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
  15 #include <asm/div64.h>
  16 #include <asm/timex.h>
  17
  18 /*
  19  * Timekeeping variables
  20  */
  21 unsigned long tick_usec = TICK_USEC;            /* USER_HZ period (usec) */
  22 unsigned long tick_nsec;                        /* ACTHZ period (nsec) */
  23 static u64 tick_length, tick_length_base;
  24
  25 #define MAX_TICKADJ             500             /* microsecs */
  26 #define MAX_TICKADJ_SCALED      (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
  27                                   TICK_LENGTH_SHIFT) / HZ)
  28
  29 /*
  30  * phase-lock loop variables
  31  */
  32 /* TIME_ERROR prevents overwriting the CMOS clock */
  33 int time_state = TIME_OK;               /* clock synchronization status */
  34 int time_status = STA_UNSYNC;           /* clock status bits            */
  35 long time_offset;                       /* time adjustment (ns)         */
  36 long time_constant = 2;                 /* pll time constant            */
  37 long time_tolerance = MAXFREQ;          /* frequency tolerance (ppm)    */
  38 long time_precision = 1;                /* clock precision (us)         */
  39 long time_maxerror = NTP_PHASE_LIMIT;   /* maximum error (us)           */
  40 long time_esterror = NTP_PHASE_LIMIT;   /* estimated error (us)         */
  41 long time_freq;                         /* frequency offset (scaled ppm)*/
  42 long time_reftime;                      /* time at last adjustment (s)  */
  43 long time_adjust;
  44
  45 /**
  46  * ntp_clear - Clears the NTP state variables
  47  *
  48  * Must be called while holding a write on the xtime_lock
  49  */
  50 void ntp_clear(void)
  51 {
  52         time_adjust = 0;                /* stop active adjtime() */
  53         time_status |= STA_UNSYNC;
  54         time_maxerror = NTP_PHASE_LIMIT;
  55         time_esterror = NTP_PHASE_LIMIT;
  56
  57         ntp_update_frequency();
  58
  59         tick_length = tick_length_base;
  60         time_offset = 0;
  61 }
  62
  63 #define CLOCK_TICK_OVERFLOW     (LATCH * HZ - CLOCK_TICK_RATE)
  64 #define CLOCK_TICK_ADJUST       (((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / (s64)CLOCK_TICK_RATE)
  65
  66 void ntp_update_frequency(void)
  67 {
  68         tick_length_base = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ) << TICK_LENGTH_SHIFT;
  69         tick_length_base += (s64)CLOCK_TICK_ADJUST << TICK_LENGTH_SHIFT;
  70         tick_length_base += ((s64)time_freq * NSEC_PER_USEC) << (TICK_LENGTH_SHIFT - SHIFT_USEC);
  71
  72         do_div(tick_length_base, HZ);
  73
  74         tick_nsec = tick_length_base >> TICK_LENGTH_SHIFT;
  75 }
  76
  77 /*
  78  * this routine handles the overflow of the microsecond field
  79  *
  80  * The tricky bits of code to handle the accurate clock support
  81  * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
  82  * They were originally developed for SUN and DEC kernels.
  83  * All the kudos should go to Dave for this stuff.
  84  */
  85 void second_overflow(void)
  86 {
  87         long time_adj;
  88
  89         /* Bump the maxerror field */
  90         time_maxerror += time_tolerance >> SHIFT_USEC;
  91         if (time_maxerror > NTP_PHASE_LIMIT) {
  92                 time_maxerror = NTP_PHASE_LIMIT;
  93                 time_status |= STA_UNSYNC;
  94         }
  95
  96         /*
  97          * Leap second processing. If in leap-insert state at the end of the
  98          * day, the system clock is set back one second; if in leap-delete
  99          * state, the system clock is set ahead one second. The microtime()
 100          * routine or external clock driver will insure that reported time is
 101          * always monotonic. The ugly divides should be replaced.
