Initial import

1 files changed, 965 insertions, 0 deletions

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
new file mode 100644
index 000000000..7a6810030
--- /dev/null
+++ b/kernel/time/ntp.c
@@ -0,0 +1,965 @@
+/*
+ * 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 "ntp_internal.h"
+
+/*
+ * NTP timekeeping variables:
+ *
+ * Note: All of the NTP state is protected by the timekeeping locks.
+ */
+
+
+/* USER_HZ period (usecs): */
+unsigned long			tick_usec = TICK_USEC;
+
+/* SHIFTED_HZ period (nsecs): */
+unsigned long			tick_nsec;
+
+static u64			tick_length;
+static u64			tick_length_base;
+
+#define MAX_TICKADJ		500LL		/* usecs */
+#define MAX_TICKADJ_SCALED \
+	(((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
+
+/*
+ * phase-lock loop variables
+ */
+
+/*
+ * clock synchronization status
+ *
+ * (TIME_ERROR prevents overwriting the CMOS clock)
+ */
+static int			time_state = TIME_OK;
+
+/* clock status bits:							*/
+static int			time_status = STA_UNSYNC;
+
+/* time adjustment (nsecs):						*/
+static s64			time_offset;
+
+/* pll time constant:							*/
+static long			time_constant = 2;
+
+/* maximum error (usecs):						*/
+static long			time_maxerror = NTP_PHASE_LIMIT;
+
+/* estimated error (usecs):						*/
+static long			time_esterror = NTP_PHASE_LIMIT;
+
+/* frequency offset (scaled nsecs/secs):				*/
+static s64			time_freq;
+
+/* time at last adjustment (secs):					*/
+static 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
+ */
+static inline void pps_clear(void)
+{
+	pps_reset_freq_interval();
+	pps_tf[0] = 0;
+	pps_tf[1] = 0;
+	pps_tf[2] = 0;
+	pps_fbase.tv_sec = pps_fbase.tv_nsec = 0;
+	pps_freq = 0;
+}
+
+/* Decrease pps_valid to indicate that another second has passed since
+ * the last PPS signal. When it reaches 0, indicate that PPS signal is
+ * missing.
+ */
+static inline void pps_dec_valid(void)
+{
+	if (pps_valid > 0)
+		pps_valid--;
+	else {
+		time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
+				 STA_PPSWANDER | STA_PPSERROR);
+		pps_clear();
+	}
+}
+
+static inline void pps_set_freq(s64 freq)
+{
+	pps_freq = freq;
+}
+
+static inline int is_error_status(int status)
+{
+	return (status & (STA_UNSYNC|STA_CLOCKERR))
+		/* PPS signal lost when either PPS time or
+		 * PPS frequency synchronization requested
+		 */
+		|| ((status & (STA_PPSFREQ|STA_PPSTIME))
+			&& !(status & STA_PPSSIGNAL))
+		/* PPS jitter exceeded when
+		 * PPS time synchronization requested */
+		|| ((status & (STA_PPSTIME|STA_PPSJITTER))
+			== (STA_PPSTIME|STA_PPSJITTER))
+		/* PPS wander exceeded or calibration error when
+		 * PPS frequency synchronization requested
+		 */
+		|| ((status & STA_PPSFREQ)
+			&& (status & (STA_PPSWANDER|STA_PPSERROR)));
+}
+
+static inline void pps_fill_timex(struct timex *txc)
+{
+	txc->ppsfreq	   = shift_right((pps_freq >> PPM_SCALE_INV_SHIFT) *
+					 PPM_SCALE_INV, NTP_SCALE_SHIFT);
+	txc->jitter	   = pps_jitter;
+	if (!(time_status & STA_NANO))
+		txc->jitter /= NSEC_PER_USEC;
+	txc->shift	   = pps_shift;
+	txc->stabil	   = pps_stabil;
+	txc->jitcnt	   = pps_jitcnt;
+	txc->calcnt	   = pps_calcnt;
+	txc->errcnt	   = pps_errcnt;
+	txc->stbcnt	   = pps_stbcnt;
+}
+
+#else /* !CONFIG_NTP_PPS */
+
+static inline s64 ntp_offset_chunk(s64 offset)
+{
+	return shift_right(offset, SHIFT_PLL + time_constant);
+}
+
+static inline void pps_reset_freq_interval(void) {}
+static inline void pps_clear(void) {}
+static inline void pps_dec_valid(void) {}
+static inline void pps_set_freq(s64 freq) {}
+
+static inline int is_error_status(int status)
+{
+	return status & (STA_UNSYNC|STA_CLOCKERR);
+}
+
+static inline void pps_fill_timex(struct timex *txc)
+{
+	/* PPS is not implemented, so these are zero */
+	txc->ppsfreq	   = 0;
+	txc->jitter	   = 0;
+	txc->shift	   = 0;
+	txc->stabil	   = 0;
+	txc->jitcnt	   = 0;
+	txc->calcnt	   = 0;
+	txc->errcnt	   = 0;
+	txc->stbcnt	   = 0;
+}
+
+#endif /* CONFIG_NTP_PPS */
+
+
+/**
+ * ntp_synced - Returns 1 if the NTP status is not UNSYNC
