path: root/kernel/time/ntp.c

// 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"

/**
 * struct ntp_data - Structure holding all NTP related state
 * @tick_usec:		USER_HZ period in microseconds
 * @tick_length:	Adjusted tick length
 * @tick_length_base:	Base value for @tick_length
 * @time_state:		State of the clock synchronization
 * @time_status:	Clock status bits
 * @time_offset:	Time adjustment in nanoseconds
 * @time_constant:	PLL time constant
 * @time_maxerror:	Maximum error in microseconds holding the NTP sync distance
 *			(NTP dispersion + delay / 2)
 * @time_esterror:	Estimated error in microseconds holding NTP dispersion
 * @time_freq:		Frequency offset scaled nsecs/secs
 * @time_reftime:	Time at last adjustment in seconds
 * @time_adjust:	Adjustment value
 * @ntp_tick_adj:	Constant boot-param configurable NTP tick adjustment (upscaled)
 * @ntp_next_leap_sec:	Second value of the next pending leapsecond, or TIME64_MAX if no leap
 *
 * @pps_valid:		PPS signal watchdog counter
 * @pps_tf:		PPS phase median filter
 * @pps_jitter:		PPS current jitter in nanoseconds
 * @pps_fbase:		PPS beginning of the last freq interval
 * @pps_shift:		PPS current interval duration in seconds (shift value)
 * @pps_intcnt:		PPS interval counter
 * @pps_freq:		PPS frequency offset in scaled ns/s
 * @pps_stabil:		PPS current stability in scaled ns/s
 * @pps_calcnt:		PPS monitor: calibration intervals
 * @pps_jitcnt:		PPS monitor: jitter limit exceeded
 * @pps_stbcnt:		PPS monitor: stability limit exceeded
 * @pps_errcnt:		PPS monitor: calibration errors
 *
 * Protected by the timekeeping locks.
 */
struct ntp_data {
	unsigned long		tick_usec;
	u64			tick_length;
	u64			tick_length_base;
	int			time_state;
	int			time_status;
	s64			time_offset;
	long			time_constant;
	long			time_maxerror;
	long			time_esterror;
	s64			time_freq;
	time64_t		time_reftime;
	long			time_adjust;
	s64			ntp_tick_adj;
	time64_t		ntp_next_leap_sec;
#ifdef CONFIG_NTP_PPS
	int			pps_valid;
	long			pps_tf[3];
	long			pps_jitter;
	struct timespec64	pps_fbase;
	int			pps_shift;
	int			pps_intcnt;
	s64			pps_freq;
	long			pps_stabil;
	long			pps_calcnt;
	long			pps_jitcnt;
	long			pps_stbcnt;
	long			pps_errcnt;
#endif
};

static struct ntp_data tk_ntp_data = {
	.tick_usec		= USER_TICK_USEC,
	.time_state		= TIME_OK,
	.time_status		= STA_UNSYNC,
	.time_constant		= 2,
	.time_maxerror		= NTP_PHASE_LIMIT,
	.time_esterror		= NTP_PHASE_LIMIT,
	.ntp_next_leap_sec	= TIME64_MAX,
};

#define SECS_PER_DAY		86400
#define MAX_TICKADJ		500LL		/* usecs */
#define MAX_TICKADJ_SCALED \
	(((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
#define MAX_TAI_OFFSET		100000

#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) */

/*
 * 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(struct ntp_data *ntpdata, s64 offset)
{
	if (ntpdata->time_status & STA_PPSTIME && ntpdata->time_status & STA_PPSSIGNAL)
		return offset;
	else
		return shift_right(offset, SHIFT_PLL + ntpdata->time_constant);
}

static inline void pps_reset_freq_interval(struct ntp_data *ntpdata)
{
	/* The PPS calibration interval may end surprisingly early */
	ntpdata->pps_shift = PPS_INTMIN;
	ntpdata->pps_intcnt = 0;
}

/**
 * pps_clear - Clears the PPS state variables
 * @ntpdata:	Pointer to ntp data
 */
static inline void pps_clear(struct ntp_data *ntpdata)
{
	pps_reset_freq_interval(ntpdata);
	ntpdata->pps_tf[0] = 0;
	ntpdata->pps_tf[1] = 0;
	ntpdata->pps_tf[2] = 0;
	ntpdata->pps_fbase.tv_sec = ntpdata->pps_fbase.tv_nsec = 0;
	ntpdata->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(struct ntp_data *ntpdata)
{
	if (ntpdata->pps_valid > 0) {
		ntpdata->pps_valid--;
	} else {
		ntpdata->time_status