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
19 #include "tick-internal.h"
20
21 /*
22 * NTP timekeeping variables:
23 */
24
25 DEFINE_SPINLOCK(ntp_lock);
26
27
28 /* USER_HZ period (usecs): */
29 unsigned long tick_usec = TICK_USEC;
30
31 /* ACTHZ period (nsecs): */
32 unsigned long tick_nsec;
33
34 static u64 tick_length;
35 static u64 tick_length_base;
36
37 #define MAX_TICKADJ 500LL /* usecs */
38 #define MAX_TICKADJ_SCALED \
39 (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
40
41 /*
42 * phase-lock loop variables
43 */
44
45 /*
46 * clock synchronization status
47 *
48 * (TIME_ERROR prevents overwriting the CMOS clock)
49 */
50 static int time_state = TIME_OK;
51
52 /* clock status bits: */
53 static int time_status = STA_UNSYNC;
54
55 /* TAI offset (secs): */
56 static long time_tai;
57
58 /* time adjustment (nsecs): */
59 static s64 time_offset;
60
61 /* pll time constant: */
62 static long time_constant = 2;
63
64 /* maximum error (usecs): */
65 static long time_maxerror = NTP_PHASE_LIMIT;
66
67 /* estimated error (usecs): */
68 static long time_esterror = NTP_PHASE_LIMIT;
69
70 /* frequency offset (scaled nsecs/secs): */
71 static s64 time_freq;
72
73 /* time at last adjustment (secs): */
74 static long time_reftime;
75
76 static long time_adjust;
77
78 /* constant (boot-param configurable) NTP tick adjustment (upscaled) */
79 static s64 ntp_tick_adj;
80
81 #ifdef CONFIG_NTP_PPS
82
83 /*
84 * The following variables are used when a pulse-per-second (PPS) signal
85 * is available. They establish the engineering parameters of the clock
86 * discipline loop when controlled by the PPS signal.
87 */
88 #define PPS_VALID 10 /* PPS signal watchdog max (s) */
89 #define PPS_POPCORN 4 /* popcorn spike threshold (shift) */
90 #define PPS_INTMIN 2 /* min freq interval (s) (shift) */
91 #define PPS_INTMAX 8 /* max freq interval (s) (shift) */
92 #define PPS_INTCOUNT 4 /* number of consecutive good intervals to
93 increase pps_shift or consecutive bad
94 intervals to decrease it */
95 #define PPS_MAXWANDER 100000 /* max PPS freq wander (ns/s) */
96
97 static int pps_valid; /* signal watchdog counter */
98 static long pps_tf[3]; /* phase median filter */
99 static long pps_jitter; /* current jitter (ns) */
100 static struct timespec pps_fbase; /* beginning of the last freq interval */
101 static int pps_shift; /* current interval duration (s) (shift) */
102 static int pps_intcnt; /* interval counter */
103 static s64 pps_freq; /* frequency offset (scaled ns/s) */
104 static long pps_stabil; /* current stability (scaled ns/s) */
105
106 /*
107 * PPS signal quality monitors
108 */
109 static long pps_calcnt; /* calibration intervals */
110 static long pps_jitcnt; /* jitter limit exceeded */
111 static long pps_stbcnt; /* stability limit exceeded */
112 static long pps_errcnt; /* calibration errors */
113
114
115 /* PPS kernel consumer compensates the whole phase error immediately.
116 * Otherwise, reduce the offset by a fixed factor times the time constant.
