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/timer.h>
  14 #include <linux/timex.h>
  15 #include <linux/jiffies.h>
  16 #include <linux/hrtimer.h>
  17 #include <linux/capability.h>
  18 #include <asm/div64.h>
  19 #include <asm/timex.h>
  20
  21 /*
  22  * Timekeeping variables
  23  */
  24 unsigned long tick_usec = TICK_USEC;            /* USER_HZ period (usec) */
  25 unsigned long tick_nsec;                        /* ACTHZ period (nsec) */
  26 static u64 tick_length, tick_length_base;
  27
  28 #define MAX_TICKADJ             500             /* microsecs */
  29 #define MAX_TICKADJ_SCALED      (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
  30                                   TICK_LENGTH_SHIFT) / NTP_INTERVAL_FREQ)
  31
  32 /*
  33  * phase-lock loop variables
  34  */
  35 /* TIME_ERROR prevents overwriting the CMOS clock */
  36 static int time_state = TIME_OK;        /* clock synchronization status */
  37 int time_status = STA_UNSYNC;           /* clock status bits            */
  38 static s64 time_offset;         /* time adjustment (ns)         */
  39 static long time_constant = 2;          /* pll time constant            */
  40 long time_maxerror = NTP_PHASE_LIMIT;   /* maximum error (us)           */
  41 long time_esterror = NTP_PHASE_LIMIT;   /* estimated error (us)         */
  42 long time_freq;                         /* frequency offset (scaled ppm)*/
  43 static long time_reftime;               /* time at last adjustment (s)  */
  44 long time_adjust;
  45 static long ntp_tick_adj;
  46
  47 static void ntp_update_frequency(void)
  48 {
  49         u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
  50                                 << TICK_LENGTH_SHIFT;
  51         second_length += (s64)ntp_tick_adj << TICK_LENGTH_SHIFT;
  52         second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);
  53
  54         tick_length_base = second_length;
  55
  56         do_div(second_length, HZ);
  57         tick_nsec = second_length >> TICK_LENGTH_SHIFT;
  58
  59         do_div(tick_length_base, NTP_INTERVAL_FREQ);
  60 }
  61
  62 /**
  63  * ntp_clear - Clears the NTP state variables
  64  *
  65  * Must be called while holding a write on the xtime_lock
  66  */
  67 void ntp_clear(void)
  68 {
  69         time_adjust = 0;                /* stop active adjtime() */
  70         time_status |= STA_UNSYNC;
  71         time_maxerror = NTP_PHASE_LIMIT;
  72         time_esterror = NTP_PHASE_LIMIT;
  73
  74         ntp_update_frequency();
  75
  76         tick_length = tick_length_base;
  77         time_offset = 0;
  78 }
  79
  80 /*
  81  * this routine handles the overflow of the microsecond field
  82  *
  83  * The tricky bits of code to handle the accurate clock support
  84  * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
  85  * They were originally developed for SUN and DEC kernels.
  86  * All the kudos should go to Dave for this stuff.
  87  */
  88 void second_overflow(void)
  89 {
  90         long time_adj;
  91
  92         /* Bump the maxerror field */
  93         time_maxerror += MAXFREQ >> SHIFT_USEC;
  94         if (time_maxerror > NTP_PHASE_LIMIT) {
  95                 time_maxerror = NTP_PHASE_LIMIT;
  96                 time_status |= STA_UNSYNC;
  97         }
  98
  99         /*
 100          * Leap second processing. If in leap-insert state at the end of the
 101          * day, the system clock is set back one second; if in leap-delete
 102          * state, the system clock is set ahead one second. The microtime()
 103          * routine or external clock driver will insure that reported time is
 104          * always monotonic. The ugly divides should be replaced.
