ntp: fix calculation of the next jiffie to trigger RTC sync

[linux/fpc-iii.git] / kernel / time / timekeeping.c

/*
 *  linux/kernel/time/timekeeping.c
 *
 *  Kernel timekeeping code and accessor functions
 *
 *  This code was moved from linux/kernel/timer.c.
 *  Please see that file for copyright and history logs.
 *
 */

#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/sysdev.h>
#include <linux/clocksource.h>
#include <linux/jiffies.h>
#include <linux/time.h>
#include <linux/tick.h>


/*
 * This read-write spinlock protects us from races in SMP while
 * playing with xtime and avenrun.
 */
__cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);


/*
 * The current time
 * wall_to_monotonic is what we need to add to xtime (or xtime corrected
 * for sub jiffie times) to get to monotonic time.  Monotonic is pegged
 * at zero at system boot time, so wall_to_monotonic will be negative,
 * however, we will ALWAYS keep the tv_nsec part positive so we can use
 * the usual normalization.
 *
 * wall_to_monotonic is moved after resume from suspend for the monotonic
 * time not to jump. We need to add total_sleep_time to wall_to_monotonic
 * to get the real boot based time offset.
 *
 * - wall_to_monotonic is no longer the boot time, getboottime must be
 * used instead.
 */
struct timespec xtime __attribute__ ((aligned (16)));
struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
static unsigned long total_sleep_time;          /* seconds */

static struct timespec xtime_cache __attribute__ ((aligned (16)));
void update_xtime_cache(u64 nsec)
{
        xtime_cache = xtime;
        timespec_add_ns(&xtime_cache, nsec);
}

struct clocksource *clock;


#ifdef CONFIG_GENERIC_TIME
/**
 * __get_nsec_offset - Returns nanoseconds since last call to periodic_hook
 *
 * private function, must hold xtime_lock lock when being
 * called. Returns the number of nanoseconds since the
 * last call to update_wall_time() (adjusted by NTP scaling)
 */
static inline s64 __get_nsec_offset(void)
{
        cycle_t cycle_now, cycle_delta;
        s64 ns_offset;

        /* read clocksource: */
        cycle_now = clocksource_read(clock);

        /* calculate the delta since the last update_wall_time: */
        cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

        /* convert to nanoseconds: */
        ns_offset = cyc2ns(clock, cycle_delta);

        return ns_offset;
}

/**
 * getnstimeofday - Returns the time of day in a timespec
 * @ts:         pointer to the timespec to be set
 *
 * Returns the time of day in a timespec.
 */
void getnstimeofday(struct timespec *ts)
{
        unsigned long seq;
        s64 nsecs;

        do {
                seq = read_seqbegin(&xtime_lock);

                *ts = xtime;
                nsecs = __get_nsec_offset();

        } while (read_seqretry(&xtime_lock, seq));

        timespec_add_ns(ts, nsecs);
}

EXPORT_SYMBOL(getnstimeofday);

/**
 * do_gettimeofday - Returns the time of day in a timeval
 * @tv:         pointer to the timeval to be set
 *
 * NOTE: Users should be converted to using getnstimeofday()
 */
void do_gettimeofday(struct timeval *tv)
{
        struct timespec now;

        getnstimeofday(&now);
        tv->tv_sec = now.tv_sec;
        tv->tv_usec = now.tv_nsec/1000;
}

EXPORT_SYMBOL(do_gettimeofday);
/**
 * do_settimeofday - Sets the time of day
 * @tv:         pointer to the timespec variable containing the new time
 *
 * Sets the time of day to the new time and update NTP and notify hrtimers
 */
int do_settimeofday(struct timespec *tv)
{
        unsigned long flags;
        time_t wtm_sec, sec = tv->tv_sec;
        long wtm_nsec, nsec = tv->tv_nsec;

        if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
                return -EINVAL;

        write_seqlock_irqsave(&xtime_lock, flags);

        nsec -= __get_nsec_offset();

        wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
        wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);

        set_normalized_timespec(&xtime, sec, nsec);
        set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
        update_xtime_cache(0);

        clock->error = 0;
        ntp_clear();

        update_vsyscall(&xtime, clock);

        write_sequnlock_irqrestore(&xtime_lock, flags);

        /* signal hrtimers about time change */
        clock_was_set();

        return 0;
}

EXPORT_SYMBOL(do_settimeofday);

/**
 * change_clocksource - Swaps clocksources if a new one is available
 *
 * Accumulates current time interval and initializes new clocksource
 */
static void change_clocksource(void)
{
        struct clocksource *new;
        cycle_t now;
        u64 nsec;

        new = clocksource_get_next();

        if (clock == new)
                return;

        new->cycle_last = 0;
        now = clocksource_read(new);
        nsec =  __get_nsec_offset();
        timespec_add_ns(&xtime, nsec);

        clock = new;
        clock->cycle_last = now;

        clock->error = 0;
        clock->xtime_nsec = 0;
        clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);

        tick_clock_notify();

