2 * linux/kernel/time/ntp.c
4 * NTP state machine interfaces and logic.
6 * This code was mainly moved from kernel/timer.c and kernel/time.c
7 * Please see those files for relevant copyright info and historical
12 #include <linux/time.h>
13 #include <linux/timer.h>
14 #include <linux/timex.h>
15 #include <linux/jiffies.h>
16 #include <linux/hrtimer.h>
17 #include <linux/capability.h>
18 #include <linux/math64.h>
19 #include <linux/clocksource.h>
20 #include <asm/timex.h>
23 * Timekeeping variables
25 unsigned long tick_usec
= TICK_USEC
; /* USER_HZ period (usec) */
26 unsigned long tick_nsec
; /* ACTHZ period (nsec) */
28 static u64 tick_length_base
;
30 static struct hrtimer leap_timer
;
32 #define MAX_TICKADJ 500 /* microsecs */
33 #define MAX_TICKADJ_SCALED (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
34 NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
37 * phase-lock loop variables
39 /* TIME_ERROR prevents overwriting the CMOS clock */
40 static int time_state
= TIME_OK
; /* clock synchronization status */
41 int time_status
= STA_UNSYNC
; /* clock status bits */
42 static long time_tai
; /* TAI offset (s) */
43 static s64 time_offset
; /* time adjustment (ns) */
44 static long time_constant
= 2; /* pll time constant */
45 long time_maxerror
= NTP_PHASE_LIMIT
; /* maximum error (us) */
46 long time_esterror
= NTP_PHASE_LIMIT
; /* estimated error (us) */
47 static s64 time_freq
; /* frequency offset (scaled ns/s)*/
48 static long time_reftime
; /* time at last adjustment (s) */
50 static long ntp_tick_adj
;
52 static void ntp_update_frequency(void)
54 u64 second_length
= (u64
)(tick_usec
* NSEC_PER_USEC
* USER_HZ
)
56 second_length
+= (s64
)ntp_tick_adj
<< NTP_SCALE_SHIFT
;
57 second_length
+= time_freq
;
59 tick_length_base
= second_length
;
61 tick_nsec
= div_u64(second_length
, HZ
) >> NTP_SCALE_SHIFT
;
62 tick_length_base
= div_u64(tick_length_base
, NTP_INTERVAL_FREQ
);
65 static void ntp_update_offset(long offset
)
70 if (!(time_status
& STA_PLL
))
73 if (!(time_status
& STA_NANO
))
74 offset
*= NSEC_PER_USEC
;
77 * Scale the phase adjustment and
78 * clamp to the operating range.
80 offset
= min(offset
, MAXPHASE
);
81 offset
= max(offset
, -MAXPHASE
);
84 * Select how the frequency is to be controlled
85 * and in which mode (PLL or FLL).
87 if (time_status
& STA_FREQHOLD
|| time_reftime
== 0)
88 time_reftime
= xtime
.tv_sec
;
89 mtemp
= xtime
.tv_sec
- time_reftime
;
90 time_reftime
= xtime
.tv_sec
;
92 freq_adj
= (s64
)offset
* mtemp
;
93 freq_adj
<<= NTP_SCALE_SHIFT
- 2 * (SHIFT_PLL
+ 2 + time_constant
);
94 time_status
&= ~STA_MODE
;
95 if (mtemp
>= MINSEC
&& (time_status
& STA_FLL
|| mtemp
> MAXSEC
)) {
96 freq_adj
+= div_s64((s64
)offset
<< (NTP_SCALE_SHIFT
- SHIFT_FLL
),
98 time_status
|= STA_MODE
;
100 freq_adj
+= time_freq
;
101 freq_adj
= min(freq_adj
, MAXFREQ_SCALED
);
102 time_freq
= max(freq_adj
, -MAXFREQ_SCALED
);
104 time_offset
= div_s64((s64
)offset
<< NTP_SCALE_SHIFT
, NTP_INTERVAL_FREQ
);
108 * ntp_clear - Clears the NTP state variables
110 * Must be called while holding a write on the xtime_lock
114 time_adjust
= 0; /* stop active adjtime() */
115 time_status
|= STA_UNSYNC
;
116 time_maxerror
= NTP_PHASE_LIMIT
;
117 time_esterror
= NTP_PHASE_LIMIT
;
119 ntp_update_frequency();
121 tick_length
= tick_length_base
;
126 * Leap second processing. If in leap-insert state at the end of the
127 * day, the system clock is set back one second; if in leap-delete
128 * state, the system clock is set ahead one second.
