kernel/time/ntp.c - linux - Git at Google

 /*
  * linux/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/mm.h>
 #include <linux/time.h>
 #include <linux/timer.h>
 #include <linux/timex.h>
 #include <linux/jiffies.h>
 #include <linux/hrtimer.h>
 #include <linux/capability.h>
 #include <asm/div64.h>
 #include <asm/timex.h>

 /*
  * Timekeeping variables
  */
 unsigned long tick_usec = TICK_USEC; 		/* USER_HZ period (usec) */
 unsigned long tick_nsec;			/* ACTHZ period (nsec) */
 static u64 tick_length, tick_length_base;

 #define MAX_TICKADJ		500		/* microsecs */
 #define MAX_TICKADJ_SCALED	(((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
 				  TICK_LENGTH_SHIFT) / NTP_INTERVAL_FREQ)

 /*
  * phase-lock loop variables
  */
 /* TIME_ERROR prevents overwriting the CMOS clock */
 static int time_state = TIME_OK;	/* clock synchronization status	*/
 int time_status = STA_UNSYNC;		/* clock status bits		*/
 static s64 time_offset;		/* time adjustment (ns)		*/
 static long time_constant = 2;		/* pll time constant		*/
 long time_maxerror = NTP_PHASE_LIMIT;	/* maximum error (us)		*/
 long time_esterror = NTP_PHASE_LIMIT;	/* estimated error (us)		*/
 long time_freq;				/* frequency offset (scaled ppm)*/
 static long time_reftime;		/* time at last adjustment (s)	*/
 long time_adjust;
 static long ntp_tick_adj;

 static void ntp_update_frequency(void)
 {
 	u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
 				<< TICK_LENGTH_SHIFT;
 	second_length += (s64)ntp_tick_adj << TICK_LENGTH_SHIFT;
 	second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);

 	tick_length_base = second_length;

 	do_div(second_length, HZ);
 	tick_nsec = second_length >> TICK_LENGTH_SHIFT;

 	do_div(tick_length_base, 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;
 }

 /*
  * 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)
 {
 	long time_adj;

 	/* Bump the maxerror field */
 	time_maxerror += MAXFREQ >> SHIFT_USEC;
 	if (time_maxerror > NTP_PHASE_LIMIT) {
 		time_maxerror = NTP_PHASE_LIMIT;
 		time_status |= STA_UNSYNC;
 	}

 	/*
 	 * 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. The microtime()
 	 * routine or external clock driver will insure that reported time is
 	 * always monotonic. The ugly divides should be replaced.
 	 */
 	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 (xtime.tv_sec % 86400 == 0) {
 			xtime.tv_sec--;
 			wall_to_monotonic.tv_sec++;
 			time_state = TIME_OOP;
 			printk(KERN_NOTICE "Clock: inserting leap second "
 					"23:59:60 UTC\n");
 		}
 		break;
 	case TIME_DEL:
 		if ((xtime.tv_sec + 1) % 86400 == 0) {
 			xtime.tv_sec++;
 			wall_to_monotonic.tv_sec--;
 			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;
 	}

 	/*
 	 * Compute the phase adjustment for the next second. The offset is
 	 * reduced by a fixed factor times the time constant.
 	 */
 	tick_length = tick_length_base;
 	time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
 	time_offset -= time_adj;
 	tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);

 	if (unlikely(time_adjust)) {
 		if (time_adjust > MAX_TICKADJ) {
 			time_adjust -= MAX_TICKADJ;
 			tick_length += MAX_TICKADJ_SCALED;
 		} else if (time_adjust < -MAX_TICKADJ) {
 			time_adjust += MAX_TICKADJ;
 			tick_length -= MAX_TICKADJ_SCALED;
 		} else {
 			tick_length += (s64)(time_adjust * NSEC_PER_USEC /
 					NTP_INTERVAL_FREQ) << TICK_LENGTH_SHIFT;
 			time_adjust = 0;
 		}
 	}
 }

 /*
  * Return how long ticks are at the moment, that is, how much time
  * update_wall_time_one_tick will add to xtime next time we call it
  * (assuming no calls to do_adjtimex in the meantime).
  * The return value is in fixed-point nanoseconds shifted by the
  * specified number of bits to the right of the binary point.
  * This function has no side-effects.
  */
 u64 current_tick_length(void)
 {
 	return tick_length;
 }