        /*
         * We're holding xtime lock and waking up klogd would deadlock
         * us on enqueue.  So no printing!
        printk(KERN_INFO "Time: %s clocksource has been installed.\n",
               clock->name);
         */
}
#else
static inline void change_clocksource(void) { }
static inline s64 __get_nsec_offset(void) { return 0; }
#endif

/**
 * timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
 */
int timekeeping_valid_for_hres(void)
{
        unsigned long seq;
        int ret;

        do {
                seq = read_seqbegin(&xtime_lock);

                ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

        } while (read_seqretry(&xtime_lock, seq));

        return ret;
}

/**
 * read_persistent_clock -  Return time in seconds from the persistent clock.
 *
 * Weak dummy function for arches that do not yet support it.
 * Returns seconds from epoch using the battery backed persistent clock.
 * Returns zero if unsupported.
 *
 *  XXX - Do be sure to remove it once all arches implement it.
 */
unsigned long __attribute__((weak)) read_persistent_clock(void)
{
        return 0;
}

/*
 * timekeeping_init - Initializes the clocksource and common timekeeping values
 */
void __init timekeeping_init(void)
{
        unsigned long flags;
        unsigned long sec = read_persistent_clock();

        write_seqlock_irqsave(&xtime_lock, flags);

        ntp_init();

        clock = clocksource_get_next();
        clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
        clock->cycle_last = clocksource_read(clock);

        xtime.tv_sec = sec;
        xtime.tv_nsec = 0;
        set_normalized_timespec(&wall_to_monotonic,
                -xtime.tv_sec, -xtime.tv_nsec);
        update_xtime_cache(0);
        total_sleep_time = 0;
        write_sequnlock_irqrestore(&xtime_lock, flags);
}

/* flag for if timekeeping is suspended */
static int timekeeping_suspended;
/* time in seconds when suspend began */
static unsigned long timekeeping_suspend_time;
/* xtime offset when we went into suspend */
static s64 timekeeping_suspend_nsecs;

/**
 * timekeeping_resume - Resumes the generic timekeeping subsystem.
 * @dev:        unused
 *
 * This is for the generic clocksource timekeeping.
 * xtime/wall_to_monotonic/jiffies/etc are
 * still managed by arch specific suspend/resume code.
 */
static int timekeeping_resume(struct sys_device *dev)
{
        unsigned long flags;
        unsigned long now = read_persistent_clock();

        clocksource_resume();

        write_seqlock_irqsave(&xtime_lock, flags);

        if (now && (now > timekeeping_suspend_time)) {
                unsigned long sleep_length = now - timekeeping_suspend_time;

                xtime.tv_sec += sleep_length;
                wall_to_monotonic.tv_sec -= sleep_length;
                total_sleep_time += sleep_length;
        }
        /* Make sure that we have the correct xtime reference */
        timespec_add_ns(&xtime, timekeeping_suspend_nsecs);
        update_xtime_cache(0);
        /* re-base the last cycle value */
        clock->cycle_last = 0;
        clock->cycle_last = clocksource_read(clock);
        clock->error = 0;
        timekeeping_suspended = 0;
        write_sequnlock_irqrestore(&xtime_lock, flags);

        touch_softlockup_watchdog();

        clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);

        /* Resume hrtimers */
        hres_timers_resume();

        return 0;
}

static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
{
        unsigned long flags;

        timekeeping_suspend_time = read_persistent_clock();

        write_seqlock_irqsave(&xtime_lock, flags);
        /* Get the current xtime offset */
        timekeeping_suspend_nsecs = __get_nsec_offset();
        timekeeping_suspended = 1;
        write_sequnlock_irqrestore(&xtime_lock, flags);

        clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);

        return 0;
}

/* sysfs resume/suspend bits for timekeeping */
static struct sysdev_class timekeeping_sysclass = {
        .name           = "timekeeping",
        .resume         = timekeeping_resume,
        .suspend        = timekeeping_suspend,
};

static struct sys_device device_timer = {
        .id             = 0,
        .cls            = &timekeeping_sysclass,
};

static int __init timekeeping_init_device(void)
{
        int error = sysdev_class_register(&timekeeping_sysclass);
        if (!error)
                error = sysdev_register(&device_timer);
        return error;
}

device_initcall(timekeeping_init_device);

/*
 * If the error is already larger, we look ahead even further
 * to compensate for late or lost adjustments.
 */
static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
                                                 s64 *offset)
{
        s64 tick_error, i;
        u32 look_ahead, adj;
        s32 error2, mult;

