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 #include <linux/capability.h>
  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                         time_state = TIME_OOP;
 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                         time_state = TIME_WAIT;
 129                         printk(KERN_NOTICE "Clock: deleting leap second "
 130                                         "23:59:59 UTC\n");
 131                 }
 132                 break;
 133         case TIME_OOP:
 134                 time_state = TIME_WAIT;
 135                 break;
 136         case TIME_WAIT:
 137                 if (!(time_status & (STA_INS | STA_DEL)))
 138                 time_state = TIME_OK;
 139         }
 140
 141         /*
 142          * Compute the phase adjustment for the next second. The offset is
 143          * reduced by a fixed factor times the time constant.
 144          */
 145         tick_length = tick_length_base;
 146         time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
 147         time_offset -= time_adj;
 148         tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);
 149
 150         if (unlikely(time_adjust)) {
 151                 if (time_adjust > MAX_TICKADJ) {
 152                         time_adjust -= MAX_TICKADJ;
 153                         tick_length += MAX_TICKADJ_SCALED;
 154                 } else if (time_adjust < -MAX_TICKADJ) {
 155                         time_adjust += MAX_TICKADJ;
 156                         tick_length -= MAX_TICKADJ_SCALED;
 157                 } else {
 158                         tick_length += (s64)(time_adjust * NSEC_PER_USEC /
 159                                         NTP_INTERVAL_FREQ) << TICK_LENGTH_SHIFT;
 160                         time_adjust = 0;
 161                 }
 162         }
 163 }
 164
 165 /*
 166  * Return how long ticks are at the moment, that is, how much time
 167  * update_wall_time_one_tick will add to xtime next time we call it
 168  * (assuming no calls to do_adjtimex in the meantime).
 169  * The return value is in fixed-point nanoseconds shifted by the
 170  * specified number of bits to the right of the binary point.
 171  * This function has no side-effects.
 172  */
 173 u64 current_tick_length(void)
 174 {
 175         return tick_length;
 176 }
 177
 178
 179 void __attribute__ ((weak)) notify_arch_cmos_timer(void)
 180 {
 181         return;
 182 }
 183
 184 /* adjtimex mainly allows reading (and writing, if superuser) of
 185  * kernel time-keeping variables. used by xntpd.
 186  */
 187 int do_adjtimex(struct timex *txc)
 188 {
 189         long mtemp, save_adjust, rem;
 190         s64 freq_adj, temp64;
 191         int result;
 192
 193         /* In order to modify anything, you gotta be super-user! */
 194         if (txc->modes && !capable(CAP_SYS_TIME))
 195                 return -EPERM;
 196
 197         /* Now we validate the data before disabling interrupts */
 198
 199         if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
 200           /* singleshot must not be used with any other mode bits */
 201                 if (txc->modes != ADJ_OFFSET_SINGLESHOT)
 202                         return -EINVAL;
 203
 204         if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
 205           /* adjustment Offset limited to +- .512 seconds */
 206                 if (txc->offset <= - MAXPHASE || txc->offset >= MAXPHASE )
 207                         return -EINVAL;
 208
 209         /* if the quartz is off by more than 10% something is VERY wrong ! */
 210         if (txc->modes & ADJ_TICK)
 211                 if (txc->tick <  900000/USER_HZ ||
 212                     txc->tick > 1100000/USER_HZ)
 213                         return -EINVAL;
 214
 215         write_seqlock_irq(&xtime_lock);
 216         result = time_state;    /* mostly `TIME_OK' */
 217
 218         /* Save for later - semantics of adjtime is to return old value */
 219         save_adjust = time_adjust;
 220
 221 #if 0   /* STA_CLOCKERR is never set yet */
 222         time_status &= ~STA_CLOCKERR;           /* reset STA_CLOCKERR */
 223 #endif
 224         /* If there are input parameters, then process them */
 225         if (txc->modes)
 226         {
 227             if (txc->modes & ADJ_STATUS)        /* only set allowed bits */
 228                 time_status =  (txc->status & ~STA_RONLY) |
 229                               (time_status & STA_RONLY);
 230
 231             if (txc->modes & ADJ_FREQUENCY) {   /* p. 22 */
 232                 if (txc->freq > MAXFREQ || txc->freq < -MAXFREQ) {
 233                     result = -EINVAL;
 234                     goto leave;
