Version:  2.0.40 2.2.26 2.4.37 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18

Linux/kernel/time/ntp.c

  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  */
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 
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  */
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  */
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 
161 static inline void pps_set_freq(s64 freq)
162 {
163         pps_freq = freq;
164 }
165 
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 
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 
202 static inline s64 ntp_offset_chunk(s64 offset)
203 {
204         return shift_right(offset, SHIFT_PLL + time_constant);
205 }
206 
207 static inline void pps_reset_freq_interval(void) {}
208 static inline void pps_clear(void) {}
209 static inline void pps_dec_valid(void) {}
210 static inline void pps_set_freq(s64 freq) {}
211 
212 static inline int is_error_status(int status)
213 {
214         return status & (STA_UNSYNC|STA_CLOCKERR);
215 }
216 
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  */
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  */
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 
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 
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  */
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 
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  */
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 
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 
522 void ntp_notify_cmos_timer(void)
523 {
524         queue_delayed_work(system_power_efficient_wq, &sync_cmos_work, 0);
525 }
526 
527 #else
528 void ntp_notify_cmos_timer(void) { }
529 #endif
530 
531 
532 /*
533  * Propagate a new txc->status value into the NTP state:
534  */
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 
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  */
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         return 0;
637 }
638 
639 
640 /*
641  * adjtimex mainly allows reading (and writing, if superuser) of
642  * kernel time-keeping variables. used by xntpd.
643  */
644 int __do_adjtimex(struct timex *txc, struct timespec64 *ts, s32 *time_tai)
645 {
646         int result;
647 
648         if (txc->modes & ADJ_ADJTIME) {
649                 long save_adjust = time_adjust;
650 
651                 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
652                         /* adjtime() is independent from ntp_adjtime() */
653                         time_adjust = txc->offset;
654                         ntp_update_frequency();
655                 }
656                 txc->offset = save_adjust;
657         } else {
658 
659                 /* If there are input parameters, then process them: */
660                 if (txc->modes)
661                         process_adjtimex_modes(txc, ts, time_tai);
662 
663                 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
664                                   NTP_SCALE_SHIFT);
665                 if (!(time_status & STA_NANO))
666                         txc->offset /= NSEC_PER_USEC;
667         }
668 
669         result = time_state;    /* mostly `TIME_OK' */
670         /* check for errors */
671         if (is_error_status(time_status))
672                 result = TIME_ERROR;
673 
674         txc->freq          = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
675                                          PPM_SCALE_INV, NTP_SCALE_SHIFT);
676         txc->maxerror      = time_maxerror;
677         txc->esterror      = time_esterror;
678         txc->status        = time_status;
679         txc->constant      = time_constant;
680         txc->precision     = 1;
681         txc->tolerance     = MAXFREQ_SCALED / PPM_SCALE;
682         txc->tick          = tick_usec;
683         txc->tai           = *time_tai;
684 
685         /* fill PPS status fields */
686         pps_fill_timex(txc);
687 
688         txc->time.tv_sec = (time_t)ts->tv_sec;
689         txc->time.tv_usec = ts->tv_nsec;
690         if (!(time_status & STA_NANO))
691                 txc->time.tv_usec /= NSEC_PER_USEC;
692 
693         return result;
694 }
695 
696 #ifdef  CONFIG_NTP_PPS
697 
698 /* actually struct pps_normtime is good old struct timespec, but it is
699  * semantically different (and it is the reason why it was invented):
700  * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
701  * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
702 struct pps_normtime {
703         __kernel_time_t sec;    /* seconds */
704         long            nsec;   /* nanoseconds */
705 };
706 
707 /* normalize the timestamp so that nsec is in the
708    ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
709 static inline struct pps_normtime pps_normalize_ts(struct timespec ts)
710 {
711         struct pps_normtime norm = {
712                 .sec = ts.tv_sec,
713                 .nsec = ts.tv_nsec
714         };
715 
716         if (norm.nsec > (NSEC_PER_SEC >> 1)) {
717                 norm.nsec -= NSEC_PER_SEC;
718                 norm.sec++;
719         }
720 
721         return norm;
722 }
723 
724 /* get current phase correction and jitter */
725 static inline long pps_phase_filter_get(long *jitter)
726 {
727         *jitter = pps_tf[0] - pps_tf[1];
728         if (*jitter < 0)
729                 *jitter = -*jitter;
730 
731         /* TODO: test various filters */
732         return pps_tf[0];
733 }
734 
735 /* add the sample to the phase filter */
736 static inline void pps_phase_filter_add(long err)
737 {
738         pps_tf[2] = pps_tf[1];
739         pps_tf[1] = pps_tf[0];
740         pps_tf[0] = err;
741 }
742 
743 /* decrease frequency calibration interval length.