+ *
+ */
+static inline int ntp_synced(void)
+{
+	return !(time_status & STA_UNSYNC);
+}
+
+
+/*
+ * NTP methods:
+ */
+
+/*
+ * Update (tick_length, tick_length_base, tick_nsec), based
+ * on (tick_usec, ntp_tick_adj, time_freq):
+ */
+static void ntp_update_frequency(void)
+{
+	u64 second_length;
+	u64 new_base;
+
+	second_length		 = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
+						<< NTP_SCALE_SHIFT;
+
+	second_length		+= ntp_tick_adj;
+	second_length		+= time_freq;
+
+	tick_nsec		 = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
+	new_base		 = div_u64(second_length, NTP_INTERVAL_FREQ);
+
+	/*
+	 * Don't wait for the next second_overflow, apply
+	 * the change to the tick length immediately:
+	 */
+	tick_length		+= new_base - tick_length_base;
+	tick_length_base	 = new_base;
+}
+
+static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
+{
+	time_status &= ~STA_MODE;
+
+	if (secs < MINSEC)
+		return 0;
+
+	if (!(time_status & STA_FLL) && (secs <= MAXSEC))
+		return 0;
+
+	time_status |= STA_MODE;
+
+	return div64_long(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
+}
+
+static void ntp_update_offset(long offset)
+{
+	s64 freq_adj;
+	s64 offset64;
+	long secs;
+
+	if (!(time_status & STA_PLL))
+		return;
+
+	if (!(time_status & STA_NANO))
+		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
+ */
+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;
+}
+
+
+/*
+ * this routine handles the overflow of the microsecond field
+ *
+ * The tricky bits of code to handle the accurate clock support
+ * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
+ * They were originally developed for SUN and DEC kernels.
+ * All the kudos should go to Dave for this stuff.
+ *
+ * Also handles leap second processing, and returns leap offset
+ */
+int second_overflow(unsigned long secs)
+{
+	s64 delta;
+	int leap = 0;
+
+	/*
+	 * 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;
+			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_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:
+	return leap;
+}
+
+#ifdef CONFIG_GENERIC_CMOS_UPDATE
+int __weak update_persistent_clock64(struct timespec64 now64)
+{
+	struct timespec now;
+
+	now = timespec64_to_timespec(now64);
+	return update_persistent_clock(now);
+}
+#endif
+
+#if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC)
+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 timespec64 now;
+	struct timespec 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...
+	 * We want the clock to be within a couple of ticks from the target.
+	 */
+	if (!ntp_synced()) {
+		/*
+		 * Not synced, exit, do not restart a timer (if one is
+		 * running, let it run out).
+		 */
+		return;
+	}
+
+	getnstimeofday64(&now);
+	if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec * 5) {
+		struct timespec64 adjust = now;
+
+		fail = -ENODEV;
+		if (persistent_clock_is_local)
+			adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
+#ifdef CONFIG_GENERIC_CMOS_UPDATE
+		fail = update_persistent_clock64(adjust);
+#endif
+
+#ifdef CONFIG_RTC_SYSTOHC
+		if (fail == -ENODEV)
+			fail = rtc_set_ntp_time(adjust);
+#endif
+	}
+
+	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 || fail == -ENODEV)
+		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;
+	}
+	queue_delayed_work(system_power_efficient_wq,
+			   &sync_cmos_work, timespec_to_jiffies(&next));
+}
+
+void ntp_notify_cmos_timer(void)
+{
+	queue_delayed_work(system_power_efficient_wq, &sync_cmos_work, 0);
+}
+
+#else
+void ntp_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 timespec64 *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;
+}
+
+
+static inline void process_adjtimex_modes(struct timex *txc,
+						struct timespec64 *ts,
+						s32 *time_tai)
+{
+	if (txc->modes & ADJ_STATUS)
+		process_adj_status(txc, ts);
+
+	if (txc->modes & ADJ_NANO)
+		time_status |= STA_NANO;
+
+	if (txc->modes & ADJ_MICRO)
+		time_status &= ~STA_NANO;
+
+	if (txc->modes & ADJ_FREQUENCY) {
