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
  18 /*
  19  * NTP timekeeping variables:
  20  */
  21
  22 /* USER_HZ period (usecs): */
  23 unsigned long                   tick_usec = TICK_USEC;
  24
  25 /* ACTHZ period (nsecs): */
  26 unsigned long                   tick_nsec;
  27
  28 u64                             tick_length;
  29 static u64                      tick_length_base;
  30
  31 static struct hrtimer           leap_timer;
  32
  33 #define MAX_TICKADJ             500LL           /* usecs */
  34 #define MAX_TICKADJ_SCALED \
  35         (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
  36
  37 /*
  38  * phase-lock loop variables
  39  */
  40
  41 /*
  42  * clock synchronization status
  43  *
  44  * (TIME_ERROR prevents overwriting the CMOS clock)
  45  */
  46 static int                      time_state = TIME_OK;
  47
  48 /* clock status bits:                                                   */
  49 int                             time_status = STA_UNSYNC;
  50
  51 /* TAI offset (secs):                                                   */
  52 static long                     time_tai;
  53
  54 /* time adjustment (nsecs):                                             */
  55 static s64                      time_offset;
  56
  57 /* pll time constant:                                                   */
  58 static long                     time_constant = 2;
  59
  60 /* maximum error (usecs):                                               */
  61 static long                     time_maxerror = NTP_PHASE_LIMIT;
  62
  63 /* estimated error (usecs):                                             */
  64 static long                     time_esterror = NTP_PHASE_LIMIT;
  65
  66 /* frequency offset (scaled nsecs/secs):                                */
  67 static s64                      time_freq;
  68
  69 /* time at last adjustment (secs):                                      */
  70 static long                     time_reftime;
  71
  72 static long                     time_adjust;
  73
  74 /* constant (boot-param configurable) NTP tick adjustment (upscaled)    */
  75 static s64                      ntp_tick_adj;
  76
  77 /*
  78  * NTP methods:
  79  */
  80
  81 /*
  82  * Update (tick_length, tick_length_base, tick_nsec), based
  83  * on (tick_usec, ntp_tick_adj, time_freq):
  84  */
  85 static void ntp_update_frequency(void)
  86 {
  87         u64 second_length;
  88         u64 new_base;
  89
  90         second_length            = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
  91                                                 << NTP_SCALE_SHIFT;
  92
  93         second_length           += ntp_tick_adj;
  94         second_length           += time_freq;
  95
  96         tick_nsec                = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
  97         new_base                 = div_u64(second_length, NTP_INTERVAL_FREQ);
  98
  99         /*
 100          * Don't wait for the next second_overflow, apply
 101          * the change to the tick length immediately:
 102          */
 103         tick_length             += new_base - tick_length_base;
 104         tick_length_base         = new_base;
 105 }
 106
 107 static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
 108 {
 109         time_status &= ~STA_MODE;
 110
 111         if (secs < MINSEC)
 112                 return 0;
 113
 114         if (!(time_status & STA_FLL) && (secs <= MAXSEC))
 115                 return 0;
 116
 117         time_status |= STA_MODE;
 118
 119         return div_s64(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
 120 }
 121
 122 static void ntp_update_offset(long offset)
 123 {
 124         s64 freq_adj;
 125         s64 offset64;
 126         long secs;
 127
 128         if (!(time_status & STA_PLL))
 129                 return;
 130
 131         if (!(time_status & STA_NANO))
 132                 offset *= NSEC_PER_USEC;
 133
 134         /*
 135          * Scale the phase adjustment and
 136          * clamp to the operating range.
 137          */
 138         offset = min(offset, MAXPHASE);
 139         offset = max(offset, -MAXPHASE);
 140
 141         /*
 142          * Select how the frequency is to be controlled
 143          * and in which mode (PLL or FLL).
 144          */
 145         secs = get_seconds() - time_reftime;
 146         if (unlikely(time_status & STA_FREQHOLD))
 147                 secs = 0;
 148
 149         time_reftime = get_seconds();
 150
 151         offset64    = offset;
 152         freq_adj    = ntp_update_offset_fll(offset64, secs);
 153
 154         /*
 155          * Clamp update interval to reduce PLL gain with low
 156          * sampling rate (e.g. intermittent network connection)
 157          * to avoid instability.
