Version:  2.0.40 2.2.26 2.4.37 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 3.19 4.0 4.1

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 "ntp_internal.h"
 21 
 22 /*
 23  * NTP timekeeping variables:
 24  *
 25  * Note: All of the NTP state is protected by the timekeeping locks.
 26  */
 27 
 28 
 29 /* USER_HZ period (usecs): */
 30 unsigned long                   tick_usec = TICK_USEC;
 31 
 32 /* SHIFTED_HZ period (nsecs): */
 33 unsigned long                   tick_nsec;
 34 
 35 static u64                      tick_length;
 36 static u64                      tick_length_base;
 37 
 38 #define MAX_TICKADJ             500LL           /* usecs */
 39 #define MAX_TICKADJ_SCALED \
 40         (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
 41 
 42 /*
 43  * phase-lock loop variables
 44  */
 45 
 46 /*
 47  * clock synchronization status
 48  *
 49  * (TIME_ERROR prevents overwriting the CMOS clock)
 50  */
 51 static int                      time_state = TIME_OK;
 52 
 53 /* clock status bits:                                                   */
 54 static int                      time_status = STA_UNSYNC;
 55 
 56 /* time adjustment (nsecs):                                             */
 57 static s64                      time_offset;
 58 
 59 /* pll time constant:                                                   */
 60 static long                     time_constant = 2;
 61 
 62 /* maximum error (usecs):                                               */
 63 static long                     time_maxerror = NTP_PHASE_LIMIT;
 64 
 65 /* estimated error (usecs):                                             */
 66 static long                     time_esterror = NTP_PHASE_LIMIT;
 67 
 68 /* frequency offset (scaled nsecs/secs):                                */
 69 static s64                      time_freq;
 70 
 71 /* time at last adjustment (secs):                                      */
 72 static long                     time_reftime;
 73 
 74 static long                     time_adjust;
 75 
 76 /* constant (boot-param configurable) NTP tick adjustment (upscaled)    */
 77 static s64                      ntp_tick_adj;
 78 
 79 #ifdef CONFIG_NTP_PPS
 80 
 81 /*
 82  * The following variables are used when a pulse-per-second (PPS) signal
 83  * is available. They establish the engineering parameters of the clock
 84  * discipline loop when controlled by the PPS signal.
 85  */
 86 #define PPS_VALID       10      /* PPS signal watchdog max (s) */
 87 #define PPS_POPCORN     4       /* popcorn spike threshold (shift) */
 88 #define PPS_INTMIN      2       /* min freq interval (s) (shift) */
 89 #define PPS_INTMAX      8       /* max freq interval (s) (shift) */
 90 #define PPS_INTCOUNT    4       /* number of consecutive good intervals to
 91                                    increase pps_shift or consecutive bad
 92                                    intervals to decrease it */
 93 #define PPS_MAXWANDER   100000  /* max PPS freq wander (ns/s) */
 94 
 95 static int pps_valid;           /* signal watchdog counter */
 96 static long pps_tf[3];          /* phase median filter */
 97 static long pps_jitter;         /* current jitter (ns) */
 98 static struct timespec pps_fbase; /* beginning of the last freq interval */
 99 static int pps_shift;           /* current interval duration (s) (shift) */
100 static int pps_intcnt;          /* interval counter */
101 static s64 pps_freq;            /* frequency offset (scaled ns/s) */
102 static long pps_stabil;         /* current stability (scaled ns/s) */
103 
104 /*
105  * PPS signal quality monitors
106  */
107 static long pps_calcnt;         /* calibration intervals */
108 static long pps_jitcnt;         /* jitter limit exceeded */
109 static long pps_stbcnt;         /* stability limit exceeded */
110 static long pps_errcnt;         /* calibration errors */
111 
112 
113 /* PPS kernel consumer compensates the whole phase error immediately.
114  * Otherwise, reduce the offset by a fixed factor times the time constant.
