_scale;
	interval <<= adj_scale;
	offset <<= adj_scale;

	/*
	 * So the following can be confusing.
	 *
	 * To keep things simple, lets assume mult_adj == 1 for now.
	 *
	 * When mult_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.
	 */
	if ((mult_adj > 0) && (tk->tkr_mono.mult + mult_adj < mult_adj)) {
		/* NTP adjustment caused clocksource mult overflow */
		WARN_ON_ONCE(1);
		return;
	}

	tk->tkr_mono.mult += mult_adj;
	tk->xtime_interval += interval;
	tk->tkr_mono.xtime_nsec -= offset;
	tk->ntp_error -= (interval - offset) << tk->ntp_error_shift;
}

/*
 * Calculate the multiplier adjustment needed to match the frequency
 * specified by NTP
 */
static __always_inline void timekeeping_freqadjust(struct timekeeper *tk,
							s64 offset)
{
	s64 interval = tk->cycle_interval;
	s64 xinterval = tk->xtime_interval;
	s64 tick_error;
	bool negative;
	u32 adj;

	/* Remove any current error adj from freq calculation */
	if (tk->ntp_err_mult)
		xinterval -= tk->cycle_interval;

	tk->ntp_tick = ntp_tick_length();

	/* Calculate current error per tick */
	tick_error = ntp_tick_length() >> tk->ntp_error_shift;
	tick_error -= (xinterval + tk->xtime_remainder);

	/* Don't worry about correcting it if its small */
	if (likely((tick_error >= 0) && (tick_error <= interval)))
		return;

	/* preserve the direction of correction */
	negative = (tick_error < 0);

	/* Sort out the magnitude of the correction */
	tick_error = abs(tick_error);
	for (adj = 0; tick_error > interval; adj++)
		tick_error >>= 1;

	/* scale the corrections */
	timekeeping_apply_adjustment(tk, offset, negative, adj);
}

/*
 * Adjust the timekeeper's multiplier to the correct frequency
 * and also to reduce the accumulated error value.
 */
static void timekeeping_adjust(struct timekeeper *tk, s64 offset)
{
	/* Correct for the current frequency error */
	timekeeping_freqadjust(tk, offset);

	/* Next make a small adjustment to fix any cumulative error */
	if (!tk->ntp_err_mult && (tk->ntp_error > 0)) {
		tk->ntp_err_mult = 1;
		timekeeping_apply_adjustment(tk, offset, 0, 0);
	} else if (tk->ntp_err_mult && (tk->ntp_error <= 0)) {
		/* Undo any existing error adjustment */
		timekeeping_apply_adjustment(tk, offset, 1, 0);
		tk->ntp_err_mult = 0;
	}

	if (unlikely(tk->tkr_mono.clock->maxadj &&
		(abs(tk->tkr_mono.mult - tk->tkr_mono.clock->mult)
			> tk->tkr_mono.clock->maxadj))) {
		printk_once(KERN_WARNING
			"Adjusting %s more than 11%% (%ld vs %ld)\n",
			tk->tkr_mono.clock->name, (long)tk->tkr_mono.mult,
			(long)tk->tkr_mono.clock->mult + tk->tkr_mono.clock->maxadj);
	}

	/*
	 * It may be possible that when we entered this function, xtime_nsec
	 * was very small.  Further, if we're slightly speeding the clocksource
	 * in the code above, its possible the required corrective factor to
	 * xtime_nsec could cause it to underflow.
	 *
	 * Now, since we already accumulated the second, 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)tk->tkr_mono.xtime_nsec < 0)) {
		s64 neg = -(s64)tk->tkr_mono.xtime_nsec;
		tk->tkr_mono.xtime_nsec = 0;
		tk->ntp_error += neg << tk->ntp_error_shift;
	}
}

/**
 * accumulate_nsecs_to_secs - Accumulates nsecs into secs
 *
 * Helper function that accumulates the nsecs greater than a second
 * from the xtime_nsec field to the xtime_secs field.
 * It also calls into the NTP code to handle leapsecond processing.
 *
 */
static inline unsigned int accumulate_nsecs_to_secs(struct timekeeper *tk)
{
	u64 nsecps = (u64)NSEC_PER_SEC << tk->tkr_mono.shift;
	unsigned int clock_set = 0;

	while (tk->tkr_mono.xtime_nsec >= nsecps) {
		int leap;

		tk->tkr_mono.xtime_nsec -= nsecps;
		tk->xtime_sec++;

		/* Figure out if its a leap sec and apply if needed */
		leap = second_overflow(tk->xtime_sec);
		if (unlikely(leap)) {
			struct timespec64 ts;

			tk->xtime_sec += leap;

			ts.tv_sec = leap;
			ts.tv_nsec = 0;
			tk_set_wall_to_mono(tk,
				timespec64_sub(tk->wall_to_monotonic, ts));