117 */
ntp_offset_chunk(s64 offset)118 static inline s64 ntp_offset_chunk(s64 offset)
119 {
120 if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
121 return offset;
122 else
123 return shift_right(offset, SHIFT_PLL + time_constant);
124 }
125
pps_reset_freq_interval(void)126 static inline void pps_reset_freq_interval(void)
127 {
128 /* the PPS calibration interval may end
129 surprisingly early */
130 pps_shift = PPS_INTMIN;
131 pps_intcnt = 0;
132 }
133
134 /**
135 * pps_clear - Clears the PPS state variables
136 *
137 * Must be called while holding a write on the ntp_lock
138 */
pps_clear(void)139 static inline void pps_clear(void)
140 {
141 pps_reset_freq_interval();
142 pps_tf[0] = 0;
143 pps_tf[1] = 0;
144 pps_tf[2] = 0;
145 pps_fbase.tv_sec = pps_fbase.tv_nsec = 0;
146 pps_freq = 0;
147 }
148
149 /* Decrease pps_valid to indicate that another second has passed since
150 * the last PPS signal. When it reaches 0, indicate that PPS signal is
151 * missing.
152 *
153 * Must be called while holding a write on the ntp_lock
154 */
pps_dec_valid(void)155 static inline void pps_dec_valid(void)
156 {
157 if (pps_valid > 0)
158 pps_valid--;
159 else {
160 time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
161 STA_PPSWANDER | STA_PPSERROR);
162 pps_clear();
163 }
164 }
165
pps_set_freq(s64 freq)166 static inline void pps_set_freq(s64 freq)
167 {
168 pps_freq = freq;
169 }
170
is_error_status(int status)171 static inline int is_error_status(int status)
172 {
173 return (time_status & (STA_UNSYNC|STA_CLOCKERR))
174 /* PPS signal lost when either PPS time or
175 * PPS frequency synchronization requested
176 */
177 || ((time_status & (STA_PPSFREQ|STA_PPSTIME))
178 && !(time_status & STA_PPSSIGNAL))
179 /* PPS jitter exceeded when
180 * PPS time synchronization requested */
181 || ((time_status & (STA_PPSTIME|STA_PPSJITTER))
182 == (STA_PPSTIME|STA_PPSJITTER))
183 /* PPS wander exceeded or calibration error when
184 * PPS frequency synchronization requested
185 */
186 || ((time_status & STA_PPSFREQ)
187 && (time_status & (STA_PPSWANDER|STA_PPSERROR)));
188 }
189
pps_fill_timex(struct timex * txc)190 static inline void pps_fill_timex(struct timex *txc)
191 {
192 txc->ppsfreq = shift_right((pps_freq >> PPM_SCALE_INV_SHIFT) *
193 PPM_SCALE_INV, NTP_SCALE_SHIFT);
194 txc->jitter = pps_jitter;
195 if (!(time_status & STA_NANO))
196 txc->jitter /= NSEC_PER_USEC;
197 txc->shift = pps_shift;
198 txc->stabil = pps_stabil;
199 txc->jitcnt = pps_jitcnt;
200 txc->calcnt = pps_calcnt;
201 txc->errcnt = pps_errcnt;
202 txc->stbcnt = pps_stbcnt;
203 }
204
205 #else /* !CONFIG_NTP_PPS */
206
ntp_offset_chunk(s64 offset)207 static inline s64 ntp_offset_chunk(s64 offset)
208 {
209 return shift_right(offset, SHIFT_PLL + time_constant);
210 }
211
pps_reset_freq_interval(void)212 static inline void pps_reset_freq_interval(void) {}
pps_clear(void)213 static inline void pps_clear(void) {}
pps_dec_valid(void)214 static inline void pps_dec_valid(void) {}
pps_set_freq(s64 freq)215 static inline void pps_set_freq(s64 freq) {}
216
is_error_status(int status)217 static inline int is_error_status(int status)
218 {
219 return status & (STA_UNSYNC|STA_CLOCKERR);
220 }
221
pps_fill_timex(struct timex * txc)222 static inline void pps_fill_timex(struct timex *txc)
223 {
224 /* PPS is not implemented, so these are zero */
225 txc->ppsfreq = 0;
226 txc->jitter = 0;
227 txc->shift = 0;
228 txc->stabil = 0;
229 txc->jitcnt = 0;
230 txc->calcnt = 0;
231 txc->errcnt = 0;
232 txc->stbcnt = 0;
233 }
234
235 #endif /* CONFIG_NTP_PPS */
236
237
238 /**
239 * ntp_synced - Returns 1 if the NTP status is not UNSYNC
