1 // SPDX-License-Identifier: GPL-2.0
3 * NTP state machine interfaces and logic.
5 * This code was mainly moved from kernel/timer.c and kernel/time.c
6 * Please see those files for relevant copyright info and historical
9 #include <linux/capability.h>
10 #include <linux/clocksource.h>
11 #include <linux/workqueue.h>
12 #include <linux/hrtimer.h>
13 #include <linux/jiffies.h>
14 #include <linux/math64.h>
15 #include <linux/timex.h>
16 #include <linux/time.h>
18 #include <linux/module.h>
19 #include <linux/rtc.h>
20 #include <linux/math64.h>
22 #include "ntp_internal.h"
23 #include "timekeeping_internal.h"
27 * NTP timekeeping variables:
29 * Note: All of the NTP state is protected by the timekeeping locks.
33 /* USER_HZ period (usecs): */
34 unsigned long tick_usec = TICK_USEC;
36 /* SHIFTED_HZ period (nsecs): */
37 unsigned long tick_nsec;
39 static u64 tick_length;
40 static u64 tick_length_base;
42 #define SECS_PER_DAY 86400
43 #define MAX_TICKADJ 500LL /* usecs */
44 #define MAX_TICKADJ_SCALED \
45 (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
46 #define MAX_TAI_OFFSET 100000
49 * phase-lock loop variables
53 * clock synchronization status
55 * (TIME_ERROR prevents overwriting the CMOS clock)
57 static int time_state = TIME_OK;
59 /* clock status bits: */
60 static int time_status = STA_UNSYNC;
62 /* time adjustment (nsecs): */
63 static s64 time_offset;
65 /* pll time constant: */
66 static long time_constant = 2;
68 /* maximum error (usecs): */
69 static long time_maxerror = NTP_PHASE_LIMIT;
71 /* estimated error (usecs): */
72 static long time_esterror = NTP_PHASE_LIMIT;
74 /* frequency offset (scaled nsecs/secs): */
77 /* time at last adjustment (secs): */
78 static time64_t time_reftime;
80 static long time_adjust;
82 /* constant (boot-param configurable) NTP tick adjustment (upscaled) */
83 static s64 ntp_tick_adj;
85 /* second value of the next pending leapsecond, or TIME64_MAX if no leap */
86 static time64_t ntp_next_leap_sec = TIME64_MAX;
91 * The following variables are used when a pulse-per-second (PPS) signal
92 * is available. They establish the engineering parameters of the clock
93 * discipline loop when controlled by the PPS signal.
95 #define PPS_VALID 10 /* PPS signal watchdog max (s) */
96 #define PPS_POPCORN 4 /* popcorn spike threshold (shift) */
97 #define PPS_INTMIN 2 /* min freq interval (s) (shift) */
98 #define PPS_INTMAX 8 /* max freq interval (s) (shift) */
99 #define PPS_INTCOUNT 4 /* number of consecutive good intervals to
100 increase pps_shift or consecutive bad
101 intervals to decrease it */
102 #define PPS_MAXWANDER 100000 /* max PPS freq wander (ns/s) */
104 static int pps_valid; /* signal watchdog counter */
105 static long pps_tf[3]; /* phase median filter */
106 static long pps_jitter; /* current jitter (ns) */
107 static struct timespec64 pps_fbase; /* beginning of the last freq interval */
108 static int pps_shift; /* current interval duration (s) (shift) */
109 static int pps_intcnt; /* interval counter */
110 static s64 pps_freq; /* frequency offset (scaled ns/s) */
111 static long pps_stabil; /* current stability (scaled ns/s) */
114 * PPS signal quality monitors
116 static long pps_calcnt; /* calibration intervals */
117 static long pps_jitcnt; /* jitter limit exceeded */
118 static long pps_stbcnt; /* stability limit exceeded */
119 static long pps_errcnt; /* calibration errors */
122 /* PPS kernel consumer compensates the whole phase error immediately.
