Linux 4.15.6

[linux/fpc-iii.git] / kernel / time / ntp.c

// SPDX-License-Identifier: GPL-2.0
/*
 * NTP state machine interfaces and logic.
 *
 * This code was mainly moved from kernel/timer.c and kernel/time.c
 * Please see those files for relevant copyright info and historical
 * changelogs.
 */
#include <linux/capability.h>
#include <linux/clocksource.h>
#include <linux/workqueue.h>
#include <linux/hrtimer.h>
#include <linux/jiffies.h>
#include <linux/math64.h>
#include <linux/timex.h>
#include <linux/time.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/rtc.h>
#include <linux/math64.h>

#include "ntp_internal.h"
#include "timekeeping_internal.h"


/*
 * NTP timekeeping variables:
 *
 * Note: All of the NTP state is protected by the timekeeping locks.
 */


/* USER_HZ period (usecs): */
unsigned long                   tick_usec = TICK_USEC;

/* SHIFTED_HZ period (nsecs): */
unsigned long                   tick_nsec;

static u64                      tick_length;
static u64                      tick_length_base;

#define SECS_PER_DAY            86400
#define MAX_TICKADJ             500LL           /* usecs */
#define MAX_TICKADJ_SCALED \
        (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)

/*
 * phase-lock loop variables
 */

/*
 * clock synchronization status
 *
 * (TIME_ERROR prevents overwriting the CMOS clock)
 */
static int                      time_state = TIME_OK;

/* clock status bits:                                                   */
static int                      time_status = STA_UNSYNC;

/* time adjustment (nsecs):                                             */
static s64                      time_offset;

/* pll time constant:                                                   */
static long                     time_constant = 2;

/* maximum error (usecs):                                               */
static long                     time_maxerror = NTP_PHASE_LIMIT;

/* estimated error (usecs):                                             */
static long                     time_esterror = NTP_PHASE_LIMIT;

/* frequency offset (scaled nsecs/secs):                                */
static s64                      time_freq;

/* time at last adjustment (secs):                                      */
static time64_t         time_reftime;

static long                     time_adjust;

/* constant (boot-param configurable) NTP tick adjustment (upscaled)    */
static s64                      ntp_tick_adj;

/* second value of the next pending leapsecond, or TIME64_MAX if no leap */
static time64_t                 ntp_next_leap_sec = TIME64_MAX;

#ifdef CONFIG_NTP_PPS

/*
 * The following variables are used when a pulse-per-second (PPS) signal
 * is available. They establish the engineering parameters of the clock
 * discipline loop when controlled by the PPS signal.
 */
#define PPS_VALID       10      /* PPS signal watchdog max (s) */
#define PPS_POPCORN     4       /* popcorn spike threshold (shift) */
#define PPS_INTMIN      2       /* min freq interval (s) (shift) */
#define PPS_INTMAX      8       /* max freq interval (s) (shift) */
#define PPS_INTCOUNT    4       /* number of consecutive good intervals to
                                   increase pps_shift or consecutive bad
                                   intervals to decrease it */
#define PPS_MAXWANDER   100000  /* max PPS freq wander (ns/s) */

static int pps_valid;           /* signal watchdog counter */
static long pps_tf[3];          /* phase median filter */
static long pps_jitter;         /* current jitter (ns) */
static struct timespec64 pps_fbase; /* beginning of the last freq interval */
static int pps_shift;           /* current interval duration (s) (shift) */
static int pps_intcnt;          /* interval counter */
static s64 pps_freq;            /* frequency offset (scaled ns/s) */
static long pps_stabil;         /* current stability (scaled ns/s) */

/*
 * PPS signal quality monitors
 */
static long pps_calcnt;         /* calibration intervals */
static long pps_jitcnt;         /* jitter limit exceeded */
static long pps_stbcnt;         /* stability limit exceeded */
static long pps_errcnt;         /* calibration errors */