744  * It is halved after four consecutive unstable intervals.
745  */
746 static inline void pps_dec_freq_interval(void)
747 {
748         if (--pps_intcnt <= -PPS_INTCOUNT) {
749                 pps_intcnt = -PPS_INTCOUNT;
750                 if (pps_shift > PPS_INTMIN) {
751                         pps_shift--;
752                         pps_intcnt = 0;
753                 }
754         }
755 }
756 
757 /* increase frequency calibration interval length.
758  * It is doubled after four consecutive stable intervals.
759  */
760 static inline void pps_inc_freq_interval(void)
761 {
762         if (++pps_intcnt >= PPS_INTCOUNT) {
763                 pps_intcnt = PPS_INTCOUNT;
764                 if (pps_shift < PPS_INTMAX) {
765                         pps_shift++;
766                         pps_intcnt = 0;
767                 }
768         }
769 }
770 
771 /* update clock frequency based on MONOTONIC_RAW clock PPS signal
772  * timestamps
773  *
774  * At the end of the calibration interval the difference between the
775  * first and last MONOTONIC_RAW clock timestamps divided by the length
776  * of the interval becomes the frequency update. If the interval was
777  * too long, the data are discarded.
778  * Returns the difference between old and new frequency values.
779  */
780 static long hardpps_update_freq(struct pps_normtime freq_norm)
781 {
782         long delta, delta_mod;
783         s64 ftemp;
784 
785         /* check if the frequency interval was too long */
786         if (freq_norm.sec > (2 << pps_shift)) {
787                 time_status |= STA_PPSERROR;
788                 pps_errcnt++;
789                 pps_dec_freq_interval();
790                 printk_deferred(KERN_ERR
791                         "hardpps: PPSERROR: interval too long - %ld s\n",
792                         freq_norm.sec);
793                 return 0;
794         }
795 
796         /* here the raw frequency offset and wander (stability) is
797          * calculated. If the wander is less than the wander threshold
798          * the interval is increased; otherwise it is decreased.
799          */
800         ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT,
801                         freq_norm.sec);
802         delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT);
803         pps_freq = ftemp;
804         if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) {
805                 printk_deferred(KERN_WARNING
806                                 "hardpps: PPSWANDER: change=%ld\n", delta);
807                 time_status |= STA_PPSWANDER;
808                 pps_stbcnt++;
809                 pps_dec_freq_interval();
810         } else {        /* good sample */
811                 pps_inc_freq_interval();
812         }
813 
814         /* the stability metric is calculated as the average of recent
815          * frequency changes, but is used only for performance
816          * monitoring
817          */
818         delta_mod = delta;
819         if (delta_mod < 0)
820                 delta_mod = -delta_mod;
821         pps_stabil += (div_s64(((s64)delta_mod) <<
822                                 (NTP_SCALE_SHIFT - SHIFT_USEC),
823                                 NSEC_PER_USEC) - pps_stabil) >> PPS_INTMIN;
824 
825         /* if enabled, the system clock frequency is updated */
826         if ((time_status & STA_PPSFREQ) != 0 &&
827             (time_status & STA_FREQHOLD) == 0) {
828                 time_freq = pps_freq;
829                 ntp_update_frequency();
830         }
831 
832         return delta;
833 }
834 
835 /* correct REALTIME clock phase error against PPS signal */
836 static void hardpps_update_phase(long error)
837 {
838         long correction = -error;
839         long jitter;
840 
841         /* add the sample to the median filter */
842         pps_phase_filter_add(correction);
843         correction = pps_phase_filter_get(&jitter);
844 
845         /* Nominal jitter is due to PPS signal noise. If it exceeds the
846          * threshold, the sample is discarded; otherwise, if so enabled,
847          * the time offset is updated.
