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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 (time_status & (STA_UNSYNC|STA_CLOCKERR))
169                 /* PPS signal lost when either PPS time or
170                  * PPS frequency synchronization requested
171                  */
172                 || ((time_status & (STA_PPSFREQ|STA_PPSTIME))
173                         && !(time_status & STA_PPSSIGNAL))
174                 /* PPS jitter exceeded when
175                  * PPS time synchronization requested */
176                 || ((time_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                 || ((time_status & STA_PPSFREQ)
182                         && (time_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 timespec now, next;
470         int fail = 1;
471 
472         /*
473          * If we have an externally synchronized Linux clock, then update
474          * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
475          * called as close as possible to 500 ms before the new second starts.
476          * This code is run on a timer.  If the clock is set, that timer
477          * may not expire at the correct time.  Thus, we adjust...
478          * We want the clock to be within a couple of ticks from the target.
479          */
480         if (!ntp_synced()) {
481                 /*
482                  * Not synced, exit, do not restart a timer (if one is
483                  * running, let it run out).
484                  */
485                 return;
486         }
487 
488         getnstimeofday(&now);
489         if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec * 5) {
490                 struct timespec adjust = now;
491 
492                 fail = -ENODEV;
493                 if (persistent_clock_is_local)
494                         adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
495 #ifdef CONFIG_GENERIC_CMOS_UPDATE
496                 fail = update_persistent_clock(adjust);
497 #endif
498 #ifdef CONFIG_RTC_SYSTOHC
499                 if (fail == -ENODEV)
500                         fail = rtc_set_ntp_time(adjust);
501 #endif
502         }
503 
504         next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
505         if (next.tv_nsec <= 0)
506                 next.tv_nsec += NSEC_PER_SEC;
507 
508         if (!fail || fail == -ENODEV)
509                 next.tv_sec = 659;
510         else
511                 next.tv_sec = 0;
512 
513         if (next.tv_nsec >= NSEC_PER_SEC) {
514                 next.tv_sec++;
515                 next.tv_nsec -= NSEC_PER_SEC;
516         }
517         schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
518 }
519 
520 void ntp_notify_cmos_timer(void)
521 {
522         schedule_delayed_work(&sync_cmos_work, 0);
523 }
524 
525 #else
526 void ntp_notify_cmos_timer(void) { }
527 #endif
528 
529 
530 /*
531  * Propagate a new txc->status value into the NTP state:
532  */
533 static inline void process_adj_status(struct timex *txc, struct timespec *ts)
534 {
535         if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
536                 time_state = TIME_OK;
537                 time_status = STA_UNSYNC;
538                 /* restart PPS frequency calibration */
539                 pps_reset_freq_interval();
540         }
541 
542         /*
543          * If we turn on PLL adjustments then reset the
544          * reference time to current time.
545          */
546         if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
547                 time_reftime = get_seconds();
548 
549         /* only set allowed bits */
550         time_status &= STA_RONLY;
551         time_status |= txc->status & ~STA_RONLY;
552 }
553 
554 
555 static inline void process_adjtimex_modes(struct timex *txc,
556                                                 struct timespec *ts,
557                                                 s32 *time_tai)
558 {
559         if (txc->modes & ADJ_STATUS)
560                 process_adj_status(txc, ts);
561 
562         if (txc->modes & ADJ_NANO)
563                 time_status |= STA_NANO;
564 
565         if (txc->modes & ADJ_MICRO)
566                 time_status &= ~STA_NANO;
567 
