timekeeping: Add warnings when overflows or underflows are observed

[cascardo/linux.git] / 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;

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;

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

/* Flag for if there is a persistent clock on this platform */
bool __read_mostly persistent_clock_exist = false;

static inline void tk_normalize_xtime(struct timekeeper *tk)
{
        while (tk->tkr.xtime_nsec >= ((u64)NSEC_PER_SEC << tk->tkr.shift)) {
                tk->tkr.xtime_nsec -= (u64)NSEC_PER_SEC << tk->tkr.shift;
                tk->xtime_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.xtime_nsec >> tk->tkr.shift);
        return ts;
}

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

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

#ifdef CONFIG_DEBUG_TIMEKEEPING
#define WARNING_FREQ (HZ*300) /* 5 minute rate-limiting */
/*
 * These simple flag variables are managed
 * without locks, which is racy, but ok since
 * we don't really care about being super
 * precise about how many events were seen,
 * just that a problem was observed.
 */
static int timekeeping_underflow_seen;
static int timekeeping_overflow_seen;

/* last_warning is only modified under the timekeeping lock */
static long timekeeping_last_warning;

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

        cycle_t max_cycles = tk->tkr.clock->max_cycles;
        const char *name = tk->tkr.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 (timekeeping_underflow_seen) {
                if (jiffies - timekeeping_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");
                        timekeeping_last_warning = jiffies;
                }
                timekeeping_underflow_seen = 0;
        }

        if (timekeeping_overflow_seen) {
                if (jiffies - timekeeping_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");
                        timekeeping_last_warning = jiffies;
                }
                timekeeping_overflow_seen = 0;
        }
}

static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr)
{
        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 = tkr->read(tkr->clock);
                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))) {
                timekeeping_underflow_seen = 1;
                delta = 0;
        }

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

        /* 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.clock;
        tk->tkr.clock = clock;
        tk->tkr.read = clock->read;
        tk->tkr.mask = clock->mask;
        tk->tkr.cycle_last = tk->tkr.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;
        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 =
                ((u64) interval * clock->mult) >> clock->shift;

         /* 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.xtime_nsec >>= -shift_change;
                else
                        tk->tkr.xtime_nsec <<= shift_change;
        }
        tk->tkr.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.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 s64 timekeeping_get_ns(struct tk_read_base *tkr)
{
        cycle_t delta;
        s64 nsec;

        delta = timekeeping_get_delta(tkr);

        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_raw(struct timekeeper *tk)
{
        struct clocksource *clock = tk->tkr.clock;
        cycle_t delta;
        s64 nsec;

        delta = timekeeping_get_delta(&tk->tkr);

        /* convert delta to nanoseconds. */
        nsec = clocksource_cyc2ns(delta, clock->mult, clock->shift);

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

/**
 * 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.
 *
 * So we handle this differently than the other timekeeping accessor
 * functions which retry when the sequence count has changed. The
 * update side does:
 *
 * smp_wmb();   <- Ensure that the last base[1] update is visible
 * tkf->seq++;
 * smp_wmb();   <- Ensure that the seqcount update is visible
 * update(tkf->base[0], tkr);
 * smp_wmb();   <- Ensure that the base[0] update is visible
 * tkf->seq++;
 * smp_wmb();   <- Ensure that the seqcount update is visible
 * update(tkf->base[1], tkr);
 *
 * The reader side does:
 *
 * do {
 *      seq = tkf->seq;
 *      smp_rmb();
 *      idx = seq & 0x01;
 *      now = now(tkf->base[idx]);
 *      smp_rmb();
 * } while (seq != tkf->seq)
 *
 * As long as we update base[0] readers are forced off to
 * base[1]. Once base[0] is updated readers are redirected to base[0]
 * and the base[1] update takes place.
 *
 * 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_read_base *base = tk_fast_mono.base;

        /* Force readers off to base[1] */
        raw_write_seqcount_latch(&tk_fast_mono.seq);

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

        /* Force readers back to base[0] */
        raw_write_seqcount_latch(&tk_fast_mono.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.
 */
u64 notrace ktime_get_mono_fast_ns(void)
{
        struct tk_read_base *tkr;
        unsigned int seq;
        u64 now;

        do {
                seq = raw_read_seqcount(&tk_fast_mono.seq);
                tkr = tk_fast_mono.base + (seq & 0x01);
                now = ktime_to_ns(tkr->base_mono) + timekeeping_get_ns(tkr);