240 *
241 */
ntp_synced(void)242 static inline int ntp_synced(void)
243 {
244 return !(time_status & STA_UNSYNC);
245 }
246
247
248 /*
249 * NTP methods:
250 */
251
252 /*
253 * Update (tick_length, tick_length_base, tick_nsec), based
254 * on (tick_usec, ntp_tick_adj, time_freq):
255 */
ntp_update_frequency(void)256 static void ntp_update_frequency(void)
257 {
258 u64 second_length;
259 u64 new_base;
260
261 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
262 << NTP_SCALE_SHIFT;
263
264 second_length += ntp_tick_adj;
265 second_length += time_freq;
266
267 tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
268 new_base = div_u64(second_length, NTP_INTERVAL_FREQ);
269
270 /*
271 * Don't wait for the next second_overflow, apply
272 * the change to the tick length immediately:
273 */
274 tick_length += new_base - tick_length_base;
275 tick_length_base = new_base;
276 }
277
ntp_update_offset_fll(s64 offset64,long secs)278 static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
279 {
280 time_status &= ~STA_MODE;
281
282 if (secs < MINSEC)
283 return 0;
284
285 if (!(time_status & STA_FLL) && (secs <= MAXSEC))
286 return 0;
287
288 time_status |= STA_MODE;
289
290 return div64_long(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
291 }
292
ntp_update_offset(long offset)293 static void ntp_update_offset(long offset)
294 {
295 s64 freq_adj;
296 s64 offset64;
297 long secs;
298
299 if (!(time_status & STA_PLL))
300 return;
301
302 if (!(time_status & STA_NANO))
303 offset *= NSEC_PER_USEC;
304
305 /*
306 * Scale the phase adjustment and
307 * clamp to the operating range.
308 */
309 offset = min(offset, MAXPHASE);
310 offset = max(offset, -MAXPHASE);
311
312 /*
313 * Select how the frequency is to be controlled
314 * and in which mode (PLL or FLL).
315 */
316 secs = get_seconds() - time_reftime;
317 if (unlikely(time_status & STA_FREQHOLD))
318 secs = 0;
319
320 time_reftime = get_seconds();
321
322 offset64 = offset;
323 freq_adj = ntp_update_offset_fll(offset64, secs);
324
325 /*
326 * Clamp update interval to reduce PLL gain with low
327 * sampling rate (e.g. intermittent network connection)
328 * to avoid instability.
329 */
330 if (unlikely(secs > 1 << (SHIFT_PLL + 1 + time_constant)))
331 secs = 1 << (SHIFT_PLL + 1 + time_constant);
332
333 freq_adj += (offset64 * secs) <<
334 (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
335
336 freq_adj = min(freq_adj + time_freq, MAXFREQ_SCALED);
337
338 time_freq = max(freq_adj, -MAXFREQ_SCALED);
339
340 time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
341 }
342
343 /**
344 * ntp_clear - Clears the NTP state variables
345 */
ntp_clear(void)346 void ntp_clear(void)
347 {
348 unsigned long flags;
349
350 spin_lock_irqsave(&ntp_lock, flags);
351
352 time_adjust = 0; /* stop active adjtime() */
353 time_status |= STA_UNSYNC;
354 time_maxerror = NTP_PHASE_LIMIT;
355 time_esterror = NTP_PHASE_LIMIT;
356
357 ntp_update_frequency();
358
359 tick_length = tick_length_base;
360 time_offset = 0;
361
362 /* Clear PPS state variables */
363 pps_clear();
364 spin_unlock_irqrestore(&ntp_lock, flags);
365
366 }
367
368
ntp_tick_length(void)369 u64 ntp_tick_length(void)
370 {
371 unsigned long flags;
372 s64 ret;
373
374 spin_lock_irqsave(&ntp_lock, flags);
375 ret = tick_length;
376 spin_unlock_irqrestore(&ntp_lock, flags);
377 return ret;
378 }
379
380
381 /*
382 * this routine handles the overflow of the microsecond field
383 *
384 * The tricky bits of code to handle the accurate clock support
385 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
386 * They were originally developed for SUN and DEC kernels.