568         if (txc->modes & ADJ_FREQUENCY) {
569                 time_freq = txc->freq * PPM_SCALE;
570                 time_freq = min(time_freq, MAXFREQ_SCALED);
571                 time_freq = max(time_freq, -MAXFREQ_SCALED);
572                 /* update pps_freq */
573                 pps_set_freq(time_freq);
574         }
575 
576         if (txc->modes & ADJ_MAXERROR)
577                 time_maxerror = txc->maxerror;
578 
579         if (txc->modes & ADJ_ESTERROR)
580                 time_esterror = txc->esterror;
581 
582         if (txc->modes & ADJ_TIMECONST) {
583                 time_constant = txc->constant;
584                 if (!(time_status & STA_NANO))
585                         time_constant += 4;
586                 time_constant = min(time_constant, (long)MAXTC);
587                 time_constant = max(time_constant, 0l);
588         }
589 
590         if (txc->modes & ADJ_TAI && txc->constant > 0)
591                 *time_tai = txc->constant;
592 
593         if (txc->modes & ADJ_OFFSET)
594                 ntp_update_offset(txc->offset);
595 
596         if (txc->modes & ADJ_TICK)
597                 tick_usec = txc->tick;
598 
599         if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
600                 ntp_update_frequency();
601 }
602 
603 
604 
605 /**
606  * ntp_validate_timex - Ensures the timex is ok for use in do_adjtimex
607  */
608 int ntp_validate_timex(struct timex *txc)
609 {
610         if (txc->modes & ADJ_ADJTIME) {
611                 /* singleshot must not be used with any other mode bits */
612                 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
613                         return -EINVAL;
614                 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
615                     !capable(CAP_SYS_TIME))
616                         return -EPERM;
617         } else {
618                 /* In order to modify anything, you gotta be super-user! */
619                  if (txc->modes && !capable(CAP_SYS_TIME))
620                         return -EPERM;
621                 /*
622                  * if the quartz is off by more than 10% then
623                  * something is VERY wrong!
624                  */
625                 if (txc->modes & ADJ_TICK &&
626                     (txc->tick <  900000/USER_HZ ||
627                      txc->tick > 1100000/USER_HZ))
628                         return -EINVAL;
629         }
630 
631         if ((txc->modes & ADJ_SETOFFSET) && (!capable(CAP_SYS_TIME)))
632                 return -EPERM;
633 
634         return 0;
635 }
636 
637 
638 /*
639  * adjtimex mainly allows reading (and writing, if superuser) of
640  * kernel time-keeping variables. used by xntpd.
641  */
642 int __do_adjtimex(struct timex *txc, struct timespec *ts, s32 *time_tai)
643 {
644         int result;
645 
646         if (txc->modes & ADJ_ADJTIME) {
647                 long save_adjust = time_adjust;
648 
649                 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
650                         /* adjtime() is independent from ntp_adjtime() */
651                         time_adjust = txc->offset;
652                         ntp_update_frequency();
653                 }
654                 txc->offset = save_adjust;
655         } else {
656 
657                 /* If there are input parameters, then process them: */
658                 if (txc->modes)
659                         process_adjtimex_modes(txc, ts, time_tai);
660 
661                 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
662                                   NTP_SCALE_SHIFT);
663                 if (!(time_status & STA_NANO))
664                         txc->offset /= NSEC_PER_USEC;
665         }
666 
667         result = time_state;    /* mostly `TIME_OK' */
668         /* check for errors */
669         if (is_error_status(time_status))
670                 result = TIME_ERROR;
671 
672         txc->freq          = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
673                                          PPM_SCALE_INV, NTP_SCALE_SHIFT);
674         txc->maxerror      = time_maxerror;
675         txc->esterror      = time_esterror;
