1 /*
2 * NTP state machine interfaces and logic.
3 *
4 * This code was mainly moved from kernel/timer.c and kernel/time.c
5 * Please see those files for relevant copyright info and historical
6 * changelogs.
7 */
8 #include <linux/capability.h>
9 #include <linux/clocksource.h>
10 #include <linux/workqueue.h>
11 #include <linux/hrtimer.h>
12 #include <linux/jiffies.h>
13 #include <linux/math64.h>
14 #include <linux/timex.h>
15 #include <linux/time.h>
16 #include <linux/mm.h>
17 #include <linux/module.h>
18 #include <linux/rtc.h>
19
20 #include "tick-internal.h"
21 #include "ntp_internal.h"
22
23 /*
24 * NTP timekeeping variables:
25 *
26 * Note: All of the NTP state is protected by the timekeeping locks.
27 */
28
29
30 /* USER_HZ period (usecs): */
31 unsigned long tick_usec = TICK_USEC;
32
33 /* SHIFTED_HZ period (nsecs): */
34 unsigned long tick_nsec;
35
36 static u64 tick_length;
37 static u64 tick_length_base;
38
39 #define MAX_TICKADJ 500LL /* usecs */
40 #define MAX_TICKADJ_SCALED \
41 (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
42
43 /*
44 * phase-lock loop variables
45 */
46
47 /*
48 * clock synchronization status
49 *
50 * (TIME_ERROR prevents overwriting the CMOS clock)
51 */
52 static int time_state = TIME_OK;
53
54 /* clock status bits: */
55 static int time_status = STA_UNSYNC;
56
57 /* time adjustment (nsecs): */
58 static s64 time_offset;
59
60 /* pll time constant: */
61 static long time_constant = 2;
62
63 /* maximum error (usecs): */
64 static long time_maxerror = NTP_PHASE_LIMIT;
65
66 /* estimated error (usecs): */
67 static long time_esterror = NTP_PHASE_LIMIT;
68
69 /* frequency offset (scaled nsecs/secs): */
70 static s64 time_freq;
71
72 /* time at last adjustment (secs): */
73 static long time_reftime;
74
75 static long time_adjust;
76
77 /* constant (boot-param configurable) NTP tick adjustment (upscaled) */
78 static s64 ntp_tick_adj;
79
80 #ifdef CONFIG_NTP_PPS
81
82 /*
83 * The following variables are used when a pulse-per-second (PPS) signal
84 * is available. They establish the engineering parameters of the clock
85 * discipline loop when controlled by the PPS signal.
86 */
87 #define PPS_VALID 10 /* PPS signal watchdog max (s) */
88 #define PPS_POPCORN 4 /* popcorn spike threshold (shift) */
89 #define PPS_INTMIN 2 /* min freq interval (s) (shift) */
90 #define PPS_INTMAX 8 /* max freq interval (s) (shift) */
91 #define PPS_INTCOUNT 4 /* number of consecutive good intervals to
92 increase pps_shift or consecutive bad
93 intervals to decrease it */
94 #define PPS_MAXWANDER 100000 /* max PPS freq wander (ns/s) */
95
96 static int pps_valid; /* signal watchdog counter */
97 static long pps_tf[3]; /* phase median filter */
98 static long pps_jitter; /* current jitter (ns) */
99 static struct timespec pps_fbase; /* beginning of the last freq interval */
100 static int pps_shift; /* current interval duration (s) (shift) */
101 static int pps_intcnt; /* interval counter */
102 static s64 pps_freq; /* frequency offset (scaled ns/s) */
103 static long pps_stabil; /* current stability (scaled ns/s) */
104
105 /*
106 * PPS signal quality monitors
107 */
108 static long pps_calcnt; /* calibration intervals */
109 static long pps_jitcnt; /* jitter limit exceeded */
110 static long pps_stbcnt; /* stability limit exceeded */
111 static long pps_errcnt; /* calibration errors */
112
113
114 /* PPS kernel consumer compensates the whole phase error immediately.
