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; 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 } 452