/* PPS kernel consumer compensates the whole phase error immediately.
 * Otherwise, reduce the offset by a fixed factor times the time constant.
 */
static inline s64 ntp_offset_chunk(s64 offset)
{
        if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
                return offset;
        else
                return shift_right(offset, SHIFT_PLL + time_constant);
}

static inline void pps_reset_freq_interval(void)
{
        /* the PPS calibration interval may end
           surprisingly early */
        pps_shift = PPS_INTMIN;
        pps_intcnt = 0;
}

/**
 * pps_clear - Clears the PPS state variables
 */
static inline void pps_clear(void)
{
        pps_reset_freq_interval();
        pps_tf[0] = 0;
        pps_tf[1] = 0;
        pps_tf[2] = 0;
        pps_fbase.tv_sec = pps_fbase.tv_nsec = 0;
        pps_freq = 0;
}

/* Decrease pps_valid to indicate that another second has passed since
 * the last PPS signal. When it reaches 0, indicate that PPS signal is
 * missing.
 */
static inline void pps_dec_valid(void)
{
        if (pps_valid > 0)
                pps_valid--;
        else {
                time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
                                 STA_PPSWANDER | STA_PPSERROR);
                pps_clear();
        }
}

static inline void pps_set_freq(s64 freq)
{
        pps_freq = freq;
}

static inline int is_error_status(int status)
{
        return (status & (STA_UNSYNC|STA_CLOCKERR))
                /* PPS signal lost when either PPS time or
                 * PPS frequency synchronization requested
                 */
                || ((status & (STA_PPSFREQ|STA_PPSTIME))
                        && !(status & STA_PPSSIGNAL))
                /* PPS jitter exceeded when
                 * PPS time synchronization requested */
                || ((status & (STA_PPSTIME|STA_PPSJITTER))
                        == (STA_PPSTIME|STA_PPSJITTER))
                /* PPS wander exceeded or calibration error when
                 * PPS frequency synchronization requested
                 */
                || ((status & STA_PPSFREQ)
                        && (status & (STA_PPSWANDER|STA_PPSERROR)));
}

static inline void pps_fill_timex(struct timex *txc)
{
        txc->ppsfreq       = shift_right((pps_freq >> PPM_SCALE_INV_SHIFT) *
                                         PPM_SCALE_INV, NTP_SCALE_SHIFT);
        txc->jitter        = pps_jitter;
        if (!(time_status & STA_NANO))
                txc->jitter /= NSEC_PER_USEC;
        txc->shift         = pps_shift;
        txc->stabil        = pps_stabil;
        txc->jitcnt        = pps_jitcnt;
        txc->calcnt        = pps_calcnt;
        txc->errcnt        = pps_errcnt;
        txc->stbcnt        = pps_stbcnt;
}

#else /* !CONFIG_NTP_PPS */

static inline s64 ntp_offset_chunk(s64 offset)
{
        return shift_right(offset, SHIFT_PLL + time_constant);
}

static inline void pps_reset_freq_interval(void) {}
static inline void pps_clear(void) {}
static inline void pps_dec_valid(void) {}
static inline void pps_set_freq(s64 freq) {}

static inline int is_error_status(int status)
{
        return status & (STA_UNSYNC|STA_CLOCKERR);
}

static inline void pps_fill_timex(struct timex *txc)
{
        /* PPS is not implemented, so these are zero */
        txc->ppsfreq       = 0;
        txc->jitter        = 0;
        txc->shift         = 0;
        txc->stabil        = 0;
        txc->jitcnt        = 0;
        txc->calcnt        = 0;
        txc->errcnt        = 0;
        txc->stbcnt        = 0;
}

#endif /* CONFIG_NTP_PPS */


/**
 * ntp_synced - Returns 1 if the NTP status is not UNSYNC
 *
 */
static inline int ntp_synced(void)
{
        return !(time_status & STA_UNSYNC);
}