115  */
116 static inline s64 ntp_offset_chunk(s64 offset)
117 {
118         if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
119                 return offset;
120         else
121                 return shift_right(offset, SHIFT_PLL + time_constant);
122 }
123 
124 static inline void pps_reset_freq_interval(void)
125 {
126         /* the PPS calibration interval may end
127            surprisingly early */
128         pps_shift = PPS_INTMIN;
129         pps_intcnt = 0;
130 }
131 
132 /**
133  * pps_clear - Clears the PPS state variables
134  */
135 static inline void pps_clear(void)
136 {
137         pps_reset_freq_interval();
138         pps_tf[0] = 0;
139         pps_tf[1] = 0;
140         pps_tf[2] = 0;
141         pps_fbase.tv_sec = pps_fbase.tv_nsec = 0;
142         pps_freq = 0;
143 }
144 
145 /* Decrease pps_valid to indicate that another second has passed since
146  * the last PPS signal. When it reaches 0, indicate that PPS signal is
147  * missing.
148  */
149 static inline void pps_dec_valid(void)
150 {
151         if (pps_valid > 0)
152                 pps_valid--;
153         else {
154                 time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
155                                  STA_PPSWANDER | STA_PPSERROR);
156                 pps_clear();
157         }
158 }
159 
160 static inline void pps_set_freq(s64 freq)
161 {
162         pps_freq = freq;
163 }
164 
165 static inline int is_error_status(int status)
166 {
167         return (status & (STA_UNSYNC|STA_CLOCKERR))
168                 /* PPS signal lost when either PPS time or
169                  * PPS frequency synchronization requested
170                  */
171                 || ((status & (STA_PPSFREQ|STA_PPSTIME))
172                         && !(status & STA_PPSSIGNAL))
173                 /* PPS jitter exceeded when
174                  * PPS time synchronization requested */
175                 || ((status & (STA_PPSTIME|STA_PPSJITTER))
176                         == (STA_PPSTIME|STA_PPSJITTER))
177                 /* PPS wander exceeded or calibration error when
178                  * PPS frequency synchronization requested
179                  */
180                 || ((status & STA_PPSFREQ)
181                         && (status & (STA_PPSWANDER|STA_PPSERROR)));
182 }
183 
184 static inline void pps_fill_timex(struct timex *txc)
185 {
186         txc->ppsfreq       = shift_right((pps_freq >> PPM_SCALE_INV_SHIFT) *
187                                          PPM_SCALE_INV, NTP_SCALE_SHIFT);
188         txc->jitter        = pps_jitter;
189         if (!(time_status & STA_NANO))
190                 txc->jitter /= NSEC_PER_USEC;
191         txc->shift         = pps_shift;
192         txc->stabil        = pps_stabil;
193         txc->jitcnt        = pps_jitcnt;
194         txc->calcnt        = pps_calcnt;
195         txc->errcnt        = pps_errcnt;
196         txc->stbcnt        = pps_stbcnt;
197 }
198 
199 #else /* !CONFIG_NTP_PPS */
200 
201 static inline s64 ntp_offset_chunk(s64 offset)
202 {
203         return shift_right(offset, SHIFT_PLL + time_constant);
204 }
205 
206 static inline void pps_reset_freq_interval(void) {}
207 static inline void pps_clear(void) {}
208 static inline void pps_dec_valid(void) {}
209 static inline void pps_set_freq(s64 freq) {}
210 
211 static inline int is_error_status(int status)
212 {
213         return status & (STA_UNSYNC|STA_CLOCKERR);
214 }
215 
216 static inline void pps_fill_timex(struct timex *txc)
217 {
218         /* PPS is not implemented, so these are zero */
219         txc->ppsfreq       = 0;
220         txc->jitter        = 0;
221         txc->shift         = 0;
222         txc->stabil        = 0;
223         txc->jitcnt        = 0;
224         txc->calcnt        = 0;
225         txc->errcnt        = 0;
226         txc->stbcnt        = 0;
227 }
228 
229 #endif /* CONFIG_NTP_PPS */
230 
231 
232 /**
233  * ntp_synced - Returns 1 if the NTP status is not UNSYNC
234  *
235  */
236 static inline int ntp_synced(void)
237 {
238         return !(time_status & STA_UNSYNC);
239 }
240 
241 
242 /*
243  * NTP methods:
244  */
245 
246 /*
247  * Update (tick_length, tick_length_base, tick_nsec), based
248  * on (tick_usec, ntp_tick_adj, time_freq):
249  */
250 static void ntp_update_frequency(void)
251 {
252         u64 second_length;
253         u64 new_base;
254 
255         second_length            = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
256                                                 << NTP_SCALE_SHIFT;
257 
258         second_length           += ntp_tick_adj;
259         second_length           += time_freq;
260 
261         tick_nsec                = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
262         new_base                 = div_u64(second_length, NTP_INTERVAL_FREQ);
263 
264         /*
265          * Don't wait for the next second_overflow, apply
266          * the change to the tick length immediately:
267          */
268         tick_length             += new_base - tick_length_base;
269         tick_length_base         = new_base;
270 }
271 
272 static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
273 {
274         time_status &= ~STA_MODE;
275 
276         if (secs < MINSEC)
277                 return 0;
278 
279         if (!(time_status & STA_FLL) && (secs <= MAXSEC))
280                 return 0;
281 
282         time_status |= STA_MODE;
283 
284         return div64_long(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
285 }
286 
287 static void ntp_update_offset(long offset)
288 {
289         s64 freq_adj;
290         s64 offset64;
291         long secs;
292 
293         if (!(time_status & STA_PLL))
294                 return;
295 
296         if (!(time_status & STA_NANO))
297                 offset *= NSEC_PER_USEC;
298 
299         /*
300          * Scale the phase adjustment and
301          * clamp to the operating range.