676         txc->status        = time_status;
677         txc->constant      = time_constant;
678         txc->precision     = 1;
679         txc->tolerance     = MAXFREQ_SCALED / PPM_SCALE;
680         txc->tick          = tick_usec;
681         txc->tai           = *time_tai;
682 
683         /* fill PPS status fields */
684         pps_fill_timex(txc);
685 
686         txc->time.tv_sec = ts->tv_sec;
687         txc->time.tv_usec = ts->tv_nsec;
688         if (!(time_status & STA_NANO))
689                 txc->time.tv_usec /= NSEC_PER_USEC;
690 
691         return result;
692 }
693 
694 #ifdef  CONFIG_NTP_PPS
695 
696 /* actually struct pps_normtime is good old struct timespec, but it is
697  * semantically different (and it is the reason why it was invented):
698  * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
699  * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
700 struct pps_normtime {
701         __kernel_time_t sec;    /* seconds */
702         long            nsec;   /* nanoseconds */
703 };
704 
705 /* normalize the timestamp so that nsec is in the
706    ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
707 static inline struct pps_normtime pps_normalize_ts(struct timespec ts)
708 {
709         struct pps_normtime norm = {
710                 .sec = ts.tv_sec,
711                 .nsec = ts.tv_nsec
712         };
713 
714         if (norm.nsec > (NSEC_PER_SEC >> 1)) {
715                 norm.nsec -= NSEC_PER_SEC;
716                 norm.sec++;
717         }
718 
719         return norm;
720 }
721 
722 /* get current phase correction and jitter */
723 static inline long pps_phase_filter_get(long *jitter)
724 {
725         *jitter = pps_tf[0] - pps_tf[1];
726         if (*jitter < 0)
727                 *jitter = -*jitter;
728 
729         /* TODO: test various filters */
730         return pps_tf[0];
731 }
732 
733 /* add the sample to the phase filter */
734 static inline void pps_phase_filter_add(long err)
735 {
736         pps_tf[2] = pps_tf[1];
737         pps_tf[1] = pps_tf[0];
738         pps_tf[0] = err;
739 }
740 
741 /* decrease frequency calibration interval length.
742  * It is halved after four consecutive unstable intervals.
743  */
744 static inline void pps_dec_freq_interval(void)
745 {
746         if (--pps_intcnt <= -PPS_INTCOUNT) {
747                 pps_intcnt = -PPS_INTCOUNT;
748                 if (pps_shift > PPS_INTMIN) {
749                         pps_shift--;
750                         pps_intcnt = 0;
751                 }
752         }
753 }
754 
755 /* increase frequency calibration interval length.
756  * It is doubled after four consecutive stable intervals.
757  */
758 static inline void pps_inc_freq_interval(void)
759 {
760         if (++pps_intcnt >= PPS_INTCOUNT) {
761                 pps_intcnt = PPS_INTCOUNT;
762                 if (pps_shift < PPS_INTMAX) {
763                         pps_shift++;
764                         pps_intcnt = 0;
765                 }
766         }
767 }
768 
769 /* update clock frequency based on MONOTONIC_RAW clock PPS signal
770  * timestamps
771  *
772  * At the end of the calibration interval the difference between the
773  * first and last MONOTONIC_RAW clock timestamps divided by the length
774  * of the interval becomes the frequency update. If the interval was
775  * too long, the data are discarded.
776  * Returns the difference between old and new frequency values.
777  */
778 static long hardpps_update_freq(struct pps_normtime freq_norm)
779 {
780         long delta, delta_mod;
781         s64 ftemp;
782 
783         /* check if the frequency interval was too long */
784         if (freq_norm.sec > (2 << pps_shift)) {
785                 time_status |= STA_PPSERROR;
786                 pps_errcnt++;
787                 pps_dec_freq_interval();
788                 pr_err("hardpps: PPSERROR: interval too long - %ld s\n",
789                                 freq_norm.sec);
790                 return 0;
791         }
792 
793         /* here the raw frequency offset and wander (stability) is
794          * calculated. If the wander is less than the wander threshold
795          * the interval is increased; otherwise it is decreased.
