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    = (offset64 * secs) <<
 153                         (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
 154
 155         freq_adj    += ntp_update_offset_fll(offset64, secs);
 156
 157         freq_adj    = min(freq_adj + time_freq, MAXFREQ_SCALED);
 158
 159         time_freq   = max(freq_adj, -MAXFREQ_SCALED);
 160
 161         time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
 162 }
 163
 164 /**
 165  * ntp_clear - Clears the NTP state variables
 166  *
 167  * Must be called while holding a write on the xtime_lock
 168  */
 169 void ntp_clear(void)
 170 {
 171         time_adjust     = 0;            /* stop active adjtime() */
 172         time_status     |= STA_UNSYNC;
 173         time_maxerror   = NTP_PHASE_LIMIT;
 174         time_esterror   = NTP_PHASE_LIMIT;
 175
 176         ntp_update_frequency();
 177
 178         tick_length     = tick_length_base;
 179         time_offset     = 0;
 180 }
 181
 182 /*
 183  * Leap second processing. If in leap-insert state at the end of the
 184  * day, the system clock is set back one second; if in leap-delete
 185  * state, the system clock is set ahead one second.
 186  */
 187 static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
 188 {
 189         enum hrtimer_restart res = HRTIMER_NORESTART;
 190
 191         write_seqlock(&xtime_lock);
 192
 193         switch (time_state) {
 194         case TIME_OK:
 195                 break;
 196         case TIME_INS:
 197                 timekeeping_leap_insert(-1);
 198                 time_state = TIME_OOP;
 199                 printk(KERN_NOTICE
 200                         "Clock: inserting leap second 23:59:60 UTC\n");
 201                 hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC);
 202                 res = HRTIMER_RESTART;
 203                 break;
 204         case TIME_DEL:
 205                 timekeeping_leap_insert(1);
 206                 time_tai--;
 207                 time_state = TIME_WAIT;
 208                 printk(KERN_NOTICE
 209                         "Clock: deleting leap second 23:59:59 UTC\n");
 210                 break;
 211         case TIME_OOP:
 212                 time_tai++;
 213                 time_state = TIME_WAIT;
 214                 /* fall through */
 215         case TIME_WAIT:
 216                 if (!(time_status & (STA_INS | STA_DEL)))
 217                         time_state = TIME_OK;
 218                 break;
 219         }
 220
 221         write_sequnlock(&xtime_lock);
 222
 223         return res;
 224 }
 225
 226 /*
 227  * this routine handles the overflow of the microsecond field
 228  *
 229  * The tricky bits of code to handle the accurate clock support
 230  * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
 231  * They were originally developed for SUN and DEC kernels.
 232  * All the kudos should go to Dave for this stuff.
 233  */
 234 void second_overflow(void)
 235 {
 236         s64 delta;
 237
 238         /* Bump the maxerror field */
 239         time_maxerror += MAXFREQ / NSEC_PER_USEC;
 240         if (time_maxerror > NTP_PHASE_LIMIT) {
 241                 time_maxerror = NTP_PHASE_LIMIT;
 242                 time_status |= STA_UNSYNC;
 243         }
 244
 245         /*
 246          * Compute the phase adjustment for the next second. The offset is
 247          * reduced by a fixed factor times the time constant.
 248          */
 249         tick_length      = tick_length_base;
 250
 251         delta            = shift_right(time_offset, SHIFT_PLL + time_constant);
 252         time_offset     -= delta;
 253         tick_length     += delta;
 254
 255         if (!time_adjust)
 256                 return;
 257
 258         if (time_adjust > MAX_TICKADJ) {
 259                 time_adjust -= MAX_TICKADJ;
 260                 tick_length += MAX_TICKADJ_SCALED;
 261                 return;
 262         }
 263
 264         if (time_adjust < -MAX_TICKADJ) {
 265                 time_adjust += MAX_TICKADJ;
 266                 tick_length -= MAX_TICKADJ_SCALED;
 267                 return;
 268         }
 269
 270         tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
 271                                                          << NTP_SCALE_SHIFT;
 272         time_adjust = 0;
 273 }
 274
 275 #ifdef CONFIG_GENERIC_CMOS_UPDATE
 276
 277 /* Disable the cmos update - used by virtualization and embedded */
 278 int no_sync_cmos_clock  __read_mostly;
 279
 280 static void sync_cmos_clock(struct work_struct *work);
 281
 282 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
 283
 284 static void sync_cmos_clock(struct work_struct *work)
 285 {
 286         struct timespec now, next;
 287         int fail = 1;
 288
 289         /*
 290          * If we have an externally synchronized Linux clock, then update
 291          * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
 292          * called as close as possible to 500 ms before the new second starts.
