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 <linux/math64.h>
  19 #include <linux/clocksource.h>
  20 #include <asm/timex.h>
  21
  22 /*
  23  * Timekeeping variables
  24  */
  25 unsigned long tick_usec = TICK_USEC;            /* USER_HZ period (usec) */
  26 unsigned long tick_nsec;                        /* ACTHZ period (nsec) */
  27 u64 tick_length;
  28 static u64 tick_length_base;
  29
  30 static struct hrtimer leap_timer;
  31
  32 #define MAX_TICKADJ             500             /* microsecs */
  33 #define MAX_TICKADJ_SCALED      (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
  34                                   NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
  35
  36 /*
  37  * phase-lock loop variables
  38  */
  39 /* TIME_ERROR prevents overwriting the CMOS clock */
  40 static int time_state = TIME_OK;        /* clock synchronization status */
  41 int time_status = STA_UNSYNC;           /* clock status bits            */
  42 static long time_tai;                   /* TAI offset (s)               */
  43 static s64 time_offset;                 /* time adjustment (ns)         */
  44 static long time_constant = 2;          /* pll time constant            */
  45 long time_maxerror = NTP_PHASE_LIMIT;   /* maximum error (us)           */
  46 long time_esterror = NTP_PHASE_LIMIT;   /* estimated error (us)         */
  47 static s64 time_freq;                   /* frequency offset (scaled ns/s)*/
  48 static long time_reftime;               /* time at last adjustment (s)  */
  49 long time_adjust;
  50 static long ntp_tick_adj;
  51
  52 static void ntp_update_frequency(void)
  53 {
  54         u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
  55                                 << NTP_SCALE_SHIFT;
  56         second_length += (s64)ntp_tick_adj << NTP_SCALE_SHIFT;
  57         second_length += time_freq;
  58
  59         tick_length_base = second_length;
  60
  61         tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
  62         tick_length_base = div_u64(tick_length_base, NTP_INTERVAL_FREQ);
  63 }
  64
  65 static void ntp_update_offset(long offset)
  66 {
  67         long mtemp;
  68         s64 freq_adj;
  69
  70         if (!(time_status & STA_PLL))
  71                 return;
  72
  73         if (!(time_status & STA_NANO))
  74                 offset *= NSEC_PER_USEC;
  75
  76         /*
  77          * Scale the phase adjustment and
  78          * clamp to the operating range.
  79          */
  80         offset = min(offset, MAXPHASE);
  81         offset = max(offset, -MAXPHASE);
  82
  83         /*
  84          * Select how the frequency is to be controlled
  85          * and in which mode (PLL or FLL).
  86          */
  87         if (time_status & STA_FREQHOLD || time_reftime == 0)
  88                 time_reftime = xtime.tv_sec;
  89         mtemp = xtime.tv_sec - time_reftime;
  90         time_reftime = xtime.tv_sec;
  91
  92         freq_adj = (s64)offset * mtemp;
  93         freq_adj <<= NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant);
  94         time_status &= ~STA_MODE;
  95         if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
  96                 freq_adj += div_s64((s64)offset << (NTP_SCALE_SHIFT - SHIFT_FLL),
  97                                     mtemp);
  98                 time_status |= STA_MODE;
  99         }
 100         freq_adj += time_freq;
 101         freq_adj = min(freq_adj, MAXFREQ_SCALED);
 102         time_freq = max(freq_adj, -MAXFREQ_SCALED);
 103
 104         time_offset = div_s64((s64)offset << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
 105 }
 106
 107 /**
 108  * ntp_clear - Clears the NTP state variables
 109  *
 110  * Must be called while holding a write on the xtime_lock
 111  */
 112 void ntp_clear(void)
 113 {
 114         time_adjust = 0;                /* stop active adjtime() */
 115         time_status |= STA_UNSYNC;
 116         time_maxerror = NTP_PHASE_LIMIT;
 117         time_esterror = NTP_PHASE_LIMIT;
 118
 119         ntp_update_frequency();
 120
 121         tick_length = tick_length_base;
 122         time_offset = 0;
 123 }
 124
 125 /*
 126  * Leap second processing. If in leap-insert state at the end of the
 127  * day, the system clock is set back one second; if in leap-delete
 128  * state, the system clock is set ahead one second.