        } while (read_seqcount_retry(&tk_fast_mono.seq, seq));
        return now;
}
EXPORT_SYMBOL_GPL(ktime_get_mono_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;
}

/**
 * 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;

        memcpy(&tkr_dummy, tkr, sizeof(tkr_dummy));
        cycles_at_suspend = tkr->read(tkr->clock);
        tkr_dummy.read = dummy_clock_read;
        update_fast_timekeeper(&tkr_dummy);
}

#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.clock, tk->tkr.mult,
                            tk->tkr.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.xtime_nsec & ((1ULL << tk->tkr.shift) - 1);
        tk->tkr.xtime_nsec -= remainder;
        tk->tkr.xtime_nsec += 1ULL << tk->tkr.shift;
        tk->ntp_error += remainder << tk->ntp_error_shift;
        tk->ntp_error -= (1ULL << tk->tkr.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);

/*
 * 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.base_mono = ns_to_ktime(seconds * NSEC_PER_SEC + nsec);

        /* Update the monotonic raw base */
        tk->base_raw = timespec64_to_ktime(tk->raw_time);

        /*
         * 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.xtime_nsec >> tk->tkr.shift);
        if (nsec >= NSEC_PER_SEC)
                seconds++;
        tk->ktime_sec = seconds;
}

/* 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_ktime_data(tk);

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

        if (action & TK_MIRROR)
                memcpy(&shadow_timekeeper, &tk_core.timekeeper,
                       sizeof(tk_core.timekeeper));

        update_fast_timekeeper(&tk->tkr);
}

/**
 * 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)
{
        struct clocksource *clock = tk->tkr.clock;
        cycle_t cycle_now, delta;
        s64 nsec;

        cycle_now = tk->tkr.read(clock);
        delta = clocksource_delta(cycle_now, tk->tkr.cycle_last, tk->tkr.mask);
        tk->tkr.cycle_last = cycle_now;

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

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

        tk_normalize_xtime(tk);

        nsec = clocksource_cyc2ns(delta, clock->mult, clock->shift);
        timespec64_add_ns(&tk->raw_time, nsec);
}

/**
 * __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);

        } 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.base_mono;
                nsecs = timekeeping_get_ns(&tk->tkr);

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

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

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.base_mono, *offset);
                nsecs = timekeeping_get_ns(&tk->tkr);

        } 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->base_raw;
                nsecs = timekeeping_get_ns_raw(tk);

        } 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);
                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

/**
 * 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)
{
        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 = timespec64_to_timespec(tk->raw_time);
                ts_real->tv_sec = tk->xtime_sec;
                ts_real->tv_nsec = 0;

                nsecs_raw = timekeeping_get_ns_raw(tk);
                nsecs_real = timekeeping_get_ns(&tk->tkr);

        } while (read_seqcount_retry(&tk_core.seq, 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 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;

        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;

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

        tk_set_xtime(tk, ts);

        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 0;
}
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 ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC)
                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_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.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.clock == clock)
                return 0;
        stop_machine(change_clocksource, clock, NULL);
        tick_clock_notify();
        return tk->tkr.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;
        struct timespec64 ts64;
        unsigned long seq;
        s64 nsecs;

        do {
                seq = read_seqcount_begin(&tk_core.seq);
                nsecs = timekeeping_get_ns_raw(tk);
                ts64 = tk->raw_time;

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

        timespec64_add_ns(&ts64, nsecs);
        *ts = ts64;
}
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.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.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;
}

/**
 * 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 __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 timekeeper *tk = &tk_core.timekeeper;
        struct clocksource *clock;
        unsigned long flags;
        struct timespec64 now, boot, tmp;
        struct timespec ts;

        read_persistent_clock(&ts);
        now = timespec_to_timespec64(ts);
        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_exist = true;

        read_boot_clock(&ts);
        boot = timespec_to_timespec64(ts);
        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_time.tv_sec = 0;
        tk->raw_time.tv_nsec = 0;
        tk->base_raw.tv64 = 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);

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

/* time in seconds when suspend began */
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);
}

/**
 * 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_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_sleeptime64(struct timespec64 *delta)
{
        struct timekeeper *tk = &tk_core.timekeeper;
        unsigned long flags;

        /*
         * Make sure we don't set the clock twice, as timekeeping_resume()
         * already did it
         */
        if (has_persistent_clock())
                return;

