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 static int time_state = TIME_OK;        /* clock synchronization status */
  34 int time_status = STA_UNSYNC;           /* clock status bits            */
  35 static long time_offset;                /* time adjustment (ns)         */
  36 static long time_constant = 2;          /* pll time constant            */
  37 long time_maxerror = NTP_PHASE_LIMIT;   /* maximum error (us)           */
  38 long time_esterror = NTP_PHASE_LIMIT;   /* estimated error (us)         */
  39 long time_freq;                         /* frequency offset (scaled ppm)*/
  40 static long time_reftime;               /* time at last adjustment (s)  */
  41 long time_adjust;
  42
  43 #define CLOCK_TICK_OVERFLOW     (LATCH * HZ - CLOCK_TICK_RATE)
  44 #define CLOCK_TICK_ADJUST       (((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / \
  45                                         (s64)CLOCK_TICK_RATE)
  46
  47 static void ntp_update_frequency(void)
  48 {
  49         tick_length_base = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ) << TICK_LENGTH_SHIFT;
  50         tick_length_base += (s64)CLOCK_TICK_ADJUST << TICK_LENGTH_SHIFT;
  51         tick_length_base += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);
  52
  53         do_div(tick_length_base, HZ);
  54
  55         tick_nsec = tick_length_base >> TICK_LENGTH_SHIFT;
  56 }
  57
  58 /**
  59  * ntp_clear - Clears the NTP state variables
  60  *
  61  * Must be called while holding a write on the xtime_lock
  62  */
  63 void ntp_clear(void)
  64 {
  65         time_adjust = 0;                /* stop active adjtime() */
  66         time_status |= STA_UNSYNC;
  67         time_maxerror = NTP_PHASE_LIMIT;
  68         time_esterror = NTP_PHASE_LIMIT;
  69
  70         ntp_update_frequency();
  71
  72         tick_length = tick_length_base;
  73         time_offset = 0;
  74 }
  75
  76 /*
  77  * this routine handles the overflow of the microsecond field
  78  *
  79  * The tricky bits of code to handle the accurate clock support
  80  * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
  81  * They were originally developed for SUN and DEC kernels.
  82  * All the kudos should go to Dave for this stuff.
  83  */
  84 void second_overflow(void)
  85 {
  86         long time_adj;
  87
  88         /* Bump the maxerror field */
  89         time_maxerror += MAXFREQ >> SHIFT_USEC;
  90         if (time_maxerror > NTP_PHASE_LIMIT) {
  91                 time_maxerror = NTP_PHASE_LIMIT;
  92                 time_status |= STA_UNSYNC;
  93         }
  94
  95         /*
  96          * Leap second processing. If in leap-insert state at the end of the
  97          * day, the system clock is set back one second; if in leap-delete
  98          * state, the system clock is set ahead one second. The microtime()
  99          * routine or external clock driver will insure that reported time is
 100          * always monotonic. The ugly divides should be replaced.
 101          */
 102         switch (time_state) {
 103         case TIME_OK:
 104                 if (time_status & STA_INS)
 105                         time_state = TIME_INS;
 106                 else if (time_status & STA_DEL)
 107                         time_state = TIME_DEL;
 108                 break;
 109         case TIME_INS:
 110                 if (xtime.tv_sec % 86400 == 0) {
 111                         xtime.tv_sec--;
 112                         wall_to_monotonic.tv_sec++;
 113                         /*
 114                          * The timer interpolator will make time change
 115                          * gradually instead of an immediate jump by one second
 116                          */
 117                         time_interpolator_update(-NSEC_PER_SEC);
 118                         time_state = TIME_OOP;
 119                         clock_was_set();
 120                         printk(KERN_NOTICE "Clock: inserting leap second "
 121                                         "23:59:60 UTC\n");
 122                 }
 123                 break;
 124         case TIME_DEL:
 125                 if ((xtime.tv_sec + 1) % 86400 == 0) {
 126                         xtime.tv_sec++;
 127                         wall_to_monotonic.tv_sec--;
 128                         /*
 129                          * Use of time interpolator for a gradual change of
 130                          * time
 131                          */
 132                         time_interpolator_update(NSEC_PER_SEC);
 133                         time_state = TIME_WAIT;
 134                         clock_was_set();
 135                         printk(KERN_NOTICE "Clock: deleting leap second "
 136                                         "23:59:59 UTC\n");
 137                 }
 138                 break;
 139         case TIME_OOP:
 140                 time_state = TIME_WAIT;
 141                 break;
 142         case TIME_WAIT:
 143                 if (!(time_status & (STA_INS | STA_DEL)))
 144                 time_state = TIME_OK;
 145         }
 146
 147         /*
 148          * Compute the phase adjustment for the next second. The offset is
 149          * reduced by a fixed factor times the time constant.