/*
 * NTP methods:
 */

/*
 * Update (tick_length, tick_length_base, tick_nsec), based
 * on (tick_usec, ntp_tick_adj, time_freq):
 */
static void ntp_update_frequency(void)
{
        u64 second_length;
        u64 new_base;

        second_length            = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
                                                << NTP_SCALE_SHIFT;

        second_length           += ntp_tick_adj;
        second_length           += time_freq;

        tick_nsec                = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
        new_base                 = div_u64(second_length, NTP_INTERVAL_FREQ);

        /*
         * Don't wait for the next second_overflow, apply
         * the change to the tick length immediately:
         */
        tick_length             += new_base - tick_length_base;
        tick_length_base         = new_base;
}

static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
{
        time_status &= ~STA_MODE;

        if (secs < MINSEC)
                return 0;

        if (!(time_status & STA_FLL) && (secs <= MAXSEC))
                return 0;

        time_status |= STA_MODE;

        return div64_long(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
}

static void ntp_update_offset(long offset)
{
        s64 freq_adj;
        s64 offset64;
        long secs;

        if (!(time_status & STA_PLL))
                return;

        if (!(time_status & STA_NANO)) {
                /* Make sure the multiplication below won't overflow */
                offset = clamp(offset, -USEC_PER_SEC, USEC_PER_SEC);
                offset *= NSEC_PER_USEC;
        }

        /*
         * Scale the phase adjustment and
         * clamp to the operating range.
         */
        offset = clamp(offset, -MAXPHASE, MAXPHASE);

        /*
         * Select how the frequency is to be controlled
         * and in which mode (PLL or FLL).
         */
        secs = (long)(__ktime_get_real_seconds() - time_reftime);
        if (unlikely(time_status & STA_FREQHOLD))
                secs = 0;

        time_reftime = __ktime_get_real_seconds();

        offset64    = offset;
        freq_adj    = ntp_update_offset_fll(offset64, secs);

        /*
         * Clamp update interval to reduce PLL gain with low
         * sampling rate (e.g. intermittent network connection)
         * to avoid instability.
         */
        if (unlikely(secs > 1 << (SHIFT_PLL + 1 + time_constant)))
                secs = 1 << (SHIFT_PLL + 1 + time_constant);

        freq_adj    += (offset64 * secs) <<
                        (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));

        freq_adj    = min(freq_adj + time_freq, MAXFREQ_SCALED);

        time_freq   = max(freq_adj, -MAXFREQ_SCALED);

        time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
}

/**
 * ntp_clear - Clears the NTP state variables
 */
void ntp_clear(void)
{
        time_adjust     = 0;            /* stop active adjtime() */
        time_status     |= STA_UNSYNC;
        time_maxerror   = NTP_PHASE_LIMIT;
        time_esterror   = NTP_PHASE_LIMIT;

        ntp_update_frequency();

        tick_length     = tick_length_base;
        time_offset     = 0;

        ntp_next_leap_sec = TIME64_MAX;
        /* Clear PPS state variables */
        pps_clear();
}


u64 ntp_tick_length(void)
{
        return tick_length;
}

/**
 * ntp_get_next_leap - Returns the next leapsecond in CLOCK_REALTIME ktime_t
 *
 * Provides the time of the next leapsecond against CLOCK_REALTIME in
 * a ktime_t format. Returns KTIME_MAX if no leapsecond is pending.
 */
ktime_t ntp_get_next_leap(void)
{
        ktime_t ret;

        if ((time_state == TIME_INS) && (time_status & STA_INS))
                return ktime_set(ntp_next_leap_sec, 0);
        ret = KTIME_MAX;
        return ret;
}

/*
 * this routine handles the overflow of the microsecond field
 *
 * The tricky bits of code to handle the accurate clock support
 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
 * They were originally developed for SUN and DEC kernels.
 * All the kudos should go to Dave for this stuff.
 *
 * Also handles leap second processing, and returns leap offset
 */
int second_overflow(time64_t secs)
{
        s64 delta;
        int leap = 0;
        s32 rem;

