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 long                            time_maxerror = NTP_PHASE_LIMIT;
  62
  63 /* estimated error (usecs):                                             */
  64 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 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 = xtime.tv_sec - time_reftime;
 146         if (unlikely(time_status & STA_FREQHOLD))
 147                 secs = 0;
 148
 149         time_reftime = xtime.tv_sec;
 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                 xtime.tv_sec--;
 198                 wall_to_monotonic.tv_sec++;
 199                 time_state = TIME_OOP;
 200                 printk(KERN_NOTICE
 201                         "Clock: inserting leap second 23:59:60 UTC\n");
 202                 hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC);
 203                 res = HRTIMER_RESTART;
 204                 break;
 205         case TIME_DEL:
 206                 xtime.tv_sec++;
 207                 time_tai--;
 208                 wall_to_monotonic.tv_sec--;
 209                 time_state = TIME_WAIT;
 210                 printk(KERN_NOTICE
 211                         "Clock: deleting leap second 23:59:59 UTC\n");
 212                 break;
 213         case TIME_OOP:
 214                 time_tai++;
 215                 time_state = TIME_WAIT;
 216                 /* fall through */
 217         case TIME_WAIT:
 218                 if (!(time_status & (STA_INS | STA_DEL)))
 219                         time_state = TIME_OK;
 220                 break;
 221         }
 222         update_vsyscall(&xtime, clock);
 223
 224         write_sequnlock(&xtime_lock);
 225
 226         return res;
 227 }
 228
 229 /*
 230  * this routine handles the overflow of the microsecond field
 231  *
 232  * The tricky bits of code to handle the accurate clock support
 233  * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
 234  * They were originally developed for SUN and DEC kernels.
 235  * All the kudos should go to Dave for this stuff.
 236  */
 237 void second_overflow(void)
 238 {
 239         s64 delta;
 240
 241         /* Bump the maxerror field */
 242         time_maxerror += MAXFREQ / NSEC_PER_USEC;
 243         if (time_maxerror > NTP_PHASE_LIMIT) {
 244                 time_maxerror = NTP_PHASE_LIMIT;
 245                 time_status |= STA_UNSYNC;
 246         }
 247
 248         /*
 249          * Compute the phase adjustment for the next second. The offset is
 250          * reduced by a fixed factor times the time constant.
 251          */
 252         tick_length      = tick_length_base;
 253
 254         delta            = shift_right(time_offset, SHIFT_PLL + time_constant);
 255         time_offset     -= delta;
 256         tick_length     += delta;
 257
 258         if (!time_adjust)
 259                 return;
 260
 261         if (time_adjust > MAX_TICKADJ) {
 262                 time_adjust -= MAX_TICKADJ;
 263                 tick_length += MAX_TICKADJ_SCALED;
 264                 return;
 265         }
 266
 267         if (time_adjust < -MAX_TICKADJ) {
 268                 time_adjust += MAX_TICKADJ;
 269                 tick_length -= MAX_TICKADJ_SCALED;
 270                 return;
 271         }
 272
 273         tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
 274                                                          << NTP_SCALE_SHIFT;
 275         time_adjust = 0;
 276 }
 277
 278 #ifdef CONFIG_GENERIC_CMOS_UPDATE
 279
 280 /* Disable the cmos update - used by virtualization and embedded */
 281 int no_sync_cmos_clock  __read_mostly;
 282
 283 static void sync_cmos_clock(struct work_struct *work);
 284
 285 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
 286
 287 static void sync_cmos_clock(struct work_struct *work)
 288 {
 289         struct timespec now, next;
 290         int fail = 1;
 291
 292         /*
 293          * If we have an externally synchronized Linux clock, then update
 294          * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
 295          * called as close as possible to 500 ms before the new second starts.
 296          * This code is run on a timer.  If the clock is set, that timer
 297          * may not expire at the correct time.  Thus, we adjust...
 298          */
 299         if (!ntp_synced()) {
 300                 /*
 301                  * Not synced, exit, do not restart a timer (if one is
 302                  * running, let it run out).