387 * All the kudos should go to Dave for this stuff.
388 *
389 * Also handles leap second processing, and returns leap offset
390 */
second_overflow(unsigned long secs)391 int second_overflow(unsigned long secs)
392 {
393 s64 delta;
394 int leap = 0;
395 unsigned long flags;
396
397 spin_lock_irqsave(&ntp_lock, flags);
398
399 /*
400 * Leap second processing. If in leap-insert state at the end of the
401 * day, the system clock is set back one second; if in leap-delete
402 * state, the system clock is set ahead one second.
403 */
404 switch (time_state) {
405 case TIME_OK:
406 if (time_status & STA_INS)
407 time_state = TIME_INS;
408 else if (time_status & STA_DEL)
409 time_state = TIME_DEL;
410 break;
411 case TIME_INS:
412 if (!(time_status & STA_INS))
413 time_state = TIME_OK;
414 else if (secs % 86400 == 0) {
415 leap = -1;
416 time_state = TIME_OOP;
417 time_tai++;
418 printk(KERN_NOTICE
419 "Clock: inserting leap second 23:59:60 UTC\n");
420 }
421 break;
422 case TIME_DEL:
423 if (!(time_status & STA_DEL))
424 time_state = TIME_OK;
425 else if ((secs + 1) % 86400 == 0) {
426 leap = 1;
427 time_tai--;
428 time_state = TIME_WAIT;
429 printk(KERN_NOTICE
430 "Clock: deleting leap second 23:59:59 UTC\n");
431 }
432 break;
433 case TIME_OOP:
434 time_state = TIME_WAIT;
435 break;
436
437 case TIME_WAIT:
438 if (!(time_status & (STA_INS | STA_DEL)))
439 time_state = TIME_OK;
440 break;
441 }
442
443
444 /* Bump the maxerror field */
445 time_maxerror += MAXFREQ / NSEC_PER_USEC;
446 if (time_maxerror > NTP_PHASE_LIMIT) {
447 time_maxerror = NTP_PHASE_LIMIT;
448 time_status |= STA_UNSYNC;
449 }
450
451 /* Compute the phase adjustment for the next second */
452 tick_length = tick_length_base;
453
454 delta = ntp_offset_chunk(time_offset);
455 time_offset -= delta;
456 tick_length += delta;
457
458 /* Check PPS signal */
459 pps_dec_valid();
460
461 if (!time_adjust)
462 goto out;
463
464 if (time_adjust > MAX_TICKADJ) {
465 time_adjust -= MAX_TICKADJ;
466 tick_length += MAX_TICKADJ_SCALED;
467 goto out;
468 }
469
470 if (time_adjust < -MAX_TICKADJ) {
471 time_adjust += MAX_TICKADJ;
472 tick_length -= MAX_TICKADJ_SCALED;
473 goto out;
474 }
475
476 tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
477 << NTP_SCALE_SHIFT;
478 time_adjust = 0;
479
480
481
482 out:
483 spin_unlock_irqrestore(&ntp_lock, flags);
484
485 return leap;
486 }
487
488 #ifdef CONFIG_GENERIC_CMOS_UPDATE
489
490 static void sync_cmos_clock(struct work_struct *work);
491
492 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
493
sync_cmos_clock(struct work_struct * work)494 static void sync_cmos_clock(struct work_struct *work)
495 {
496 struct timespec now, next;
497 int fail = 1;
498
499 /*
500 * If we have an externally synchronized Linux clock, then update
501 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
502 * called as close as possible to 500 ms before the new second starts.