        /*
         * Leap second processing. If in leap-insert state at the end of the
         * day, the system clock is set back one second; if in leap-delete
         * state, the system clock is set ahead one second.
         */
        switch (time_state) {
        case TIME_OK:
                if (time_status & STA_INS) {
                        time_state = TIME_INS;
                        div_s64_rem(secs, SECS_PER_DAY, &rem);
                        ntp_next_leap_sec = secs + SECS_PER_DAY - rem;
                } else if (time_status & STA_DEL) {
                        time_state = TIME_DEL;
                        div_s64_rem(secs + 1, SECS_PER_DAY, &rem);
                        ntp_next_leap_sec = secs + SECS_PER_DAY - rem;
                }
                break;
        case TIME_INS:
                if (!(time_status & STA_INS)) {
                        ntp_next_leap_sec = TIME64_MAX;
                        time_state = TIME_OK;
                } else if (secs == ntp_next_leap_sec) {
                        leap = -1;
                        time_state = TIME_OOP;
                        printk(KERN_NOTICE
                                "Clock: inserting leap second 23:59:60 UTC\n");
                }
                break;
        case TIME_DEL:
                if (!(time_status & STA_DEL)) {
                        ntp_next_leap_sec = TIME64_MAX;
                        time_state = TIME_OK;
                } else if (secs == ntp_next_leap_sec) {
                        leap = 1;
                        ntp_next_leap_sec = TIME64_MAX;
                        time_state = TIME_WAIT;
                        printk(KERN_NOTICE
                                "Clock: deleting leap second 23:59:59 UTC\n");
                }
                break;
        case TIME_OOP:
                ntp_next_leap_sec = TIME64_MAX;
                time_state = TIME_WAIT;
                break;
        case TIME_WAIT:
                if (!(time_status & (STA_INS | STA_DEL)))
                        time_state = TIME_OK;
                break;
        }


        /* Bump the maxerror field */
        time_maxerror += MAXFREQ / NSEC_PER_USEC;
        if (time_maxerror > NTP_PHASE_LIMIT) {
                time_maxerror = NTP_PHASE_LIMIT;
                time_status |= STA_UNSYNC;
        }

        /* Compute the phase adjustment for the next second */
        tick_length      = tick_length_base;

        delta            = ntp_offset_chunk(time_offset);
        time_offset     -= delta;
        tick_length     += delta;

        /* Check PPS signal */
        pps_dec_valid();

        if (!time_adjust)
                goto out;

        if (time_adjust > MAX_TICKADJ) {
                time_adjust -= MAX_TICKADJ;
                tick_length += MAX_TICKADJ_SCALED;
                goto out;
        }

        if (time_adjust < -MAX_TICKADJ) {
                time_adjust += MAX_TICKADJ;
                tick_length -= MAX_TICKADJ_SCALED;
                goto out;
        }

        tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
                                                         << NTP_SCALE_SHIFT;
        time_adjust = 0;

out:
        return leap;
}

static void sync_hw_clock(struct work_struct *work);
static DECLARE_DELAYED_WORK(sync_work, sync_hw_clock);

static void sched_sync_hw_clock(struct timespec64 now,
                                unsigned long target_nsec, bool fail)

{
        struct timespec64 next;

        getnstimeofday64(&next);
        if (!fail)
                next.tv_sec = 659;
        else {
                /*
                 * Try again as soon as possible. Delaying long periods
                 * decreases the accuracy of the work queue timer. Due to this
                 * the algorithm is very likely to require a short-sleep retry
                 * after the above long sleep to synchronize ts_nsec.
                 */
                next.tv_sec = 0;
        }