 102          */
 103         switch (time_state) {
 104         case TIME_OK:
 105                 if (time_status & STA_INS)
 106                         time_state = TIME_INS;
 107                 else if (time_status & STA_DEL)
 108                         time_state = TIME_DEL;
 109                 break;
 110         case TIME_INS:
 111                 if (xtime.tv_sec % 86400 == 0) {
 112                         xtime.tv_sec--;
 113                         wall_to_monotonic.tv_sec++;
 114                         /*
 115                          * The timer interpolator will make time change
 116                          * gradually instead of an immediate jump by one second
 117                          */
 118                         time_interpolator_update(-NSEC_PER_SEC);
 119                         time_state = TIME_OOP;
 120                         clock_was_set();
 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                         /*
 130                          * Use of time interpolator for a gradual change of
 131                          * time
 132                          */
 133                         time_interpolator_update(NSEC_PER_SEC);
 134                         time_state = TIME_WAIT;
 135                         clock_was_set();
 136                         printk(KERN_NOTICE "Clock: deleting leap second "
 137                                         "23:59:59 UTC\n");
 138                 }
 139                 break;
 140         case TIME_OOP:
 141                 time_state = TIME_WAIT;
 142                 break;
 143         case TIME_WAIT:
 144                 if (!(time_status & (STA_INS | STA_DEL)))
 145                 time_state = TIME_OK;
 146         }
 147
 148         /*
 149          * Compute the phase adjustment for the next second. In PLL mode, the
 150          * offset is reduced by a fixed factor times the time constant. In FLL
 151          * mode the offset is used directly. In either mode, the maximum phase
 152          * adjustment for each second is clamped so as to spread the adjustment
 153          * over not more than the number of seconds between updates.
 154          */
 155         tick_length = tick_length_base;
 156         time_adj = time_offset;
 157         if (!(time_status & STA_FLL))
 158                 time_adj = shift_right(time_adj, SHIFT_KG + time_constant);
 159         time_adj = min(time_adj, -((MAXPHASE / HZ) << SHIFT_UPDATE) / MINSEC);
 160         time_adj = max(time_adj, ((MAXPHASE / HZ) << SHIFT_UPDATE) / MINSEC);
 161         time_offset -= time_adj;
 162         tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);
 163
 164         if (unlikely(time_adjust)) {
 165                 if (time_adjust > MAX_TICKADJ) {
 166                         time_adjust -= MAX_TICKADJ;
 167                         tick_length += MAX_TICKADJ_SCALED;
 168                 } else if (time_adjust < -MAX_TICKADJ) {
 169                         time_adjust += MAX_TICKADJ;
 170                         tick_length -= MAX_TICKADJ_SCALED;
 171                 } else {
 172                         time_adjust = 0;
 173                         tick_length += (s64)(time_adjust * NSEC_PER_USEC /
 174                                              HZ) << TICK_LENGTH_SHIFT;
 175                 }
 176         }
 177 }
 178
 179 /*
 180  * Return how long ticks are at the moment, that is, how much time
 181  * update_wall_time_one_tick will add to xtime next time we call it
 182  * (assuming no calls to do_adjtimex in the meantime).
 183  * The return value is in fixed-point nanoseconds shifted by the
 184  * specified number of bits to the right of the binary point.
 185  * This function has no side-effects.
 186  */
 187 u64 current_tick_length(void)
 188 {
 189         return tick_length;
 190 }
 191
 192
 193 void __attribute__ ((weak)) notify_arch_cmos_timer(void)
 194 {
 195         return;
 196 }
 197
 198 /* adjtimex mainly allows reading (and writing, if superuser) of
 199  * kernel time-keeping variables. used by xntpd.
 200  */
 201 int do_adjtimex(struct timex *txc)
 202 {
 203         long ltemp, mtemp, save_adjust;
 204         int result;
 205
 206         /* In order to modify anything, you gotta be super-user! */
 207         if (txc->modes && !capable(CAP_SYS_TIME))
 208                 return -EPERM;
 209
 210         /* Now we validate the data before disabling interrupts */
 211
 212         if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
 213           /* singleshot must not be used with any other mode bits */
 214                 if (txc->modes != ADJ_OFFSET_SINGLESHOT)
 215                         return -EINVAL;
 216
 217         if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
 218           /* adjustment Offset limited to +- .512 seconds */
 219                 if (txc->offset <= - MAXPHASE || txc->offset >= MAXPHASE )
 220                         return -EINVAL;
 221
 222         /* if the quartz is off by more than 10% something is VERY wrong ! */
 223         if (txc->modes & ADJ_TICK)
 224                 if (txc->tick <  900000/USER_HZ ||
 225                     txc->tick > 1100000/USER_HZ)
 226                         return -EINVAL;
 227
 228         write_seqlock_irq(&xtime_lock);
 229         result = time_state;    /* mostly `TIME_OK' */
 230
 231         /* Save for later - semantics of adjtime is to return old value */
 232         save_adjust = time_adjust;
 233
 234 #if 0   /* STA_CLOCKERR is never set yet */
 235         time_status &= ~STA_CLOCKERR;           /* reset STA_CLOCKERR */
 236 #endif