        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();
}

/**
 * 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.
 */
void timekeeping_resume(void)
{
        struct timekeeper *tk = &tk_core.timekeeper;
        struct clocksource *clock = tk->tkr.clock;
        unsigned long flags;
        struct timespec64 ts_new, ts_delta;
        struct timespec tmp;
        cycle_t cycle_now, cycle_delta;
        bool suspendtime_found = false;

        read_persistent_clock(&tmp);
        ts_new = timespec_to_timespec64(tmp);

        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->tkr.read(clock);
        if ((clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&
                cycle_now > tk->tkr.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.cycle_last,
                                                tk->tkr.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);
                suspendtime_found = true;
        } else if (timespec64_compare(&ts_new, &timekeeping_suspend_time) > 0) {
                ts_delta = timespec64_sub(ts_new, timekeeping_suspend_time);
                suspendtime_found = true;
        }

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

        /* Re-base the last cycle value */
        tk->tkr.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();

        clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);

        /* Resume hrtimers */
        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;
        struct timespec tmp;

        read_persistent_clock(&tmp);
        timekeeping_suspend_time = timespec_to_timespec64(tmp);

        /*
         * 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_exist = true;

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

        clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
        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.mult + mult_adj < mult_adj)) {
                /* NTP adjustment caused clocksource mult overflow */
                WARN_ON_ONCE(1);
                return;
        }

        tk->tkr.mult += mult_adj;
        tk->xtime_interval += interval;
        tk->tkr.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.clock->maxadj &&
                (abs(tk->tkr.mult - tk->tkr.clock->mult)
                        > tk->tkr.clock->maxadj))) {
                printk_once(KERN_WARNING
                        "Adjusting %s more than 11%% (%ld vs %ld)\n",
                        tk->tkr.clock->name, (long)tk->tkr.mult,
                        (long)tk->tkr.clock->mult + tk->tkr.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.xtime_nsec < 0)) {
                s64 neg = -(s64)tk->tkr.xtime_nsec;
                tk->tkr.xtime_nsec = 0;
                tk->ntp_error += neg << tk->ntp_error_shift;
        }
}

/**
 * accumulate_nsecs_to_secs - Accumulates nsecs into secs
 *
 * Helper function that accumulates a the nsecs greater then 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.shift;
        unsigned int clock_set = 0;

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

                tk->tkr.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 raw_nsecs;

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

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

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

        /* Accumulate raw time */
        raw_nsecs = (u64)tk->raw_interval << shift;
        raw_nsecs += tk->raw_time.tv_nsec;
        if (raw_nsecs >= NSEC_PER_SEC) {
                u64 raw_secs = raw_nsecs;
                raw_nsecs = do_div(raw_secs, NSEC_PER_SEC);
                tk->raw_time.tv_sec += raw_secs;
        }
        tk->raw_time.tv_nsec = raw_nsecs;

        /* 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->tkr.read(tk->tkr.clock),
                                   tk->tkr.cycle_last, tk->tkr.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.
         */
        memcpy(real_tk, tk, sizeof(*tk));
        timekeeping_update(real_tk, clock_set);
        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 timespec current_kernel_time(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 timespec64_to_timespec(now);
}
EXPORT_SYMBOL(current_kernel_time);

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_tick - hrtimer helper
 * @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 monotonic time at last tick and various offsets
 */
ktime_t ktime_get_update_offsets_tick(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.base_mono;
                nsecs = tk->tkr.xtime_nsec >> tk->tkr.shift;

                *offs_real = tk->offs_real;
                *offs_boot = tk->offs_boot;
                *offs_tai = tk->offs_tai;
        } while (read_seqcount_retry(&tk_core.seq, seq));

        return ktime_add_ns(base, nsecs);
}

#ifdef CONFIG_HIGH_RES_TIMERS
/**
 * ktime_get_update_offsets_now - hrtimer helper
 * @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
 * Called from hrtimer_interrupt() or retrigger_next_event()
 */
ktime_t ktime_get_update_offsets_now(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.base_mono;
                nsecs = timekeeping_get_ns(&tk->tkr);

                *offs_real = tk->offs_real;
                *offs_boot = tk->offs_boot;
                *offs_tai = tk->offs_tai;
        } while (read_seqcount_retry(&tk_core.seq, seq));

        return ktime_add_ns(base, nsecs);
}
#endif

/**
 * 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);
        }
        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 timespec *phase_ts, const struct timespec *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();
}