302          */
303         offset = min(offset, MAXPHASE);
304         offset = max(offset, -MAXPHASE);
305 
306         /*
307          * Select how the frequency is to be controlled
308          * and in which mode (PLL or FLL).
309          */
310         secs = get_seconds() - time_reftime;
311         if (unlikely(time_status & STA_FREQHOLD))
312                 secs = 0;
313 
314         time_reftime = get_seconds();
315 
316         offset64    = offset;
317         freq_adj    = ntp_update_offset_fll(offset64, secs);
318 
319         /*
320          * Clamp update interval to reduce PLL gain with low
321          * sampling rate (e.g. intermittent network connection)
322          * to avoid instability.
323          */
324         if (unlikely(secs > 1 << (SHIFT_PLL + 1 + time_constant)))
325                 secs = 1 << (SHIFT_PLL + 1 + time_constant);
326 
327         freq_adj    += (offset64 * secs) <<
328                         (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
329 
330         freq_adj    = min(freq_adj + time_freq, MAXFREQ_SCALED);
331 
332         time_freq   = max(freq_adj, -MAXFREQ_SCALED);
333 
334         time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
335 }
336 
337 /**
338  * ntp_clear - Clears the NTP state variables
339  */
340 void ntp_clear(void)
341 {
342         time_adjust     = 0;            /* stop active adjtime() */
343         time_status     |= STA_UNSYNC;
344         time_maxerror   = NTP_PHASE_LIMIT;
345         time_esterror   = NTP_PHASE_LIMIT;
346 
347         ntp_update_frequency();
348 
349         tick_length     = tick_length_base;
350         time_offset     = 0;
351 
352         /* Clear PPS state variables */
353         pps_clear();
354 }
355 
356 
357 u64 ntp_tick_length(void)
358 {
359         return tick_length;
360 }
361 
362 
363 /*
364  * this routine handles the overflow of the microsecond field
365  *
366  * The tricky bits of code to handle the accurate clock support
367  * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
368  * They were originally developed for SUN and DEC kernels.
369  * All the kudos should go to Dave for this stuff.
370  *
371  * Also handles leap second processing, and returns leap offset
372  */
373 int second_overflow(unsigned long secs)
374 {
375         s64 delta;
376         int leap = 0;
377 
378         /*
379          * Leap second processing. If in leap-insert state at the end of the
380          * day, the system clock is set back one second; if in leap-delete
381          * state, the system clock is set ahead one second.