130 static enum hrtimer_restart
ntp_leap_second(struct hrtimer
*timer
)
132 enum hrtimer_restart res
= HRTIMER_NORESTART
;
134 write_seqlock_irq(&xtime_lock
);
136 switch (time_state
) {
141 wall_to_monotonic
.tv_sec
++;
142 time_state
= TIME_OOP
;
143 printk(KERN_NOTICE
"Clock: "
144 "inserting leap second 23:59:60 UTC\n");
145 hrtimer_add_expires_ns(&leap_timer
, NSEC_PER_SEC
);
146 res
= HRTIMER_RESTART
;
151 wall_to_monotonic
.tv_sec
--;
152 time_state
= TIME_WAIT
;
153 printk(KERN_NOTICE
"Clock: "
154 "deleting leap second 23:59:59 UTC\n");
158 time_state
= TIME_WAIT
;
161 if (!(time_status
& (STA_INS
| STA_DEL
)))
162 time_state
= TIME_OK
;
165 update_vsyscall(&xtime
, clock
);
167 write_sequnlock_irq(&xtime_lock
);
173 * this routine handles the overflow of the microsecond field
175 * The tricky bits of code to handle the accurate clock support
176 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
177 * They were originally developed for SUN and DEC kernels.
178 * All the kudos should go to Dave for this stuff.
180 void second_overflow(void)
184 /* Bump the maxerror field */
185 time_maxerror
+= MAXFREQ
/ NSEC_PER_USEC
;
186 if (time_maxerror
> NTP_PHASE_LIMIT
) {
187 time_maxerror
= NTP_PHASE_LIMIT
;
188 time_status
|= STA_UNSYNC
;
192 * Compute the phase adjustment for the next second. The offset is
193 * reduced by a fixed factor times the time constant.
195 tick_length
= tick_length_base
;
196 time_adj
= shift_right(time_offset
, SHIFT_PLL
+ time_constant
);
197 time_offset
-= time_adj
;
198 tick_length
+= time_adj
;
200 if (unlikely(time_adjust
)) {
201 if (time_adjust
> MAX_TICKADJ
) {
202 time_adjust
-= MAX_TICKADJ
;
203 tick_length
+= MAX_TICKADJ_SCALED
;
204 } else if (time_adjust
< -MAX_TICKADJ
) {
205 time_adjust
+= MAX_TICKADJ
;
206 tick_length
-= MAX_TICKADJ_SCALED
;
208 tick_length
+= (s64
)(time_adjust
* NSEC_PER_USEC
/
209 NTP_INTERVAL_FREQ
) << NTP_SCALE_SHIFT
;
215 #ifdef CONFIG_GENERIC_CMOS_UPDATE
217 /* Disable the cmos update - used by virtualization and embedded */
218 int no_sync_cmos_clock __read_mostly
;
220 static void sync_cmos_clock(unsigned long dummy
);
222 static DEFINE_TIMER(sync_cmos_timer
, sync_cmos_clock
, 0, 0);
224 static void sync_cmos_clock(unsigned long dummy
)
226 struct timespec now
, next
;
230 * If we have an externally synchronized Linux clock, then update
231 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
232 * called as close as possible to 500 ms before the new second starts.
233 * This code is run on a timer. If the clock is set, that timer
234 * may not expire at the correct time. Thus, we adjust...
238 * Not synced, exit, do not restart a timer (if one is
239 * running, let it run out).
243 getnstimeofday(&now
);
244 if (abs(now
.tv_nsec
- (NSEC_PER_SEC
/ 2)) <= tick_nsec
/ 2)
245 fail
= update_persistent_clock(now
);
247 next
.tv_nsec
= (NSEC_PER_SEC
/ 2) - now
.tv_nsec
;
248 if (next
.tv_nsec
<= 0)
249 next
.tv_nsec
+= NSEC_PER_SEC
;
256 if (next
.tv_nsec
>= NSEC_PER_SEC
) {
258 next
.tv_nsec
-= NSEC_PER_SEC
;
260 mod_timer(&sync_cmos_timer
, jiffies
+ timespec_to_jiffies(&next
));
263 static void notify_cmos_timer(void)
265 if (!no_sync_cmos_clock
)
266 mod_timer(&sync_cmos_timer
, jiffies
+ 1);
270 static inline void notify_cmos_timer(void) { }
273 /* adjtimex mainly allows reading (and writing, if superuser) of
274 * kernel time-keeping variables. used by xntpd.
