// 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/audit.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 = …; /* SHIFTED_HZ period (nsecs): */ unsigned long tick_nsec; static u64 tick_length; static u64 tick_length_base; #define SECS_PER_DAY … #define MAX_TICKADJ … #define MAX_TICKADJ_SCALED … #define MAX_TAI_OFFSET … /* * phase-lock loop variables */ /* * clock synchronization status * * (TIME_ERROR prevents overwriting the CMOS clock) */ static int time_state = …; /* clock status bits: */ static int time_status = …; /* time adjustment (nsecs): */ static s64 time_offset; /* pll time constant: */ static long time_constant = …; /* maximum error (usecs): */ static long time_maxerror = …; /* estimated error (usecs): */ static long time_esterror = …; /* 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 = …; #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 … #define PPS_POPCORN … #define PPS_INTMIN … #define PPS_INTMAX … #define PPS_INTCOUNT … #define PPS_MAXWANDER … 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 __kernel_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 = pps_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) { … } 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) { … } static inline void pps_fill_timex(struct __kernel_timex *txc) { … } #endif /* CONFIG_NTP_PPS */ /** * ntp_synced - Returns 1 if the NTP status is not UNSYNC * */ static inline int ntp_synced(void) { … } /* * 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) { … } static inline s64 ntp_update_offset_fll(s64 offset64, long secs) { … } static void ntp_update_offset(long offset) { … } /** * ntp_clear - Clears the NTP state variables */ void ntp_clear(void) { … } u64 ntp_tick_length(void) { … } /** * 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) { … } /* * 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(time64_t secs) { … } #if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC) static void sync_hw_clock(struct work_struct *work); static DECLARE_WORK(sync_work, sync_hw_clock); static struct hrtimer sync_hrtimer; #define SYNC_PERIOD_NS … static enum hrtimer_restart sync_timer_callback(struct hrtimer *timer) { … } static void sched_sync_hw_clock(unsigned long offset_nsec, bool retry) { … } /* * Check whether @now is correct versus the required time to update the RTC * and calculate the value which needs to be written to the RTC so that the * next seconds increment of the RTC after the write is aligned with the next * seconds increment of clock REALTIME. * * tsched t1 write(t2.tv_sec - 1sec)) t2 RTC increments seconds * * t2.tv_nsec == 0 * tsched = t2 - set_offset_nsec * newval = t2 - NSEC_PER_SEC * * ==> neval = tsched + set_offset_nsec - NSEC_PER_SEC * * As the execution of this code is not guaranteed to happen exactly at * tsched this allows it to happen within a fuzzy region: * * abs(now - tsched) < FUZZ * * If @now is not inside the allowed window the function returns false. */ static inline bool rtc_tv_nsec_ok(unsigned long set_offset_nsec, struct timespec64 *to_set, const struct timespec64 *now) { … } #ifdef CONFIG_GENERIC_CMOS_UPDATE int __weak update_persistent_clock64(struct timespec64 now64) { … } #else static inline int update_persistent_clock64(struct timespec64 now64) { return -ENODEV; } #endif #ifdef CONFIG_RTC_SYSTOHC /* Save NTP synchronized time to the RTC */ static int update_rtc(struct timespec64 *to_set, unsigned long *offset_nsec) { … } #else static inline int update_rtc(struct timespec64 *to_set, unsigned long *offset_nsec) { return -ENODEV; } #endif /* * 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) { … } void ntp_notify_cmos_timer(void) { … } static void __init ntp_init_cmos_sync(void) { … } #else /* CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC) */ static inline void __init ntp_init_cmos_sync(void) { } #endif /* !CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC) */ /* * Propagate a new txc->status value into the NTP state: */ static inline void process_adj_status(const struct __kernel_timex *txc) { … } static inline void process_adjtimex_modes(const struct __kernel_timex *txc, s32 *time_tai) { … } /* * adjtimex mainly allows reading (and writing, if superuser) of * kernel time-keeping variables. used by xntpd. */ int __do_adjtimex(struct __kernel_timex *txc, const struct timespec64 *ts, s32 *time_tai, struct audit_ntp_data *ad) { … } #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) { … } __setup(…); void __init ntp_init(void) { … }
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