115 * Otherwise, reduce the offset by a fixed factor times the time constant.
116 */
ntp_offset_chunk(s64 offset)117 static inline s64 ntp_offset_chunk(s64 offset)
118 {
119 if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
120 return offset;
121 else
122 return shift_right(offset, SHIFT_PLL + time_constant);
123 }
124
pps_reset_freq_interval(void)125 static inline void pps_reset_freq_interval(void)
126 {
127 /* the PPS calibration interval may end
128 surprisingly early */
129 pps_shift = PPS_INTMIN;
130 pps_intcnt = 0;
131 }
132
133 /**
134 * pps_clear - Clears the PPS state variables
135 */
pps_clear(void)136 static inline void pps_clear(void)
137 {
138 pps_reset_freq_interval();
139 pps_tf[0] = 0;
140 pps_tf[1] = 0;
141 pps_tf[2] = 0;
142 pps_fbase.tv_sec = pps_fbase.tv_nsec = 0;
143 pps_freq = 0;
144 }
145
146 /* Decrease pps_valid to indicate that another second has passed since
147 * the last PPS signal. When it reaches 0, indicate that PPS signal is
148 * missing.
149 */
pps_dec_valid(void)150 static inline void pps_dec_valid(void)
151 {
152 if (pps_valid > 0)
153 pps_valid--;
154 else {
155 time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
156 STA_PPSWANDER | STA_PPSERROR);
157 pps_clear();
158 }
159 }
160
pps_set_freq(s64 freq)161 static inline void pps_set_freq(s64 freq)
162 {
163 pps_freq = freq;
164 }
165
is_error_status(int status)166 static inline int is_error_status(int status)
167 {
168 return (status & (STA_UNSYNC|STA_CLOCKERR))
169 /* PPS signal lost when either PPS time or
170 * PPS frequency synchronization requested
171 */
172 || ((status & (STA_PPSFREQ|STA_PPSTIME))
173 && !(status & STA_PPSSIGNAL))
174 /* PPS jitter exceeded when
175 * PPS time synchronization requested */
176 || ((status & (STA_PPSTIME|STA_PPSJITTER))
177 == (STA_PPSTIME|STA_PPSJITTER))
178 /* PPS wander exceeded or calibration error when
179 * PPS frequency synchronization requested
180 */
181 || ((status & STA_PPSFREQ)
182 && (status & (STA_PPSWANDER|STA_PPSERROR)));
183 }
184
pps_fill_timex(struct timex * txc)185 static inline void pps_fill_timex(struct timex *txc)
186 {
187 txc->ppsfreq = shift_right((pps_freq >> PPM_SCALE_INV_SHIFT) *
188 PPM_SCALE_INV, NTP_SCALE_SHIFT);
189 txc->jitter = pps_jitter;
190 if (!(time_status & STA_NANO))
191 txc->jitter /= NSEC_PER_USEC;
192 txc->shift = pps_shift;
193 txc->stabil = pps_stabil;
194 txc->jitcnt = pps_jitcnt;
195 txc->calcnt = pps_calcnt;
196 txc->errcnt = pps_errcnt;
197 txc->stbcnt = pps_stbcnt;
198 }
199
200 #else /* !CONFIG_NTP_PPS */
201
ntp_offset_chunk(s64 offset)202 static inline s64 ntp_offset_chunk(s64 offset)
203 {
204 return shift_right(offset, SHIFT_PLL + time_constant);
205 }
206
pps_reset_freq_interval(void)207 static inline void pps_reset_freq_interval(void) {}
pps_clear(void)208 static inline void pps_clear(void) {}
pps_dec_valid(void)209 static inline void pps_dec_valid(void) {}
pps_set_freq(s64 freq)210 static inline void pps_set_freq(s64 freq) {}
211
is_error_status(int status)212 static inline int is_error_status(int status)
213 {
214 return status & (STA_UNSYNC|STA_CLOCKERR);
215 }
216
pps_fill_timex(struct timex * txc)217 static inline void pps_fill_timex(struct timex *txc)
218 {
219 /* PPS is not implemented, so these are zero */
220 txc->ppsfreq = 0;
221 txc->jitter = 0;
222 txc->shift = 0;
223 txc->stabil = 0;
224 txc->jitcnt = 0;
225 txc->calcnt = 0;
226 txc->errcnt = 0;
227 txc->stbcnt = 0;
228 }
229