        /* Compute the needed delay that will get to tv_nsec == target_nsec */
        next.tv_nsec = target_nsec - next.tv_nsec;
        if (next.tv_nsec <= 0)
                next.tv_nsec += NSEC_PER_SEC;
        if (next.tv_nsec >= NSEC_PER_SEC) {
                next.tv_sec++;
                next.tv_nsec -= NSEC_PER_SEC;
        }

        queue_delayed_work(system_power_efficient_wq, &sync_work,
                           timespec64_to_jiffies(&next));
}

static void sync_rtc_clock(void)
{
        unsigned long target_nsec;
        struct timespec64 adjust, now;
        int rc;

        if (!IS_ENABLED(CONFIG_RTC_SYSTOHC))
                return;

        getnstimeofday64(&now);

        adjust = now;
        if (persistent_clock_is_local)
                adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);

        /*
         * The current RTC in use will provide the target_nsec it wants to be
         * called at, and does rtc_tv_nsec_ok internally.
         */
        rc = rtc_set_ntp_time(adjust, &target_nsec);
        if (rc == -ENODEV)
                return;

        sched_sync_hw_clock(now, target_nsec, rc);
}

#ifdef CONFIG_GENERIC_CMOS_UPDATE
int __weak update_persistent_clock(struct timespec now)
{
        return -ENODEV;
}

int __weak update_persistent_clock64(struct timespec64 now64)
{
        struct timespec now;

        now = timespec64_to_timespec(now64);
        return update_persistent_clock(now);
}
#endif

static bool sync_cmos_clock(void)
{
        static bool no_cmos;
        struct timespec64 now;
        struct timespec64 adjust;
        int rc = -EPROTO;
        long target_nsec = NSEC_PER_SEC / 2;

        if (!IS_ENABLED(CONFIG_GENERIC_CMOS_UPDATE))
                return false;

        if (no_cmos)
                return false;

        /*
         * Historically update_persistent_clock64() has followed x86
         * semantics, which match the MC146818A/etc RTC. This RTC will store
         * 'adjust' and then in .5s it will advance once second.
         *
         * Architectures are strongly encouraged to use rtclib and not
         * implement this legacy API.
         */
        getnstimeofday64(&now);
        if (rtc_tv_nsec_ok(-1 * target_nsec, &adjust, &now)) {
                if (persistent_clock_is_local)
                        adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
                rc = update_persistent_clock64(adjust);
                /*
                 * The machine does not support update_persistent_clock64 even
                 * though it defines CONFIG_GENERIC_CMOS_UPDATE.
                 */
                if (rc == -ENODEV) {
                        no_cmos = true;
                        return false;
                }
        }

        sched_sync_hw_clock(now, target_nsec, rc);
        return true;
}

/*
 * If we have an externally synchronized Linux clock, then update RTC clock
 * accordingly every ~11 minutes. Generally RTCs can only store second
 * precision, but many RTCs will adjust the phase of their second tick to
 * match the moment of update. This infrastructure arranges to call to the RTC
 * set at the correct moment to phase synchronize the RTC second tick over
 * with the kernel clock.
 */
static void sync_hw_clock(struct work_struct *work)
{
        if (!ntp_synced())
                return;

        if (sync_cmos_clock())
                return;

        sync_rtc_clock();
}

void ntp_notify_cmos_timer(void)
{
        if (!ntp_synced())
                return;

        if (IS_ENABLED(CONFIG_GENERIC_CMOS_UPDATE) ||
            IS_ENABLED(CONFIG_RTC_SYSTOHC))
                queue_delayed_work(system_power_efficient_wq, &sync_work, 0);
}

/*
 * Propagate a new txc->status value into the NTP state:
 */
static inline void process_adj_status(struct timex *txc, struct timespec64 *ts)
{
        if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
                time_state = TIME_OK;
                time_status = STA_UNSYNC;
                ntp_next_leap_sec = TIME64_MAX;
                /* restart PPS frequency calibration */
                pps_reset_freq_interval();
        }

        /*
         * If we turn on PLL adjustments then reset the
         * reference time to current time.
         */
        if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
                time_reftime = __ktime_get_real_seconds();