 129  */
 130 static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
 131 {
 132         enum hrtimer_restart res = HRTIMER_NORESTART;
 133
 134         write_seqlock_irq(&xtime_lock);
 135
 136         switch (time_state) {
 137         case TIME_OK:
 138                 break;
 139         case TIME_INS:
 140                 xtime.tv_sec--;
 141                 wall_to_monotonic.tv_sec++;
 142                 time_state = TIME_OOP;
 143                 printk(KERN_NOTICE "Clock: "
 144                        "inserting leap second 23:59:60 UTC\n");
 145                 leap_timer.expires = ktime_add_ns(leap_timer.expires,
 146                                                   NSEC_PER_SEC);
 147                 res = HRTIMER_RESTART;
 148                 break;
 149         case TIME_DEL:
 150                 xtime.tv_sec++;
 151                 time_tai--;
 152                 wall_to_monotonic.tv_sec--;
 153                 time_state = TIME_WAIT;
 154                 printk(KERN_NOTICE "Clock: "
 155                        "deleting leap second 23:59:59 UTC\n");
 156                 break;
 157         case TIME_OOP:
 158                 time_tai++;
 159                 time_state = TIME_WAIT;
 160                 /* fall through */
 161         case TIME_WAIT:
 162                 if (!(time_status & (STA_INS | STA_DEL)))
 163                         time_state = TIME_OK;
 164                 break;
 165         }
 166         update_vsyscall(&xtime, clock);
 167
 168         write_sequnlock_irq(&xtime_lock);
 169
 170         return res;
 171 }
 172
 173 /*
 174  * this routine handles the overflow of the microsecond field
 175  *
 176  * The tricky bits of code to handle the accurate clock support
 177  * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
 178  * They were originally developed for SUN and DEC kernels.
 179  * All the kudos should go to Dave for this stuff.
 180  */
 181 void second_overflow(void)
 182 {
 183         s64 time_adj;
 184
 185         /* Bump the maxerror field */
 186         time_maxerror += MAXFREQ / NSEC_PER_USEC;
 187         if (time_maxerror > NTP_PHASE_LIMIT) {
 188                 time_maxerror = NTP_PHASE_LIMIT;
 189                 time_status |= STA_UNSYNC;
 190         }
 191
 192         /*
 193          * Compute the phase adjustment for the next second. The offset is
 194          * reduced by a fixed factor times the time constant.
 195          */
 196         tick_length = tick_length_base;
 197         time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
 198         time_offset -= time_adj;
 199         tick_length += time_adj;
 200
 201         if (unlikely(time_adjust)) {
 202                 if (time_adjust > MAX_TICKADJ) {
 203                         time_adjust -= MAX_TICKADJ;
 204                         tick_length += MAX_TICKADJ_SCALED;
 205                 } else if (time_adjust < -MAX_TICKADJ) {
 206                         time_adjust += MAX_TICKADJ;
 207                         tick_length -= MAX_TICKADJ_SCALED;
 208                 } else {
 209                         tick_length += (s64)(time_adjust * NSEC_PER_USEC /
 210                                         NTP_INTERVAL_FREQ) << NTP_SCALE_SHIFT;
 211                         time_adjust = 0;
 212                 }
 213         }
 214 }
 215
 216 #ifdef CONFIG_GENERIC_CMOS_UPDATE
 217
 218 /* Disable the cmos update - used by virtualization and embedded */
 219 int no_sync_cmos_clock  __read_mostly;
 220
 221 static void sync_cmos_clock(unsigned long dummy);
 222
 223 static DEFINE_TIMER(sync_cmos_timer, sync_cmos_clock, 0, 0);
 224
 225 static void sync_cmos_clock(unsigned long dummy)
 226 {
 227         struct timespec now, next;
 228         int fail = 1;
 229
 230         /*
 231          * If we have an externally synchronized Linux clock, then update
 232          * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
 233          * called as close as possible to 500 ms before the new second starts.
 234          * This code is run on a timer.  If the clock is set, that timer
 235          * may not expire at the correct time.  Thus, we adjust...