503 * This code is run on a timer. If the clock is set, that timer
504 * may not expire at the correct time. Thus, we adjust...
505 */
506 if (!ntp_synced()) {
507 /*
508 * Not synced, exit, do not restart a timer (if one is
509 * running, let it run out).
510 */
511 return;
512 }
513
514 getnstimeofday(&now);
515 if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
516 fail = update_persistent_clock(now);
517
518 next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
519 if (next.tv_nsec <= 0)
520 next.tv_nsec += NSEC_PER_SEC;
521
522 if (!fail)
523 next.tv_sec = 659;
524 else
525 next.tv_sec = 0;
526
527 if (next.tv_nsec >= NSEC_PER_SEC) {
528 next.tv_sec++;
529 next.tv_nsec -= NSEC_PER_SEC;
530 }
531 schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
532 }
533
notify_cmos_timer(void)534 static void notify_cmos_timer(void)
535 {
536 schedule_delayed_work(&sync_cmos_work, 0);
537 }
538
539 #else
notify_cmos_timer(void)540 static inline void notify_cmos_timer(void) { }
541 #endif
542
543
544 /*
545 * Propagate a new txc->status value into the NTP state:
546 */
process_adj_status(struct timex * txc,struct timespec * ts)547 static inline void process_adj_status(struct timex *txc, struct timespec *ts)
548 {
549 if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
550 time_state = TIME_OK;
551 time_status = STA_UNSYNC;
552 /* restart PPS frequency calibration */
553 pps_reset_freq_interval();
554 }
555
556 /*
557 * If we turn on PLL adjustments then reset the
558 * reference time to current time.
559 */
560 if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
561 time_reftime = get_seconds();
562
563 /* only set allowed bits */
564 time_status &= STA_RONLY;
565 time_status |= txc->status & ~STA_RONLY;
566
567 }
568 /*
569 * Called with the xtime lock held, so we can access and modify
570 * all the global NTP state:
571 */
process_adjtimex_modes(struct timex * txc,struct timespec * ts)572 static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts)
573 {
574 if (txc->modes & ADJ_STATUS)
575 process_adj_status(txc, ts);
576
577 if (txc->modes & ADJ_NANO)
578 time_status |= STA_NANO;
579
580 if (txc->modes & ADJ_MICRO)
581 time_status &= ~STA_NANO;
582
583 if (txc->modes & ADJ_FREQUENCY) {
584 time_freq = txc->freq * PPM_SCALE;
585 time_freq = min(time_freq, MAXFREQ_SCALED);
586 time_freq = max(time_freq, -MAXFREQ_SCALED);
587 /* update pps_freq */
588 pps_set_freq(time_freq);
589 }
590
591 if (txc->modes & ADJ_MAXERROR)
592 time_maxerror = txc->maxerror;
593
594 if (txc->modes & ADJ_ESTERROR)
595 time_esterror = txc->esterror;
596
597 if (txc->modes & ADJ_TIMECONST) {
598 time_constant = txc->constant;
599 if (!(time_status & STA_NANO))
600 time_constant += 4;
601 time_constant = min(time_constant, (long)MAXTC);
602 time_constant = max(time_constant, 0l);
603 }
604
605 if (txc->modes & ADJ_TAI && txc->constant > 0)
606 time_tai = txc->constant;
607
608 if (txc->modes & ADJ_OFFSET)
609 ntp_update_offset(txc->offset);
610
611 if (txc->modes & ADJ_TICK)
612 tick_usec = txc->tick;
613
614 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
615 ntp_update_frequency();
616 }
617
618 /*
619 * adjtimex mainly allows reading (and writing, if superuser) of
620 * kernel time-keeping variables. used by xntpd.