        /*
         * Use the current error value to determine how much to look ahead.
         * The larger the error the slower we adjust for it to avoid problems
         * with losing too many ticks, otherwise we would overadjust and
         * produce an even larger error.  The smaller the adjustment the
         * faster we try to adjust for it, as lost ticks can do less harm
         * here.  This is tuned so that an error of about 1 msec is adjusted
         * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
         */
        error2 = clock->error >> (NTP_SCALE_SHIFT + 22 - 2 * SHIFT_HZ);
        error2 = abs(error2);
        for (look_ahead = 0; error2 > 0; look_ahead++)
                error2 >>= 2;

        /*
         * Now calculate the error in (1 << look_ahead) ticks, but first
         * remove the single look ahead already included in the error.
         */
        tick_error = tick_length >> (NTP_SCALE_SHIFT - clock->shift + 1);
        tick_error -= clock->xtime_interval >> 1;
        error = ((error - tick_error) >> look_ahead) + tick_error;

        /* Finally calculate the adjustment shift value.  */
        i = *interval;
        mult = 1;
        if (error < 0) {
                error = -error;
                *interval = -*interval;
                *offset = -*offset;
                mult = -1;
        }
        for (adj = 0; error > i; adj++)
                error >>= 1;

        *interval <<= adj;
        *offset <<= adj;
        return mult << adj;
}

/*
 * Adjust the multiplier to reduce the error value,
 * this is optimized for the most common adjustments of -1,0,1,
 * for other values we can do a bit more work.
 */
static void clocksource_adjust(s64 offset)
{
        s64 error, interval = clock->cycle_interval;
        int adj;

        error = clock->error >> (NTP_SCALE_SHIFT - clock->shift - 1);
        if (error > interval) {
                error >>= 2;
                if (likely(error <= interval))
                        adj = 1;
                else
                        adj = clocksource_bigadjust(error, &interval, &offset);
        } else if (error < -interval) {
                error >>= 2;
                if (likely(error >= -interval)) {
                        adj = -1;
                        interval = -interval;
                        offset = -offset;
                } else
                        adj = clocksource_bigadjust(error, &interval, &offset);
        } else
                return;

        clock->mult += adj;
        clock->xtime_interval += interval;
        clock->xtime_nsec -= offset;
        clock->error -= (interval - offset) <<
                        (NTP_SCALE_SHIFT - clock->shift);
}

/**
 * update_wall_time - Uses the current clocksource to increment the wall time
 *
 * Called from the timer interrupt, must hold a write on xtime_lock.
 */
void update_wall_time(void)
{
        cycle_t offset;

        /* Make sure we're fully resumed: */
        if (unlikely(timekeeping_suspended))
                return;

#ifdef CONFIG_GENERIC_TIME
        offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask;
#else
        offset = clock->cycle_interval;
#endif
        clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift;

        /* normally this loop will run just once, however in the
         * case of lost or late ticks, it will accumulate correctly.
         */
        while (offset >= clock->cycle_interval) {
                /* accumulate one interval */
                clock->xtime_nsec += clock->xtime_interval;
                clock->cycle_last += clock->cycle_interval;
                offset -= clock->cycle_interval;

                if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
                        clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
                        xtime.tv_sec++;
                        second_overflow();
                }

                /* accumulate error between NTP and clock interval */
                clock->error += tick_length;
                clock->error -= clock->xtime_interval << (NTP_SCALE_SHIFT - clock->shift);
        }

        /* correct the clock when NTP error is too big */
        clocksource_adjust(offset);

        /* store full nanoseconds into xtime */
        xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
        clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;

        update_xtime_cache(cyc2ns(clock, offset));

        /* check to see if there is a new clocksource to use */
        change_clocksource();
        update_vsyscall(&xtime, clock);
}

/**
 * getboottime - Return the real time of system boot.
 * @ts:         pointer to the timespec to be set
 *
 * Returns the time of day in a timespec.
 *
 * This is based on the wall_to_monotonic offset and the total suspend
 * time. Calls to settimeofday will affect the value returned (which
 * basically means that however wrong your real time clock is at boot time,
 * you get the right time here).
 */
void getboottime(struct timespec *ts)
{
        set_normalized_timespec(ts,
                - (wall_to_monotonic.tv_sec + total_sleep_time),
                - wall_to_monotonic.tv_nsec);
}

/**
 * monotonic_to_bootbased - Convert the monotonic time to boot based.
 * @ts:         pointer to the timespec to be converted
 */
void monotonic_to_bootbased(struct timespec *ts)
{
        ts->tv_sec += total_sleep_time;
}

unsigned long get_seconds(void)
{
        return xtime_cache.tv_sec;
}
EXPORT_SYMBOL(get_seconds);


struct timespec current_kernel_time(void)
{
        struct timespec now;
        unsigned long seq;

        do {
                seq = read_seqbegin(&xtime_lock);

                now = xtime_cache;
        } while (read_seqretry(&xtime_lock, seq));

        return now;
}
EXPORT_SYMBOL(current_kernel_time);