 #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(unsigned long dummy);

 static DEFINE_TIMER(sync_cmos_timer, sync_cmos_clock, 0, 0);

 static void sync_cmos_clock(unsigned long dummy)
 {
 	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;
 	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;
 	}
 	mod_timer(&sync_cmos_timer, jiffies + timespec_to_jiffies(&next));
 }

 static void notify_cmos_timer(void)
 {
 	if (!no_sync_cmos_clock)
 		mod_timer(&sync_cmos_timer, jiffies + 1);
 }

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

 /* adjtimex mainly allows reading (and writing, if superuser) of
  * kernel time-keeping variables. used by xntpd.
  */
 int do_adjtimex(struct timex *txc)
 {
 	long mtemp, save_adjust, rem;
 	s64 freq_adj, temp64;
 	int result;

 	/* In order to modify anything, you gotta be super-user! */
 	if (txc->modes && !capable(CAP_SYS_TIME))
 		return -EPERM;

 	/* Now we validate the data before disabling interrupts */

 	if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT) {
 	  /* singleshot must not be used with any other mode bits */
 		if (txc->modes != ADJ_OFFSET_SINGLESHOT &&
 					txc->modes != ADJ_OFFSET_SS_READ)
 			return -EINVAL;
 	}

 	if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
 	  /* adjustment Offset limited to +- .512 seconds */
 		if (txc->offset <= - MAXPHASE || txc->offset >= MAXPHASE )
 			return -EINVAL;

 	/* if the quartz is off by more than 10% something is VERY wrong ! */
 	if (txc->modes & ADJ_TICK)
 		if (txc->tick <  900000/USER_HZ ||
 		    txc->tick > 1100000/USER_HZ)
 			return -EINVAL;

 	write_seqlock_irq(&xtime_lock);
 	result = time_state;	/* mostly `TIME_OK' */

 	/* Save for later - semantics of adjtime is to return old value */
 	save_adjust = time_adjust;

 #if 0	/* STA_CLOCKERR is never set yet */
 	time_status &= ~STA_CLOCKERR;		/* reset STA_CLOCKERR */
 #endif
 	/* If there are input parameters, then process them */
 	if (txc->modes)
 	{
 	    if (txc->modes & ADJ_STATUS)	/* only set allowed bits */
 		time_status =  (txc->status & ~STA_RONLY) |
 			      (time_status & STA_RONLY);

 	    if (txc->modes & ADJ_FREQUENCY) {	/* p. 22 */
 		if (txc->freq > MAXFREQ || txc->freq < -MAXFREQ) {
 		    result = -EINVAL;
 		    goto leave;
 		}
 		time_freq = ((s64)txc->freq * NSEC_PER_USEC)
 				>> (SHIFT_USEC - SHIFT_NSEC);
 	    }

 	    if (txc->modes & ADJ_MAXERROR) {
 		if (txc->maxerror < 0 || txc->maxerror >= NTP_PHASE_LIMIT) {
 		    result = -EINVAL;
 		    goto leave;
 		}
 		time_maxerror = txc->maxerror;
 	    }

 	    if (txc->modes & ADJ_ESTERROR) {
 		if (txc->esterror < 0 || txc->esterror >= NTP_PHASE_LIMIT) {
 		    result = -EINVAL;
 		    goto leave;
 		}
 		time_esterror = txc->esterror;
 	    }

 	    if (txc->modes & ADJ_TIMECONST) {	/* p. 24 */
 		if (txc->constant < 0) {	/* NTP v4 uses values > 6 */
 		    result = -EINVAL;
 		    goto leave;
 		}
 		time_constant = min(txc->constant + 4, (long)MAXTC);
 	    }

 	    if (txc->modes & ADJ_OFFSET) {	/* values checked earlier */
 		if (txc->modes == ADJ_OFFSET_SINGLESHOT) {
 		    /* adjtime() is independent from ntp_adjtime() */
 		    time_adjust = txc->offset;
 		}
 		else if (time_status & STA_PLL) {
 		    time_offset = txc->offset * NSEC_PER_USEC;

 		    /*
 		     * Scale the phase adjustment and
 		     * clamp to the operating range.
 		     */
 		    time_offset = min(time_offset, (s64)MAXPHASE * NSEC_PER_USEC);
 		    time_offset = max(time_offset, (s64)-MAXPHASE * NSEC_PER_USEC);

