kernel/time/ntp.c

   1 /*
   2  * linux/kernel/time/ntp.c
   3  *
   4  * NTP state machine interfaces and logic.
   5  *
   6  * This code was mainly moved from kernel/timer.c and kernel/time.c
   7  * Please see those files for relevant copyright info and historical
   8  * changelogs.
   9  */
  10
  11 #include <linux/mm.h>
  12 #include <linux/time.h>
  13 #include <linux/timex.h>
  14 #include <linux/jiffies.h>
  15 #include <linux/hrtimer.h>
  16 #include <linux/capability.h>
  17 #include <linux/math64.h>
  18 #include <linux/clocksource.h>
  19 #include <linux/workqueue.h>
  20 #include <asm/timex.h>
  21
  22 /*
  23  * Timekeeping variables
  24  */
  25 unsigned long tick_usec = TICK_USEC;            /* USER_HZ period (usec) */
  26 unsigned long tick_nsec;                        /* ACTHZ period (nsec) */
  27 u64 tick_length;
  28 static u64 tick_length_base;
  29
  30 static struct hrtimer leap_timer;
  31
  32 #define MAX_TICKADJ             500             /* microsecs */
  33 #define MAX_TICKADJ_SCALED      (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
  34                                   NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
  35
  36 /*
  37  * phase-lock loop variables
  38  */
  39 /* TIME_ERROR prevents overwriting the CMOS clock */
  40 static int time_state = TIME_OK;        /* clock synchronization status */
  41 int time_status = STA_UNSYNC;           /* clock status bits            */
  42 static long time_tai;                   /* TAI offset (s)               */
  43 static s64 time_offset;                 /* time adjustment (ns)         */
  44 static long time_constant = 2;          /* pll time constant            */
  45 long time_maxerror = NTP_PHASE_LIMIT;   /* maximum error (us)           */
  46 long time_esterror = NTP_PHASE_LIMIT;   /* estimated error (us)         */
  47 static s64 time_freq;                   /* frequency offset (scaled ns/s)*/
  48 static long time_reftime;               /* time at last adjustment (s)  */
  49 long time_adjust;
  50 static long ntp_tick_adj;
  51
  52 static void ntp_update_frequency(void)
  53 {
  54         u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
  55                                 << NTP_SCALE_SHIFT;
  56         second_length += (s64)ntp_tick_adj << NTP_SCALE_SHIFT;
  57         second_length += time_freq;
  58
  59         tick_length_base = second_length;
  60
  61         tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
  62         tick_length_base = div_u64(tick_length_base, NTP_INTERVAL_FREQ);
  63 }
  64
  65 static void ntp_update_offset(long offset)
  66 {
  67         long mtemp;
  68         s64 freq_adj;
  69
  70         if (!(time_status & STA_PLL))
  71                 return;
  72
  73         if (!(time_status & STA_NANO))
  74                 offset *= NSEC_PER_USEC;
  75
  76         /*
  77          * Scale the phase adjustment and
  78          * clamp to the operating range.
  79          */
  80         offset = min(offset, MAXPHASE);
  81         offset = max(offset, -MAXPHASE);
  82
  83         /*
  84          * Select how the frequency is to be controlled
  85          * and in which mode (PLL or FLL).
  86          */
  87         if (time_status & STA_FREQHOLD || time_reftime == 0)
  88                 time_reftime = xtime.tv_sec;
  89         mtemp = xtime.tv_sec - time_reftime;
  90         time_reftime = xtime.tv_sec;
  91
  92         freq_adj = (s64)offset * mtemp;
  93         freq_adj <<= NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant);
  94         time_status &= ~STA_MODE;
  95         if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
  96                 freq_adj += div_s64((s64)offset << (NTP_SCALE_SHIFT - SHIFT_FLL),
  97                                     mtemp);
  98                 time_status |= STA_MODE;
  99         }
 100         freq_adj += time_freq;
 101         freq_adj = min(freq_adj, MAXFREQ_SCALED);
 102         time_freq = max(freq_adj, -MAXFREQ_SCALED);
 103
 104         time_offset = div_s64((s64)offset << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
 105 }
 106
 107 /**
 108  * ntp_clear - Clears the NTP state variables
 109  *
 110  * Must be called while holding a write on the xtime_lock
 111  */
 112 void ntp_clear(void)
 113 {
 114         time_adjust = 0;                /* stop active adjtime() */
 115         time_status |= STA_UNSYNC;
 116         time_maxerror = NTP_PHASE_LIMIT;
 117         time_esterror = NTP_PHASE_LIMIT;
 118
 119         ntp_update_frequency();
 120
 121         tick_length = tick_length_base;
 122         time_offset = 0;
 123 }
 124
 125 /*
 126  * Leap second processing. If in leap-insert state at the end of the
 127  * day, the system clock is set back one second; if in leap-delete
 128  * state, the system clock is set ahead one second.