621 */
do_adjtimex(struct timex * txc)622 int do_adjtimex(struct timex *txc)
623 {
624 struct timespec ts;
625 int result;
626
627 /* Validate the data before disabling interrupts */
628 if (txc->modes & ADJ_ADJTIME) {
629 /* singleshot must not be used with any other mode bits */
630 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
631 return -EINVAL;
632 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
633 !capable(CAP_SYS_TIME))
634 return -EPERM;
635 } else {
636 /* In order to modify anything, you gotta be super-user! */
637 if (txc->modes && !capable(CAP_SYS_TIME))
638 return -EPERM;
639
640 /*
641 * if the quartz is off by more than 10% then
642 * something is VERY wrong!
643 */
644 if (txc->modes & ADJ_TICK &&
645 (txc->tick < 900000/USER_HZ ||
646 txc->tick > 1100000/USER_HZ))
647 return -EINVAL;
648 }
649
650 if (txc->modes & ADJ_SETOFFSET) {
651 struct timespec delta;
652 delta.tv_sec = txc->time.tv_sec;
653 delta.tv_nsec = txc->time.tv_usec;
654 if (!capable(CAP_SYS_TIME))
655 return -EPERM;
656 if (!(txc->modes & ADJ_NANO))
657 delta.tv_nsec *= 1000;
658 result = timekeeping_inject_offset(&delta);
659 if (result)
660 return result;
661 }
662
663 getnstimeofday(&ts);
664
665 spin_lock_irq(&ntp_lock);
666
667 if (txc->modes & ADJ_ADJTIME) {
668 long save_adjust = time_adjust;
669
670 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
671 /* adjtime() is independent from ntp_adjtime() */
672 time_adjust = txc->offset;
673 ntp_update_frequency();
674 }
675 txc->offset = save_adjust;
676 } else {
677
678 /* If there are input parameters, then process them: */
679 if (txc->modes)
680 process_adjtimex_modes(txc, &ts);
681
682 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
683 NTP_SCALE_SHIFT);
684 if (!(time_status & STA_NANO))
685 txc->offset /= NSEC_PER_USEC;
686 }
687
688 result = time_state; /* mostly `TIME_OK' */
689 /* check for errors */
690 if (is_error_status(time_status))
691 result = TIME_ERROR;
692
693 txc->freq = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
694 PPM_SCALE_INV, NTP_SCALE_SHIFT);
695 txc->maxerror = time_maxerror;
696 txc->esterror = time_esterror;
697 txc->status = time_status;
698 txc->constant = time_constant;
699 txc->precision = 1;
700 txc->tolerance = MAXFREQ_SCALED / PPM_SCALE;
701 txc->tick = tick_usec;
702 txc->tai = time_tai;
703
704 /* fill PPS status fields */
705 pps_fill_timex(txc);
706
707 spin_unlock_irq(&ntp_lock);
708
709 txc->time.tv_sec = ts.tv_sec;
710 txc->time.tv_usec = ts.tv_nsec;
711 if (!(time_status & STA_NANO))
712 txc->time.tv_usec /= NSEC_PER_USEC;
713
714 notify_cmos_timer();
715
716 return result;
717 }
718
719 #ifdef CONFIG_NTP_PPS
720
721 /* actually struct pps_normtime is good old struct timespec, but it is
722 * semantically different (and it is the reason why it was invented):
723 * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
724 * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
725 struct pps_normtime {
726 __kernel_time_t sec; /* seconds */
727 long nsec; /* nanoseconds */
728 };
729
730 /* normalize the timestamp so that nsec is in the
731 ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
pps_normalize_ts(struct timespec ts)732 static inline struct pps_normtime pps_normalize_ts(struct timespec ts)
733 {
734 struct pps_normtime norm = {
735 .sec = ts.tv_sec,
736 .nsec = ts.tv_nsec
737 };
738
739 if (norm.nsec > (NSEC_PER_SEC >> 1)) {
740 norm.nsec -= NSEC_PER_SEC;
741 norm.sec++;
742 }
743
744 return norm;
745 }
746
747 /* get current phase correction and jitter */
pps_phase_filter_get(long * jitter)748 static inline long pps_phase_filter_get(long *jitter)
749 {
750 *jitter = pps_tf[0] - pps_tf[1];
751 if (*jitter < 0)
752 *jitter = -*jitter;
753
754 /* TODO: test various filters */
755 return pps_tf[0];
756 }
757
758 /* add the sample to the phase filter */
pps_phase_filter_add(long err)759 static inline void pps_phase_filter_add(long err)
760 {
761 pps_tf[2] = pps_tf[1];
762 pps_tf[1] = pps_tf[0];
763 pps_tf[0] = err;
764 }
765
766 /* decrease frequency calibration interval length.