382          */
383         switch (time_state) {
384         case TIME_OK:
385                 if (time_status & STA_INS)
386                         time_state = TIME_INS;
387                 else if (time_status & STA_DEL)
388                         time_state = TIME_DEL;
389                 break;
390         case TIME_INS:
391                 if (!(time_status & STA_INS))
392                         time_state = TIME_OK;
393                 else if (secs % 86400 == 0) {
394                         leap = -1;
395                         time_state = TIME_OOP;
396                         printk(KERN_NOTICE
397                                 "Clock: inserting leap second 23:59:60 UTC\n");
398                 }
399                 break;
400         case TIME_DEL:
401                 if (!(time_status & STA_DEL))
402                         time_state = TIME_OK;
403                 else if ((secs + 1) % 86400 == 0) {
404                         leap = 1;
405                         time_state = TIME_WAIT;
406                         printk(KERN_NOTICE
407                                 "Clock: deleting leap second 23:59:59 UTC\n");
408                 }
409                 break;
410         case TIME_OOP:
411                 time_state = TIME_WAIT;
412                 break;
413 
414         case TIME_WAIT:
415                 if (!(time_status & (STA_INS | STA_DEL)))
416                         time_state = TIME_OK;
417                 break;
418         }
419 
420 
421         /* Bump the maxerror field */
422         time_maxerror += MAXFREQ / NSEC_PER_USEC;
423         if (time_maxerror > NTP_PHASE_LIMIT) {
424                 time_maxerror = NTP_PHASE_LIMIT;
425                 time_status |= STA_UNSYNC;
426         }
427 
428         /* Compute the phase adjustment for the next second */
429         tick_length      = tick_length_base;
430 
431         delta            = ntp_offset_chunk(time_offset);
432         time_offset     -= delta;
433         tick_length     += delta;
434 
435         /* Check PPS signal */
436         pps_dec_valid();
437 
438         if (!time_adjust)
439                 goto out;
440 
441         if (time_adjust > MAX_TICKADJ) {
442                 time_adjust -= MAX_TICKADJ;
443                 tick_length += MAX_TICKADJ_SCALED;
444                 goto out;
445         }
446 
447         if (time_adjust < -MAX_TICKADJ) {
448                 time_adjust += MAX_TICKADJ;
449                 tick_length -= MAX_TICKADJ_SCALED;
450                 goto out;
451         }
452 
453         tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
454                                                          << NTP_SCALE_SHIFT;
455         time_adjust = 0;
456 
457 out:
458         return leap;
459 }
460 
461 #ifdef CONFIG_GENERIC_CMOS_UPDATE
462 int __weak update_persistent_clock64(struct timespec64 now64)
463 {
464         struct timespec now;
465 
466         now = timespec64_to_timespec(now64);
467         return update_persistent_clock(now);
468 }
469 #endif
470 
471 #if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC)
472 static void sync_cmos_clock(struct work_struct *work);
473 
474 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
475 
476 static void sync_cmos_clock(struct work_struct *work)
477 {
478         struct timespec64 now;
479         struct timespec next;
480         int fail = 1;
481 
482         /*
483          * If we have an externally synchronized Linux clock, then update
484          * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
485          * called as close as possible to 500 ms before the new second starts.
486          * This code is run on a timer.  If the clock is set, that timer
487          * may not expire at the correct time.  Thus, we adjust...
488          * We want the clock to be within a couple of ticks from the target.
489          */
490         if (!ntp_synced()) {
491                 /*
492                  * Not synced, exit, do not restart a timer (if one is
493                  * running, let it run out).
494                  */
495                 return;
496         }
497 
498         getnstimeofday64(&now);
499         if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec * 5) {
500                 struct timespec64 adjust = now;
501 
502                 fail = -ENODEV;
503                 if (persistent_clock_is_local)
504                         adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
505 #ifdef CONFIG_GENERIC_CMOS_UPDATE
506                 fail = update_persistent_clock64(adjust);
507 #endif
508 
509 #ifdef CONFIG_RTC_SYSTOHC
510                 if (fail == -ENODEV)
511                         fail = rtc_set_ntp_time(adjust);
512 #endif
513         }
514 
515         next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
516         if (next.tv_nsec <= 0)
517                 next.tv_nsec += NSEC_PER_SEC;
518 
519         if (!fail || fail == -ENODEV)
520                 next.tv_sec = 659;
521         else
522                 next.tv_sec = 0;
523 
524         if (next.tv_nsec >= NSEC_PER_SEC) {
525                 next.tv_sec++;
526                 next.tv_nsec -= NSEC_PER_SEC;
527         }
528         queue_delayed_work(system_power_efficient_wq,
529                            &sync_cmos_work, timespec_to_jiffies(&next));
530 }
531 
532 void ntp_notify_cmos_timer(void)
533 {
534         queue_delayed_work(system_power_efficient_wq, &sync_cmos_work, 0);
535 }
536 
537 #else
538 void ntp_notify_cmos_timer(void) { }
539 #endif
540 
541 
542 /*
543  * Propagate a new txc->status value into the NTP state:
544  */
545 static inline void process_adj_status(struct timex *txc, struct timespec64 *ts)
546 {
547         if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
548                 time_state = TIME_OK;
549                 time_status = STA_UNSYNC;
550                 /* restart PPS frequency calibration */
551                 pps_reset_freq_interval();
552         }
553 
554         /*
555          * If we turn on PLL adjustments then reset the
556          * reference time to current time.