123 * Otherwise, reduce the offset by a fixed factor times the time constant.
125 static inline s64 ntp_offset_chunk(s64 offset)
127 if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
130 return shift_right(offset, SHIFT_PLL + time_constant);
133 static inline void pps_reset_freq_interval(void)
135 /* the PPS calibration interval may end
136 surprisingly early */
137 pps_shift = PPS_INTMIN;
142 * pps_clear - Clears the PPS state variables
144 static inline void pps_clear(void)
146 pps_reset_freq_interval();
150 pps_fbase.tv_sec = pps_fbase.tv_nsec = 0;
154 /* Decrease pps_valid to indicate that another second has passed since
155 * the last PPS signal. When it reaches 0, indicate that PPS signal is
158 static inline void pps_dec_valid(void)
163 time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
164 STA_PPSWANDER | STA_PPSERROR);
169 static inline void pps_set_freq(s64 freq)
174 static inline int is_error_status(int status)
176 return (status & (STA_UNSYNC|STA_CLOCKERR))
177 /* PPS signal lost when either PPS time or
178 * PPS frequency synchronization requested
180 || ((status & (STA_PPSFREQ|STA_PPSTIME))
181 && !(status & STA_PPSSIGNAL))
182 /* PPS jitter exceeded when
183 * PPS time synchronization requested */
184 || ((status & (STA_PPSTIME|STA_PPSJITTER))
185 == (STA_PPSTIME|STA_PPSJITTER))
186 /* PPS wander exceeded or calibration error when
187 * PPS frequency synchronization requested
189 || ((status & STA_PPSFREQ)
190 && (status & (STA_PPSWANDER|STA_PPSERROR)));
193 static inline void pps_fill_timex(struct timex *txc)
195 txc->ppsfreq = shift_right((pps_freq >> PPM_SCALE_INV_SHIFT) *
196 PPM_SCALE_INV, NTP_SCALE_SHIFT);
197 txc->jitter = pps_jitter;
198 if (!(time_status & STA_NANO))
199 txc->jitter /= NSEC_PER_USEC;
200 txc->shift = pps_shift;
201 txc->stabil = pps_stabil;
202 txc->jitcnt = pps_jitcnt;
203 txc->calcnt = pps_calcnt;
204 txc->errcnt = pps_errcnt;
205 txc->stbcnt = pps_stbcnt;
208 #else /* !CONFIG_NTP_PPS */
210 static inline s64 ntp_offset_chunk(s64 offset)
212 return shift_right(offset, SHIFT_PLL + time_constant);
215 static inline void pps_reset_freq_interval(void) {}
216 static inline void pps_clear(void) {}
217 static inline void pps_dec_valid(void) {}
218 static inline void pps_set_freq(s64 freq) {}
220 static inline int is_error_status(int status)
222 return status & (STA_UNSYNC|STA_CLOCKERR);
225 static inline void pps_fill_timex(struct timex *txc)
227 /* PPS is not implemented, so these are zero */
238 #endif /* CONFIG_NTP_PPS */
242 * ntp_synced - Returns 1 if the NTP status is not UNSYNC
245 static inline int ntp_synced(void)
247 return !(time_status & STA_UNSYNC);
256 * Update (tick_length, tick_length_base, tick_nsec), based
257 * on (tick_usec, ntp_tick_adj, time_freq):
259 static void ntp_update_frequency(void)
264 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
267 second_length += ntp_tick_adj;
268 second_length += time_freq;
270 tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
271 new_base = div_u64(second_length, NTP_INTERVAL_FREQ);
274 * Don't wait for the next second_overflow, apply
275 * the change to the tick length immediately:
277 tick_length += new_base - tick_length_base;
278 tick_length_base = new_base;
281 static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
283 time_status &= ~STA_MODE;
288 if (!(time_status & STA_FLL) && (secs <= MAXSEC))
291 time_status |= STA_MODE;
293 return div64_long(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
296 static void ntp_update_offset(long offset)
302 if (!(time_status & STA_PLL))
305 if (!(time_status & STA_NANO)) {
306 /* Make sure the multiplication below won't overflow */
307 offset = clamp(offset, -USEC_PER_SEC, USEC_PER_SEC);
308 offset *= NSEC_PER_USEC;
312 * Scale the phase adjustment and
313 * clamp to the operating range.