230 #endif /* CONFIG_NTP_PPS */
231
232
233 /**
234 * ntp_synced - Returns 1 if the NTP status is not UNSYNC
235 *
236 */
ntp_synced(void)237 static inline int ntp_synced(void)
238 {
239 return !(time_status & STA_UNSYNC);
240 }
241
242
243 /*
244 * NTP methods:
245 */
246
247 /*
248 * Update (tick_length, tick_length_base, tick_nsec), based
249 * on (tick_usec, ntp_tick_adj, time_freq):
250 */
ntp_update_frequency(void)251 static void ntp_update_frequency(void)
252 {
253 u64 second_length;
254 u64 new_base;
255
256 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
257 << NTP_SCALE_SHIFT;
258
259 second_length += ntp_tick_adj;
260 second_length += time_freq;
261
262 tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
263 new_base = div_u64(second_length, NTP_INTERVAL_FREQ);
264
265 /*
266 * Don't wait for the next second_overflow, apply
267 * the change to the tick length immediately:
268 */
269 tick_length += new_base - tick_length_base;
270 tick_length_base = new_base;
271 }
272
ntp_update_offset_fll(s64 offset64,long secs)273 static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
274 {
275 time_status &= ~STA_MODE;
276
277 if (secs < MINSEC)
278 return 0;
279
280 if (!(time_status & STA_FLL) && (secs <= MAXSEC))
281 return 0;
282
283 time_status |= STA_MODE;
284
285 return div64_long(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
286 }
287
ntp_update_offset(long offset)288 static void ntp_update_offset(long offset)
289 {
290 s64 freq_adj;
291 s64 offset64;
292 long secs;
293
294 if (!(time_status & STA_PLL))
295 return;
296
297 if (!(time_status & STA_NANO))
298 offset *= NSEC_PER_USEC;
299
300 /*
301 * Scale the phase adjustment and
302 * clamp to the operating range.
303 */
304 offset = min(offset, MAXPHASE);
305 offset = max(offset, -MAXPHASE);
306
307 /*
308 * Select how the frequency is to be controlled
309 * and in which mode (PLL or FLL).
310 */
311 secs = get_seconds() - time_reftime;
312 if (unlikely(time_status & STA_FREQHOLD))
313 secs = 0;
314
315 time_reftime = get_seconds();
316
317 offset64 = offset;
318 freq_adj = ntp_update_offset_fll(offset64, secs);
319
320 /*
321 * Clamp update interval to reduce PLL gain with low
322 * sampling rate (e.g. intermittent network connection)
323 * to avoid instability.
324 */
325 if (unlikely(secs > 1 << (SHIFT_PLL + 1 + time_constant)))
326 secs = 1 << (SHIFT_PLL + 1 + time_constant);
327
328 freq_adj += (offset64 * secs) <<
329 (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
330
331 freq_adj = min(freq_adj + time_freq, MAXFREQ_SCALED);
332
333 time_freq = max(freq_adj, -MAXFREQ_SCALED);
334
335 time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
336 }
337
338 /**
339 * ntp_clear - Clears the NTP state variables
340 */
ntp_clear(void)341 void ntp_clear(void)
342 {
343 time_adjust = 0; /* stop active adjtime() */
344 time_status |= STA_UNSYNC;
345 time_maxerror = NTP_PHASE_LIMIT;
346 time_esterror = NTP_PHASE_LIMIT;
347
348 ntp_update_frequency();
349
350 tick_length = tick_length_base;
351 time_offset = 0;
352
353 /* Clear PPS state variables */
354 pps_clear();
355 }
356
357
ntp_tick_length(void)358 u64 ntp_tick_length(void)
359 {
360 return tick_length;
361 }
362
363
364 /*
365 * this routine handles the overflow of the microsecond field
366 *
367 * The tricky bits of code to handle the accurate clock support
368 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
369 * They were originally developed for SUN and DEC kernels.