 236          */
 237         if (!ntp_synced())
 238                 /*
 239                  * Not synced, exit, do not restart a timer (if one is
 240                  * running, let it run out).
 241                  */
 242                 return;
 243
 244         getnstimeofday(&now);
 245         if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
 246                 fail = update_persistent_clock(now);
 247
 248         next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
 249         if (next.tv_nsec <= 0)
 250                 next.tv_nsec += NSEC_PER_SEC;
 251
 252         if (!fail)
 253                 next.tv_sec = 659;
 254         else
 255                 next.tv_sec = 0;
 256
 257         if (next.tv_nsec >= NSEC_PER_SEC) {
 258                 next.tv_sec++;
 259                 next.tv_nsec -= NSEC_PER_SEC;
 260         }
 261         mod_timer(&sync_cmos_timer, jiffies + timespec_to_jiffies(&next));
 262 }
 263
 264 static void notify_cmos_timer(void)
 265 {
 266         if (!no_sync_cmos_clock)
 267                 mod_timer(&sync_cmos_timer, jiffies + 1);
 268 }
 269
 270 #else
 271 static inline void notify_cmos_timer(void) { }
 272 #endif
 273
 274 /* adjtimex mainly allows reading (and writing, if superuser) of
 275  * kernel time-keeping variables. used by xntpd.
 276  */
 277 int do_adjtimex(struct timex *txc)
 278 {
 279         struct timespec ts;
 280         long save_adjust, sec;
 281         int result;
 282
 283         /* In order to modify anything, you gotta be super-user! */
 284         if (txc->modes && !capable(CAP_SYS_TIME))
 285                 return -EPERM;
 286
 287         /* Now we validate the data before disabling interrupts */
 288
 289         if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT) {
 290                 /* singleshot must not be used with any other mode bits */
 291                 if (txc->modes & ~ADJ_OFFSET_SS_READ)
 292                         return -EINVAL;
 293         }
 294
 295         /* if the quartz is off by more than 10% something is VERY wrong ! */
 296         if (txc->modes & ADJ_TICK)
 297                 if (txc->tick <  900000/USER_HZ ||
 298                     txc->tick > 1100000/USER_HZ)
 299                         return -EINVAL;
 300
 301         if (time_state != TIME_OK && txc->modes & ADJ_STATUS)
 302                 hrtimer_cancel(&leap_timer);
 303         getnstimeofday(&ts);
 304
 305         write_seqlock_irq(&xtime_lock);
 306
 307         /* Save for later - semantics of adjtime is to return old value */
 308         save_adjust = time_adjust;
 309
 310         /* If there are input parameters, then process them */
 311         if (txc->modes) {
 312                 if (txc->modes & ADJ_STATUS) {
 313                         if ((time_status & STA_PLL) &&
 314                             !(txc->status & STA_PLL)) {
 315                                 time_state = TIME_OK;
 316                                 time_status = STA_UNSYNC;
 317                         }
 318                         /* only set allowed bits */
 319                         time_status &= STA_RONLY;
 320                         time_status |= txc->status & ~STA_RONLY;
 321
 322                         switch (time_state) {
 323                         case TIME_OK:
 324                         start_timer:
 325                                 sec = ts.tv_sec;
 326                                 if (time_status & STA_INS) {
 327                                         time_state = TIME_INS;
 328                                         sec += 86400 - sec % 86400;
 329                                         hrtimer_start(&leap_timer, ktime_set(sec, 0), HRTIMER_MODE_ABS);
 330                                 } else if (time_status & STA_DEL) {
 331                                         time_state = TIME_DEL;
 332                                         sec += 86400 - (sec + 1) % 86400;
 333                                         hrtimer_start(&leap_timer, ktime_set(sec, 0), HRTIMER_MODE_ABS);
 334                                 }
 335                                 break;
 336                         case TIME_INS:
 337                         case TIME_DEL:
 338                                 time_state = TIME_OK;
 339                                 goto start_timer;
 340                                 break;
 341                         case TIME_WAIT:
 342                                 if (!(time_status & (STA_INS | STA_DEL)))