557          */
558         if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
559                 time_reftime = get_seconds();
560 
561         /* only set allowed bits */
562         time_status &= STA_RONLY;
563         time_status |= txc->status & ~STA_RONLY;
564 }
565 
566 
567 static inline void process_adjtimex_modes(struct timex *txc,
568                                                 struct timespec64 *ts,
569                                                 s32 *time_tai)
570 {
571         if (txc->modes & ADJ_STATUS)
572                 process_adj_status(txc, ts);
573 
574         if (txc->modes & ADJ_NANO)
575                 time_status |= STA_NANO;
576 
577         if (txc->modes & ADJ_MICRO)
578                 time_status &= ~STA_NANO;
579 
580         if (txc->modes & ADJ_FREQUENCY) {
581                 time_freq = txc->freq * PPM_SCALE;
582                 time_freq = min(time_freq, MAXFREQ_SCALED);
583                 time_freq = max(time_freq, -MAXFREQ_SCALED);
584                 /* update pps_freq */
585                 pps_set_freq(time_freq);
586         }
587 
588         if (txc->modes & ADJ_MAXERROR)
589                 time_maxerror = txc->maxerror;
590 
591         if (txc->modes & ADJ_ESTERROR)
592                 time_esterror = txc->esterror;
593 
594         if (txc->modes & ADJ_TIMECONST) {
595                 time_constant = txc->constant;
596                 if (!(time_status & STA_NANO))
597                         time_constant += 4;
598                 time_constant = min(time_constant, (long)MAXTC);
599                 time_constant = max(time_constant, 0l);
600         }
601 
602         if (txc->modes & ADJ_TAI && txc->constant > 0)
603                 *time_tai = txc->constant;
604 
605         if (txc->modes & ADJ_OFFSET)
606                 ntp_update_offset(txc->offset);
607 
608         if (txc->modes & ADJ_TICK)
609                 tick_usec = txc->tick;
610 
611         if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
612                 ntp_update_frequency();
613 }
614 
615 
616 
617 /**
618  * ntp_validate_timex - Ensures the timex is ok for use in do_adjtimex
619  */
620 int ntp_validate_timex(struct timex *txc)
621 {
622         if (txc->modes & ADJ_ADJTIME) {
623                 /* singleshot must not be used with any other mode bits */
624                 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
625                         return -EINVAL;
626                 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
627                     !capable(CAP_SYS_TIME))
628                         return -EPERM;
629         } else {
630                 /* In order to modify anything, you gotta be super-user! */
631                  if (txc->modes && !capable(CAP_SYS_TIME))
632                         return -EPERM;
633                 /*
634                  * if the quartz is off by more than 10% then
635                  * something is VERY wrong!
636                  */
637                 if (txc->modes & ADJ_TICK &&
638                     (txc->tick <  900000/USER_HZ ||
639                      txc->tick > 1100000/USER_HZ))
640                         return -EINVAL;
641         }
642 
643         if ((txc->modes & ADJ_SETOFFSET) && (!capable(CAP_SYS_TIME)))
644                 return -EPERM;
645 
646         /*
647          * Check for potential multiplication overflows that can
648          * only happen on 64-bit systems:
649          */
650         if ((txc->modes & ADJ_FREQUENCY) && (BITS_PER_LONG == 64)) {
651                 if (LLONG_MIN / PPM_SCALE > txc->freq)
652                         return -EINVAL;
653                 if (LLONG_MAX / PPM_SCALE < txc->freq)
654                         return -EINVAL;
655         }
656 
657         return 0;
658 }
659 
660 
661 /*
662  * adjtimex mainly allows reading (and writing, if superuser) of
663  * kernel time-keeping variables. used by xntpd.
