ntp: Access tick_length variable via ntp_tick_length()

[deliverable/linux.git] / kernel / time / ntp.c

/*
 * 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:
 */

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

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

static u64                      tick_length;
static u64                      tick_length_base;

static struct hrtimer           leap_timer;

#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;
}

/**
 * pps_clear - Clears the PPS state variables
 *
 * Must be called while holding a write on the xtime_lock
 */
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 xtime_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 */


/**
 * 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 div_s64(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);
}

/**
 * ntp_clear - Clears the NTP state variables
 *
 * Must be called while holding a write on the xtime_lock
 */
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;

        /* Clear PPS state variables */
        pps_clear();
}


u64 ntp_tick_length(void)
{
        return tick_length;
}


/*
 * 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.
 */
static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
{
        enum hrtimer_restart res = HRTIMER_NORESTART;

        write_seqlock(&xtime_lock);

        switch (time_state) {
        case TIME_OK:
                break;
        case TIME_INS:
                timekeeping_leap_insert(-1);
                time_state = TIME_OOP;
                printk(KERN_NOTICE
                        "Clock: inserting leap second 23:59:60 UTC\n");
                hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC);
                res = HRTIMER_RESTART;
                break;
        case TIME_DEL:
                timekeeping_leap_insert(1);
                time_tai--;
                time_state = TIME_WAIT;
                printk(KERN_NOTICE
                        "Clock: deleting leap second 23:59:59 UTC\n");
                break;
        case TIME_OOP:
                time_tai++;
                time_state = TIME_WAIT;
                /* fall through */
        case TIME_WAIT:
                if (!(time_status & (STA_INS | STA_DEL)))
                        time_state = TIME_OK;
                break;
        }

        write_sequnlock(&xtime_lock);

        return res;
}

/*
 * 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.
 */
void second_overflow(void)
{
        s64 delta;

        /* 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)
                return;

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

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

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

#ifdef CONFIG_GENERIC_CMOS_UPDATE

/* Disable the cmos update - used by virtualization and embedded */
int no_sync_cmos_clock  __read_mostly;

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)
{
        if (!no_sync_cmos_clock)
                schedule_delayed_work(&sync_cmos_work, 0);
}

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

/*
 * Start the leap seconds timer:
 */
static inline void ntp_start_leap_timer(struct timespec *ts)
{
        long now = ts->tv_sec;

        if (time_status & STA_INS) {
                time_state = TIME_INS;
                now += 86400 - now % 86400;
                hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);

                return;
        }

        if (time_status & STA_DEL) {
                time_state = TIME_DEL;
                now += 86400 - (now + 1) % 86400;
                hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
        }
}

/*
 * 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;

        switch (time_state) {
        case TIME_OK:
                ntp_start_leap_timer(ts);
                break;
        case TIME_INS:
        case TIME_DEL:
                time_state = TIME_OK;
                ntp_start_leap_timer(ts);
        case TIME_WAIT:
                if (!(time_status & (STA_INS | STA_DEL)))
                        time_state = TIME_OK;
                break;
        case TIME_OOP:
                hrtimer_restart(&leap_timer);
                break;
        }
}
/*
 * Called with the xtime 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_STATUS && time_state != TIME_OK)
                        hrtimer_cancel(&leap_timer);
        }

        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);

        write_seqlock_irq(&xtime_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);

        write_sequnlock_irq(&xtime_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);

        write_seqlock_irqsave(&xtime_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;
                write_sequnlock_irqrestore(&xtime_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;
                write_sequnlock_irqrestore(&xtime_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);

        write_sequnlock_irqrestore(&xtime_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();
        hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
        leap_timer.function = ntp_leap_second;
}