ntp.c

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/*
 * 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 "tick-internal.h"

/*
 * NTP timekeeping variables:
 */

DEFINE_SPINLOCK(ntp_lock);


/* 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 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;

/* TAI offset (secs):                           */
static long         time_tai;

/* 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 long         time_reftime;

static long         time_adjust;

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

#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 timespec 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;
}

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.
 *
 * Must be called while holding a write on the ntp_lock
 */
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 (time_status & (STA_UNSYNC|STA_CLOCKERR))
        /* PPS signal lost when either PPS time or
         * PPS frequency synchronization requested
         */
        || ((time_status & (STA_PPSFREQ|STA_PPSTIME))
            && !(time_status & STA_PPSSIGNAL))
        /* PPS jitter exceeded when
         * PPS time synchronization requested */
        || ((time_status & (STA_PPSTIME|STA_PPSJITTER))
            == (STA_PPSTIME|STA_PPSJITTER))
        /* PPS wander exceeded or calibration error when
         * PPS frequency synchronization requested
         */
        || ((time_status & STA_PPSFREQ)
            && (time_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 */


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))
        offset *= NSEC_PER_USEC;

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

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

    time_reftime = get_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);
}

void ntp_clear(void)
{
    unsigned long flags;

    spin_lock_irqsave(&ntp_lock, flags);

    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;

    /* Clear PPS state variables */
    pps_clear();
    spin_unlock_irqrestore(&ntp_lock, flags);

}


u64 ntp_tick_length(void)
{
    unsigned long flags;
    s64 ret;

    spin_lock_irqsave(&ntp_lock, flags);
    ret = tick_length;
    spin_unlock_irqrestore(&ntp_lock, flags);
    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 ([email protected]) 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(unsigned long secs)
{
    s64 delta;
    int leap = 0;
    unsigned long flags;

    spin_lock_irqsave(&ntp_lock, flags);

    /*
     * 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;
        else if (time_status & STA_DEL)
            time_state = TIME_DEL;
        break;
    case TIME_INS:
        if (!(time_status & STA_INS))
            time_state = TIME_OK;
        else if (secs % 86400 == 0) {
            leap = -1;
            time_state = TIME_OOP;
            time_tai++;
            printk(KERN_NOTICE
                "Clock: inserting leap second 23:59:60 UTC\n");
        }
        break;
    case TIME_DEL:
        if (!(time_status & STA_DEL))
            time_state = TIME_OK;
        else if ((secs + 1) % 86400 == 0) {
            leap = 1;
            time_tai--;
            time_state = TIME_WAIT;
            printk(KERN_NOTICE
                "Clock: deleting leap second 23:59:59 UTC\n");
        }
        break;
    case TIME_OOP:
        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:
    spin_unlock_irqrestore(&ntp_lock, flags);

    return leap;
}

#ifdef CONFIG_GENERIC_CMOS_UPDATE

static void sync_cmos_clock(struct work_struct *work);

static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);

static void sync_cmos_clock(struct work_struct *work)
{
    struct timespec now, next;
    int fail = 1;

    /*
     * If we have an externally synchronized Linux clock, then update
     * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
     * called as close as possible to 500 ms before the new second starts.
     * This code is run on a timer.  If the clock is set, that timer
     * may not expire at the correct time.  Thus, we adjust...
     */
    if (!ntp_synced()) {
        /*
         * Not synced, exit, do not restart a timer (if one is
         * running, let it run out).
         */
        return;
    }

    getnstimeofday(&now);
    if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
        fail = update_persistent_clock(now);

    next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
    if (next.tv_nsec <= 0)
        next.tv_nsec += NSEC_PER_SEC;

    if (!fail)
        next.tv_sec = 659;
    else
        next.tv_sec = 0;

    if (next.tv_nsec >= NSEC_PER_SEC) {
        next.tv_sec++;
        next.tv_nsec -= NSEC_PER_SEC;
    }
    schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
}

static void notify_cmos_timer(void)
{
    schedule_delayed_work(&sync_cmos_work, 0);
}

#else
static inline void notify_cmos_timer(void) { }
#endif


/*
 * Propagate a new txc->status value into the NTP state:
 */
static inline void process_adj_status(struct timex *txc, struct timespec *ts)
{
    if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
        time_state = TIME_OK;
        time_status = STA_UNSYNC;
        /* 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 = get_seconds();

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

/*
 * Called with ntp_lock held, so we can access and modify
 * all the global NTP state:
 */
static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts)
{
    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 timespec ts;
    int result;

    /* Validate the data before disabling interrupts */
    if (txc->modes & ADJ_ADJTIME) {
        /* singleshot must not be used with any other mode bits */
        if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
            return -EINVAL;
        if (!(txc->modes & ADJ_OFFSET_READONLY) &&
            !capable(CAP_SYS_TIME))
            return -EPERM;
    } else {
        /* In order to modify anything, you gotta be super-user! */
         if (txc->modes && !capable(CAP_SYS_TIME))
            return -EPERM;

        /*
         * if the quartz is off by more than 10% then
         * something is VERY wrong!
         */
        if (txc->modes & ADJ_TICK &&
            (txc->tick <  900000/USER_HZ ||
             txc->tick > 1100000/USER_HZ))
            return -EINVAL;
    }

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

    getnstimeofday(&ts);

    spin_lock_irq(&ntp_lock);

    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);

        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);

    spin_unlock_irq(&ntp_lock);

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

    notify_cmos_timer();

    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 {
    __kernel_time_t 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 timespec 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();
        pr_err("hardpps: PPSERROR: interval too long - %ld 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) {
        pr_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)) {
        pr_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 timespec *phase_ts, const struct timespec *raw_ts)
{
    struct pps_normtime pts_norm, freq_norm;
    unsigned long flags;

    pts_norm = pps_normalize_ts(*phase_ts);

    spin_lock_irqsave(&ntp_lock, flags);

    /* 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;
        spin_unlock_irqrestore(&ntp_lock, flags);
        return;
    }

    /* ok, now we have a base for frequency calculation */
    freq_norm = pps_normalize_ts(timespec_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;
        spin_unlock_irqrestore(&ntp_lock, flags);
        pr_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);

    spin_unlock_irqrestore(&ntp_lock, flags);
}
EXPORT_SYMBOL(hardpps);

#endif  /* CONFIG_NTP_PPS */

static int __init ntp_tick_adj_setup(char *str)
{
    ntp_tick_adj = simple_strtol(str, NULL, 0);
    ntp_tick_adj <<= NTP_SCALE_SHIFT;

    return 1;
}

__setup("ntp_tick_adj=", ntp_tick_adj_setup);

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