 129  */
 130 static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
 131 {
 132         enum hrtimer_restart res = HRTIMER_NORESTART;
 133
 134         write_seqlock(&xtime_lock);
 135
 136         switch (time_state) {
 137         case TIME_OK:
 138                 break;
 139         case TIME_INS:
 140                 xtime.tv_sec--;
 141                 wall_to_monotonic.tv_sec++;
 142                 time_state = TIME_OOP;
 143                 printk(KERN_NOTICE "Clock: "
 144                        "inserting leap second 23:59:60 UTC\n");
 145                 hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC);
 146                 res = HRTIMER_RESTART;
 147                 break;
 148         case TIME_DEL:
 149                 xtime.tv_sec++;
 150                 time_tai--;
 151                 wall_to_monotonic.tv_sec--;
 152                 time_state = TIME_WAIT;
 153                 printk(KERN_NOTICE "Clock: "
 154                        "deleting leap second 23:59:59 UTC\n");
 155                 break;
 156         case TIME_OOP:
 157                 time_tai++;
 158                 time_state = TIME_WAIT;
 159                 /* fall through */
 160         case TIME_WAIT:
 161                 if (!(time_status & (STA_INS | STA_DEL)))
 162                         time_state = TIME_OK;
 163                 break;
 164         }
 165         update_vsyscall(&xtime, clock);
 166
 167         write_sequnlock(&xtime_lock);
 168
 169         return res;
 170 }
 171
 172 /*
 173  * this routine handles the overflow of the microsecond field
 174  *
 175  * The tricky bits of code to handle the accurate clock support
 176  * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
 177  * They were originally developed for SUN and DEC kernels.
 178  * All the kudos should go to Dave for this stuff.
 179  */
 180 void second_overflow(void)
 181 {
 182         s64 time_adj;
 183
 184         /* Bump the maxerror field */
 185         time_maxerror += MAXFREQ / NSEC_PER_USEC;
 186         if (time_maxerror > NTP_PHASE_LIMIT) {
 187                 time_maxerror = NTP_PHASE_LIMIT;
 188                 time_status |= STA_UNSYNC;
 189         }
 190
 191         /*
 192          * Compute the phase adjustment for the next second. The offset is
 193          * reduced by a fixed factor times the time constant.
 194          */
 195         tick_length = tick_length_base;
 196         time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
 197         time_offset -= time_adj;
 198         tick_length += time_adj;
 199
 200         if (unlikely(time_adjust)) {
 201                 if (time_adjust > MAX_TICKADJ) {
 202                         time_adjust -= MAX_TICKADJ;
 203                         tick_length += MAX_TICKADJ_SCALED;
 204                 } else if (time_adjust < -MAX_TICKADJ) {
 205                         time_adjust += MAX_TICKADJ;
 206                         tick_length -= MAX_TICKADJ_SCALED;
 207                 } else {
 208                         tick_length += (s64)(time_adjust * NSEC_PER_USEC /
 209                                         NTP_INTERVAL_FREQ) << NTP_SCALE_SHIFT;
 210                         time_adjust = 0;
 211                 }
 212         }
 213 }
 214
 215 #ifdef CONFIG_GENERIC_CMOS_UPDATE
 216
 217 /* Disable the cmos update - used by virtualization and embedded */
 218 int no_sync_cmos_clock  __read_mostly;
 219
 220 static void sync_cmos_clock(struct work_struct *work);
 221
 222 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
 223
 224 static void sync_cmos_clock(struct work_struct *work)
 225 {
 226         struct timespec now, next;
 227         int fail = 1;
 228
 229         /*
 230          * If we have an externally synchronized Linux clock, then update
 231          * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
 232          * called as close as possible to 500 ms before the new second starts.