 237         /* If there are input parameters, then process them */
 238         if (txc->modes)
 239         {
 240             if (txc->modes & ADJ_STATUS)        /* only set allowed bits */
 241                 time_status =  (txc->status & ~STA_RONLY) |
 242                               (time_status & STA_RONLY);
 243
 244             if (txc->modes & ADJ_FREQUENCY) {   /* p. 22 */
 245                 if (txc->freq > MAXFREQ || txc->freq < -MAXFREQ) {
 246                     result = -EINVAL;
 247                     goto leave;
 248                 }
 249                 time_freq = txc->freq;
 250             }
 251
 252             if (txc->modes & ADJ_MAXERROR) {
 253                 if (txc->maxerror < 0 || txc->maxerror >= NTP_PHASE_LIMIT) {
 254                     result = -EINVAL;
 255                     goto leave;
 256                 }
 257                 time_maxerror = txc->maxerror;
 258             }
 259
 260             if (txc->modes & ADJ_ESTERROR) {
 261                 if (txc->esterror < 0 || txc->esterror >= NTP_PHASE_LIMIT) {
 262                     result = -EINVAL;
 263                     goto leave;
 264                 }
 265                 time_esterror = txc->esterror;
 266             }
 267
 268             if (txc->modes & ADJ_TIMECONST) {   /* p. 24 */
 269                 if (txc->constant < 0) {        /* NTP v4 uses values > 6 */
 270                     result = -EINVAL;
 271                     goto leave;
 272                 }
 273                 time_constant = txc->constant;
 274             }
 275
 276             if (txc->modes & ADJ_OFFSET) {      /* values checked earlier */
 277                 if (txc->modes == ADJ_OFFSET_SINGLESHOT) {
 278                     /* adjtime() is independent from ntp_adjtime() */
 279                     time_adjust = txc->offset;
 280                 }
 281                 else if (time_status & STA_PLL) {
 282                     ltemp = txc->offset;
 283
 284                     /*
 285                      * Scale the phase adjustment and
 286                      * clamp to the operating range.
 287                      */
 288                     time_offset = min(ltemp, MAXPHASE);
 289                     time_offset = max(time_offset, -MAXPHASE);
 290
 291                     /*
 292                      * Select whether the frequency is to be controlled
 293                      * and in which mode (PLL or FLL). Clamp to the operating
 294                      * range. Ugly multiply/divide should be replaced someday.
 295                      */
 296
 297                     if (time_status & STA_FREQHOLD || time_reftime == 0)
 298                         time_reftime = xtime.tv_sec;
 299                     mtemp = xtime.tv_sec - time_reftime;
 300                     time_reftime = xtime.tv_sec;
 301                     if (time_status & STA_FLL) {
 302                         if (mtemp >= MINSEC) {
 303                             ltemp = ((time_offset << 12) / mtemp) << (SHIFT_USEC - 12);
 304                             time_freq += shift_right(ltemp, SHIFT_KH);
 305                         } else /* calibration interval too short (p. 12) */
 306                                 result = TIME_ERROR;
 307                     } else {    /* PLL mode */
 308                         if (mtemp < MAXSEC) {
 309                             ltemp *= mtemp;
 310                             time_freq += shift_right(ltemp,(time_constant +
 311                                                        time_constant +
 312                                                        SHIFT_KF - SHIFT_USEC));
 313                         } else /* calibration interval too long (p. 12) */
 314                                 result = TIME_ERROR;
 315                     }
 316                     time_freq = min(time_freq, time_tolerance);
 317                     time_freq = max(time_freq, -time_tolerance);
 318                     time_offset = (time_offset * NSEC_PER_USEC / HZ) << SHIFT_UPDATE;
 319                 } /* STA_PLL */
 320             } /* txc->modes & ADJ_OFFSET */
 321             if (txc->modes & ADJ_TICK)
 322                 tick_usec = txc->tick;
 323
 324             if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 325                     ntp_update_frequency();
 326         } /* txc->modes */
 327 leave:  if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
 328                 result = TIME_ERROR;
 329
 330         if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
 331             txc->offset    = save_adjust;
 332         else
 333             txc->offset    = shift_right(time_offset, SHIFT_UPDATE) * HZ / 1000;
 334         txc->freq          = time_freq;
 335         txc->maxerror      = time_maxerror;
 336         txc->esterror      = time_esterror;
 337         txc->status        = time_status;
 338         txc->constant      = time_constant;
 339         txc->precision     = time_precision;
 340         txc->tolerance     = time_tolerance;
 341         txc->tick          = tick_usec;
 342
 343         /* PPS is not implemented, so these are zero */
 344         txc->ppsfreq       = 0;
 345         txc->jitter        = 0;
 346         txc->shift         = 0;
 347         txc->stabil        = 0;
 348         txc->jitcnt        = 0;
 349         txc->calcnt        = 0;
 350         txc->errcnt        = 0;
 351         txc->stbcnt        = 0;
 352         write_sequnlock_irq(&xtime_lock);
 353         do_gettimeofday(&txc->time);
 354         notify_arch_cmos_timer();
 355         return(result);
 356 }