 303                  */
 304                 return;
 305         }
 306
 307         getnstimeofday(&now);
 308         if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
 309                 fail = update_persistent_clock(now);
 310
 311         next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
 312         if (next.tv_nsec <= 0)
 313                 next.tv_nsec += NSEC_PER_SEC;
 314
 315         if (!fail)
 316                 next.tv_sec = 659;
 317         else
 318                 next.tv_sec = 0;
 319
 320         if (next.tv_nsec >= NSEC_PER_SEC) {
 321                 next.tv_sec++;
 322                 next.tv_nsec -= NSEC_PER_SEC;
 323         }
 324         schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
 325 }
 326
 327 static void notify_cmos_timer(void)
 328 {
 329         if (!no_sync_cmos_clock)
 330                 schedule_delayed_work(&sync_cmos_work, 0);
 331 }
 332
 333 #else
 334 static inline void notify_cmos_timer(void) { }
 335 #endif
 336
 337 /*
 338  * Start the leap seconds timer:
 339  */
 340 static inline void ntp_start_leap_timer(struct timespec *ts)
 341 {
 342         long now = ts->tv_sec;
 343
 344         if (time_status & STA_INS) {
 345                 time_state = TIME_INS;
 346                 now += 86400 - now % 86400;
 347                 hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
 348
 349                 return;
 350         }
 351
 352         if (time_status & STA_DEL) {
 353                 time_state = TIME_DEL;
 354                 now += 86400 - (now + 1) % 86400;
 355                 hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
 356         }
 357 }
 358
 359 /*
 360  * Propagate a new txc->status value into the NTP state:
 361  */
 362 static inline void process_adj_status(struct timex *txc, struct timespec *ts)
 363 {
 364         if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
 365                 time_state = TIME_OK;
 366                 time_status = STA_UNSYNC;
 367         }
 368
 369         /*
 370          * If we turn on PLL adjustments then reset the
 371          * reference time to current time.
 372          */
 373         if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
 374                 time_reftime = xtime.tv_sec;
 375
 376         /* only set allowed bits */
 377         time_status &= STA_RONLY;
 378         time_status |= txc->status & ~STA_RONLY;
 379
 380         switch (time_state) {
 381         case TIME_OK:
 382                 ntp_start_leap_timer(ts);
 383                 break;
 384         case TIME_INS:
 385         case TIME_DEL:
 386                 time_state = TIME_OK;
 387                 ntp_start_leap_timer(ts);
 388         case TIME_WAIT:
 389                 if (!(time_status & (STA_INS | STA_DEL)))
 390                         time_state = TIME_OK;
 391                 break;
 392         case TIME_OOP:
 393                 hrtimer_restart(&leap_timer);
 394                 break;
 395         }
 396 }
 397 /*
 398  * Called with the xtime lock held, so we can access and modify
 399  * all the global NTP state:
 400  */
 401 static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts)
 402 {
 403         if (txc->modes & ADJ_STATUS)
 404                 process_adj_status(txc, ts);
 405
 406         if (txc->modes & ADJ_NANO)
 407                 time_status |= STA_NANO;
 408
 409         if (txc->modes & ADJ_MICRO)
 410                 time_status &= ~STA_NANO;
 411
 412         if (txc->modes & ADJ_FREQUENCY) {
 413                 time_freq = txc->freq * PPM_SCALE;
 414                 time_freq = min(time_freq, MAXFREQ_SCALED);
 415                 time_freq = max(time_freq, -MAXFREQ_SCALED);
 416         }
 417
 418         if (txc->modes & ADJ_MAXERROR)
 419                 time_maxerror = txc->maxerror;
 420
 421         if (txc->modes & ADJ_ESTERROR)
 422                 time_esterror = txc->esterror;
 423
 424         if (txc->modes & ADJ_TIMECONST) {
 425                 time_constant = txc->constant;
 426                 if (!(time_status & STA_NANO))
 427                         time_constant += 4;
 428                 time_constant = min(time_constant, (long)MAXTC);
 429                 time_constant = max(time_constant, 0l);
 430         }
 431
 432         if (txc->modes & ADJ_TAI && txc->constant > 0)
 433                 time_tai = txc->constant;
 434
 435         if (txc->modes & ADJ_OFFSET)
 436                 ntp_update_offset(txc->offset);
 437
 438         if (txc->modes & ADJ_TICK)
 439                 tick_usec = txc->tick;
 440
 441         if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 442                 ntp_update_frequency();
 443 }
 444
 445 /*
 446  * adjtimex mainly allows reading (and writing, if superuser) of
 447  * kernel time-keeping variables. used by xntpd.
