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) / NTP_INTERVAL_FREQ) 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 s64 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 u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ) 50 << TICK_LENGTH_SHIFT; 51 second_length += (s64)CLOCK_TICK_ADJUST << TICK_LENGTH_SHIFT; 52 second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC); 53 54 tick_length_base = second_length; 55 56 do_div(second_length, HZ); 57 tick_nsec = second_length >> TICK_LENGTH_SHIFT; 58 59 do_div(tick_length_base, NTP_INTERVAL_FREQ); 60 } 61 62 /** 63 * ntp_clear - Clears the NTP state variables 64 * 65 * Must be called while holding a write on the xtime_lock 66 */ 67 void ntp_clear(void) 68 { 69 time_adjust = 0; /* stop active adjtime() */ 70 time_status |= STA_UNSYNC; 71 time_maxerror = NTP_PHASE_LIMIT; 72 time_esterror = NTP_PHASE_LIMIT; 73 74 ntp_update_frequency(); 75 76 tick_length = tick_length_base; 77 time_offset = 0; 78 } 79 80 /* 81 * this routine handles the overflow of the microsecond field 82 * 83 * The tricky bits of code to handle the accurate clock support 84 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame. 85 * They were originally developed for SUN and DEC kernels. 86 * All the kudos should go to Dave for this stuff. 87 */ 88 void second_overflow(void) 89 { 90 long time_adj; 91 92 /* Bump the maxerror field */ 93 time_maxerror += MAXFREQ >> SHIFT_USEC; 94 if (time_maxerror > NTP_PHASE_LIMIT) { 95 time_maxerror = NTP_PHASE_LIMIT; 96 time_status |= STA_UNSYNC; 97 } 98 99 /* 100 * Leap second processing. If in leap-insert state at the end of the 101 * day, the system clock is set back one second; if in leap-delete 102 * state, the system clock is set ahead one second. The microtime() 103 * routine or external clock driver will insure that reported time is 104 * always monotonic. The ugly divides should be replaced. 105 */ 106 switch (time_state) { 107 case TIME_OK: 108 if (time_status & STA_INS) 109 time_state = TIME_INS; 110 else if (time_status & STA_DEL) 111 time_state = TIME_DEL; 112 break; 113 case TIME_INS: 114 if (xtime.tv_sec % 86400 == 0) { 115 xtime.tv_sec--; 116 wall_to_monotonic.tv_sec++; 117 /* 118 * The timer interpolator will make time change 119 * gradually instead of an immediate jump by one second 120 */ 121 time_interpolator_update(-NSEC_PER_SEC); 122 time_state = TIME_OOP; 123 clock_was_set(); 124 printk(KERN_NOTICE "Clock: inserting leap second " 125 "23:59:60 UTC\n"); 126 } 127 break; 128 case TIME_DEL: 129 if ((xtime.tv_sec + 1) % 86400 == 0) { 130 xtime.tv_sec++; 131 wall_to_monotonic.tv_sec--; 132 /* 133 * Use of time interpolator for a gradual change of 134 * time 135 */ 136 time_interpolator_update(NSEC_PER_SEC); 137 time_state = TIME_WAIT; 138 clock_was_set(); 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 } 361