315 offset = clamp(offset, -MAXPHASE, MAXPHASE);
318 * Select how the frequency is to be controlled
319 * and in which mode (PLL or FLL).
321 secs = (long)(__ktime_get_real_seconds() - time_reftime);
322 if (unlikely(time_status & STA_FREQHOLD))
325 time_reftime = __ktime_get_real_seconds();
328 freq_adj = ntp_update_offset_fll(offset64, secs);
331 * Clamp update interval to reduce PLL gain with low
332 * sampling rate (e.g. intermittent network connection)
333 * to avoid instability.
335 if (unlikely(secs > 1 << (SHIFT_PLL + 1 + time_constant)))
336 secs = 1 << (SHIFT_PLL + 1 + time_constant);
338 freq_adj += (offset64 * secs) <<
339 (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
341 freq_adj = min(freq_adj + time_freq, MAXFREQ_SCALED);
343 time_freq = max(freq_adj, -MAXFREQ_SCALED);
345 time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
349 * ntp_clear - Clears the NTP state variables
353 time_adjust = 0; /* stop active adjtime() */
354 time_status |= STA_UNSYNC;
355 time_maxerror = NTP_PHASE_LIMIT;
356 time_esterror = NTP_PHASE_LIMIT;
358 ntp_update_frequency();
360 tick_length = tick_length_base;
363 ntp_next_leap_sec = TIME64_MAX;
364 /* Clear PPS state variables */
369 u64 ntp_tick_length(void)
375 * ntp_get_next_leap - Returns the next leapsecond in CLOCK_REALTIME ktime_t
377 * Provides the time of the next leapsecond against CLOCK_REALTIME in
378 * a ktime_t format. Returns KTIME_MAX if no leapsecond is pending.
380 ktime_t ntp_get_next_leap(void)
384 if ((time_state == TIME_INS) && (time_status & STA_INS))
385 return ktime_set(ntp_next_leap_sec, 0);
391 * this routine handles the overflow of the microsecond field
393 * The tricky bits of code to handle the accurate clock support
394 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
395 * They were originally developed for SUN and DEC kernels.
396 * All the kudos should go to Dave for this stuff.
398 * Also handles leap second processing, and returns leap offset
400 int second_overflow(time64_t secs)
407 * Leap second processing. If in leap-insert state at the end of the
408 * day, the system clock is set back one second; if in leap-delete
409 * state, the system clock is set ahead one second.