 150          */
 151         tick_length = tick_length_base;
 152         time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
 153         time_offset -= time_adj;
 154         tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);
 155
 156         if (unlikely(time_adjust)) {
 157                 if (time_adjust > MAX_TICKADJ) {
 158                         time_adjust -= MAX_TICKADJ;
 159                         tick_length += MAX_TICKADJ_SCALED;
 160                 } else if (time_adjust < -MAX_TICKADJ) {
 161                         time_adjust += MAX_TICKADJ;
 162                         tick_length -= MAX_TICKADJ_SCALED;
 163                 } else {
 164                         tick_length += (s64)(time_adjust * NSEC_PER_USEC /
 165                                              HZ) << TICK_LENGTH_SHIFT;
 166                         time_adjust = 0;
 167                 }
 168         }
 169 }
 170
 171 /*
 172  * Return how long ticks are at the moment, that is, how much time
 173  * update_wall_time_one_tick will add to xtime next time we call it
 174  * (assuming no calls to do_adjtimex in the meantime).
 175  * The return value is in fixed-point nanoseconds shifted by the
 176  * specified number of bits to the right of the binary point.
 177  * This function has no side-effects.
 178  */
 179 u64 current_tick_length(void)
 180 {
 181         return tick_length;
 182 }
 183
 184
 185 void __attribute__ ((weak)) notify_arch_cmos_timer(void)
 186 {
 187         return;
 188 }
 189
 190 /* adjtimex mainly allows reading (and writing, if superuser) of
 191  * kernel time-keeping variables. used by xntpd.
 192  */
 193 int do_adjtimex(struct timex *txc)
 194 {
 195         long ltemp, mtemp, save_adjust;
 196         s64 freq_adj, temp64;
 197         int result;
 198
 199         /* In order to modify anything, you gotta be super-user! */
 200         if (txc->modes && !capable(CAP_SYS_TIME))
 201                 return -EPERM;
 202
 203         /* Now we validate the data before disabling interrupts */
 204
 205         if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
 206           /* singleshot must not be used with any other mode bits */
 207                 if (txc->modes != ADJ_OFFSET_SINGLESHOT)
 208                         return -EINVAL;
 209
 210         if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
 211           /* adjustment Offset limited to +- .512 seconds */
 212                 if (txc->offset <= - MAXPHASE || txc->offset >= MAXPHASE )
 213                         return -EINVAL;
 214
 215         /* if the quartz is off by more than 10% something is VERY wrong ! */
 216         if (txc->modes & ADJ_TICK)
 217                 if (txc->tick <  900000/USER_HZ ||
 218                     txc->tick > 1100000/USER_HZ)
 219                         return -EINVAL;
 220
 221         write_seqlock_irq(&xtime_lock);
 222         result = time_state;    /* mostly `TIME_OK' */
 223
 224         /* Save for later - semantics of adjtime is to return old value */
 225         save_adjust = time_adjust;
 226
 227 #if 0   /* STA_CLOCKERR is never set yet */
 228         time_status &= ~STA_CLOCKERR;           /* reset STA_CLOCKERR */
 229 #endif
 230         /* If there are input parameters, then process them */
 231         if (txc->modes)
 232         {
 233             if (txc->modes & ADJ_STATUS)        /* only set allowed bits */
 234                 time_status =  (txc->status & ~STA_RONLY) |
 235                               (time_status & STA_RONLY);
 236
 237             if (txc->modes & ADJ_FREQUENCY) {   /* p. 22 */
 238                 if (txc->freq > MAXFREQ || txc->freq < -MAXFREQ) {
 239                     result = -EINVAL;
 240                     goto leave;
 241                 }
 242                 time_freq = ((s64)txc->freq * NSEC_PER_USEC) >> (SHIFT_USEC - SHIFT_NSEC);
 243             }
 244
 245             if (txc->modes & ADJ_MAXERROR) {
 246                 if (txc->maxerror < 0 || txc->maxerror >= NTP_PHASE_LIMIT) {
 247                     result = -EINVAL;
 248                     goto leave;
 249                 }
 250                 time_maxerror = txc->maxerror;
 251             }
 252
 253             if (txc->modes & ADJ_ESTERROR) {
 254                 if (txc->esterror < 0 || txc->esterror >= NTP_PHASE_LIMIT) {
 255                     result = -EINVAL;
 256                     goto leave;