 		    /*
 		     * Select whether the frequency is to be controlled
 		     * and in which mode (PLL or FLL). Clamp to the operating
 		     * range. Ugly multiply/divide should be replaced someday.
 		     */

 		    if (time_status & STA_FREQHOLD || time_reftime == 0)
 		        time_reftime = xtime.tv_sec;
 		    mtemp = xtime.tv_sec - time_reftime;
 		    time_reftime = xtime.tv_sec;

 		    freq_adj = time_offset * mtemp;
 		    freq_adj = shift_right(freq_adj, time_constant * 2 +
 					   (SHIFT_PLL + 2) * 2 - SHIFT_NSEC);
 		    if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
 			u64 utemp64;
 			temp64 = time_offset << (SHIFT_NSEC - SHIFT_FLL);
 			if (time_offset < 0) {
 			    utemp64 = -temp64;
 			    do_div(utemp64, mtemp);
 			    freq_adj -= utemp64;
 			} else {
 			    utemp64 = temp64;
 			    do_div(utemp64, mtemp);
 			    freq_adj += utemp64;
 			}
 		    }
 		    freq_adj += time_freq;
 		    freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
 		    time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
 		    time_offset = div_long_long_rem_signed(time_offset,
 							   NTP_INTERVAL_FREQ,
 							   &rem);
 		    time_offset <<= SHIFT_UPDATE;
 		} /* STA_PLL */
 	    } /* txc->modes & ADJ_OFFSET */
 	    if (txc->modes & ADJ_TICK)
 		tick_usec = txc->tick;

 	    if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 		    ntp_update_frequency();
 	} /* txc->modes */
 leave:	if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
 		result = TIME_ERROR;

 	if ((txc->modes == ADJ_OFFSET_SINGLESHOT) ||
 			(txc->modes == ADJ_OFFSET_SS_READ))
 		txc->offset = save_adjust;
 	else
 		txc->offset = ((long)shift_right(time_offset, SHIFT_UPDATE)) *
 	    			NTP_INTERVAL_FREQ / 1000;
 	txc->freq	   = (time_freq / NSEC_PER_USEC) <<
 				(SHIFT_USEC - SHIFT_NSEC);
 	txc->maxerror	   = time_maxerror;
 	txc->esterror	   = time_esterror;
 	txc->status	   = time_status;
 	txc->constant	   = time_constant;
 	txc->precision	   = 1;
 	txc->tolerance	   = MAXFREQ;
 	txc->tick	   = tick_usec;

 	/* 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;
 	write_sequnlock_irq(&xtime_lock);
 	do_gettimeofday(&txc->time);
 	notify_cmos_timer();
 	return(result);
 }

 static int __init ntp_tick_adj_setup(char *str)
 {
 	ntp_tick_adj = simple_strtol(str, NULL, 0);
 	return 1;
 }

 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
	/*
	* linux/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/mm.h>
	#include <linux/time.h>
	#include <linux/timer.h>
	#include <linux/timex.h>
	#include <linux/jiffies.h>
	#include <linux/hrtimer.h>
	#include <linux/capability.h>
	#include <asm/div64.h>
	#include <asm/timex.h>

	/*
	* Timekeeping variables
	*/
	unsigned long tick_usec = TICK_USEC; /* USER_HZ period (usec) */
	unsigned long tick_nsec; /* ACTHZ period (nsec) */
	static u64 tick_length, tick_length_base;

	#define MAX_TICKADJ 500 /* microsecs */
	#define MAX_TICKADJ_SCALED (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
	TICK_LENGTH_SHIFT) / NTP_INTERVAL_FREQ)

	/*
	* phase-lock loop variables
	*/
	/* TIME_ERROR prevents overwriting the CMOS clock */
	static int time_state = TIME_OK; /* clock synchronization status */
	int time_status = STA_UNSYNC; /* clock status bits */
	static s64 time_offset; /* time adjustment (ns) */
	static long time_constant = 2; /* pll time constant */
	long time_maxerror = NTP_PHASE_LIMIT; /* maximum error (us) */
	long time_esterror = NTP_PHASE_LIMIT; /* estimated error (us) */
	long time_freq; /* frequency offset (scaled ppm)*/
	static long time_reftime; /* time at last adjustment (s) */
	long time_adjust;
	static long ntp_tick_adj;

	static void ntp_update_frequency(void)
	{
	u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
	<< TICK_LENGTH_SHIFT;
	second_length += (s64)ntp_tick_adj << TICK_LENGTH_SHIFT;
	second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);

	tick_length_base = second_length;

	do_div(second_length, HZ);
	tick_nsec = second_length >> TICK_LENGTH_SHIFT;

	do_div(tick_length_base, 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;
	}

	/*
	* 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)
	{
	long time_adj;