370 * All the kudos should go to Dave for this stuff.
371 *
372 * Also handles leap second processing, and returns leap offset
373 */
second_overflow(unsigned long secs)374 int second_overflow(unsigned long secs)
375 {
376 s64 delta;
377 int leap = 0;
378
379 /*
380 * Leap second processing. If in leap-insert state at the end of the
381 * day, the system clock is set back one second; if in leap-delete
382 * state, the system clock is set ahead one second.
383 */
384 switch (time_state) {
385 case TIME_OK:
386 if (time_status & STA_INS)
387 time_state = TIME_INS;
388 else if (time_status & STA_DEL)
389 time_state = TIME_DEL;
390 break;
391 case TIME_INS:
392 if (!(time_status & STA_INS))
393 time_state = TIME_OK;
394 else if (secs % 86400 == 0) {
395 leap = -1;
396 time_state = TIME_OOP;
397 printk(KERN_NOTICE
398 "Clock: inserting leap second 23:59:60 UTC\n");
399 }
400 break;
401 case TIME_DEL:
402 if (!(time_status & STA_DEL))
403 time_state = TIME_OK;
404 else if ((secs + 1) % 86400 == 0) {
405 leap = 1;
406 time_state = TIME_WAIT;
407 printk(KERN_NOTICE
408 "Clock: deleting leap second 23:59:59 UTC\n");
409 }
410 break;
411 case TIME_OOP:
412 time_state = TIME_WAIT;
413 break;
414
415 case TIME_WAIT:
416 if (!(time_status & (STA_INS | STA_DEL)))
417 time_state = TIME_OK;
418 break;
419 }
420
421
422 /* Bump the maxerror field */
423 time_maxerror += MAXFREQ / NSEC_PER_USEC;
424 if (time_maxerror > NTP_PHASE_LIMIT) {
425 time_maxerror = NTP_PHASE_LIMIT;
426 time_status |= STA_UNSYNC;
427 }
428
429 /* Compute the phase adjustment for the next second */
430 tick_length = tick_length_base;
431
432 delta = ntp_offset_chunk(time_offset);
433 time_offset -= delta;
434 tick_length += delta;
435
436 /* Check PPS signal */
437 pps_dec_valid();
438
439 if (!time_adjust)
440 goto out;
441
442 if (time_adjust > MAX_TICKADJ) {
443 time_adjust -= MAX_TICKADJ;
444 tick_length += MAX_TICKADJ_SCALED;
445 goto out;
446 }
447
448 if (time_adjust < -MAX_TICKADJ) {
449 time_adjust += MAX_TICKADJ;
450 tick_length -= MAX_TICKADJ_SCALED;
451 goto out;
452 }
453
454 tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
455 << NTP_SCALE_SHIFT;
456 time_adjust = 0;
457
458 out:
459 return leap;
460 }
461
462 #if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC)
463 static void sync_cmos_clock(struct work_struct *work);
464
465 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
466
sync_cmos_clock(struct work_struct * work)467 static void sync_cmos_clock(struct work_struct *work)
468 {
469 struct timespec64 now;
470 struct timespec next;
471 int fail = 1;
472
473 /*
474 * If we have an externally synchronized Linux clock, then update
475 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
476 * called as close as possible to 500 ms before the new second starts.
477 * This code is run on a timer. If the clock is set, that timer
478 * may not expire at the correct time. Thus, we adjust...
479 * We want the clock to be within a couple of ticks from the target.
480 */
481 if (!ntp_synced()) {
482 /*
483 * Not synced, exit, do not restart a timer (if one is
484 * running, let it run out).