411 switch (time_state) {
413 if (time_status & STA_INS) {
414 time_state = TIME_INS;
415 div_s64_rem(secs, SECS_PER_DAY, &rem);
416 ntp_next_leap_sec = secs + SECS_PER_DAY - rem;
417 } else if (time_status & STA_DEL) {
418 time_state = TIME_DEL;
419 div_s64_rem(secs + 1, SECS_PER_DAY, &rem);
420 ntp_next_leap_sec = secs + SECS_PER_DAY - rem;
424 if (!(time_status & STA_INS)) {
425 ntp_next_leap_sec = TIME64_MAX;
426 time_state = TIME_OK;
427 } else if (secs == ntp_next_leap_sec) {
429 time_state = TIME_OOP;
431 "Clock: inserting leap second 23:59:60 UTC\n");
435 if (!(time_status & STA_DEL)) {
436 ntp_next_leap_sec = TIME64_MAX;
437 time_state = TIME_OK;
438 } else if (secs == ntp_next_leap_sec) {
440 ntp_next_leap_sec = TIME64_MAX;
441 time_state = TIME_WAIT;
443 "Clock: deleting leap second 23:59:59 UTC\n");
447 ntp_next_leap_sec = TIME64_MAX;
448 time_state = TIME_WAIT;
451 if (!(time_status & (STA_INS | STA_DEL)))
452 time_state = TIME_OK;
457 /* Bump the maxerror field */
458 time_maxerror += MAXFREQ / NSEC_PER_USEC;
459 if (time_maxerror > NTP_PHASE_LIMIT) {
460 time_maxerror = NTP_PHASE_LIMIT;
461 time_status |= STA_UNSYNC;
464 /* Compute the phase adjustment for the next second */
465 tick_length = tick_length_base;
467 delta = ntp_offset_chunk(time_offset);
468 time_offset -= delta;
469 tick_length += delta;
471 /* Check PPS signal */
477 if (time_adjust > MAX_TICKADJ) {
478 time_adjust -= MAX_TICKADJ;
479 tick_length += MAX_TICKADJ_SCALED;
483 if (time_adjust < -MAX_TICKADJ) {
484 time_adjust += MAX_TICKADJ;
485 tick_length -= MAX_TICKADJ_SCALED;
489 tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
497 #ifdef CONFIG_GENERIC_CMOS_UPDATE
498 int __weak update_persistent_clock(struct timespec now)
503 int __weak update_persistent_clock64(struct timespec64 now64)
507 now = timespec64_to_timespec(now64);
508 return update_persistent_clock(now);
512 #if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC)
513 static void sync_cmos_clock(struct work_struct *work);
515 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
517 static void sync_cmos_clock(struct work_struct *work)
519 struct timespec64 now;
520 struct timespec64 next;
524 * If we have an externally synchronized Linux clock, then update
525 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
526 * called as close as possible to 500 ms before the new second starts.
527 * This code is run on a timer. If the clock is set, that timer
528 * may not expire at the correct time. Thus, we adjust...
529 * We want the clock to be within a couple of ticks from the target.
533 * Not synced, exit, do not restart a timer (if one is
534 * running, let it run out).
539 getnstimeofday64(&now);
540 if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec * 5) {
541 struct timespec64 adjust = now;
544 if (persistent_clock_is_local)
545 adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
546 #ifdef CONFIG_GENERIC_CMOS_UPDATE
547 fail = update_persistent_clock64(adjust);
550 #ifdef CONFIG_RTC_SYSTOHC
552 fail = rtc_set_ntp_time(adjust);
556 next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
557 if (next.tv_nsec <= 0)
558 next.tv_nsec += NSEC_PER_SEC;
560 if (!fail || fail == -ENODEV)
565 if (next.tv_nsec >= NSEC_PER_SEC) {
567 next.tv_nsec -= NSEC_PER_SEC;
569 queue_delayed_work(system_power_efficient_wq,
570 &sync_cmos_work, timespec64_to_jiffies(&next));
573 void ntp_notify_cmos_timer(void)
575 queue_delayed_work(system_power_efficient_wq, &sync_cmos_work, 0);
579 void ntp_notify_cmos_timer(void) { }
584 * Propagate a new txc->status value into the NTP state:
586 static inline void process_adj_status(struct timex *txc, struct timespec64 *ts)
588 if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
589 time_state = TIME_OK;
590 time_status = STA_UNSYNC;
591 ntp_next_leap_sec = TIME64_MAX;
592 /* restart PPS frequency calibration */
593 pps_reset_freq_interval();
597 * If we turn on PLL adjustments then reset the
598 * reference time to current time.