 343                                         time_state = TIME_OK;
 344                                 break;
 345                         case TIME_OOP:
 346                                 hrtimer_restart(&leap_timer);
 347                                 break;
 348                         }
 349                 }
 350
 351                 if (txc->modes & ADJ_NANO)
 352                         time_status |= STA_NANO;
 353                 if (txc->modes & ADJ_MICRO)
 354                         time_status &= ~STA_NANO;
 355
 356                 if (txc->modes & ADJ_FREQUENCY) {
 357                         time_freq = (s64)txc->freq * PPM_SCALE;
 358                         time_freq = min(time_freq, MAXFREQ_SCALED);
 359                         time_freq = max(time_freq, -MAXFREQ_SCALED);
 360                 }
 361
 362                 if (txc->modes & ADJ_MAXERROR)
 363                         time_maxerror = txc->maxerror;
 364                 if (txc->modes & ADJ_ESTERROR)
 365                         time_esterror = txc->esterror;
 366
 367                 if (txc->modes & ADJ_TIMECONST) {
 368                         time_constant = txc->constant;
 369                         if (!(time_status & STA_NANO))
 370                                 time_constant += 4;
 371                         time_constant = min(time_constant, (long)MAXTC);
 372                         time_constant = max(time_constant, 0l);
 373                 }
 374
 375                 if (txc->modes & ADJ_TAI && txc->constant > 0)
 376                         time_tai = txc->constant;
 377
 378                 if (txc->modes & ADJ_OFFSET) {
 379                         if (txc->modes == ADJ_OFFSET_SINGLESHOT)
 380                                 /* adjtime() is independent from ntp_adjtime() */
 381                                 time_adjust = txc->offset;
 382                         else
 383                                 ntp_update_offset(txc->offset);
 384                 }
 385                 if (txc->modes & ADJ_TICK)
 386                         tick_usec = txc->tick;
 387
 388                 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 389                         ntp_update_frequency();
 390         }
 391
 392         result = time_state;    /* mostly `TIME_OK' */
 393         if (time_status & (STA_UNSYNC|STA_CLOCKERR))
 394                 result = TIME_ERROR;
 395
 396         if ((txc->modes == ADJ_OFFSET_SINGLESHOT) ||
 397             (txc->modes == ADJ_OFFSET_SS_READ))
 398                 txc->offset = save_adjust;
 399         else {
 400                 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
 401                                           NTP_SCALE_SHIFT);
 402                 if (!(time_status & STA_NANO))
 403                         txc->offset /= NSEC_PER_USEC;
 404         }
 405         txc->freq          = shift_right((s32)(time_freq >> PPM_SCALE_INV_SHIFT) *
 406                                          (s64)PPM_SCALE_INV,
 407                                          NTP_SCALE_SHIFT);
 408         txc->maxerror      = time_maxerror;
 409         txc->esterror      = time_esterror;
 410         txc->status        = time_status;
 411         txc->constant      = time_constant;
 412         txc->precision     = 1;
 413         txc->tolerance     = MAXFREQ_SCALED / PPM_SCALE;
 414         txc->tick          = tick_usec;
 415         txc->tai           = time_tai;
 416
 417         /* PPS is not implemented, so these are zero */
 418         txc->ppsfreq       = 0;
 419         txc->jitter        = 0;
 420         txc->shift         = 0;
 421         txc->stabil        = 0;
 422         txc->jitcnt        = 0;
 423         txc->calcnt        = 0;
 424         txc->errcnt        = 0;
 425         txc->stbcnt        = 0;
 426         write_sequnlock_irq(&xtime_lock);
 427
 428         txc->time.tv_sec = ts.tv_sec;
 429         txc->time.tv_usec = ts.tv_nsec;
 430         if (!(time_status & STA_NANO))
 431                 txc->time.tv_usec /= NSEC_PER_USEC;
 432
 433         notify_cmos_timer();
 434
 435         return result;
 436 }
 437
 438 static int __init ntp_tick_adj_setup(char *str)
 439 {
 440         ntp_tick_adj = simple_strtol(str, NULL, 0);
 441         return 1;
 442 }
 443
 444 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
 445
 446 void __init ntp_init(void)
 447 {
 448         ntp_clear();
 449         hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
 450         leap_timer.function = ntp_leap_second;
 451 }