 105          */
 106         switch (time_state) {
 107         case TIME_OK:
 108                 if (time_status & STA_INS)
 109                         time_state = TIME_INS;
 110                 else if (time_status & STA_DEL)
 111                         time_state = TIME_DEL;
 112                 break;
 113         case TIME_INS:
 114                 if (xtime.tv_sec % 86400 == 0) {
 115                         xtime.tv_sec--;
 116                         wall_to_monotonic.tv_sec++;
 117                         time_state = TIME_OOP;
 118                         printk(KERN_NOTICE "Clock: inserting leap second "
 119                                         "23:59:60 UTC\n");
 120                 }
 121                 break;
 122         case TIME_DEL:
 123                 if ((xtime.tv_sec + 1) % 86400 == 0) {
 124                         xtime.tv_sec++;
 125                         wall_to_monotonic.tv_sec--;
 126                         time_state = TIME_WAIT;
 127                         printk(KERN_NOTICE "Clock: deleting leap second "
 128                                         "23:59:59 UTC\n");
 129                 }
 130                 break;
 131         case TIME_OOP:
 132                 time_state = TIME_WAIT;
 133                 break;
 134         case TIME_WAIT:
 135                 if (!(time_status & (STA_INS | STA_DEL)))
 136                 time_state = TIME_OK;
 137         }
 138
 139         /*
 140          * Compute the phase adjustment for the next second. The offset is
 141          * reduced by a fixed factor times the time constant.
 142          */
 143         tick_length = tick_length_base;
 144         time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
 145         time_offset -= time_adj;
 146         tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);
 147
 148         if (unlikely(time_adjust)) {
 149                 if (time_adjust > MAX_TICKADJ) {
 150                         time_adjust -= MAX_TICKADJ;
 151                         tick_length += MAX_TICKADJ_SCALED;
 152                 } else if (time_adjust < -MAX_TICKADJ) {
 153                         time_adjust += MAX_TICKADJ;
 154                         tick_length -= MAX_TICKADJ_SCALED;
 155                 } else {
 156                         tick_length += (s64)(time_adjust * NSEC_PER_USEC /
 157                                         NTP_INTERVAL_FREQ) << TICK_LENGTH_SHIFT;
 158                         time_adjust = 0;
 159                 }
 160         }
 161 }
 162
 163 /*
 164  * Return how long ticks are at the moment, that is, how much time
 165  * update_wall_time_one_tick will add to xtime next time we call it
 166  * (assuming no calls to do_adjtimex in the meantime).
 167  * The return value is in fixed-point nanoseconds shifted by the
 168  * specified number of bits to the right of the binary point.
 169  * This function has no side-effects.
 170  */
 171 u64 current_tick_length(void)
 172 {
 173         return tick_length;
 174 }
 175
 176 #ifdef CONFIG_GENERIC_CMOS_UPDATE
 177
 178 /* Disable the cmos update - used by virtualization and embedded */
 179 int no_sync_cmos_clock  __read_mostly;
 180
 181 static void sync_cmos_clock(unsigned long dummy);
 182
 183 static DEFINE_TIMER(sync_cmos_timer, sync_cmos_clock, 0, 0);
 184
 185 static void sync_cmos_clock(unsigned long dummy)
 186 {
 187         struct timespec now, next;
 188         int fail = 1;
 189
 190         /*
 191          * If we have an externally synchronized Linux clock, then update
 192          * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
 193          * called as close as possible to 500 ms before the new second starts.
 194          * This code is run on a timer.  If the clock is set, that timer
 195          * may not expire at the correct time.  Thus, we adjust...
 196          */
 197         if (!ntp_synced())
 198                 /*
 199                  * Not synced, exit, do not restart a timer (if one is
 200                  * running, let it run out).
 201                  */
 202                 return;
 203
 204         getnstimeofday(&now);
 205         if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
 206                 fail = update_persistent_clock(now);
 207
 208         next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec;
 209         if (next.tv_nsec <= 0)
 210                 next.tv_nsec += NSEC_PER_SEC;
 211
 212         if (!fail)
 213                 next.tv_sec = 659;
 214         else
 215                 next.tv_sec = 0;
 216
 217         if (next.tv_nsec >= NSEC_PER_SEC) {
 218                 next.tv_sec++;
 219                 next.tv_nsec -= NSEC_PER_SEC;
 220         }
 221         mod_timer(&sync_cmos_timer, jiffies + timespec_to_jiffies(&next));
 222 }
 223
 224 static void notify_cmos_timer(void)
 225 {
 226         if (!no_sync_cmos_clock)
 227                 mod_timer(&sync_cmos_timer, jiffies + 1);
 228 }
 229
 230 #else
 231 static inline void notify_cmos_timer(void) { }
 232 #endif
 233
 234 /* adjtimex mainly allows reading (and writing, if superuser) of
 235  * kernel time-keeping variables. used by xntpd.