796          */
797         ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT,
798                         freq_norm.sec);
799         delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT);
800         pps_freq = ftemp;
801         if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) {
802                 pr_warning("hardpps: PPSWANDER: change=%ld\n", delta);
803                 time_status |= STA_PPSWANDER;
804                 pps_stbcnt++;
805                 pps_dec_freq_interval();
806         } else {        /* good sample */
807                 pps_inc_freq_interval();
808         }
809 
810         /* the stability metric is calculated as the average of recent
811          * frequency changes, but is used only for performance
812          * monitoring
813          */
814         delta_mod = delta;
815         if (delta_mod < 0)
816                 delta_mod = -delta_mod;
817         pps_stabil += (div_s64(((s64)delta_mod) <<
818                                 (NTP_SCALE_SHIFT - SHIFT_USEC),
819                                 NSEC_PER_USEC) - pps_stabil) >> PPS_INTMIN;
820 
821         /* if enabled, the system clock frequency is updated */
822         if ((time_status & STA_PPSFREQ) != 0 &&
823             (time_status & STA_FREQHOLD) == 0) {
824                 time_freq = pps_freq;
825                 ntp_update_frequency();
826         }
827 
828         return delta;
829 }
830 
831 /* correct REALTIME clock phase error against PPS signal */
832 static void hardpps_update_phase(long error)
833 {
834         long correction = -error;
835         long jitter;
836 
837         /* add the sample to the median filter */
838         pps_phase_filter_add(correction);
839         correction = pps_phase_filter_get(&jitter);
840 
841         /* Nominal jitter is due to PPS signal noise. If it exceeds the
842          * threshold, the sample is discarded; otherwise, if so enabled,
843          * the time offset is updated.
844          */
845         if (jitter > (pps_jitter << PPS_POPCORN)) {
846                 pr_warning("hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
847                        jitter, (pps_jitter << PPS_POPCORN));
848                 time_status |= STA_PPSJITTER;
849                 pps_jitcnt++;
850         } else if (time_status & STA_PPSTIME) {
851                 /* correct the time using the phase offset */
852                 time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT,
853                                 NTP_INTERVAL_FREQ);
854                 /* cancel running adjtime() */
855                 time_adjust = 0;
856         }
857         /* update jitter */
858         pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN;
859 }
860 
861 /*
862  * __hardpps() - discipline CPU clock oscillator to external PPS signal
863  *
864  * This routine is called at each PPS signal arrival in order to
865  * discipline the CPU clock oscillator to the PPS signal. It takes two
866  * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
867  * is used to correct clock phase error and the latter is used to
868  * correct the frequency.
869  *
870  * This code is based on David Mills's reference nanokernel
871  * implementation. It was mostly rewritten but keeps the same idea.
872  */
873 void __hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)
874 {
875         struct pps_normtime pts_norm, freq_norm;
876 
877         pts_norm = pps_normalize_ts(*phase_ts);
878 
879         /* clear the error bits, they will be set again if needed */
880         time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
881 
882         /* indicate signal presence */
883         time_status |= STA_PPSSIGNAL;
884         pps_valid = PPS_VALID;
885 
886         /* when called for the first time,
887          * just start the frequency interval */
888         if (unlikely(pps_fbase.tv_sec == 0)) {
889                 pps_fbase = *raw_ts;
890                 return;
891         }
892 
893         /* ok, now we have a base for frequency calculation */
894         freq_norm = pps_normalize_ts(timespec_sub(*raw_ts, pps_fbase));
895 
896         /* check that the signal is in the range
897          * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
898         if ((freq_norm.sec == 0) ||
899                         (freq_norm.nsec > MAXFREQ * freq_norm.sec) ||
900                         (freq_norm.nsec < -MAXFREQ * freq_norm.sec)) {
901                 time_status |= STA_PPSJITTER;
902                 /* restart the frequency calibration interval */
903                 pps_fbase = *raw_ts;
904                 pr_err("hardpps: PPSJITTER: bad pulse\n");
905                 return;
906         }
907 
908         /* signal is ok */
909 
910         /* check if the current frequency interval is finished */
911         if (freq_norm.sec >= (1 << pps_shift)) {
912                 pps_calcnt++;
913                 /* restart the frequency calibration interval */
914                 pps_fbase = *raw_ts;
915                 hardpps_update_freq(freq_norm);
916         }
917 
918         hardpps_update_phase(pts_norm.nsec);
919 
920 }
921 #endif  /* CONFIG_NTP_PPS */
922 
923 static int __init ntp_tick_adj_setup(char *str)
924 {
925         ntp_tick_adj = simple_strtol(str, NULL, 0);
926         ntp_tick_adj <<= NTP_SCALE_SHIFT;
927 
928         return 1;
929 }
930 
931 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
932 
933 void __init ntp_init(void)
934 {
935         ntp_clear();
936 }
937 

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