        /* only set allowed bits */
        time_status &= STA_RONLY;
        time_status |= txc->status & ~STA_RONLY;
}


static inline void process_adjtimex_modes(struct timex *txc,
                                                struct timespec64 *ts,
                                                s32 *time_tai)
{
        if (txc->modes & ADJ_STATUS)
                process_adj_status(txc, ts);

        if (txc->modes & ADJ_NANO)
                time_status |= STA_NANO;

        if (txc->modes & ADJ_MICRO)
                time_status &= ~STA_NANO;

        if (txc->modes & ADJ_FREQUENCY) {
                time_freq = txc->freq * PPM_SCALE;
                time_freq = min(time_freq, MAXFREQ_SCALED);
                time_freq = max(time_freq, -MAXFREQ_SCALED);
                /* update pps_freq */
                pps_set_freq(time_freq);
        }

        if (txc->modes & ADJ_MAXERROR)
                time_maxerror = txc->maxerror;

        if (txc->modes & ADJ_ESTERROR)
                time_esterror = txc->esterror;

        if (txc->modes & ADJ_TIMECONST) {
                time_constant = txc->constant;
                if (!(time_status & STA_NANO))
                        time_constant += 4;
                time_constant = min(time_constant, (long)MAXTC);
                time_constant = max(time_constant, 0l);
        }

        if (txc->modes & ADJ_TAI && txc->constant > 0)
                *time_tai = txc->constant;

        if (txc->modes & ADJ_OFFSET)
                ntp_update_offset(txc->offset);

        if (txc->modes & ADJ_TICK)
                tick_usec = txc->tick;

        if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
                ntp_update_frequency();
}


/*
 * adjtimex mainly allows reading (and writing, if superuser) of
 * kernel time-keeping variables. used by xntpd.
 */
int __do_adjtimex(struct timex *txc, struct timespec64 *ts, s32 *time_tai)
{
        int result;

        if (txc->modes & ADJ_ADJTIME) {
                long save_adjust = time_adjust;

                if (!(txc->modes & ADJ_OFFSET_READONLY)) {
                        /* adjtime() is independent from ntp_adjtime() */
                        time_adjust = txc->offset;
                        ntp_update_frequency();
                }
                txc->offset = save_adjust;
        } else {

                /* If there are input parameters, then process them: */
                if (txc->modes)
                        process_adjtimex_modes(txc, ts, time_tai);

                txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
                                  NTP_SCALE_SHIFT);
                if (!(time_status & STA_NANO))
                        txc->offset /= NSEC_PER_USEC;
        }

        result = time_state;    /* mostly `TIME_OK' */
        /* check for errors */
        if (is_error_status(time_status))
                result = TIME_ERROR;

        txc->freq          = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
                                         PPM_SCALE_INV, NTP_SCALE_SHIFT);
        txc->maxerror      = time_maxerror;
        txc->esterror      = time_esterror;
        txc->status        = time_status;
        txc->constant      = time_constant;
        txc->precision     = 1;
        txc->tolerance     = MAXFREQ_SCALED / PPM_SCALE;
        txc->tick          = tick_usec;
        txc->tai           = *time_tai;

        /* fill PPS status fields */
        pps_fill_timex(txc);

        txc->time.tv_sec = (time_t)ts->tv_sec;
        txc->time.tv_usec = ts->tv_nsec;
        if (!(time_status & STA_NANO))
                txc->time.tv_usec /= NSEC_PER_USEC;

