time: ntp: simplify ntp_tick_adj calculations

[linux-2.6/cjktty.git] / 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/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>

/*
 * NTP timekeeping variables:
 */

/* USER_HZ period (usecs): */
unsigned long                   tick_usec = TICK_USEC;

/* ACTHZ period (nsecs): */
unsigned long                   tick_nsec;

u64                             tick_length;
static u64                      tick_length_base;

static struct hrtimer           leap_timer;

#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:                                                   */
int                             time_status = STA_UNSYNC;

/* TAI offset (secs):                                                   */
static long                     time_tai;

/* time adjustment (nsecs):                                             */
static s64                      time_offset;

/* pll time constant:                                                   */
static long                     time_constant = 2;

/* maximum error (usecs):                                               */
long                            time_maxerror = NTP_PHASE_LIMIT;

/* estimated error (usecs):                                             */
long                            time_esterror = NTP_PHASE_LIMIT;

/* frequency offset (scaled nsecs/secs):                                */
static s64                      time_freq;

/* time at last adjustment (secs):                                      */
static long                     time_reftime;

long                            time_adjust;

/* constant (boot-param configurable) NTP tick adjustment (upscaled)    */
static s64                      ntp_tick_adj;

/*
 * 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 div_s64(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 = xtime.tv_sec - time_reftime;
        if (unlikely(time_status & STA_FREQHOLD))
                secs = 0;

        time_reftime = xtime.tv_sec;

        offset64    = offset;
        freq_adj    = (offset64 * secs) <<
                        (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));

        freq_adj    += ntp_update_offset_fll(offset64, secs);

        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
 *
 * 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;
}

/*
 * 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.
 */
static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
{
        enum hrtimer_restart res = HRTIMER_NORESTART;

        write_seqlock(&xtime_lock);

        switch (time_state) {
        case TIME_OK:
                break;
        case TIME_INS:
                xtime.tv_sec--;
                wall_to_monotonic.tv_sec++;
                time_state = TIME_OOP;
                printk(KERN_NOTICE
                        "Clock: inserting leap second 23:59:60 UTC\n");
                hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC);
                res = HRTIMER_RESTART;
                break;
        case TIME_DEL:
                xtime.tv_sec++;
                time_tai--;
                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_tai++;
                time_state = TIME_WAIT;
                /* fall through */
        case TIME_WAIT:
                if (!(time_status & (STA_INS | STA_DEL)))
                        time_state = TIME_OK;
                break;
        }
        update_vsyscall(&xtime, clock);

        write_sequnlock(&xtime_lock);

        return res;
}

/*
 * 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)
{
        s64 time_adj;

        /* 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. 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     += time_adj;

        if (!time_adjust)
                return;

        if (time_adjust > MAX_TICKADJ) {
                time_adjust -= MAX_TICKADJ;
                tick_length += MAX_TICKADJ_SCALED;
                return;
        }

        if (time_adjust < -MAX_TICKADJ) {
                time_adjust += MAX_TICKADJ;
                tick_length -= MAX_TICKADJ_SCALED;
                return;
        }

        tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
                                                         << NTP_SCALE_SHIFT;
        time_adjust = 0;
}

#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(struct work_struct *work);

static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);

static void sync_cmos_clock(struct work_struct *work)
{
        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 - (TICK_NSEC / 2);
        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;
        }
        schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
}

static void notify_cmos_timer(void)
{
        if (!no_sync_cmos_clock)
                schedule_delayed_work(&sync_cmos_work, 0);
}

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

/*
 * Start the leap seconds timer:
 */
static inline void ntp_start_leap_timer(struct timespec *ts)
{
        long now = ts->tv_sec;

        if (time_status & STA_INS) {
                time_state = TIME_INS;
                now += 86400 - now % 86400;
                hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);

                return;
        }

        if (time_status & STA_DEL) {
                time_state = TIME_DEL;
                now += 86400 - (now + 1) % 86400;
                hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
        }
}

/*
 * Propagate a new txc->status value into the NTP state:
 */
static inline void process_adj_status(struct timex *txc, struct timespec *ts)
{
        if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
                time_state = TIME_OK;
                time_status = STA_UNSYNC;
        }
        /* only set allowed bits */
        time_status &= STA_RONLY;

        /*
         * 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 = xtime.tv_sec;

        time_status |= txc->status & ~STA_RONLY;

        switch (time_state) {
        case TIME_OK:
                ntp_start_leap_timer(ts);
                break;
        case TIME_INS:
        case TIME_DEL:
                time_state = TIME_OK;
                ntp_start_leap_timer(ts);
        case TIME_WAIT:
                if (!(time_status & (STA_INS | STA_DEL)))
                        time_state = TIME_OK;
                break;
        case TIME_OOP:
                hrtimer_restart(&leap_timer);
                break;
        }
}
/*
 * Called with the xtime lock held, so we can access and modify
 * all the global NTP state:
 */
static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts)
{
        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);
        }

        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();
}

/*
 * adjtimex mainly allows reading (and writing, if superuser) of
 * kernel time-keeping variables. used by xntpd.
 */
int do_adjtimex(struct timex *txc)
{
        struct timespec ts;
        int result;

        /* Validate the data before disabling interrupts */
        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_STATUS && time_state != TIME_OK)
                        hrtimer_cancel(&leap_timer);
        }

        getnstimeofday(&ts);

        write_seqlock_irq(&xtime_lock);

        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);

                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' */
        if (time_status & (STA_UNSYNC|STA_CLOCKERR))
                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;

        /* 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);

        txc->time.tv_sec = ts.tv_sec;
        txc->time.tv_usec = ts.tv_nsec;
        if (!(time_status & STA_NANO))
                txc->time.tv_usec /= NSEC_PER_USEC;

        notify_cmos_timer();

        return result;
}

static int __init ntp_tick_adj_setup(char *str)
{
        ntp_tick_adj = simple_strtol(str, NULL, 0);
        ntp_tick_adj <<= NTP_SCALE_SHIFT;

        return 1;
}

__setup("ntp_tick_adj=", ntp_tick_adj_setup);

void __init ntp_init(void)
{
        ntp_clear();
        hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
        leap_timer.function = ntp_leap_second;
}