664  */
665 int __do_adjtimex(struct timex *txc, struct timespec64 *ts, s32 *time_tai)
666 {
667         int result;
668 
669         if (txc->modes & ADJ_ADJTIME) {
670                 long save_adjust = time_adjust;
671 
672                 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
673                         /* adjtime() is independent from ntp_adjtime() */
674                         time_adjust = txc->offset;
675                         ntp_update_frequency();
676                 }
677                 txc->offset = save_adjust;
678         } else {
679 
680                 /* If there are input parameters, then process them: */
681                 if (txc->modes)
682                         process_adjtimex_modes(txc, ts, time_tai);
683 
684                 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
685                                   NTP_SCALE_SHIFT);
686                 if (!(time_status & STA_NANO))
687                         txc->offset /= NSEC_PER_USEC;
688         }
689 
690         result = time_state;    /* mostly `TIME_OK' */
691         /* check for errors */
692         if (is_error_status(time_status))
693                 result = TIME_ERROR;
694 
695         txc->freq          = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
696                                          PPM_SCALE_INV, NTP_SCALE_SHIFT);
697         txc->maxerror      = time_maxerror;
698         txc->esterror      = time_esterror;
699         txc->status        = time_status;
700         txc->constant      = time_constant;
701         txc->precision     = 1;
702         txc->tolerance     = MAXFREQ_SCALED / PPM_SCALE;
703         txc->tick          = tick_usec;
704         txc->tai           = *time_tai;
705 
706         /* fill PPS status fields */
707         pps_fill_timex(txc);
708 
709         txc->time.tv_sec = (time_t)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         return result;
715 }
716 
717 #ifdef  CONFIG_NTP_PPS
718 
719 /* actually struct pps_normtime is good old struct timespec, but it is
720  * semantically different (and it is the reason why it was invented):
721  * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
722  * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
723 struct pps_normtime {
724         __kernel_time_t sec;    /* seconds */
725         long            nsec;   /* nanoseconds */
726 };
727 
728 /* normalize the timestamp so that nsec is in the
729    ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
730 static inline struct pps_normtime pps_normalize_ts(struct timespec ts)
731 {
732         struct pps_normtime norm = {
733                 .sec = ts.tv_sec,
734                 .nsec = ts.tv_nsec
735         };
736 
737         if (norm.nsec > (NSEC_PER_SEC >> 1)) {
738                 norm.nsec -= NSEC_PER_SEC;
739                 norm.sec++;
740         }
741 
742         return norm;
743 }
744 
745 /* get current phase correction and jitter */
746 static inline long pps_phase_filter_get(long *jitter)
747 {
748         *jitter = pps_tf[0] - pps_tf[1];
749         if (*jitter < 0)
750                 *jitter = -*jitter;
751 
752         /* TODO: test various filters */
753         return pps_tf[0];
754 }
755 
756 /* add the sample to the phase filter */
757 static inline void pps_phase_filter_add(long err)
758 {
759         pps_tf[2] = pps_tf[1];
760         pps_tf[1] = pps_tf[0];
761         pps_tf[0] = err;
762 }
763 
764 /* decrease frequency calibration interval length.
765  * It is halved after four consecutive unstable intervals.
766  */
767 static inline void pps_dec_freq_interval(void)
768 {
769         if (--pps_intcnt <= -PPS_INTCOUNT) {
770                 pps_intcnt = -PPS_INTCOUNT;
771                 if (pps_shift > PPS_INTMIN) {
772                         pps_shift--;
773                         pps_intcnt = 0;
774                 }
775         }
776 }
777 
778 /* increase frequency calibration interval length.
779  * It is doubled after four consecutive stable intervals.
780  */
781 static inline void pps_inc_freq_interval(void)
782 {
783         if (++pps_intcnt >= PPS_INTCOUNT) {
784                 pps_intcnt = PPS_INTCOUNT;
785                 if (pps_shift < PPS_INTMAX) {
786                         pps_shift++;
787                         pps_intcnt = 0;
788                 }
789         }
790 }
791 
792 /* update clock frequency based on MONOTONIC_RAW clock PPS signal
793  * timestamps
794  *
795  * At the end of the calibration interval the difference between the
796  * first and last MONOTONIC_RAW clock timestamps divided by the length
797  * of the interval becomes the frequency update. If the interval was
798  * too long, the data are discarded.