 233          * This code is run on a timer.  If the clock is set, that timer
 234          * may not expire at the correct time.  Thus, we adjust...
 235          */
 236         if (!ntp_synced())
 237                 /*
 238                  * Not synced, exit, do not restart a timer (if one is
 239                  * running, let it run out).
 240                  */
 241                 return;
 242
 243         getnstimeofday(&now);
 244         if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
 245                 fail = update_persistent_clock(now);
 246
 247         next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
 248         if (next.tv_nsec <= 0)
 249                 next.tv_nsec += NSEC_PER_SEC;
 250
 251         if (!fail)
 252                 next.tv_sec = 659;
 253         else
 254                 next.tv_sec = 0;
 255
 256         if (next.tv_nsec >= NSEC_PER_SEC) {
 257                 next.tv_sec++;
 258                 next.tv_nsec -= NSEC_PER_SEC;
 259         }
 260         schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
 261 }
 262
 263 static void notify_cmos_timer(void)
 264 {
 265         if (!no_sync_cmos_clock)
 266                 schedule_delayed_work(&sync_cmos_work, 0);
 267 }
 268
 269 #else
 270 static inline void notify_cmos_timer(void) { }
 271 #endif
 272
 273 /* adjtimex mainly allows reading (and writing, if superuser) of
 274  * kernel time-keeping variables. used by xntpd.
 275  */
 276 int do_adjtimex(struct timex *txc)
 277 {
 278         struct timespec ts;
 279         int result;
 280
 281         /* Validate the data before disabling interrupts */
 282         if (txc->modes & ADJ_ADJTIME) {
 283                 /* singleshot must not be used with any other mode bits */
 284                 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
 285                         return -EINVAL;
 286                 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
 287                     !capable(CAP_SYS_TIME))
 288                         return -EPERM;
 289         } else {
 290                 /* In order to modify anything, you gotta be super-user! */
 291                  if (txc->modes && !capable(CAP_SYS_TIME))
 292                         return -EPERM;
 293
 294                 /* if the quartz is off by more than 10% something is VERY wrong! */
 295                 if (txc->modes & ADJ_TICK &&
 296                     (txc->tick <  900000/USER_HZ ||
 297                      txc->tick > 1100000/USER_HZ))
 298                                 return -EINVAL;
 299
 300                 if (txc->modes & ADJ_STATUS && time_state != TIME_OK)
 301                         hrtimer_cancel(&leap_timer);
 302         }
 303
 304         getnstimeofday(&ts);
 305
 306         write_seqlock_irq(&xtime_lock);
 307
 308         /* If there are input parameters, then process them */
 309         if (txc->modes & ADJ_ADJTIME) {
 310                 long save_adjust = time_adjust;
 311
 312                 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
 313                         /* adjtime() is independent from ntp_adjtime() */
 314                         time_adjust = txc->offset;
 315                         ntp_update_frequency();
 316                 }
 317                 txc->offset = save_adjust;
 318                 goto adj_done;
 319         }
 320         if (txc->modes) {
 321                 long sec;
 322
 323                 if (txc->modes & ADJ_STATUS) {
 324                         if ((time_status & STA_PLL) &&
 325                             !(txc->status & STA_PLL)) {
 326                                 time_state = TIME_OK;
 327                                 time_status = STA_UNSYNC;
 328                         }
 329                         /* only set allowed bits */
 330                         time_status &= STA_RONLY;
 331                         time_status |= txc->status & ~STA_RONLY;
 332
 333                         switch (time_state) {
 334                         case TIME_OK:
 335                         start_timer:
 336                                 sec = ts.tv_sec;
 337                                 if (time_status & STA_INS) {
 338                                         time_state = TIME_INS;
 339                                         sec += 86400 - sec % 86400;
 340                                         hrtimer_start(&leap_timer, ktime_set(sec, 0), HRTIMER_MODE_ABS);
 341                                 } else if (time_status & STA_DEL) {
 342                                         time_state = TIME_DEL;