 293          * This code is run on a timer.  If the clock is set, that timer
 294          * may not expire at the correct time.  Thus, we adjust...
 295          */
 296         if (!ntp_synced()) {
 297                 /*
 298                  * Not synced, exit, do not restart a timer (if one is
 299                  * running, let it run out).
 300                  */
 301                 return;
 302         }
 303
 304         getnstimeofday(&now);
 305         if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
 306                 fail = update_persistent_clock(now);
 307
 308         next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
 309         if (next.tv_nsec <= 0)
 310                 next.tv_nsec += NSEC_PER_SEC;
 311
 312         if (!fail)
 313                 next.tv_sec = 659;
 314         else
 315                 next.tv_sec = 0;
 316
 317         if (next.tv_nsec >= NSEC_PER_SEC) {
 318                 next.tv_sec++;
 319                 next.tv_nsec -= NSEC_PER_SEC;
 320         }
 321         schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
 322 }
 323
 324 static void notify_cmos_timer(void)
 325 {
 326         if (!no_sync_cmos_clock)
 327                 schedule_delayed_work(&sync_cmos_work, 0);
 328 }
 329
 330 #else
 331 static inline void notify_cmos_timer(void) { }
 332 #endif
 333
 334 /*
 335  * Start the leap seconds timer:
 336  */
 337 static inline void ntp_start_leap_timer(struct timespec *ts)
 338 {
 339         long now = ts->tv_sec;
 340
 341         if (time_status & STA_INS) {
 342                 time_state = TIME_INS;
 343                 now += 86400 - now % 86400;
 344                 hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
 345
 346                 return;
 347         }
 348
 349         if (time_status & STA_DEL) {
 350                 time_state = TIME_DEL;
 351                 now += 86400 - (now + 1) % 86400;
 352                 hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
 353         }
 354 }
 355
 356 /*
 357  * Propagate a new txc->status value into the NTP state:
 358  */
 359 static inline void process_adj_status(struct timex *txc, struct timespec *ts)
 360 {
 361         if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
 362                 time_state = TIME_OK;
 363                 time_status = STA_UNSYNC;
 364         }
 365
 366         /*
 367          * If we turn on PLL adjustments then reset the
 368          * reference time to current time.
 369          */
 370         if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
 371                 time_reftime = get_seconds();
 372
 373         /* only set allowed bits */
 374         time_status &= STA_RONLY;
 375         time_status |= txc->status & ~STA_RONLY;
 376
 377         switch (time_state) {
 378         case TIME_OK:
 379                 ntp_start_leap_timer(ts);
 380                 break;
 381         case TIME_INS:
 382         case TIME_DEL:
 383                 time_state = TIME_OK;
 384                 ntp_start_leap_timer(ts);
 385         case TIME_WAIT:
 386                 if (!(time_status & (STA_INS | STA_DEL)))
 387                         time_state = TIME_OK;
 388                 break;
 389         case TIME_OOP:
 390                 hrtimer_restart(&leap_timer);
 391                 break;
 392         }
 393 }
 394 /*
 395  * Called with the xtime lock held, so we can access and modify
 396  * all the global NTP state:
 397  */
 398 static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts)
 399 {
 400         if (txc->modes & ADJ_STATUS)
 401                 process_adj_status(txc, ts);
 402
 403         if (txc->modes & ADJ_NANO)
 404                 time_status |= STA_NANO;
 405
 406         if (txc->modes & ADJ_MICRO)
 407                 time_status &= ~STA_NANO;
 408
 409         if (txc->modes & ADJ_FREQUENCY) {
 410                 time_freq = txc->freq * PPM_SCALE;
 411                 time_freq = min(time_freq, MAXFREQ_SCALED);
 412                 time_freq = max(time_freq, -MAXFREQ_SCALED);
 413         }
 414
 415         if (txc->modes & ADJ_MAXERROR)
 416                 time_maxerror = txc->maxerror;
 417
 418         if (txc->modes & ADJ_ESTERROR)
 419                 time_esterror = txc->esterror;
 420
 421         if (txc->modes & ADJ_TIMECONST) {
 422                 time_constant = txc->constant;
 423                 if (!(time_status & STA_NANO))
 424                         time_constant += 4;
 425                 time_constant = min(time_constant, (long)MAXTC);
 426                 time_constant = max(time_constant, 0l);
 427         }
 428
 429         if (txc->modes & ADJ_TAI && txc->constant > 0)
 430                 time_tai = txc->constant;
 431
 432         if (txc->modes & ADJ_OFFSET)
 433                 ntp_update_offset(txc->offset);
 434
 435         if (txc->modes & ADJ_TICK)
 436                 tick_usec = txc->tick;
 437
 438         if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 439                 ntp_update_frequency();
 440 }
 441
 442 /*
 443  * adjtimex mainly allows reading (and writing, if superuser) of
 444  * kernel time-keeping variables. used by xntpd.