276 int do_adjtimex(struct timex
*txc
)
279 long save_adjust
, sec
;
282 /* In order to modify anything, you gotta be super-user! */
283 if (txc
->modes
&& !capable(CAP_SYS_TIME
))
286 /* Now we validate the data before disabling interrupts */
288 if ((txc
->modes
& ADJ_OFFSET_SINGLESHOT
) == ADJ_OFFSET_SINGLESHOT
) {
289 /* singleshot must not be used with any other mode bits */
290 if (txc
->modes
& ~ADJ_OFFSET_SS_READ
)
294 /* if the quartz is off by more than 10% something is VERY wrong ! */
295 if (txc
->modes
& ADJ_TICK
)
296 if (txc
->tick
< 900000/USER_HZ
||
297 txc
->tick
> 1100000/USER_HZ
)
300 if (time_state
!= TIME_OK
&& txc
->modes
& ADJ_STATUS
)
301 hrtimer_cancel(&leap_timer
);
304 write_seqlock_irq(&xtime_lock
);
306 /* Save for later - semantics of adjtime is to return old value */
307 save_adjust
= time_adjust
;
309 /* If there are input parameters, then process them */
311 if (txc
->modes
& ADJ_STATUS
) {
312 if ((time_status
& STA_PLL
) &&
313 !(txc
->status
& STA_PLL
)) {
314 time_state
= TIME_OK
;
315 time_status
= STA_UNSYNC
;
317 /* only set allowed bits */
318 time_status
&= STA_RONLY
;
319 time_status
|= txc
->status
& ~STA_RONLY
;
321 switch (time_state
) {
325 if (time_status
& STA_INS
) {
326 time_state
= TIME_INS
;
327 sec
+= 86400 - sec
% 86400;
328 hrtimer_start(&leap_timer
, ktime_set(sec
, 0), HRTIMER_MODE_ABS
);
329 } else if (time_status
& STA_DEL
) {
330 time_state
= TIME_DEL
;
331 sec
+= 86400 - (sec
+ 1) % 86400;
332 hrtimer_start(&leap_timer
, ktime_set(sec
, 0), HRTIMER_MODE_ABS
);
337 time_state
= TIME_OK
;
341 if (!(time_status
& (STA_INS
| STA_DEL
)))
342 time_state
= TIME_OK
;
345 hrtimer_restart(&leap_timer
);
350 if (txc
->modes
& ADJ_NANO
)
351 time_status
|= STA_NANO
;
352 if (txc
->modes
& ADJ_MICRO
)
353 time_status
&= ~STA_NANO
;
355 if (txc
->modes
& ADJ_FREQUENCY
) {
356 time_freq
= (s64
)txc
->freq
* PPM_SCALE
;
357 time_freq
= min(time_freq
, MAXFREQ_SCALED
);
358 time_freq
= max(time_freq
, -MAXFREQ_SCALED
);
361 if (txc
->modes
& ADJ_MAXERROR
)
362 time_maxerror
= txc
->maxerror
;
363 if (txc
->modes
& ADJ_ESTERROR
)
364 time_esterror
= txc
->esterror
;
366 if (txc
->modes
& ADJ_TIMECONST
) {
367 time_constant
= txc
->constant
;
368 if (!(time_status
& STA_NANO
))
370 time_constant
= min(time_constant
, (long)MAXTC
);
371 time_constant
= max(time_constant
, 0l);
374 if (txc
->modes
& ADJ_TAI
&& txc
->constant
> 0)
375 time_tai
= txc
->constant
;
377 if (txc
->modes
& ADJ_OFFSET
) {
378 if (txc
->modes
== ADJ_OFFSET_SINGLESHOT
)
379 /* adjtime() is independent from ntp_adjtime() */
380 time_adjust
= txc
->offset
;
382 ntp_update_offset(txc
->offset
);
384 if (txc
->modes
& ADJ_TICK
)
385 tick_usec
= txc
->tick
;
387 if (txc
->modes
& (ADJ_TICK
|ADJ_FREQUENCY
|ADJ_OFFSET
))
388 ntp_update_frequency();
391 result
= time_state
; /* mostly `TIME_OK' */
392 if (time_status
& (STA_UNSYNC
|STA_CLOCKERR
))
395 if ((txc
->modes
== ADJ_OFFSET_SINGLESHOT
) ||
396 (txc
->modes
== ADJ_OFFSET_SS_READ
))
397 txc
->offset
= save_adjust
;
399 txc
->offset
= shift_right(time_offset
* NTP_INTERVAL_FREQ
,
401 if (!(time_status
& STA_NANO
))
402 txc
->offset
/= NSEC_PER_USEC
;
404 txc
->freq
= shift_right((s32
)(time_freq
>> PPM_SCALE_INV_SHIFT
) *
407 txc
->maxerror
= time_maxerror
;
408 txc
->esterror
= time_esterror
;
409 txc
->status
= time_status
;
410 txc
->constant
= time_constant
;
412 txc
->tolerance
= MAXFREQ_SCALED
/ PPM_SCALE
;
413 txc
->tick
= tick_usec
;
416 /* PPS is not implemented, so these are zero */
425 write_sequnlock_irq(&xtime_lock
);
427 txc
->time
.tv_sec
= ts
.tv_sec
;
428 txc
->time
.tv_usec
= ts
.tv_nsec
;
429 if (!(time_status
& STA_NANO
))
430 txc
->time
.tv_usec
/= NSEC_PER_USEC
;
437 static int __init
ntp_tick_adj_setup(char *str
)
439 ntp_tick_adj
= simple_strtol(str
, NULL
, 0);
443 __setup("ntp_tick_adj=", ntp_tick_adj_setup
);
445 void __init
ntp_init(void)
448 hrtimer_init(&leap_timer
, CLOCK_REALTIME
, HRTIMER_MODE_ABS
);
449 leap_timer
.function
= ntp_leap_second
;