 236  */
 237 int do_adjtimex(struct timex *txc)
 238 {
 239         long mtemp, save_adjust, rem;
 240         s64 freq_adj, temp64;
 241         int result;
 242
 243         /* In order to modify anything, you gotta be super-user! */
 244         if (txc->modes && !capable(CAP_SYS_TIME))
 245                 return -EPERM;
 246
 247         /* Now we validate the data before disabling interrupts */
 248
 249         if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT) {
 250           /* singleshot must not be used with any other mode bits */
 251                 if (txc->modes != ADJ_OFFSET_SINGLESHOT &&
 252                                         txc->modes != ADJ_OFFSET_SS_READ)
 253                         return -EINVAL;
 254         }
 255
 256         if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
 257           /* adjustment Offset limited to +- .512 seconds */
 258                 if (txc->offset <= - MAXPHASE || txc->offset >= MAXPHASE )
 259                         return -EINVAL;
 260
 261         /* if the quartz is off by more than 10% something is VERY wrong ! */
 262         if (txc->modes & ADJ_TICK)
 263                 if (txc->tick <  900000/USER_HZ ||
 264                     txc->tick > 1100000/USER_HZ)
 265                         return -EINVAL;
 266
 267         write_seqlock_irq(&xtime_lock);
 268         result = time_state;    /* mostly `TIME_OK' */
 269
 270         /* Save for later - semantics of adjtime is to return old value */
 271         save_adjust = time_adjust;
 272
 273 #if 0   /* STA_CLOCKERR is never set yet */
 274         time_status &= ~STA_CLOCKERR;           /* reset STA_CLOCKERR */
 275 #endif
 276         /* If there are input parameters, then process them */
 277         if (txc->modes)
 278         {
 279             if (txc->modes & ADJ_STATUS)        /* only set allowed bits */
 280                 time_status =  (txc->status & ~STA_RONLY) |
 281                               (time_status & STA_RONLY);
 282
 283             if (txc->modes & ADJ_FREQUENCY) {   /* p. 22 */
 284                 if (txc->freq > MAXFREQ || txc->freq < -MAXFREQ) {
 285                     result = -EINVAL;
 286                     goto leave;
 287                 }
 288                 time_freq = ((s64)txc->freq * NSEC_PER_USEC)
 289                                 >> (SHIFT_USEC - SHIFT_NSEC);
 290             }
 291
 292             if (txc->modes & ADJ_MAXERROR) {
 293                 if (txc->maxerror < 0 || txc->maxerror >= NTP_PHASE_LIMIT) {
 294                     result = -EINVAL;
 295                     goto leave;
 296                 }
 297                 time_maxerror = txc->maxerror;
 298             }
 299
 300             if (txc->modes & ADJ_ESTERROR) {
 301                 if (txc->esterror < 0 || txc->esterror >= NTP_PHASE_LIMIT) {
 302                     result = -EINVAL;
 303                     goto leave;
 304                 }
 305                 time_esterror = txc->esterror;
 306             }
 307
 308             if (txc->modes & ADJ_TIMECONST) {   /* p. 24 */
 309                 if (txc->constant < 0) {        /* NTP v4 uses values > 6 */
 310                     result = -EINVAL;
 311                     goto leave;
 312                 }
 313                 time_constant = min(txc->constant + 4, (long)MAXTC);
 314             }
 315
 316             if (txc->modes & ADJ_OFFSET) {      /* values checked earlier */
 317                 if (txc->modes == ADJ_OFFSET_SINGLESHOT) {
 318                     /* adjtime() is independent from ntp_adjtime() */
 319                     time_adjust = txc->offset;
 320                 }
 321                 else if (time_status & STA_PLL) {
 322                     time_offset = txc->offset * NSEC_PER_USEC;
 323
 324                     /*
 325                      * Scale the phase adjustment and
 326                      * clamp to the operating range.