 445  */
 446 int do_adjtimex(struct timex *txc)
 447 {
 448         struct timespec ts;
 449         int result;
 450
 451         /* Validate the data before disabling interrupts */
 452         if (txc->modes & ADJ_ADJTIME) {
 453                 /* singleshot must not be used with any other mode bits */
 454                 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
 455                         return -EINVAL;
 456                 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
 457                     !capable(CAP_SYS_TIME))
 458                         return -EPERM;
 459         } else {
 460                 /* In order to modify anything, you gotta be super-user! */
 461                  if (txc->modes && !capable(CAP_SYS_TIME))
 462                         return -EPERM;
 463
 464                 /*
 465                  * if the quartz is off by more than 10% then
 466                  * something is VERY wrong!
 467                  */
 468                 if (txc->modes & ADJ_TICK &&
 469                     (txc->tick <  900000/USER_HZ ||
 470                      txc->tick > 1100000/USER_HZ))
 471                         return -EINVAL;
 472
 473                 if (txc->modes & ADJ_STATUS && time_state != TIME_OK)
 474                         hrtimer_cancel(&leap_timer);
 475         }
 476
 477         getnstimeofday(&ts);
 478
 479         write_seqlock_irq(&xtime_lock);
 480
 481         if (txc->modes & ADJ_ADJTIME) {
 482                 long save_adjust = time_adjust;
 483
 484                 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
 485                         /* adjtime() is independent from ntp_adjtime() */
 486                         time_adjust = txc->offset;
 487                         ntp_update_frequency();
 488                 }
 489                 txc->offset = save_adjust;
 490         } else {
 491
 492                 /* If there are input parameters, then process them: */
 493                 if (txc->modes)
 494                         process_adjtimex_modes(txc, &ts);
 495
 496                 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
 497                                   NTP_SCALE_SHIFT);
 498                 if (!(time_status & STA_NANO))
 499                         txc->offset /= NSEC_PER_USEC;
 500         }
 501
 502         result = time_state;    /* mostly `TIME_OK' */
 503         if (time_status & (STA_UNSYNC|STA_CLOCKERR))
 504                 result = TIME_ERROR;
 505
 506         txc->freq          = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
 507                                          PPM_SCALE_INV, NTP_SCALE_SHIFT);
 508         txc->maxerror      = time_maxerror;
 509         txc->esterror      = time_esterror;
 510         txc->status        = time_status;
 511         txc->constant      = time_constant;
 512         txc->precision     = 1;
 513         txc->tolerance     = MAXFREQ_SCALED / PPM_SCALE;
 514         txc->tick          = tick_usec;
 515         txc->tai           = time_tai;
 516
 517         /* PPS is not implemented, so these are zero */
 518         txc->ppsfreq       = 0;
 519         txc->jitter        = 0;
 520         txc->shift         = 0;
 521         txc->stabil        = 0;
 522         txc->jitcnt        = 0;
 523         txc->calcnt        = 0;
 524         txc->errcnt        = 0;
 525         txc->stbcnt        = 0;
 526
 527         write_sequnlock_irq(&xtime_lock);
 528
 529         txc->time.tv_sec = ts.tv_sec;
 530         txc->time.tv_usec = ts.tv_nsec;
 531         if (!(time_status & STA_NANO))
 532                 txc->time.tv_usec /= NSEC_PER_USEC;
 533
 534         notify_cmos_timer();
 535
 536         return result;
 537 }
 538
 539 static int __init ntp_tick_adj_setup(char *str)
 540 {
 541         ntp_tick_adj = simple_strtol(str, NULL, 0);
 542         ntp_tick_adj <<= NTP_SCALE_SHIFT;
 543
 544         return 1;
 545 }
 546
 547 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
 548
 549 void __init ntp_init(void)
 550 {
 551         ntp_clear();
 552         hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
 553         leap_timer.function = ntp_leap_second;
 554 }