	/* Bump the maxerror field */
	time_maxerror += MAXFREQ >> SHIFT_USEC;
	if (time_maxerror > NTP_PHASE_LIMIT) {
	time_maxerror = NTP_PHASE_LIMIT;
	time_status \|= STA_UNSYNC;
	}

	/*
	* 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. The microtime()
	* routine or external clock driver will insure that reported time is
	* always monotonic. The ugly divides should be replaced.
	*/
	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 (xtime.tv_sec % 86400 == 0) {
	xtime.tv_sec--;
	wall_to_monotonic.tv_sec++;
	time_state = TIME_OOP;
	printk(KERN_NOTICE "Clock: inserting leap second "
	"23:59:60 UTC\n");
	}
	break;
	case TIME_DEL:
	if ((xtime.tv_sec + 1) % 86400 == 0) {
	xtime.tv_sec++;
	wall_to_monotonic.tv_sec--;
	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;
	}

	/*
	* Compute the phase adjustment for the next second. The offset is
	* reduced by a fixed factor times the time constant.
	*/
	tick_length = tick_length_base;
	time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
	time_offset -= time_adj;
	tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);

	if (unlikely(time_adjust)) {
	if (time_adjust > MAX_TICKADJ) {
	time_adjust -= MAX_TICKADJ;
	tick_length += MAX_TICKADJ_SCALED;
	} else if (time_adjust < -MAX_TICKADJ) {
	time_adjust += MAX_TICKADJ;
	tick_length -= MAX_TICKADJ_SCALED;
	} else {
	tick_length += (s64)(time_adjust * NSEC_PER_USEC /
	NTP_INTERVAL_FREQ) << TICK_LENGTH_SHIFT;
	time_adjust = 0;
	}
	}
	}

	/*
	* Return how long ticks are at the moment, that is, how much time
	* update_wall_time_one_tick will add to xtime next time we call it
	* (assuming no calls to do_adjtimex in the meantime).
	* The return value is in fixed-point nanoseconds shifted by the
	* specified number of bits to the right of the binary point.
	* This function has no side-effects.
	*/
	u64 current_tick_length(void)
	{
	return tick_length;
	}

	#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(unsigned long dummy);

	static DEFINE_TIMER(sync_cmos_timer, sync_cmos_clock, 0, 0);

	static void sync_cmos_clock(unsigned long dummy)
	{
	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;
	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;
	}
	mod_timer(&sync_cmos_timer, jiffies + timespec_to_jiffies(&next));
	}

	static void notify_cmos_timer(void)
	{
	if (!no_sync_cmos_clock)
	mod_timer(&sync_cmos_timer, jiffies + 1);
	}

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

	/* adjtimex mainly allows reading (and writing, if superuser) of
	* kernel time-keeping variables. used by xntpd.
	*/
	int do_adjtimex(struct timex *txc)
	{
	long mtemp, save_adjust, rem;
	s64 freq_adj, temp64;
	int result;

	/* In order to modify anything, you gotta be super-user! */
	if (txc->modes && !capable(CAP_SYS_TIME))
	return -EPERM;

	/* Now we validate the data before disabling interrupts */

	if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT) {
	/* singleshot must not be used with any other mode bits */
	if (txc->modes != ADJ_OFFSET_SINGLESHOT &&
	txc->modes != ADJ_OFFSET_SS_READ)
	return -EINVAL;
	}

	if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
	/* adjustment Offset limited to +- .512 seconds */
	if (txc->offset <= - MAXPHASE \|\| txc->offset >= MAXPHASE )
	return -EINVAL;

	/* if the quartz is off by more than 10% something is VERY wrong ! */
	if (txc->modes & ADJ_TICK)
	if (txc->tick < 900000/USER_HZ \|\|
	txc->tick > 1100000/USER_HZ)
	return -EINVAL;

	write_seqlock_irq(&xtime_lock);
	result = time_state; /* mostly `TIME_OK' */

	/* Save for later - semantics of adjtime is to return old value */
	save_adjust = time_adjust;