 343                                         sec += 86400 - (sec + 1) % 86400;
 344                                         hrtimer_start(&leap_timer, ktime_set(sec, 0), HRTIMER_MODE_ABS);
 345                                 }
 346                                 break;
 347                         case TIME_INS:
 348                         case TIME_DEL:
 349                                 time_state = TIME_OK;
 350                                 goto start_timer;
 351                                 break;
 352                         case TIME_WAIT:
 353                                 if (!(time_status & (STA_INS | STA_DEL)))
 354                                         time_state = TIME_OK;
 355                                 break;
 356                         case TIME_OOP:
 357                                 hrtimer_restart(&leap_timer);
 358                                 break;
 359                         }
 360                 }
 361
 362                 if (txc->modes & ADJ_NANO)
 363                         time_status |= STA_NANO;
 364                 if (txc->modes & ADJ_MICRO)
 365                         time_status &= ~STA_NANO;
 366
 367                 if (txc->modes & ADJ_FREQUENCY) {
 368                         time_freq = (s64)txc->freq * PPM_SCALE;
 369                         time_freq = min(time_freq, MAXFREQ_SCALED);
 370                         time_freq = max(time_freq, -MAXFREQ_SCALED);
 371                 }
 372
 373                 if (txc->modes & ADJ_MAXERROR)
 374                         time_maxerror = txc->maxerror;
 375                 if (txc->modes & ADJ_ESTERROR)
 376                         time_esterror = txc->esterror;
 377
 378                 if (txc->modes & ADJ_TIMECONST) {
 379                         time_constant = txc->constant;
 380                         if (!(time_status & STA_NANO))
 381                                 time_constant += 4;
 382                         time_constant = min(time_constant, (long)MAXTC);
 383                         time_constant = max(time_constant, 0l);
 384                 }
 385
 386                 if (txc->modes & ADJ_TAI && txc->constant > 0)
 387                         time_tai = txc->constant;
 388
 389                 if (txc->modes & ADJ_OFFSET)
 390                         ntp_update_offset(txc->offset);
 391                 if (txc->modes & ADJ_TICK)
 392                         tick_usec = txc->tick;
 393
 394                 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 395                         ntp_update_frequency();
 396         }
 397
 398         txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
 399                                   NTP_SCALE_SHIFT);
 400         if (!(time_status & STA_NANO))
 401                 txc->offset /= NSEC_PER_USEC;
 402
 403 adj_done:
 404         result = time_state;    /* mostly `TIME_OK' */
 405         if (time_status & (STA_UNSYNC|STA_CLOCKERR))
 406                 result = TIME_ERROR;
 407
 408         txc->freq          = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
 409                                          (s64)PPM_SCALE_INV, NTP_SCALE_SHIFT);
 410         txc->maxerror      = time_maxerror;
 411         txc->esterror      = time_esterror;
 412         txc->status        = time_status;
 413         txc->constant      = time_constant;
 414         txc->precision     = 1;
 415         txc->tolerance     = MAXFREQ_SCALED / PPM_SCALE;
 416         txc->tick          = tick_usec;
 417         txc->tai           = time_tai;
 418
 419         /* PPS is not implemented, so these are zero */
 420         txc->ppsfreq       = 0;
 421         txc->jitter        = 0;
 422         txc->shift         = 0;
 423         txc->stabil        = 0;
 424         txc->jitcnt        = 0;
 425         txc->calcnt        = 0;
 426         txc->errcnt        = 0;
 427         txc->stbcnt        = 0;
 428         write_sequnlock_irq(&xtime_lock);
 429
 430         txc->time.tv_sec = ts.tv_sec;
 431         txc->time.tv_usec = ts.tv_nsec;
 432         if (!(time_status & STA_NANO))
 433                 txc->time.tv_usec /= NSEC_PER_USEC;
 434
 435         notify_cmos_timer();
 436
 437         return result;
 438 }
 439
 440 static int __init ntp_tick_adj_setup(char *str)
 441 {
 442         ntp_tick_adj = simple_strtol(str, NULL, 0);
 443         return 1;
 444 }
 445
 446 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
 447
 448 void __init ntp_init(void)
 449 {
 450         ntp_clear();
 451         hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
 452         leap_timer.function = ntp_leap_second;
 453 }