600 if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
601 time_reftime = __ktime_get_real_seconds();
603 /* only set allowed bits */
604 time_status &= STA_RONLY;
605 time_status |= txc->status & ~STA_RONLY;
609 static inline void process_adjtimex_modes(struct timex *txc,
610 struct timespec64 *ts,
613 if (txc->modes & ADJ_STATUS)
614 process_adj_status(txc, ts);
616 if (txc->modes & ADJ_NANO)
617 time_status |= STA_NANO;
619 if (txc->modes & ADJ_MICRO)
620 time_status &= ~STA_NANO;
622 if (txc->modes & ADJ_FREQUENCY) {
623 time_freq = txc->freq * PPM_SCALE;
624 time_freq = min(time_freq, MAXFREQ_SCALED);
625 time_freq = max(time_freq, -MAXFREQ_SCALED);
626 /* update pps_freq */
627 pps_set_freq(time_freq);
630 if (txc->modes & ADJ_MAXERROR)
631 time_maxerror = txc->maxerror;
633 if (txc->modes & ADJ_ESTERROR)
634 time_esterror = txc->esterror;
636 if (txc->modes & ADJ_TIMECONST) {
637 time_constant = txc->constant;
638 if (!(time_status & STA_NANO))
640 time_constant = min(time_constant, (long)MAXTC);
641 time_constant = max(time_constant, 0l);
644 if (txc->modes & ADJ_TAI &&
645 txc->constant >= 0 && txc->constant <= MAX_TAI_OFFSET)
646 *time_tai = txc->constant;
648 if (txc->modes & ADJ_OFFSET)
649 ntp_update_offset(txc->offset);
651 if (txc->modes & ADJ_TICK)
652 tick_usec = txc->tick;
654 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
655 ntp_update_frequency();
661 * ntp_validate_timex - Ensures the timex is ok for use in do_adjtimex
663 int ntp_validate_timex(struct timex *txc)
665 if (txc->modes & ADJ_ADJTIME) {
666 /* singleshot must not be used with any other mode bits */
667 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
669 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
670 !capable(CAP_SYS_TIME))
673 /* In order to modify anything, you gotta be super-user! */
674 if (txc->modes && !capable(CAP_SYS_TIME))
677 * if the quartz is off by more than 10% then
678 * something is VERY wrong!
680 if (txc->modes & ADJ_TICK &&
681 (txc->tick < 900000/USER_HZ ||
682 txc->tick > 1100000/USER_HZ))
686 if (txc->modes & ADJ_SETOFFSET) {
687 /* In order to inject time, you gotta be super-user! */
688 if (!capable(CAP_SYS_TIME))
691 if (txc->modes & ADJ_NANO) {
694 ts.tv_sec = txc->time.tv_sec;
695 ts.tv_nsec = txc->time.tv_usec;
696 if (!timespec_inject_offset_valid(&ts))
700 if (!timeval_inject_offset_valid(&txc->time))
706 * Check for potential multiplication overflows that can
707 * only happen on 64-bit systems:
709 if ((txc->modes & ADJ_FREQUENCY) && (BITS_PER_LONG == 64)) {
710 if (LLONG_MIN / PPM_SCALE > txc->freq)
712 if (LLONG_MAX / PPM_SCALE < txc->freq)
721 * adjtimex mainly allows reading (and writing, if superuser) of
722 * kernel time-keeping variables. used by xntpd.