 327                      */
 328                     time_offset = min(time_offset, (s64)MAXPHASE * NSEC_PER_USEC);
 329                     time_offset = max(time_offset, (s64)-MAXPHASE * NSEC_PER_USEC);
 330
 331                     /*
 332                      * Select whether the frequency is to be controlled
 333                      * and in which mode (PLL or FLL). Clamp to the operating
 334                      * range. Ugly multiply/divide should be replaced someday.
 335                      */
 336
 337                     if (time_status & STA_FREQHOLD || time_reftime == 0)
 338                         time_reftime = xtime.tv_sec;
 339                     mtemp = xtime.tv_sec - time_reftime;
 340                     time_reftime = xtime.tv_sec;
 341
 342                     freq_adj = time_offset * mtemp;
 343                     freq_adj = shift_right(freq_adj, time_constant * 2 +
 344                                            (SHIFT_PLL + 2) * 2 - SHIFT_NSEC);
 345                     if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
 346                         u64 utemp64;
 347                         temp64 = time_offset << (SHIFT_NSEC - SHIFT_FLL);
 348                         if (time_offset < 0) {
 349                             utemp64 = -temp64;
 350                             do_div(utemp64, mtemp);
 351                             freq_adj -= utemp64;
 352                         } else {
 353                             utemp64 = temp64;
 354                             do_div(utemp64, mtemp);
 355                             freq_adj += utemp64;
 356                         }
 357                     }
 358                     freq_adj += time_freq;
 359                     freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
 360                     time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
 361                     time_offset = div_long_long_rem_signed(time_offset,
 362                                                            NTP_INTERVAL_FREQ,
 363                                                            &rem);
 364                     time_offset <<= SHIFT_UPDATE;
 365                 } /* STA_PLL */
 366             } /* txc->modes & ADJ_OFFSET */
 367             if (txc->modes & ADJ_TICK)
 368                 tick_usec = txc->tick;
 369
 370             if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 371                     ntp_update_frequency();
 372         } /* txc->modes */
 373 leave:  if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
 374                 result = TIME_ERROR;
 375
 376         if ((txc->modes == ADJ_OFFSET_SINGLESHOT) ||
 377                         (txc->modes == ADJ_OFFSET_SS_READ))
 378                 txc->offset = save_adjust;
 379         else
 380                 txc->offset = ((long)shift_right(time_offset, SHIFT_UPDATE)) *
 381                                 NTP_INTERVAL_FREQ / 1000;
 382         txc->freq          = (time_freq / NSEC_PER_USEC) <<
 383                                 (SHIFT_USEC - SHIFT_NSEC);
 384         txc->maxerror      = time_maxerror;
 385         txc->esterror      = time_esterror;
 386         txc->status        = time_status;
 387         txc->constant      = time_constant;
 388         txc->precision     = 1;
 389         txc->tolerance     = MAXFREQ;
 390         txc->tick          = tick_usec;
 391
 392         /* PPS is not implemented, so these are zero */
 393         txc->ppsfreq       = 0;
 394         txc->jitter        = 0;
 395         txc->shift         = 0;
 396         txc->stabil        = 0;
 397         txc->jitcnt        = 0;
 398         txc->calcnt        = 0;
 399         txc->errcnt        = 0;
 400         txc->stbcnt        = 0;
 401         write_sequnlock_irq(&xtime_lock);
 402         do_gettimeofday(&txc->time);
 403         notify_cmos_timer();
 404         return(result);
 405 }
 406
 407 static int __init ntp_tick_adj_setup(char *str)
 408 {
 409         ntp_tick_adj = simple_strtol(str, NULL, 0);
 410         return 1;
 411 }
 412
 413 __setup("ntp_tick_adj=", ntp_tick_adj_setup);