 158          */
 159         if (unlikely(secs > 1 << (SHIFT_PLL + 1 + time_constant)))
 160                 secs = 1 << (SHIFT_PLL + 1 + time_constant);
 161
 162         freq_adj    += (offset64 * secs) <<
 163                         (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
 164
 165         freq_adj    = min(freq_adj + time_freq, MAXFREQ_SCALED);
 166
 167         time_freq   = max(freq_adj, -MAXFREQ_SCALED);
 168
 169         time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
 170 }
 171
 172 /**
 173  * ntp_clear - Clears the NTP state variables
 174  *
 175  * Must be called while holding a write on the xtime_lock
 176  */
 177 void ntp_clear(void)
 178 {
 179         time_adjust     = 0;            /* stop active adjtime() */
 180         time_status     |= STA_UNSYNC;
 181         time_maxerror   = NTP_PHASE_LIMIT;
 182         time_esterror   = NTP_PHASE_LIMIT;
 183
 184         ntp_update_frequency();
 185
 186         tick_length     = tick_length_base;
 187         time_offset     = 0;
 188 }
 189
 190 /*
 191  * Leap second processing. If in leap-insert state at the end of the
 192  * day, the system clock is set back one second; if in leap-delete
 193  * state, the system clock is set ahead one second.
 194  */
 195 static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
 196 {
 197         enum hrtimer_restart res = HRTIMER_NORESTART;
 198
 199         write_seqlock(&xtime_lock);
 200
 201         switch (time_state) {
 202         case TIME_OK:
 203                 break;
 204         case TIME_INS:
 205                 timekeeping_leap_insert(-1);
 206                 time_state = TIME_OOP;
 207                 printk(KERN_NOTICE
 208                         "Clock: inserting leap second 23:59:60 UTC\n");
 209                 hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC);
 210                 res = HRTIMER_RESTART;
 211                 break;
 212         case TIME_DEL:
 213                 timekeeping_leap_insert(1);
 214                 time_tai--;
 215                 time_state = TIME_WAIT;
 216                 printk(KERN_NOTICE
 217                         "Clock: deleting leap second 23:59:59 UTC\n");
 218                 break;
 219         case TIME_OOP:
 220                 time_tai++;
 221                 time_state = TIME_WAIT;
 222                 /* fall through */
 223         case TIME_WAIT:
 224                 if (!(time_status & (STA_INS | STA_DEL)))
 225                         time_state = TIME_OK;
 226                 break;
 227         }
 228
 229         write_sequnlock(&xtime_lock);
 230
 231         return res;
 232 }
 233
 234 /*
 235  * this routine handles the overflow of the microsecond field
 236  *
 237  * The tricky bits of code to handle the accurate clock support
 238  * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
 239  * They were originally developed for SUN and DEC kernels.
 240  * All the kudos should go to Dave for this stuff.
 241  */
 242 void second_overflow(void)
 243 {
 244         s64 delta;
 245
 246         /* Bump the maxerror field */
 247         time_maxerror += MAXFREQ / NSEC_PER_USEC;
 248         if (time_maxerror > NTP_PHASE_LIMIT) {
 249                 time_maxerror = NTP_PHASE_LIMIT;
 250                 time_status |= STA_UNSYNC;
 251         }
 252
 253         /*
 254          * Compute the phase adjustment for the next second. The offset is
 255          * reduced by a fixed factor times the time constant.
 256          */
 257         tick_length      = tick_length_base;
 258
 259         delta            = shift_right(time_offset, SHIFT_PLL + time_constant);
 260         time_offset     -= delta;
 261         tick_length     += delta;
 262
 263         if (!time_adjust)
 264                 return;
 265
 266         if (time_adjust > MAX_TICKADJ) {
 267                 time_adjust -= MAX_TICKADJ;
 268                 tick_length += MAX_TICKADJ_SCALED;
 269                 return;
 270         }
 271
 272         if (time_adjust < -MAX_TICKADJ) {
 273                 time_adjust += MAX_TICKADJ;
 274                 tick_length -= MAX_TICKADJ_SCALED;
 275                 return;
 276         }
 277
 278         tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
 279                                                          << NTP_SCALE_SHIFT;
 280         time_adjust = 0;
 281 }
 282
 283 #ifdef CONFIG_GENERIC_CMOS_UPDATE
 284
 285 /* Disable the cmos update - used by virtualization and embedded */
 286 int no_sync_cmos_clock  __read_mostly;
 287
 288 static void sync_cmos_clock(struct work_struct *work);
 289
 290 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
 291
 292 static void sync_cmos_clock(struct work_struct *work)
 293 {
 294         struct timespec now, next;
 295         int fail = 1;
 296
 297         /*
 298          * If we have an externally synchronized Linux clock, then update
 299          * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
 300          * called as close as possible to 500 ms before the new second starts.