+		time_freq = txc->freq * PPM_SCALE;
+		time_freq = min(time_freq, MAXFREQ_SCALED);
+		time_freq = max(time_freq, -MAXFREQ_SCALED);
+		/* update pps_freq */
+		pps_set_freq(time_freq);
+	}
+
+	if (txc->modes & ADJ_MAXERROR)
+		time_maxerror = txc->maxerror;
+
+	if (txc->modes & ADJ_ESTERROR)
+		time_esterror = txc->esterror;
+
+	if (txc->modes & ADJ_TIMECONST) {
+		time_constant = txc->constant;
+		if (!(time_status & STA_NANO))
+			time_constant += 4;
+		time_constant = min(time_constant, (long)MAXTC);
+		time_constant = max(time_constant, 0l);
+	}
+
+	if (txc->modes & ADJ_TAI && txc->constant > 0)
+		*time_tai = txc->constant;
+
+	if (txc->modes & ADJ_OFFSET)
+		ntp_update_offset(txc->offset);
+
+	if (txc->modes & ADJ_TICK)
+		tick_usec = txc->tick;
+
+	if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
+		ntp_update_frequency();
+}
+
+
+
+/**
+ * ntp_validate_timex - Ensures the timex is ok for use in do_adjtimex
+ */
+int ntp_validate_timex(struct timex *txc)
+{
+	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) && (!capable(CAP_SYS_TIME)))
+		return -EPERM;
+
+	/*
+	 * Check for potential multiplication overflows that can
+	 * only happen on 64-bit systems:
+	 */
+	if ((txc->modes & ADJ_FREQUENCY) && (BITS_PER_LONG == 64)) {
+		if (LLONG_MIN / PPM_SCALE > txc->freq)
+			return -EINVAL;
+		if (LLONG_MAX / PPM_SCALE < txc->freq)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+
+/*
+ * adjtimex mainly allows reading (and writing, if superuser) of
+ * kernel time-keeping variables. used by xntpd.
+ */
+int __do_adjtimex(struct timex *txc, struct timespec64 *ts, s32 *time_tai)
+{
+	int result;
+
+	if (txc->modes & ADJ_ADJTIME) {
+		long save_adjust = time_adjust;
+
+		if (!(txc->modes & ADJ_OFFSET_READONLY)) {
+			/* adjtime() is independent from ntp_adjtime() */
+			time_adjust = txc->offset;
+			ntp_update_frequency();
+		}
+		txc->offset = save_adjust;
+	} else {
+
+		/* If there are input parameters, then process them: */
+		if (txc->modes)
+			process_adjtimex_modes(txc, ts, time_tai);
+
+		txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
+				  NTP_SCALE_SHIFT);
+		if (!(time_status & STA_NANO))
+			txc->offset /= NSEC_PER_USEC;
+	}
+
+	result = time_state;	/* mostly `TIME_OK' */
+	/* check for errors */
+	if (is_error_status(time_status))
+		result = TIME_ERROR;
+
+	txc->freq	   = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
+					 PPM_SCALE_INV, NTP_SCALE_SHIFT);
+	txc->maxerror	   = time_maxerror;
+	txc->esterror	   = time_esterror;
+	txc->status	   = time_status;
+	txc->constant	   = time_constant;
+	txc->precision	   = 1;
+	txc->tolerance	   = MAXFREQ_SCALED / PPM_SCALE;
+	txc->tick	   = tick_usec;
+	txc->tai	   = *time_tai;
+
+	/* fill PPS status fields */
+	pps_fill_timex(txc);
+
+	txc->time.tv_sec = (time_t)ts->tv_sec;
+	txc->time.tv_usec = ts->tv_nsec;
+	if (!(time_status & STA_NANO))
+		txc->time.tv_usec /= NSEC_PER_USEC;
+
+	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();
+		printk_deferred(KERN_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) {
+		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 timespec *phase_ts, const struct timespec *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(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;
+		printk_deferred(KERN_ERR "hardpps: PPSJITTER: bad pulse\n");
+		return;
+	}
+
+	/* signal is ok */
+
+	/* check if the current frequency interval is finished */
+	if (freq_norm.sec >= (1 << pps_shift)) {
+		pps_calcnt++;
+		/* restart the frequency calibration interval */
+		pps_fbase = *raw_ts;
+		hardpps_update_freq(freq_norm);
+	}
+
+	hardpps_update_phase(pts_norm.nsec);
+
+}
+#endif	/* CONFIG_NTP_PPS */
+
+static int __init ntp_tick_adj_setup(char *str)
+{
+	int rc = kstrtol(str, 0, (long *)&ntp_tick_adj);
+
+	if (rc)
+		return rc;
+	ntp_tick_adj <<= NTP_SCALE_SHIFT;
+
+	return 1;
+}
+
+__setup("ntp_tick_adj=", ntp_tick_adj_setup);
+
+void __init ntp_init(void)
+{
+	ntp_clear();
+}