799  * Returns the difference between old and new frequency values.
800  */
801 static long hardpps_update_freq(struct pps_normtime freq_norm)
802 {
803         long delta, delta_mod;
804         s64 ftemp;
805 
806         /* check if the frequency interval was too long */
807         if (freq_norm.sec > (2 << pps_shift)) {
808                 time_status |= STA_PPSERROR;
809                 pps_errcnt++;
810                 pps_dec_freq_interval();
811                 printk_deferred(KERN_ERR
812                         "hardpps: PPSERROR: interval too long - %ld s\n",
813                         freq_norm.sec);
814                 return 0;
815         }
816 
817         /* here the raw frequency offset and wander (stability) is
818          * calculated. If the wander is less than the wander threshold
819          * the interval is increased; otherwise it is decreased.
820          */
821         ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT,
822                         freq_norm.sec);
823         delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT);
824         pps_freq = ftemp;
825         if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) {
826                 printk_deferred(KERN_WARNING
827                                 "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 */
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                 printk_deferred(KERN_WARNING
872                                 "hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
873                                 jitter, (pps_jitter << PPS_POPCORN));
874                 time_status |= STA_PPSJITTER;
875                 pps_jitcnt++;
876         } else if (time_status & STA_PPSTIME) {
877                 /* correct the time using the phase offset */
878                 time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT,
879                                 NTP_INTERVAL_FREQ);
880                 /* cancel running adjtime() */
881                 time_adjust = 0;
882         }
883         /* update jitter */
884         pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN;
885 }
886 
887 /*
888  * __hardpps() - discipline CPU clock oscillator to external PPS signal
889  *
890  * This routine is called at each PPS signal arrival in order to
891  * discipline the CPU clock oscillator to the PPS signal. It takes two
892  * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
893  * is used to correct clock phase error and the latter is used to
894  * correct the frequency.
895  *
896  * This code is based on David Mills's reference nanokernel
897  * implementation. It was mostly rewritten but keeps the same idea.
898  */
899 void __hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)
900 {
901         struct pps_normtime pts_norm, freq_norm;
902 
903         pts_norm = pps_normalize_ts(*phase_ts);
904 
905         /* clear the error bits, they will be set again if needed */
906         time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
907 
908         /* indicate signal presence */
909         time_status |= STA_PPSSIGNAL;
910         pps_valid = PPS_VALID;
911 
912         /* when called for the first time,
913          * just start the frequency interval */
914         if (unlikely(pps_fbase.tv_sec == 0)) {
915                 pps_fbase = *raw_ts;
916                 return;
917         }
918 
919         /* ok, now we have a base for frequency calculation */
920         freq_norm = pps_normalize_ts(timespec_sub(*raw_ts, pps_fbase));
921 
922         /* check that the signal is in the range
923          * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
924         if ((freq_norm.sec == 0) ||
925                         (freq_norm.nsec > MAXFREQ * freq_norm.sec) ||
926                         (freq_norm.nsec < -MAXFREQ * freq_norm.sec)) {
927                 time_status |= STA_PPSJITTER;
928                 /* restart the frequency calibration interval */
929                 pps_fbase = *raw_ts;
930                 printk_deferred(KERN_ERR "hardpps: PPSJITTER: bad pulse\n");
931                 return;
932         }
933 
934         /* signal is ok */
935 
936         /* check if the current frequency interval is finished */
937         if (freq_norm.sec >= (1 << pps_shift)) {
938                 pps_calcnt++;
939                 /* restart the frequency calibration interval */
940                 pps_fbase = *raw_ts;
941                 hardpps_update_freq(freq_norm);
942         }
943 
944         hardpps_update_phase(pts_norm.nsec);
945 
946 }
947 #endif  /* CONFIG_NTP_PPS */
948 
949 static int __init ntp_tick_adj_setup(char *str)
950 {
951         int rc = kstrtol(str, 0, (long *)&ntp_tick_adj);
952 
953         if (rc)
954                 return rc;
955         ntp_tick_adj <<= NTP_SCALE_SHIFT;
956 
957         return 1;
958 }
959 
960 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
961 
962 void __init ntp_init(void)
963 {
964         ntp_clear();
965 }
966 

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