 257                 }
 258                 time_esterror = txc->esterror;
 259             }
 260
 261             if (txc->modes & ADJ_TIMECONST) {   /* p. 24 */
 262                 if (txc->constant < 0) {        /* NTP v4 uses values > 6 */
 263                     result = -EINVAL;
 264                     goto leave;
 265                 }
 266                 time_constant = min(txc->constant + 4, (long)MAXTC);
 267             }
 268
 269             if (txc->modes & ADJ_OFFSET) {      /* values checked earlier */
 270                 if (txc->modes == ADJ_OFFSET_SINGLESHOT) {
 271                     /* adjtime() is independent from ntp_adjtime() */
 272                     time_adjust = txc->offset;
 273                 }
 274                 else if (time_status & STA_PLL) {
 275                     ltemp = txc->offset * NSEC_PER_USEC;
 276
 277                     /*
 278                      * Scale the phase adjustment and
 279                      * clamp to the operating range.
 280                      */
 281                     time_offset = min(ltemp, MAXPHASE * NSEC_PER_USEC);
 282                     time_offset = max(time_offset, -MAXPHASE * NSEC_PER_USEC);
 283
 284                     /*
 285                      * Select whether the frequency is to be controlled
 286                      * and in which mode (PLL or FLL). Clamp to the operating
 287                      * range. Ugly multiply/divide should be replaced someday.
 288                      */
 289
 290                     if (time_status & STA_FREQHOLD || time_reftime == 0)
 291                         time_reftime = xtime.tv_sec;
 292                     mtemp = xtime.tv_sec - time_reftime;
 293                     time_reftime = xtime.tv_sec;
 294
 295                     freq_adj = (s64)time_offset * mtemp;
 296                     freq_adj = shift_right(freq_adj, time_constant * 2 +
 297                                            (SHIFT_PLL + 2) * 2 - SHIFT_NSEC);
 298                     if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
 299                         temp64 = (s64)time_offset << (SHIFT_NSEC - SHIFT_FLL);
 300                         if (time_offset < 0) {
 301                             temp64 = -temp64;
 302                             do_div(temp64, mtemp);
 303                             freq_adj -= temp64;
 304                         } else {
 305                             do_div(temp64, mtemp);
 306                             freq_adj += temp64;
 307                         }
 308                     }
 309                     freq_adj += time_freq;
 310                     freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
 311                     time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
 312                     time_offset = (time_offset / HZ) << SHIFT_UPDATE;
 313                 } /* STA_PLL */
 314             } /* txc->modes & ADJ_OFFSET */
 315             if (txc->modes & ADJ_TICK)
 316                 tick_usec = txc->tick;
 317
 318             if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 319                     ntp_update_frequency();
 320         } /* txc->modes */
 321 leave:  if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
 322                 result = TIME_ERROR;
 323
 324         if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
 325             txc->offset    = save_adjust;
 326         else
 327             txc->offset    = shift_right(time_offset, SHIFT_UPDATE) * HZ / 1000;
 328         txc->freq          = (time_freq / NSEC_PER_USEC) << (SHIFT_USEC - SHIFT_NSEC);
 329         txc->maxerror      = time_maxerror;
 330         txc->esterror      = time_esterror;
 331         txc->status        = time_status;
 332         txc->constant      = time_constant;
 333         txc->precision     = 1;
 334         txc->tolerance     = MAXFREQ;
 335         txc->tick          = tick_usec;
 336
 337         /* PPS is not implemented, so these are zero */
 338         txc->ppsfreq       = 0;
 339         txc->jitter        = 0;
 340         txc->shift         = 0;
 341         txc->stabil        = 0;
 342         txc->jitcnt        = 0;
 343         txc->calcnt        = 0;
 344         txc->errcnt        = 0;
 345         txc->stbcnt        = 0;
 346         write_sequnlock_irq(&xtime_lock);
 347         do_gettimeofday(&txc->time);
 348         notify_arch_cmos_timer();
 349         return(result);
 350 }