485 */
486 return;
487 }
488
489 getnstimeofday64(&now);
490 if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec * 5) {
491 struct timespec adjust = timespec64_to_timespec(now);
492
493 fail = -ENODEV;
494 if (persistent_clock_is_local)
495 adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
496 #ifdef CONFIG_GENERIC_CMOS_UPDATE
497 fail = update_persistent_clock(adjust);
498 #endif
499 #ifdef CONFIG_RTC_SYSTOHC
500 if (fail == -ENODEV)
501 fail = rtc_set_ntp_time(adjust);
502 #endif
503 }
504
505 next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
506 if (next.tv_nsec <= 0)
507 next.tv_nsec += NSEC_PER_SEC;
508
509 if (!fail || fail == -ENODEV)
510 next.tv_sec = 659;
511 else
512 next.tv_sec = 0;
513
514 if (next.tv_nsec >= NSEC_PER_SEC) {
515 next.tv_sec++;
516 next.tv_nsec -= NSEC_PER_SEC;
517 }
518 queue_delayed_work(system_power_efficient_wq,
519 &sync_cmos_work, timespec_to_jiffies(&next));
520 }
521
ntp_notify_cmos_timer(void)522 void ntp_notify_cmos_timer(void)
523 {
524 queue_delayed_work(system_power_efficient_wq, &sync_cmos_work, 0);
525 }
526
527 #else
ntp_notify_cmos_timer(void)528 void ntp_notify_cmos_timer(void) { }
529 #endif
530
531
532 /*
533 * Propagate a new txc->status value into the NTP state:
534 */
process_adj_status(struct timex * txc,struct timespec64 * ts)535 static inline void process_adj_status(struct timex *txc, struct timespec64 *ts)
536 {
537 if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
538 time_state = TIME_OK;
539 time_status = STA_UNSYNC;
540 /* restart PPS frequency calibration */
541 pps_reset_freq_interval();
542 }
543
544 /*
545 * If we turn on PLL adjustments then reset the
546 * reference time to current time.
547 */
548 if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
549 time_reftime = get_seconds();
550
551 /* only set allowed bits */
552 time_status &= STA_RONLY;
553 time_status |= txc->status & ~STA_RONLY;
554 }
555
556
process_adjtimex_modes(struct timex * txc,struct timespec64 * ts,s32 * time_tai)557 static inline void process_adjtimex_modes(struct timex *txc,
558 struct timespec64 *ts,
559 s32 *time_tai)
560 {
561 if (txc->modes & ADJ_STATUS)
562 process_adj_status(txc, ts);
563
564 if (txc->modes & ADJ_NANO)
565 time_status |= STA_NANO;
566
567 if (txc->modes & ADJ_MICRO)
568 time_status &= ~STA_NANO;
569
570 if (txc->modes & ADJ_FREQUENCY) {
571 time_freq = txc->freq * PPM_SCALE;
572 time_freq = min(time_freq, MAXFREQ_SCALED);
573 time_freq = max(time_freq, -MAXFREQ_SCALED);
574 /* update pps_freq */
575 pps_set_freq(time_freq);
576 }
577
578 if (txc->modes & ADJ_MAXERROR)
579 time_maxerror = txc->maxerror;
580
581 if (txc->modes & ADJ_ESTERROR)
582 time_esterror = txc->esterror;
583
584 if (txc->modes & ADJ_TIMECONST) {
585 time_constant = txc->constant;
586 if (!(time_status & STA_NANO))
587 time_constant += 4;
588 time_constant = min(time_constant, (long)MAXTC);
589 time_constant = max(time_constant, 0l);
590 }
591
592 if (txc->modes & ADJ_TAI && txc->constant > 0)
593 *time_tai = txc->constant;
594
595 if (txc->modes & ADJ_OFFSET)
596 ntp_update_offset(txc->offset);
597
598 if (txc->modes & ADJ_TICK)
599 tick_usec = txc->tick;
600
601 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
602 ntp_update_frequency();
603 }
604
605
606
607 /**
608 * ntp_validate_timex - Ensures the timex is ok for use in do_adjtimex
609 */
ntp_validate_timex(struct timex * txc)610 int ntp_validate_timex(struct timex *txc)
611 {
612 if (txc->modes & ADJ_ADJTIME) {
613 /* singleshot must not be used with any other mode bits */
614 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
615 return -EINVAL;
616 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
617 !capable(CAP_SYS_TIME))
618 return -EPERM;
619 } else {
620 /* In order to modify anything, you gotta be super-user! */
621 if (txc->modes && !capable(CAP_SYS_TIME))
622 return -EPERM;
623 /*
624 * if the quartz is off by more than 10% then
625 * something is VERY wrong!