	#if 0 /* STA_CLOCKERR is never set yet */
	time_status &= ~STA_CLOCKERR; /* reset STA_CLOCKERR */
	#endif
	/* If there are input parameters, then process them */
	if (txc->modes)
	{
	if (txc->modes & ADJ_STATUS) /* only set allowed bits */
	time_status = (txc->status & ~STA_RONLY) \|
	(time_status & STA_RONLY);

	if (txc->modes & ADJ_FREQUENCY) { /* p. 22 */
	if (txc->freq > MAXFREQ \|\| txc->freq < -MAXFREQ) {
	result = -EINVAL;
	goto leave;
	}
	time_freq = ((s64)txc->freq * NSEC_PER_USEC)
	>> (SHIFT_USEC - SHIFT_NSEC);
	}

	if (txc->modes & ADJ_MAXERROR) {
	if (txc->maxerror < 0 \|\| txc->maxerror >= NTP_PHASE_LIMIT) {
	result = -EINVAL;
	goto leave;
	}
	time_maxerror = txc->maxerror;
	}

	if (txc->modes & ADJ_ESTERROR) {
	if (txc->esterror < 0 \|\| txc->esterror >= NTP_PHASE_LIMIT) {
	result = -EINVAL;
	goto leave;
	}
	time_esterror = txc->esterror;
	}

	if (txc->modes & ADJ_TIMECONST) { /* p. 24 */
	if (txc->constant < 0) { /* NTP v4 uses values > 6 */
	result = -EINVAL;
	goto leave;
	}
	time_constant = min(txc->constant + 4, (long)MAXTC);
	}

	if (txc->modes & ADJ_OFFSET) { /* values checked earlier */
	if (txc->modes == ADJ_OFFSET_SINGLESHOT) {
	/* adjtime() is independent from ntp_adjtime() */
	time_adjust = txc->offset;
	}
	else if (time_status & STA_PLL) {
	time_offset = txc->offset * NSEC_PER_USEC;

	/*
	* Scale the phase adjustment and
	* clamp to the operating range.
	*/
	time_offset = min(time_offset, (s64)MAXPHASE * NSEC_PER_USEC);
	time_offset = max(time_offset, (s64)-MAXPHASE * NSEC_PER_USEC);

	/*
	* Select whether the frequency is to be controlled
	* and in which mode (PLL or FLL). Clamp to the operating
	* range. Ugly multiply/divide should be replaced someday.
	*/

	if (time_status & STA_FREQHOLD \|\| time_reftime == 0)
	time_reftime = xtime.tv_sec;
	mtemp = xtime.tv_sec - time_reftime;
	time_reftime = xtime.tv_sec;

	freq_adj = time_offset * mtemp;
	freq_adj = shift_right(freq_adj, time_constant * 2 +
	(SHIFT_PLL + 2) * 2 - SHIFT_NSEC);
	if (mtemp >= MINSEC && (time_status & STA_FLL \|\| mtemp > MAXSEC)) {
	u64 utemp64;
	temp64 = time_offset << (SHIFT_NSEC - SHIFT_FLL);
	if (time_offset < 0) {
	utemp64 = -temp64;
	do_div(utemp64, mtemp);
	freq_adj -= utemp64;
	} else {
	utemp64 = temp64;
	do_div(utemp64, mtemp);
	freq_adj += utemp64;
	}
	}
	freq_adj += time_freq;
	freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
	time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
	time_offset = div_long_long_rem_signed(time_offset,
	NTP_INTERVAL_FREQ,
	&rem);
	time_offset <<= SHIFT_UPDATE;
	} /* STA_PLL */
	} /* txc->modes & ADJ_OFFSET */
	if (txc->modes & ADJ_TICK)
	tick_usec = txc->tick;

	if (txc->modes & (ADJ_TICK\|ADJ_FREQUENCY\|ADJ_OFFSET))
	ntp_update_frequency();
	} /* txc->modes */
	leave: if ((time_status & (STA_UNSYNC\|STA_CLOCKERR)) != 0)
	result = TIME_ERROR;

	if ((txc->modes == ADJ_OFFSET_SINGLESHOT) \|\|
	(txc->modes == ADJ_OFFSET_SS_READ))
	txc->offset = save_adjust;
	else
	txc->offset = ((long)shift_right(time_offset, SHIFT_UPDATE)) *
	NTP_INTERVAL_FREQ / 1000;
	txc->freq = (time_freq / NSEC_PER_USEC) <<
	(SHIFT_USEC - SHIFT_NSEC);
	txc->maxerror = time_maxerror;
	txc->esterror = time_esterror;
	txc->status = time_status;
	txc->constant = time_constant;
	txc->precision = 1;
	txc->tolerance = MAXFREQ;
	txc->tick = tick_usec;

	/* 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;
	write_sequnlock_irq(&xtime_lock);
	do_gettimeofday(&txc->time);
	notify_cmos_timer();
	return(result);
	}

	static int __init ntp_tick_adj_setup(char *str)
	{
	ntp_tick_adj = simple_strtol(str, NULL, 0);
	return 1;
	}

	__setup("ntp_tick_adj=", ntp_tick_adj_setup);