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