        /* Handle leapsec adjustments */
        if (unlikely(ts->tv_sec >= ntp_next_leap_sec)) {
                if ((time_state == TIME_INS) && (time_status & STA_INS)) {
                        result = TIME_OOP;
                        txc->tai++;
                        txc->time.tv_sec--;
                }
                if ((time_state == TIME_DEL) && (time_status & STA_DEL)) {
                        result = TIME_WAIT;
                        txc->tai--;
                        txc->time.tv_sec++;
                }
                if ((time_state == TIME_OOP) &&
                                        (ts->tv_sec == ntp_next_leap_sec)) {
                        result = TIME_WAIT;
                }
        }

        return result;
}

#ifdef  CONFIG_NTP_PPS

/* actually struct pps_normtime is good old struct timespec, but it is
 * semantically different (and it is the reason why it was invented):
 * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
 * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
struct pps_normtime {
        s64             sec;    /* seconds */
        long            nsec;   /* nanoseconds */
};

/* normalize the timestamp so that nsec is in the
   ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
static inline struct pps_normtime pps_normalize_ts(struct timespec64 ts)
{
        struct pps_normtime norm = {
                .sec = ts.tv_sec,
                .nsec = ts.tv_nsec
        };

        if (norm.nsec > (NSEC_PER_SEC >> 1)) {
                norm.nsec -= NSEC_PER_SEC;
                norm.sec++;
        }

        return norm;
}

/* get current phase correction and jitter */
static inline long pps_phase_filter_get(long *jitter)
{
        *jitter = pps_tf[0] - pps_tf[1];
        if (*jitter < 0)
                *jitter = -*jitter;

        /* TODO: test various filters */
        return pps_tf[0];
}

/* add the sample to the phase filter */
static inline void pps_phase_filter_add(long err)
{
        pps_tf[2] = pps_tf[1];
        pps_tf[1] = pps_tf[0];
        pps_tf[0] = err;
}

/* decrease frequency calibration interval length.
 * It is halved after four consecutive unstable intervals.
 */
static inline void pps_dec_freq_interval(void)
{
        if (--pps_intcnt <= -PPS_INTCOUNT) {
                pps_intcnt = -PPS_INTCOUNT;
                if (pps_shift > PPS_INTMIN) {
                        pps_shift--;
                        pps_intcnt = 0;
                }
        }
}

/* increase frequency calibration interval length.
 * It is doubled after four consecutive stable intervals.
 */
static inline void pps_inc_freq_interval(void)
{
        if (++pps_intcnt >= PPS_INTCOUNT) {
                pps_intcnt = PPS_INTCOUNT;
                if (pps_shift < PPS_INTMAX) {
                        pps_shift++;
                        pps_intcnt = 0;
                }
        }
}

/* update clock frequency based on MONOTONIC_RAW clock PPS signal
 * timestamps
 *
 * At the end of the calibration interval the difference between the
 * first and last MONOTONIC_RAW clock timestamps divided by the length
 * of the interval becomes the frequency update. If the interval was
 * too long, the data are discarded.
 * Returns the difference between old and new frequency values.
 */
static long hardpps_update_freq(struct pps_normtime freq_norm)
{
        long delta, delta_mod;
        s64 ftemp;

        /* check if the frequency interval was too long */
        if (freq_norm.sec > (2 << pps_shift)) {
                time_status |= STA_PPSERROR;
                pps_errcnt++;
                pps_dec_freq_interval();
                printk_deferred(KERN_ERR
                        "hardpps: PPSERROR: interval too long - %lld s\n",
                        freq_norm.sec);
                return 0;
        }

        /* here the raw frequency offset and wander (stability) is
         * calculated. If the wander is less than the wander threshold
         * the interval is increased; otherwise it is decreased.
         */
        ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT,
                        freq_norm.sec);
        delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT);
        pps_freq = ftemp;
        if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) {
                printk_deferred(KERN_WARNING
                                "hardpps: PPSWANDER: change=%ld\n", delta);
                time_status |= STA_PPSWANDER;
                pps_stbcnt++;
                pps_dec_freq_interval();
        } else {        /* good sample */
                pps_inc_freq_interval();
        }

        /* the stability metric is calculated as the average of recent
         * frequency changes, but is used only for performance
         * monitoring
         */
        delta_mod = delta;
        if (delta_mod < 0)
                delta_mod = -delta_mod;
        pps_stabil += (div_s64(((s64)delta_mod) <<
                                (NTP_SCALE_SHIFT - SHIFT_USEC),
                                NSEC_PER_USEC) - pps_stabil) >> PPS_INTMIN;