 301          * This code is run on a timer.  If the clock is set, that timer
 302          * may not expire at the correct time.  Thus, we adjust...
 303          */
 304         if (!ntp_synced()) {
 305                 /*
 306                  * Not synced, exit, do not restart a timer (if one is
 307                  * running, let it run out).
 308                  */
 309                 return;
 310         }
 311
 312         getnstimeofday(&now);
 313         if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
 314                 fail = update_persistent_clock(now);
 315
 316         next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
 317         if (next.tv_nsec <= 0)
 318                 next.tv_nsec += NSEC_PER_SEC;
 319
 320         if (!fail)
 321                 next.tv_sec = 659;
 322         else
 323                 next.tv_sec = 0;
 324
 325         if (next.tv_nsec >= NSEC_PER_SEC) {
 326                 next.tv_sec++;
 327                 next.tv_nsec -= NSEC_PER_SEC;
 328         }
 329         schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
 330 }
 331
 332 static void notify_cmos_timer(void)
 333 {
 334         if (!no_sync_cmos_clock)
 335                 schedule_delayed_work(&sync_cmos_work, 0);
 336 }
 337
 338 #else
 339 static inline void notify_cmos_timer(void) { }
 340 #endif
 341
 342 /*
 343  * Start the leap seconds timer:
 344  */
 345 static inline void ntp_start_leap_timer(struct timespec *ts)
 346 {
 347         long now = ts->tv_sec;
 348
 349         if (time_status & STA_INS) {
 350                 time_state = TIME_INS;
 351                 now += 86400 - now % 86400;
 352                 hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
 353
 354                 return;
 355         }
 356
 357         if (time_status & STA_DEL) {
 358                 time_state = TIME_DEL;
 359                 now += 86400 - (now + 1) % 86400;
 360                 hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
 361         }
 362 }
 363
 364 /*
 365  * Propagate a new txc->status value into the NTP state:
 366  */
 367 static inline void process_adj_status(struct timex *txc, struct timespec *ts)
 368 {
 369         if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
 370                 time_state = TIME_OK;
 371                 time_status = STA_UNSYNC;
 372         }
 373
 374         /*
 375          * If we turn on PLL adjustments then reset the
 376          * reference time to current time.
 377          */
 378         if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
 379                 time_reftime = get_seconds();
 380
 381         /* only set allowed bits */
 382         time_status &= STA_RONLY;
 383         time_status |= txc->status & ~STA_RONLY;
 384
 385         switch (time_state) {
 386         case TIME_OK:
 387                 ntp_start_leap_timer(ts);
 388                 break;
 389         case TIME_INS:
 390         case TIME_DEL:
 391                 time_state = TIME_OK;
 392                 ntp_start_leap_timer(ts);
 393         case TIME_WAIT:
 394                 if (!(time_status & (STA_INS | STA_DEL)))
 395                         time_state = TIME_OK;
 396                 break;
 397         case TIME_OOP:
 398                 hrtimer_restart(&leap_timer);
 399                 break;
 400         }
 401 }
 402 /*
 403  * Called with the xtime lock held, so we can access and modify
 404  * all the global NTP state:
 405  */
 406 static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts)
 407 {
 408         if (txc->modes & ADJ_STATUS)
 409                 process_adj_status(txc, ts);
 410
 411         if (txc->modes & ADJ_NANO)
 412                 time_status |= STA_NANO;
 413
 414         if (txc->modes & ADJ_MICRO)
 415                 time_status &= ~STA_NANO;
 416
 417         if (txc->modes & ADJ_FREQUENCY) {
 418                 time_freq = txc->freq * PPM_SCALE;
 419                 time_freq = min(time_freq, MAXFREQ_SCALED);
 420                 time_freq = max(time_freq, -MAXFREQ_SCALED);
 421         }
 422
 423         if (txc->modes & ADJ_MAXERROR)
 424                 time_maxerror = txc->maxerror;
 425
 426         if (txc->modes & ADJ_ESTERROR)
 427                 time_esterror = txc->esterror;
 428
 429         if (txc->modes & ADJ_TIMECONST) {
 430                 time_constant = txc->constant;
 431                 if (!(time_status & STA_NANO))
 432                         time_constant += 4;
 433                 time_constant = min(time_constant, (long)MAXTC);
 434                 time_constant = max(time_constant, 0l);
 435         }
 436
 437         if (txc->modes & ADJ_TAI && txc->constant > 0)
 438                 time_tai = txc->constant;
 439
 440         if (txc->modes & ADJ_OFFSET)
 441                 ntp_update_offset(txc->offset);
 442
 443         if (txc->modes & ADJ_TICK)
 444                 tick_usec = txc->tick;
 445
 446         if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 447                 ntp_update_frequency();
 448 }
 449
 450 /*
 451  * adjtimex mainly allows reading (and writing, if superuser) of
 452  * kernel time-keeping variables. used by xntpd.