626 */
627 if (txc->modes & ADJ_TICK &&
628 (txc->tick < 900000/USER_HZ ||
629 txc->tick > 1100000/USER_HZ))
630 return -EINVAL;
631 }
632
633 if ((txc->modes & ADJ_SETOFFSET) && (!capable(CAP_SYS_TIME)))
634 return -EPERM;
635
636 /*
637 * Check for potential multiplication overflows that can
638 * only happen on 64-bit systems:
639 */
640 if ((txc->modes & ADJ_FREQUENCY) && (BITS_PER_LONG == 64)) {
641 if (LLONG_MIN / PPM_SCALE > txc->freq)
642 return -EINVAL;
643 if (LLONG_MAX / PPM_SCALE < txc->freq)
644 return -EINVAL;
645 }
646
647 return 0;
648 }
649
650
651 /*
652 * adjtimex mainly allows reading (and writing, if superuser) of
653 * kernel time-keeping variables. used by xntpd.
654 */
__do_adjtimex(struct timex * txc,struct timespec64 * ts,s32 * time_tai)655 int __do_adjtimex(struct timex *txc, struct timespec64 *ts, s32 *time_tai)
656 {
657 int result;
658
659 if (txc->modes & ADJ_ADJTIME) {
660 long save_adjust = time_adjust;
661
662 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
663 /* adjtime() is independent from ntp_adjtime() */
664 time_adjust = txc->offset;
665 ntp_update_frequency();
666 }
667 txc->offset = save_adjust;
668 } else {
669
670 /* If there are input parameters, then process them: */
671 if (txc->modes)
672 process_adjtimex_modes(txc, ts, time_tai);
673
674 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
675 NTP_SCALE_SHIFT);
676 if (!(time_status & STA_NANO))
677 txc->offset /= NSEC_PER_USEC;
678 }
679
680 result = time_state; /* mostly `TIME_OK' */
681 /* check for errors */
682 if (is_error_status(time_status))
683 result = TIME_ERROR;
684
685 txc->freq = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
686 PPM_SCALE_INV, NTP_SCALE_SHIFT);
687 txc->maxerror = time_maxerror;
688 txc->esterror = time_esterror;
689 txc->status = time_status;
690 txc->constant = time_constant;
691 txc->precision = 1;
692 txc->tolerance = MAXFREQ_SCALED / PPM_SCALE;
693 txc->tick = tick_usec;
694 txc->tai = *time_tai;
695
696 /* fill PPS status fields */
697 pps_fill_timex(txc);
698
699 txc->time.tv_sec = (time_t)ts->tv_sec;
700 txc->time.tv_usec = ts->tv_nsec;
701 if (!(time_status & STA_NANO))
702 txc->time.tv_usec /= NSEC_PER_USEC;
703
704 return result;
705 }
706
707 #ifdef CONFIG_NTP_PPS
708
709 /* actually struct pps_normtime is good old struct timespec, but it is
710 * semantically different (and it is the reason why it was invented):
711 * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
712 * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
713 struct pps_normtime {
714 __kernel_time_t sec; /* seconds */
715 long nsec; /* nanoseconds */
716 };
717
718 /* normalize the timestamp so that nsec is in the
719 ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
pps_normalize_ts(struct timespec ts)720 static inline struct pps_normtime pps_normalize_ts(struct timespec ts)
721 {
722 struct pps_normtime norm = {
723 .sec = ts.tv_sec,
724 .nsec = ts.tv_nsec
725 };
726
727 if (norm.nsec > (NSEC_PER_SEC >> 1)) {
728 norm.nsec -= NSEC_PER_SEC;
729 norm.sec++;
730 }
731
732 return norm;
733 }
734
735 /* get current phase correction and jitter */
pps_phase_filter_get(long * jitter)736 static inline long pps_phase_filter_get(long *jitter)
737 {
738 *jitter = pps_tf[0] - pps_tf[1];
739 if (*jitter < 0)
740 *jitter = -*jitter;
741
742 /* TODO: test various filters */
743 return pps_tf[0];
744 }
745
746 /* add the sample to the phase filter */
pps_phase_filter_add(long err)747 static inline void pps_phase_filter_add(long err)
748 {
749 pps_tf[2] = pps_tf[1];
750 pps_tf[1] = pps_tf[0];
751 pps_tf[0] = err;
752 }
753
754 /* decrease frequency calibration interval length.