 448  */
 449 int do_adjtimex(struct timex *txc)
 450 {
 451         struct timespec ts;
 452         int result;
 453
 454         /* Validate the data before disabling interrupts */
 455         if (txc->modes & ADJ_ADJTIME) {
 456                 /* singleshot must not be used with any other mode bits */
 457                 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
 458                         return -EINVAL;
 459                 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
 460                     !capable(CAP_SYS_TIME))
 461                         return -EPERM;
 462         } else {
 463                 /* In order to modify anything, you gotta be super-user! */
 464                  if (txc->modes && !capable(CAP_SYS_TIME))
 465                         return -EPERM;
 466
 467                 /*
 468                  * if the quartz is off by more than 10% then
 469                  * something is VERY wrong!
 470                  */
 471                 if (txc->modes & ADJ_TICK &&
 472                     (txc->tick <  900000/USER_HZ ||
 473                      txc->tick > 1100000/USER_HZ))
 474                         return -EINVAL;
 475
 476                 if (txc->modes & ADJ_STATUS && time_state != TIME_OK)
 477                         hrtimer_cancel(&leap_timer);
 478         }
 479
 480         getnstimeofday(&ts);
 481
 482         write_seqlock_irq(&xtime_lock);
 483
 484         if (txc->modes & ADJ_ADJTIME) {
 485                 long save_adjust = time_adjust;
 486
 487                 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
 488                         /* adjtime() is independent from ntp_adjtime() */
 489                         time_adjust = txc->offset;
 490                         ntp_update_frequency();
 491                 }
 492                 txc->offset = save_adjust;
 493         } else {
 494
 495                 /* If there are input parameters, then process them: */
 496                 if (txc->modes)
 497                         process_adjtimex_modes(txc, &ts);
 498
 499                 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
 500                                   NTP_SCALE_SHIFT);
 501                 if (!(time_status & STA_NANO))
 502                         txc->offset /= NSEC_PER_USEC;
 503         }
 504
 505         result = time_state;    /* mostly `TIME_OK' */
 506         if (time_status & (STA_UNSYNC|STA_CLOCKERR))
 507                 result = TIME_ERROR;
 508
 509         txc->freq          = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
 510                                          PPM_SCALE_INV, NTP_SCALE_SHIFT);
 511         txc->maxerror      = time_maxerror;
 512         txc->esterror      = time_esterror;
 513         txc->status        = time_status;
 514         txc->constant      = time_constant;
 515         txc->precision     = 1;
 516         txc->tolerance     = MAXFREQ_SCALED / PPM_SCALE;
 517         txc->tick          = tick_usec;
 518         txc->tai           = time_tai;
 519
 520         /* PPS is not implemented, so these are zero */
 521         txc->ppsfreq       = 0;
 522         txc->jitter        = 0;
 523         txc->shift         = 0;
 524         txc->stabil        = 0;
 525         txc->jitcnt        = 0;
 526         txc->calcnt        = 0;
 527         txc->errcnt        = 0;
 528         txc->stbcnt        = 0;
 529
 530         write_sequnlock_irq(&xtime_lock);
 531
 532         txc->time.tv_sec = ts.tv_sec;
 533         txc->time.tv_usec = ts.tv_nsec;
 534         if (!(time_status & STA_NANO))
 535                 txc->time.tv_usec /= NSEC_PER_USEC;
 536
 537         notify_cmos_timer();
 538
 539         return result;
 540 }
 541
 542 static int __init ntp_tick_adj_setup(char *str)
 543 {
 544         ntp_tick_adj = simple_strtol(str, NULL, 0);
 545         ntp_tick_adj <<= NTP_SCALE_SHIFT;
 546
 547         return 1;
 548 }
 549
 550 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
 551
 552 void __init ntp_init(void)
 553 {
 554         ntp_clear();
 555         hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
 556         leap_timer.function = ntp_leap_second;
 557 }