        /* if enabled, the system clock frequency is updated */
        if ((time_status & STA_PPSFREQ) != 0 &&
            (time_status & STA_FREQHOLD) == 0) {
                time_freq = pps_freq;
                ntp_update_frequency();
        }

        return delta;
}

/* correct REALTIME clock phase error against PPS signal */
static void hardpps_update_phase(long error)
{
        long correction = -error;
        long jitter;

        /* add the sample to the median filter */
        pps_phase_filter_add(correction);
        correction = pps_phase_filter_get(&jitter);

        /* Nominal jitter is due to PPS signal noise. If it exceeds the
         * threshold, the sample is discarded; otherwise, if so enabled,
         * the time offset is updated.
         */
        if (jitter > (pps_jitter << PPS_POPCORN)) {
                printk_deferred(KERN_WARNING
                                "hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
                                jitter, (pps_jitter << PPS_POPCORN));
                time_status |= STA_PPSJITTER;
                pps_jitcnt++;
        } else if (time_status & STA_PPSTIME) {
                /* correct the time using the phase offset */
                time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT,
                                NTP_INTERVAL_FREQ);
                /* cancel running adjtime() */
                time_adjust = 0;
        }
        /* update jitter */
        pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN;
}

/*
 * __hardpps() - discipline CPU clock oscillator to external PPS signal
 *
 * This routine is called at each PPS signal arrival in order to
 * discipline the CPU clock oscillator to the PPS signal. It takes two
 * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
 * is used to correct clock phase error and the latter is used to
 * correct the frequency.
 *
 * This code is based on David Mills's reference nanokernel
 * implementation. It was mostly rewritten but keeps the same idea.
 */
void __hardpps(const struct timespec64 *phase_ts, const struct timespec64 *raw_ts)
{
        struct pps_normtime pts_norm, freq_norm;

        pts_norm = pps_normalize_ts(*phase_ts);

        /* clear the error bits, they will be set again if needed */
        time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);

        /* indicate signal presence */
        time_status |= STA_PPSSIGNAL;
        pps_valid = PPS_VALID;

        /* when called for the first time,
         * just start the frequency interval */
        if (unlikely(pps_fbase.tv_sec == 0)) {
                pps_fbase = *raw_ts;
                return;
        }

        /* ok, now we have a base for frequency calculation */
        freq_norm = pps_normalize_ts(timespec64_sub(*raw_ts, pps_fbase));

        /* check that the signal is in the range
         * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
        if ((freq_norm.sec == 0) ||
                        (freq_norm.nsec > MAXFREQ * freq_norm.sec) ||
                        (freq_norm.nsec < -MAXFREQ * freq_norm.sec)) {
                time_status |= STA_PPSJITTER;
                /* restart the frequency calibration interval */
                pps_fbase = *raw_ts;
                printk_deferred(KERN_ERR "hardpps: PPSJITTER: bad pulse\n");
                return;
        }

        /* signal is ok */

        /* check if the current frequency interval is finished */
        if (freq_norm.sec >= (1 << pps_shift)) {
                pps_calcnt++;
                /* restart the frequency calibration interval */
                pps_fbase = *raw_ts;
                hardpps_update_freq(freq_norm);
        }

        hardpps_update_phase(pts_norm.nsec);

}
#endif  /* CONFIG_NTP_PPS */

static int __init ntp_tick_adj_setup(char *str)
{
        int rc = kstrtol(str, 0, (long *)&ntp_tick_adj);

        if (rc)
                return rc;
        ntp_tick_adj <<= NTP_SCALE_SHIFT;

        return 1;
}

__setup("ntp_tick_adj=", ntp_tick_adj_setup);

void __init ntp_init(void)
{
        ntp_clear();
}