 453  */
 454 int do_adjtimex(struct timex *txc)
 455 {
 456         struct timespec ts;
 457         int result;
 458
 459         /* Validate the data before disabling interrupts */
 460         if (txc->modes & ADJ_ADJTIME) {
 461                 /* singleshot must not be used with any other mode bits */
 462                 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
 463                         return -EINVAL;
 464                 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
 465                     !capable(CAP_SYS_TIME))
 466                         return -EPERM;
 467         } else {
 468                 /* In order to modify anything, you gotta be super-user! */
 469                  if (txc->modes && !capable(CAP_SYS_TIME))
 470                         return -EPERM;
 471
 472                 /*
 473                  * if the quartz is off by more than 10% then
 474                  * something is VERY wrong!
 475                  */
 476                 if (txc->modes & ADJ_TICK &&
 477                     (txc->tick <  900000/USER_HZ ||
 478                      txc->tick > 1100000/USER_HZ))
 479                         return -EINVAL;
 480
 481                 if (txc->modes & ADJ_STATUS && time_state != TIME_OK)
 482                         hrtimer_cancel(&leap_timer);
 483         }
 484
 485         getnstimeofday(&ts);
 486
 487         write_seqlock_irq(&xtime_lock);
 488
 489         if (txc->modes & ADJ_ADJTIME) {
 490                 long save_adjust = time_adjust;
 491
 492                 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
 493                         /* adjtime() is independent from ntp_adjtime() */
 494                         time_adjust = txc->offset;
 495                         ntp_update_frequency();
 496                 }
 497                 txc->offset = save_adjust;
 498         } else {
 499
 500                 /* If there are input parameters, then process them: */
 501                 if (txc->modes)
 502                         process_adjtimex_modes(txc, &ts);
 503
 504                 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
 505                                   NTP_SCALE_SHIFT);
 506                 if (!(time_status & STA_NANO))
 507                         txc->offset /= NSEC_PER_USEC;
 508         }
 509
 510         result = time_state;    /* mostly `TIME_OK' */
 511         if (time_status & (STA_UNSYNC|STA_CLOCKERR))
 512                 result = TIME_ERROR;
 513
 514         txc->freq          = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
 515                                          PPM_SCALE_INV, NTP_SCALE_SHIFT);
 516         txc->maxerror      = time_maxerror;
 517         txc->esterror      = time_esterror;
 518         txc->status        = time_status;
 519         txc->constant      = time_constant;
 520         txc->precision     = 1;
 521         txc->tolerance     = MAXFREQ_SCALED / PPM_SCALE;
 522         txc->tick          = tick_usec;
 523         txc->tai           = time_tai;
 524
 525         /* PPS is not implemented, so these are zero */
 526         txc->ppsfreq       = 0;
 527         txc->jitter        = 0;
 528         txc->shift         = 0;
 529         txc->stabil        = 0;
 530         txc->jitcnt        = 0;
 531         txc->calcnt        = 0;
 532         txc->errcnt        = 0;
 533         txc->stbcnt        = 0;
 534
 535         write_sequnlock_irq(&xtime_lock);
 536
 537         txc->time.tv_sec = ts.tv_sec;
 538         txc->time.tv_usec = ts.tv_nsec;
 539         if (!(time_status & STA_NANO))
 540                 txc->time.tv_usec /= NSEC_PER_USEC;
 541
 542         notify_cmos_timer();
 543
 544         return result;
 545 }
 546
 547 static int __init ntp_tick_adj_setup(char *str)
 548 {
 549         ntp_tick_adj = simple_strtol(str, NULL, 0);
 550         ntp_tick_adj <<= NTP_SCALE_SHIFT;
 551
 552         return 1;
 553 }
 554
 555 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
 556
 557 void __init ntp_init(void)
 558 {
 559         ntp_clear();
 560         hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
 561         leap_timer.function = ntp_leap_second;
 562 }