755 * It is halved after four consecutive unstable intervals.
756 */
pps_dec_freq_interval(void)757 static inline void pps_dec_freq_interval(void)
758 {
759 if (--pps_intcnt <= -PPS_INTCOUNT) {
760 pps_intcnt = -PPS_INTCOUNT;
761 if (pps_shift > PPS_INTMIN) {
762 pps_shift--;
763 pps_intcnt = 0;
764 }
765 }
766 }
767
768 /* increase frequency calibration interval length.
769 * It is doubled after four consecutive stable intervals.
770 */
pps_inc_freq_interval(void)771 static inline void pps_inc_freq_interval(void)
772 {
773 if (++pps_intcnt >= PPS_INTCOUNT) {
774 pps_intcnt = PPS_INTCOUNT;
775 if (pps_shift < PPS_INTMAX) {
776 pps_shift++;
777 pps_intcnt = 0;
778 }
779 }
780 }
781
782 /* update clock frequency based on MONOTONIC_RAW clock PPS signal
783 * timestamps
784 *
785 * At the end of the calibration interval the difference between the
786 * first and last MONOTONIC_RAW clock timestamps divided by the length
787 * of the interval becomes the frequency update. If the interval was
788 * too long, the data are discarded.
789 * Returns the difference between old and new frequency values.
790 */
hardpps_update_freq(struct pps_normtime freq_norm)791 static long hardpps_update_freq(struct pps_normtime freq_norm)
792 {
793 long delta, delta_mod;
794 s64 ftemp;
795
796 /* check if the frequency interval was too long */
797 if (freq_norm.sec > (2 << pps_shift)) {
798 time_status |= STA_PPSERROR;
799 pps_errcnt++;
800 pps_dec_freq_interval();
801 printk_deferred(KERN_ERR
802 "hardpps: PPSERROR: interval too long - %ld s\n",
803 freq_norm.sec);
804 return 0;
805 }
806
807 /* here the raw frequency offset and wander (stability) is
808 * calculated. If the wander is less than the wander threshold
809 * the interval is increased; otherwise it is decreased.
810 */
811 ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT,
812 freq_norm.sec);
813 delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT);
814 pps_freq = ftemp;
815 if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) {
816 printk_deferred(KERN_WARNING
817 "hardpps: PPSWANDER: change=%ld\n", delta);
818 time_status |= STA_PPSWANDER;
819 pps_stbcnt++;
820 pps_dec_freq_interval();
821 } else { /* good sample */
822 pps_inc_freq_interval();
823 }
824
825 /* the stability metric is calculated as the average of recent
826 * frequency changes, but is used only for performance
827 * monitoring
828 */
829 delta_mod = delta;
830 if (delta_mod < 0)
831 delta_mod = -delta_mod;
832 pps_stabil += (div_s64(((s64)delta_mod) <<
833 (NTP_SCALE_SHIFT - SHIFT_USEC),
834 NSEC_PER_USEC) - pps_stabil) >> PPS_INTMIN;
835
836 /* if enabled, the system clock frequency is updated */
837 if ((time_status & STA_PPSFREQ) != 0 &&
838 (time_status & STA_FREQHOLD) == 0) {
839 time_freq = pps_freq;
840 ntp_update_frequency();
841 }
842
843 return delta;
844 }
845
846 /* correct REALTIME clock phase error against PPS signal */
hardpps_update_phase(long error)847 static void hardpps_update_phase(long error)
848 {
849 long correction = -error;
850 long jitter;
851
852 /* add the sample to the median filter */
853 pps_phase_filter_add(correction);
854 correction = pps_phase_filter_get(&jitter);
855
856 /* Nominal jitter is due to PPS signal noise. If it exceeds the
857 * threshold, the sample is discarded; otherwise, if so enabled,
858 * the time offset is updated.