767 * It is halved after four consecutive unstable intervals.
768 */
pps_dec_freq_interval(void)769 static inline void pps_dec_freq_interval(void)
770 {
771 if (--pps_intcnt <= -PPS_INTCOUNT) {
772 pps_intcnt = -PPS_INTCOUNT;
773 if (pps_shift > PPS_INTMIN) {
774 pps_shift--;
775 pps_intcnt = 0;
776 }
777 }
778 }
779
780 /* increase frequency calibration interval length.
781 * It is doubled after four consecutive stable intervals.
782 */
pps_inc_freq_interval(void)783 static inline void pps_inc_freq_interval(void)
784 {
785 if (++pps_intcnt >= PPS_INTCOUNT) {
786 pps_intcnt = PPS_INTCOUNT;
787 if (pps_shift < PPS_INTMAX) {
788 pps_shift++;
789 pps_intcnt = 0;
790 }
791 }
792 }
793
794 /* update clock frequency based on MONOTONIC_RAW clock PPS signal
795 * timestamps
796 *
797 * At the end of the calibration interval the difference between the
798 * first and last MONOTONIC_RAW clock timestamps divided by the length
799 * of the interval becomes the frequency update. If the interval was
800 * too long, the data are discarded.
801 * Returns the difference between old and new frequency values.
802 */
hardpps_update_freq(struct pps_normtime freq_norm)803 static long hardpps_update_freq(struct pps_normtime freq_norm)
804 {
805 long delta, delta_mod;
806 s64 ftemp;
807
808 /* check if the frequency interval was too long */
809 if (freq_norm.sec > (2 << pps_shift)) {
810 time_status |= STA_PPSERROR;
811 pps_errcnt++;
812 pps_dec_freq_interval();
813 pr_err("hardpps: PPSERROR: interval too long - %ld s\n",
814 freq_norm.sec);
815 return 0;
816 }
817
818 /* here the raw frequency offset and wander (stability) is
819 * calculated. If the wander is less than the wander threshold
820 * the interval is increased; otherwise it is decreased.
821 */
822 ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT,
823 freq_norm.sec);
824 delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT);
825 pps_freq = ftemp;
826 if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) {
827 pr_warning("hardpps: PPSWANDER: change=%ld\n", delta);
828 time_status |= STA_PPSWANDER;
829 pps_stbcnt++;
830 pps_dec_freq_interval();
831 } else { /* good sample */
832 pps_inc_freq_interval();
833 }
834
835 /* the stability metric is calculated as the average of recent
836 * frequency changes, but is used only for performance
837 * monitoring
838 */
839 delta_mod = delta;
840 if (delta_mod < 0)
841 delta_mod = -delta_mod;
842 pps_stabil += (div_s64(((s64)delta_mod) <<
843 (NTP_SCALE_SHIFT - SHIFT_USEC),
844 NSEC_PER_USEC) - pps_stabil) >> PPS_INTMIN;
845
846 /* if enabled, the system clock frequency is updated */
847 if ((time_status & STA_PPSFREQ) != 0 &&
848 (time_status & STA_FREQHOLD) == 0) {
849 time_freq = pps_freq;
850 ntp_update_frequency();
851 }
852
853 return delta;
854 }
855
856 /* correct REALTIME clock phase error against PPS signal */
hardpps_update_phase(long error)857 static void hardpps_update_phase(long error)
858 {
859 long correction = -error;
860 long jitter;
861
862 /* add the sample to the median filter */
863 pps_phase_filter_add(correction);
864 correction = pps_phase_filter_get(&jitter);
865
866 /* Nominal jitter is due to PPS signal noise. If it exceeds the
867 * threshold, the sample is discarded; otherwise, if so enabled,
868 * the time offset is updated.