 235                 }
 236                 time_freq = ((s64)txc->freq * NSEC_PER_USEC)
 237                                 >> (SHIFT_USEC - SHIFT_NSEC);
 238             }
 239
 240             if (txc->modes & ADJ_MAXERROR) {
 241                 if (txc->maxerror < 0 || txc->maxerror >= NTP_PHASE_LIMIT) {
 242                     result = -EINVAL;
 243                     goto leave;
 244                 }
 245                 time_maxerror = txc->maxerror;
 246             }
 247
 248             if (txc->modes & ADJ_ESTERROR) {
 249                 if (txc->esterror < 0 || txc->esterror >= NTP_PHASE_LIMIT) {
 250                     result = -EINVAL;
 251                     goto leave;
 252                 }
 253                 time_esterror = txc->esterror;
 254             }
 255
 256             if (txc->modes & ADJ_TIMECONST) {   /* p. 24 */
 257                 if (txc->constant < 0) {        /* NTP v4 uses values > 6 */
 258                     result = -EINVAL;
 259                     goto leave;
 260                 }
 261                 time_constant = min(txc->constant + 4, (long)MAXTC);
 262             }
 263
 264             if (txc->modes & ADJ_OFFSET) {      /* values checked earlier */
 265                 if (txc->modes == ADJ_OFFSET_SINGLESHOT) {
 266                     /* adjtime() is independent from ntp_adjtime() */
 267                     time_adjust = txc->offset;
 268                 }
 269                 else if (time_status & STA_PLL) {
 270                     time_offset = txc->offset * NSEC_PER_USEC;
 271
 272                     /*
 273                      * Scale the phase adjustment and
 274                      * clamp to the operating range.
 275                      */
 276                     time_offset = min(time_offset, (s64)MAXPHASE * NSEC_PER_USEC);
 277                     time_offset = max(time_offset, (s64)-MAXPHASE * NSEC_PER_USEC);
 278
 279                     /*
 280                      * Select whether the frequency is to be controlled
 281                      * and in which mode (PLL or FLL). Clamp to the operating
 282                      * range. Ugly multiply/divide should be replaced someday.
 283                      */
 284
 285                     if (time_status & STA_FREQHOLD || time_reftime == 0)
 286                         time_reftime = xtime.tv_sec;
 287                     mtemp = xtime.tv_sec - time_reftime;
 288                     time_reftime = xtime.tv_sec;
 289
 290                     freq_adj = time_offset * mtemp;
 291                     freq_adj = shift_right(freq_adj, time_constant * 2 +
 292                                            (SHIFT_PLL + 2) * 2 - SHIFT_NSEC);
 293                     if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
 294                         temp64 = time_offset << (SHIFT_NSEC - SHIFT_FLL);
 295                         if (time_offset < 0) {
 296                             temp64 = -temp64;
 297                             do_div(temp64, mtemp);
 298                             freq_adj -= temp64;
 299                         } else {
 300                             do_div(temp64, mtemp);
 301                             freq_adj += temp64;
 302                         }
 303                     }
 304                     freq_adj += time_freq;
 305                     freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
 306                     time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
 307                     time_offset = div_long_long_rem_signed(time_offset,
 308                                                            NTP_INTERVAL_FREQ,
 309                                                            &rem);
 310                     time_offset <<= SHIFT_UPDATE;
 311                 } /* STA_PLL */
 312             } /* txc->modes & ADJ_OFFSET */
 313             if (txc->modes & ADJ_TICK)
 314                 tick_usec = txc->tick;
 315
 316             if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 317                     ntp_update_frequency();
 318         } /* txc->modes */
 319 leave:  if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
 320                 result = TIME_ERROR;
 321
 322         if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
 323                 txc->offset = save_adjust;
 324         else
 325                 txc->offset = ((long)shift_right(time_offset, SHIFT_UPDATE)) *
 326                                 NTP_INTERVAL_FREQ / 1000;
 327         txc->freq          = (time_freq / NSEC_PER_USEC) <<
 328                                 (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 }