			__timekeeping_set_tai_offset(tk, tk->tai_offset - leap);

			clock_set = TK_CLOCK_WAS_SET;
		}
	}
	return clock_set;
}

/**
 * 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(struct timekeeper *tk, cycle_t offset,
						u32 shift,
						unsigned int *clock_set)
{
	cycle_t interval = tk->cycle_interval << shift;
	u64 snsec_per_sec;

	/* If the offset is smaller than a shifted interval, do nothing */
	if (offset < interval)
		return offset;

	/* Accumulate one shifted interval */
	offset -= interval;
	tk->tkr_mono.cycle_last += interval;
	tk->tkr_raw.cycle_last  += interval;

	tk->tkr_mono.xtime_nsec += tk->xtime_interval << shift;
	*clock_set |= accumulate_nsecs_to_secs(tk);

	/* Accumulate raw time */
	tk->tkr_raw.xtime_nsec += tk->raw_interval << shift;
	snsec_per_sec = (u64)NSEC_PER_SEC << tk->tkr_raw.shift;
	while (tk->tkr_raw.xtime_nsec >= snsec_per_sec) {
		tk->tkr_raw.xtime_nsec -= snsec_per_sec;
		tk->raw_sec++;
	}

	/* Accumulate error between NTP and clock interval */
	tk->ntp_error += tk->ntp_tick << shift;
	tk->ntp_error -= (tk->xtime_interval + tk->xtime_remainder) <<
						(tk->ntp_error_shift + shift);

	return offset;
}

/**
 * update_wall_time - Uses the current clocksource to increment the wall time
 *
 */
void update_wall_time(void)
{
	struct timekeeper *real_tk = &tk_core.timekeeper;
	struct timekeeper *tk = &shadow_timekeeper;
	cycle_t offset;
	int shift = 0, maxshift;
	unsigned int clock_set = 0;
	unsigned long flags;

	raw_spin_lock_irqsave(&timekeeper_lock, flags);

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

#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
	offset = real_tk->cycle_interval;
#else
	offset = clocksource_delta(tk_clock_read(&tk->tkr_mono),
				   tk->tkr_mono.cycle_last, tk->tkr_mono.mask);
#endif

	/* Check if there's really nothing to do */
	if (offset < real_tk->cycle_interval)
		goto out;

	/* Do some additional sanity checking */
	timekeeping_check_update(real_tk, offset);

	/*
	 * 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 than the offset.  We then accumulate that
	 * chunk in one go, and then try to consume the next smaller
	 * doubled multiple.
	 */
	shift = ilog2(offset) - ilog2(tk->cycle_interval);
	shift = max(0, shift);
	/* Bound shift to one less than what overflows tick_length */
	maxshift = (64 - (ilog2(ntp_tick_length())+1)) - 1;
	shift = min(shift, maxshift);
	while (offset >= tk->cycle_interval) {
		offset = logarithmic_accumulation(tk, offset, shift,
							&clock_set);
		if (offset < tk->cycle_interval<<shift)
			shift--;
	}

	/* correct the clock when NTP error is too big */
	timekeeping_adjust(tk, offset);

	/*
	 * XXX This can be killed once everyone converts
	 * to the new update_vsyscall.
	 */
	old_vsyscall_fixup(tk);

	/*
	 * Finally, make sure that after the rounding
	 * xtime_nsec isn't larger than NSEC_PER_SEC
	 */
	clock_set |= accumulate_nsecs_to_secs(tk);

	write_seqcount_begin(&tk_core.seq);
	/*
	 * Update the real timekeeper.
	 *
	 * We could avoid this memcpy by switching pointers, but that
	 * requires changes to all other timekeeper usage sites as
	 * well, i.e. move the timekeeper pointer getter into the
	 * spinlocked/seqcount protected sections. And we trade this
	 * memcpy under the tk_core.seq against one before we start
	 * updating.
	 */
	timekeeping_update(tk, clock_set);
	memcpy(real_tk, tk, sizeof(*tk));
	/* The memcpy must come last. Do not put anything here! */
	write_seqcount_end(&tk_core.seq);
out:
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
	if (clock_set)
		/* Have to call _delayed version, since in irq context*/
		clock_was_set_delayed();
}

/**
 * getboottime64 - Return the real time of system boot.
 * @ts:		pointer to the timespec64 to be set
 *
 * Returns the wall-time of boot in a timespec64.
 *
 * 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 getboottime64(struct timespec64 *ts)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	ktime_t t = ktime_sub(tk->offs_real, tk->offs_boot);