848          */
849         if (jitter > (pps_jitter << PPS_POPCORN)) {
850                 printk_deferred(KERN_WARNING
851                                 "hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
852                                 jitter, (pps_jitter << PPS_POPCORN));
853                 time_status |= STA_PPSJITTER;
854                 pps_jitcnt++;
855         } else if (time_status & STA_PPSTIME) {
856                 /* correct the time using the phase offset */
857                 time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT,
858                                 NTP_INTERVAL_FREQ);
859                 /* cancel running adjtime() */
860                 time_adjust = 0;
861         }
862         /* update jitter */
863         pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN;
864 }
865 
866 /*
867  * __hardpps() - discipline CPU clock oscillator to external PPS signal
868  *
869  * This routine is called at each PPS signal arrival in order to
870  * discipline the CPU clock oscillator to the PPS signal. It takes two
871  * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
872  * is used to correct clock phase error and the latter is used to
873  * correct the frequency.
874  *
875  * This code is based on David Mills's reference nanokernel
876  * implementation. It was mostly rewritten but keeps the same idea.
877  */
878 void __hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)
879 {
880         struct pps_normtime pts_norm, freq_norm;
881 
882         pts_norm = pps_normalize_ts(*phase_ts);
883 
884         /* clear the error bits, they will be set again if needed */
885         time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
886 
887         /* indicate signal presence */
888         time_status |= STA_PPSSIGNAL;
889         pps_valid = PPS_VALID;
890 
891         /* when called for the first time,
892          * just start the frequency interval */
893         if (unlikely(pps_fbase.tv_sec == 0)) {
894                 pps_fbase = *raw_ts;
895                 return;
896         }
897 
898         /* ok, now we have a base for frequency calculation */
899         freq_norm = pps_normalize_ts(timespec_sub(*raw_ts, pps_fbase));
900 
901         /* check that the signal is in the range
902          * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
903         if ((freq_norm.sec == 0) ||
904                         (freq_norm.nsec > MAXFREQ * freq_norm.sec) ||
905                         (freq_norm.nsec < -MAXFREQ * freq_norm.sec)) {
906                 time_status |= STA_PPSJITTER;
907                 /* restart the frequency calibration interval */
908                 pps_fbase = *raw_ts;
909                 printk_deferred(KERN_ERR "hardpps: PPSJITTER: bad pulse\n");
910                 return;
911         }
912 
913         /* signal is ok */
914 
915         /* check if the current frequency interval is finished */
916         if (freq_norm.sec >= (1 << pps_shift)) {
917                 pps_calcnt++;
918                 /* restart the frequency calibration interval */
919                 pps_fbase = *raw_ts;
920                 hardpps_update_freq(freq_norm);
921         }
922 
923         hardpps_update_phase(pts_norm.nsec);
924 
925 }
926 #endif  /* CONFIG_NTP_PPS */
927 
928 static int __init ntp_tick_adj_setup(char *str)
929 {
930         int rc = kstrtol(str, 0, (long *)&ntp_tick_adj);
931 
932         if (rc)
933                 return rc;
934         ntp_tick_adj <<= NTP_SCALE_SHIFT;
935 
936         return 1;
937 }
938 
939 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
940 
941 void __init ntp_init(void)
942 {
943         ntp_clear();
944 }
945 

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