859 */
860 if (jitter > (pps_jitter << PPS_POPCORN)) {
861 printk_deferred(KERN_WARNING
862 "hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
863 jitter, (pps_jitter << PPS_POPCORN));
864 time_status |= STA_PPSJITTER;
865 pps_jitcnt++;
866 } else if (time_status & STA_PPSTIME) {
867 /* correct the time using the phase offset */
868 time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT,
869 NTP_INTERVAL_FREQ);
870 /* cancel running adjtime() */
871 time_adjust = 0;
872 }
873 /* update jitter */
874 pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN;
875 }
876
877 /*
878 * __hardpps() - discipline CPU clock oscillator to external PPS signal
879 *
880 * This routine is called at each PPS signal arrival in order to
881 * discipline the CPU clock oscillator to the PPS signal. It takes two
882 * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
883 * is used to correct clock phase error and the latter is used to
884 * correct the frequency.
885 *
886 * This code is based on David Mills's reference nanokernel
887 * implementation. It was mostly rewritten but keeps the same idea.
888 */
__hardpps(const struct timespec * phase_ts,const struct timespec * raw_ts)889 void __hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)
890 {
891 struct pps_normtime pts_norm, freq_norm;
892
893 pts_norm = pps_normalize_ts(*phase_ts);
894
895 /* clear the error bits, they will be set again if needed */
896 time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
897
898 /* indicate signal presence */
899 time_status |= STA_PPSSIGNAL;
900 pps_valid = PPS_VALID;
901
902 /* when called for the first time,
903 * just start the frequency interval */
904 if (unlikely(pps_fbase.tv_sec == 0)) {
905 pps_fbase = *raw_ts;
906 return;
907 }
908
909 /* ok, now we have a base for frequency calculation */
910 freq_norm = pps_normalize_ts(timespec_sub(*raw_ts, pps_fbase));
911
912 /* check that the signal is in the range
913 * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
914 if ((freq_norm.sec == 0) ||
915 (freq_norm.nsec > MAXFREQ * freq_norm.sec) ||
916 (freq_norm.nsec < -MAXFREQ * freq_norm.sec)) {
917 time_status |= STA_PPSJITTER;
918 /* restart the frequency calibration interval */
919 pps_fbase = *raw_ts;
920 printk_deferred(KERN_ERR "hardpps: PPSJITTER: bad pulse\n");
921 return;
922 }
923
924 /* signal is ok */
925
926 /* check if the current frequency interval is finished */
927 if (freq_norm.sec >= (1 << pps_shift)) {
928 pps_calcnt++;
929 /* restart the frequency calibration interval */
930 pps_fbase = *raw_ts;
931 hardpps_update_freq(freq_norm);
932 }
933
934 hardpps_update_phase(pts_norm.nsec);
935
936 }
937 #endif /* CONFIG_NTP_PPS */
938
ntp_tick_adj_setup(char * str)939 static int __init ntp_tick_adj_setup(char *str)
940 {
941 int rc = kstrtol(str, 0, (long *)&ntp_tick_adj);
942
943 if (rc)
944 return rc;
945 ntp_tick_adj <<= NTP_SCALE_SHIFT;
946
947 return 1;
948 }
949
950 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
951
ntp_init(void)952 void __init ntp_init(void)
953 {
954 ntp_clear();
955 }
956