	*ts = ktime_to_timespec64(t);
}
EXPORT_SYMBOL_GPL(getboottime64);

unsigned long get_seconds(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;

	return tk->xtime_sec;
}
EXPORT_SYMBOL(get_seconds);

struct timespec __current_kernel_time(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;

	return timespec64_to_timespec(tk_xtime(tk));
}

struct timespec64 current_kernel_time64(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	struct timespec64 now;
	unsigned long seq;

	do {
		seq = read_seqcount_begin(&tk_core.seq);

		now = tk_xtime(tk);
	} while (read_seqcount_retry(&tk_core.seq, seq));

	return now;
}
EXPORT_SYMBOL(current_kernel_time64);

struct timespec64 get_monotonic_coarse64(void)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	struct timespec64 now, mono;
	unsigned long seq;

	do {
		seq = read_seqcount_begin(&tk_core.seq);

		now = tk_xtime(tk);
		mono = tk->wall_to_monotonic;
	} while (read_seqcount_retry(&tk_core.seq, seq));

	set_normalized_timespec64(&now, now.tv_sec + mono.tv_sec,
				now.tv_nsec + mono.tv_nsec);

	return now;
}

/*
 * Must hold jiffies_lock
 */
void do_timer(unsigned long ticks)
{
	jiffies_64 += ticks;
	calc_global_load(ticks);
}

/**
 * ktime_get_update_offsets_now - hrtimer helper
 * @cwsseq:	pointer to check and store the clock was set sequence number
 * @offs_real:	pointer to storage for monotonic -> realtime offset
 * @offs_boot:	pointer to storage for monotonic -> boottime offset
 * @offs_tai:	pointer to storage for monotonic -> clock tai offset
 *
 * Returns current monotonic time and updates the offsets if the
 * sequence number in @cwsseq and timekeeper.clock_was_set_seq are
 * different.
 *
 * Called from hrtimer_interrupt() or retrigger_next_event()
 */
ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real,
				     ktime_t *offs_boot, ktime_t *offs_tai)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned int seq;
	ktime_t base;
	u64 nsecs;

	do {
		seq = read_seqcount_begin(&tk_core.seq);

		base = tk->tkr_mono.base;
		nsecs = timekeeping_get_ns(&tk->tkr_mono);
		base = ktime_add_ns(base, nsecs);

		if (*cwsseq != tk->clock_was_set_seq) {
			*cwsseq = tk->clock_was_set_seq;
			*offs_real = tk->offs_real;
			*offs_boot = tk->offs_boot;
			*offs_tai = tk->offs_tai;
		}

		/* Handle leapsecond insertion adjustments */
		if (unlikely(base.tv64 >= tk->next_leap_ktime.tv64))
			*offs_real = ktime_sub(tk->offs_real, ktime_set(1, 0));

	} while (read_seqcount_retry(&tk_core.seq, seq));

	return base;
}

/**
 * do_adjtimex() - Accessor function to NTP __do_adjtimex function
 */
int do_adjtimex(struct timex *txc)
{
	struct timekeeper *tk = &tk_core.timekeeper;
	unsigned long flags;
	struct timespec64 ts;
	s32 orig_tai, tai;
	int ret;

	/* Validate the data before disabling interrupts */
	ret = ntp_validate_timex(txc);
	if (ret)
		return ret;

	if (txc->modes & ADJ_SETOFFSET) {
		struct timespec delta;
		delta.tv_sec  = txc->time.tv_sec;
		delta.tv_nsec = txc->time.tv_usec;
		if (!(txc->modes & ADJ_NANO))
			delta.tv_nsec *= 1000;
		ret = timekeeping_inject_offset(&delta);
		if (ret)
			return ret;
	}

	getnstimeofday64(&ts);

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	write_seqcount_begin(&tk_core.seq);

	orig_tai = tai = tk->tai_offset;
	ret = __do_adjtimex(txc, &ts, &tai);

	if (tai != orig_tai) {
		__timekeeping_set_tai_offset(tk, tai);
		timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
	}
	tk_update_leap_state(tk);

	write_seqcount_end(&tk_core.seq);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

	if (tai != orig_tai)
		clock_was_set();

	ntp_notify_cmos_timer();

	return ret;
}

#ifdef CONFIG_NTP_PPS
/**
 * hardpps() - Accessor function to NTP __hardpps function
 */
void hardpps(const struct timespec64 *phase_ts, const struct timespec64 *raw_ts)
{
	unsigned long flags;

	raw_spin_lock_irqsave(&timekeeper_lock, flags);
	write_seqcount_begin(&tk_core.seq);

	__hardpps(phase_ts, raw_ts);

	write_seqcount_end(&tk_core.seq);
	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
}
EXPORT_SYMBOL(hardpps);
#endif

/**
 * 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(&jiffies_lock);
	do_timer(ticks);
	write_sequnlock(&jiffies_lock);
	update_wall_time();
}