869 */
870 if (jitter > (pps_jitter << PPS_POPCORN)) {
871 pr_warning("hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
872 jitter, (pps_jitter << PPS_POPCORN));
873 time_status |= STA_PPSJITTER;
874 pps_jitcnt++;
875 } else if (time_status & STA_PPSTIME) {
876 /* correct the time using the phase offset */
877 time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT,
878 NTP_INTERVAL_FREQ);
879 /* cancel running adjtime() */
880 time_adjust = 0;
881 }
882 /* update jitter */
883 pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN;
884 }
885
886 /*
887 * hardpps() - discipline CPU clock oscillator to external PPS signal
888 *
889 * This routine is called at each PPS signal arrival in order to
890 * discipline the CPU clock oscillator to the PPS signal. It takes two
891 * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
892 * is used to correct clock phase error and the latter is used to
893 * correct the frequency.
894 *
895 * This code is based on David Mills's reference nanokernel
896 * implementation. It was mostly rewritten but keeps the same idea.
897 */
hardpps(const struct timespec * phase_ts,const struct timespec * raw_ts)898 void hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)
899 {
900 struct pps_normtime pts_norm, freq_norm;
901 unsigned long flags;
902
903 pts_norm = pps_normalize_ts(*phase_ts);
904
905 spin_lock_irqsave(&ntp_lock, flags);
906
907 /* clear the error bits, they will be set again if needed */
908 time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
909
910 /* indicate signal presence */
911 time_status |= STA_PPSSIGNAL;
912 pps_valid = PPS_VALID;
913
914 /* when called for the first time,
915 * just start the frequency interval */
916 if (unlikely(pps_fbase.tv_sec == 0)) {
917 pps_fbase = *raw_ts;
918 spin_unlock_irqrestore(&ntp_lock, flags);
919 return;
920 }
921
922 /* ok, now we have a base for frequency calculation */
923 freq_norm = pps_normalize_ts(timespec_sub(*raw_ts, pps_fbase));
924
925 /* check that the signal is in the range
926 * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
927 if ((freq_norm.sec == 0) ||
928 (freq_norm.nsec > MAXFREQ * freq_norm.sec) ||
929 (freq_norm.nsec < -MAXFREQ * freq_norm.sec)) {
930 time_status |= STA_PPSJITTER;
931 /* restart the frequency calibration interval */
932 pps_fbase = *raw_ts;
933 spin_unlock_irqrestore(&ntp_lock, flags);
934 pr_err("hardpps: PPSJITTER: bad pulse\n");
935 return;
936 }
937
938 /* signal is ok */
939
940 /* check if the current frequency interval is finished */
941 if (freq_norm.sec >= (1 << pps_shift)) {
942 pps_calcnt++;
943 /* restart the frequency calibration interval */
944 pps_fbase = *raw_ts;
945 hardpps_update_freq(freq_norm);
946 }
947
948 hardpps_update_phase(pts_norm.nsec);
949
950 spin_unlock_irqrestore(&ntp_lock, flags);
951 }
952 EXPORT_SYMBOL(hardpps);
953
954 #endif /* CONFIG_NTP_PPS */
955
ntp_tick_adj_setup(char * str)956 static int __init ntp_tick_adj_setup(char *str)
957 {
958 ntp_tick_adj = simple_strtol(str, NULL, 0);
959 ntp_tick_adj <<= NTP_SCALE_SHIFT;
960
961 return 1;
962 }
963
964 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
965
ntp_init(void)966 void __init ntp_init(void)
967 {
968 ntp_clear();
969 }
970