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