724 int __do_adjtimex(struct timex *txc, struct timespec64 *ts, s32 *time_tai)
728 if (txc->modes & ADJ_ADJTIME) {
729 long save_adjust = time_adjust;
731 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
732 /* adjtime() is independent from ntp_adjtime() */
733 time_adjust = txc->offset;
734 ntp_update_frequency();
736 txc->offset = save_adjust;
739 /* If there are input parameters, then process them: */
741 process_adjtimex_modes(txc, ts, time_tai);
743 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
745 if (!(time_status & STA_NANO))
746 txc->offset /= NSEC_PER_USEC;
749 result = time_state; /* mostly `TIME_OK' */
750 /* check for errors */
751 if (is_error_status(time_status))
754 txc->freq = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
755 PPM_SCALE_INV, NTP_SCALE_SHIFT);
756 txc->maxerror = time_maxerror;
757 txc->esterror = time_esterror;
758 txc->status = time_status;
759 txc->constant = time_constant;
761 txc->tolerance = MAXFREQ_SCALED / PPM_SCALE;
762 txc->tick = tick_usec;
763 txc->tai = *time_tai;
765 /* fill PPS status fields */
768 txc->time.tv_sec = (time_t)ts->tv_sec;
769 txc->time.tv_usec = ts->tv_nsec;
770 if (!(time_status & STA_NANO))
771 txc->time.tv_usec /= NSEC_PER_USEC;
773 /* Handle leapsec adjustments */
774 if (unlikely(ts->tv_sec >= ntp_next_leap_sec)) {
775 if ((time_state == TIME_INS) && (time_status & STA_INS)) {
780 if ((time_state == TIME_DEL) && (time_status & STA_DEL)) {
785 if ((time_state == TIME_OOP) &&
786 (ts->tv_sec == ntp_next_leap_sec)) {
794 #ifdef CONFIG_NTP_PPS
796 /* actually struct pps_normtime is good old struct timespec, but it is
797 * semantically different (and it is the reason why it was invented):
798 * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
799 * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
800 struct pps_normtime {
801 s64 sec; /* seconds */
802 long nsec; /* nanoseconds */
805 /* normalize the timestamp so that nsec is in the
806 ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
807 static inline struct pps_normtime pps_normalize_ts(struct timespec64 ts)
809 struct pps_normtime norm = {
814 if (norm.nsec > (NSEC_PER_SEC >> 1)) {
815 norm.nsec -= NSEC_PER_SEC;
822 /* get current phase correction and jitter */
823 static inline long pps_phase_filter_get(long *jitter)
825 *jitter = pps_tf[0] - pps_tf[1];
829 /* TODO: test various filters */
833 /* add the sample to the phase filter */
834 static inline void pps_phase_filter_add(long err)
836 pps_tf[2] = pps_tf[1];
837 pps_tf[1] = pps_tf[0];
841 /* decrease frequency calibration interval length.
842 * It is halved after four consecutive unstable intervals.
844 static inline void pps_dec_freq_interval(void)
846 if (--pps_intcnt <= -PPS_INTCOUNT) {
847 pps_intcnt = -PPS_INTCOUNT;
848 if (pps_shift > PPS_INTMIN) {
855 /* increase frequency calibration interval length.
856 * It is doubled after four consecutive stable intervals.
858 static inline void pps_inc_freq_interval(void)
860 if (++pps_intcnt >= PPS_INTCOUNT) {
861 pps_intcnt = PPS_INTCOUNT;
862 if (pps_shift < PPS_INTMAX) {
869 /* update clock frequency based on MONOTONIC_RAW clock PPS signal
872 * At the end of the calibration interval the difference between the
873 * first and last MONOTONIC_RAW clock timestamps divided by the length
874 * of the interval becomes the frequency update. If the interval was
875 * too long, the data are discarded.
876 * Returns the difference between old and new frequency values.
878 static long hardpps_update_freq(struct pps_normtime freq_norm)
880 long delta, delta_mod;
883 /* check if the frequency interval was too long */
884 if (freq_norm.sec > (2 << pps_shift)) {
885 time_status |= STA_PPSERROR;
887 pps_dec_freq_interval();
888 printk_deferred(KERN_ERR
889 "hardpps: PPSERROR: interval too long - %lld s\n",
894 /* here the raw frequency offset and wander (stability) is
895 * calculated. If the wander is less than the wander threshold
896 * the interval is increased; otherwise it is decreased.
