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