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/*
* 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): */
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;
/*
* 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 = 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
*
* 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:
timekeeping_leap_insert(-1);
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:
timekeeping_leap_insert(1);
time_tai--;
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;
}
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 delta;
/* 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;
delta = shift_right(time_offset, SHIFT_PLL + time_constant);
time_offset -= delta;
tick_length += delta;
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
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