898 ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT,
900 delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT);
902 if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) {
903 printk_deferred(KERN_WARNING
904 "hardpps: PPSWANDER: change=%ld\n", delta);
905 time_status |= STA_PPSWANDER;
907 pps_dec_freq_interval();
908 } else { /* good sample */
909 pps_inc_freq_interval();
912 /* the stability metric is calculated as the average of recent
913 * frequency changes, but is used only for performance
918 delta_mod = -delta_mod;
919 pps_stabil += (div_s64(((s64)delta_mod) <<
920 (NTP_SCALE_SHIFT - SHIFT_USEC),
921 NSEC_PER_USEC) - pps_stabil) >> PPS_INTMIN;
923 /* if enabled, the system clock frequency is updated */
924 if ((time_status & STA_PPSFREQ) != 0 &&
925 (time_status & STA_FREQHOLD) == 0) {
926 time_freq = pps_freq;
927 ntp_update_frequency();
933 /* correct REALTIME clock phase error against PPS signal */
934 static void hardpps_update_phase(long error)
936 long correction = -error;
939 /* add the sample to the median filter */
940 pps_phase_filter_add(correction);
941 correction = pps_phase_filter_get(&jitter);
943 /* Nominal jitter is due to PPS signal noise. If it exceeds the
944 * threshold, the sample is discarded; otherwise, if so enabled,
945 * the time offset is updated.
947 if (jitter > (pps_jitter << PPS_POPCORN)) {
948 printk_deferred(KERN_WARNING
949 "hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
950 jitter, (pps_jitter << PPS_POPCORN));
951 time_status |= STA_PPSJITTER;
953 } else if (time_status & STA_PPSTIME) {
954 /* correct the time using the phase offset */
955 time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT,
957 /* cancel running adjtime() */
961 pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN;
965 * __hardpps() - discipline CPU clock oscillator to external PPS signal
967 * This routine is called at each PPS signal arrival in order to
968 * discipline the CPU clock oscillator to the PPS signal. It takes two
969 * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
970 * is used to correct clock phase error and the latter is used to
971 * correct the frequency.
973 * This code is based on David Mills's reference nanokernel
974 * implementation. It was mostly rewritten but keeps the same idea.
976 void __hardpps(const struct timespec64 *phase_ts, const struct timespec64 *raw_ts)
978 struct pps_normtime pts_norm, freq_norm;
980 pts_norm = pps_normalize_ts(*phase_ts);
982 /* clear the error bits, they will be set again if needed */
983 time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
985 /* indicate signal presence */
986 time_status |= STA_PPSSIGNAL;
987 pps_valid = PPS_VALID;
989 /* when called for the first time,
990 * just start the frequency interval */
991 if (unlikely(pps_fbase.tv_sec == 0)) {
996 /* ok, now we have a base for frequency calculation */
997 freq_norm = pps_normalize_ts(timespec64_sub(*raw_ts, pps_fbase));
999 /* check that the signal is in the range
1000 * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
1001 if ((freq_norm.sec == 0) ||
1002 (freq_norm.nsec > MAXFREQ * freq_norm.sec) ||
1003 (freq_norm.nsec < -MAXFREQ * freq_norm.sec)) {
1004 time_status |= STA_PPSJITTER;
1005 /* restart the frequency calibration interval */
1006 pps_fbase = *raw_ts;
1007 printk_deferred(KERN_ERR "hardpps: PPSJITTER: bad pulse\n");
1013 /* check if the current frequency interval is finished */
1014 if (freq_norm.sec >= (1 << pps_shift)) {
1016 /* restart the frequency calibration interval */
1017 pps_fbase = *raw_ts;
1018 hardpps_update_freq(freq_norm);
1021 hardpps_update_phase(pts_norm.nsec);
1024 #endif /* CONFIG_NTP_PPS */
1026 static int __init ntp_tick_adj_setup(char *str)
1028 int rc = kstrtol(str, 0, (long *)&ntp_tick_adj);
1032 ntp_tick_adj <<= NTP_SCALE_SHIFT;
1037 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
1039 void __init ntp_init(void)