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 <linux/math64.h>
18 #include <linux/clocksource.h>
19 #include <linux/workqueue.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
ntp_update_frequency(void)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
ntp_update_offset(long offset)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 */
ntp_clear(void)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 */
ntp_leap_second(struct hrtimer * timer)130 static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
131 {
132 enum hrtimer_restart res = HRTIMER_NORESTART;
133
134 write_seqlock(&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 hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC);
146 res = HRTIMER_RESTART;
147 break;
148 case TIME_DEL:
149 xtime.tv_sec++;
150 time_tai--;
151 wall_to_monotonic.tv_sec--;
152 time_state = TIME_WAIT;
153 printk(KERN_NOTICE "Clock: "
154 "deleting leap second 23:59:59 UTC\n");
155 break;
156 case TIME_OOP:
157 time_tai++;
158 time_state = TIME_WAIT;
159 /* fall through */
160 case TIME_WAIT:
161 if (!(time_status & (STA_INS | STA_DEL)))
162 time_state = TIME_OK;
163 break;
164 }
165 update_vsyscall(&xtime, clock);
166
167 write_sequnlock(&xtime_lock);
168
169 return res;
170 }
171
172 /*
173 * this routine handles the overflow of the microsecond field
174 *
175 * The tricky bits of code to handle the accurate clock support
176 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
177 * They were originally developed for SUN and DEC kernels.
178 * All the kudos should go to Dave for this stuff.
179 */
second_overflow(void)180 void second_overflow(void)
181 {
182 s64 time_adj;
183
184 /* Bump the maxerror field */
185 time_maxerror += MAXFREQ / NSEC_PER_USEC;
186 if (time_maxerror > NTP_PHASE_LIMIT) {
187 time_maxerror = NTP_PHASE_LIMIT;
188 time_status |= STA_UNSYNC;
189 }
190
191 /*
192 * Compute the phase adjustment for the next second. The offset is
193 * reduced by a fixed factor times the time constant.
194 */
195 tick_length = tick_length_base;
196 time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
197 time_offset -= time_adj;
198 tick_length += time_adj;
199
200 if (unlikely(time_adjust)) {
201 if (time_adjust > MAX_TICKADJ) {
202 time_adjust -= MAX_TICKADJ;
203 tick_length += MAX_TICKADJ_SCALED;
204 } else if (time_adjust < -MAX_TICKADJ) {
205 time_adjust += MAX_TICKADJ;
206 tick_length -= MAX_TICKADJ_SCALED;
207 } else {
208 tick_length += (s64)(time_adjust * NSEC_PER_USEC /
209 NTP_INTERVAL_FREQ) << NTP_SCALE_SHIFT;
210 time_adjust = 0;
211 }
212 }
213 }
214
215 #ifdef CONFIG_GENERIC_CMOS_UPDATE
216
217 /* Disable the cmos update - used by virtualization and embedded */
218 int no_sync_cmos_clock __read_mostly;
219
220 static void sync_cmos_clock(struct work_struct *work);
221
222 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
223
sync_cmos_clock(struct work_struct * work)224 static void sync_cmos_clock(struct work_struct *work)
225 {
226 struct timespec now, next;
227 int fail = 1;
228
229 /*
230 * If we have an externally synchronized Linux clock, then update
231 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
232 * called as close as possible to 500 ms before the new second starts.
233 * This code is run on a timer. If the clock is set, that timer
234 * may not expire at the correct time. Thus, we adjust...
235 */
236 if (!ntp_synced())
237 /*
238 * Not synced, exit, do not restart a timer (if one is
239 * running, let it run out).
240 */
241 return;
242
243 getnstimeofday(&now);
244 if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
245 fail = update_persistent_clock(now);
246
247 next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
248 if (next.tv_nsec <= 0)
249 next.tv_nsec += NSEC_PER_SEC;
250
251 if (!fail)
252 next.tv_sec = 659;
253 else
254 next.tv_sec = 0;
255
256 if (next.tv_nsec >= NSEC_PER_SEC) {
257 next.tv_sec++;
258 next.tv_nsec -= NSEC_PER_SEC;
259 }
260 schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
261 }
262
notify_cmos_timer(void)263 static void notify_cmos_timer(void)
264 {
265 if (!no_sync_cmos_clock)
266 schedule_delayed_work(&sync_cmos_work, 0);
267 }
268
269 #else
notify_cmos_timer(void)270 static inline void notify_cmos_timer(void) { }
271 #endif
272
273 /* adjtimex mainly allows reading (and writing, if superuser) of
274 * kernel time-keeping variables. used by xntpd.
275 */
do_adjtimex(struct timex * txc)276 int do_adjtimex(struct timex *txc)
277 {
278 struct timespec ts;
279 int result;
280
281 /* Validate the data before disabling interrupts */
282 if (txc->modes & ADJ_ADJTIME) {
283 /* singleshot must not be used with any other mode bits */
284 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
285 return -EINVAL;
286 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
287 !capable(CAP_SYS_TIME))
288 return -EPERM;
289 } else {
290 /* In order to modify anything, you gotta be super-user! */
291 if (txc->modes && !capable(CAP_SYS_TIME))
292 return -EPERM;
293
294 /* if the quartz is off by more than 10% something is VERY wrong! */
295 if (txc->modes & ADJ_TICK &&
296 (txc->tick < 900000/USER_HZ ||
297 txc->tick > 1100000/USER_HZ))
298 return -EINVAL;
299
300 if (txc->modes & ADJ_STATUS && time_state != TIME_OK)
301 hrtimer_cancel(&leap_timer);
302 }
303
304 getnstimeofday(&ts);
305
306 write_seqlock_irq(&xtime_lock);
307
308 /* If there are input parameters, then process them */
309 if (txc->modes & ADJ_ADJTIME) {
310 long save_adjust = time_adjust;
311
312 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
313 /* adjtime() is independent from ntp_adjtime() */
314 time_adjust = txc->offset;
315 ntp_update_frequency();
316 }
317 txc->offset = save_adjust;
318 goto adj_done;
319 }
320 if (txc->modes) {
321 long sec;
322
323 if (txc->modes & ADJ_STATUS) {
324 if ((time_status & STA_PLL) &&
325 !(txc->status & STA_PLL)) {
326 time_state = TIME_OK;
327 time_status = STA_UNSYNC;
328 }
329 /* only set allowed bits */
330 time_status &= STA_RONLY;
331 time_status |= txc->status & ~STA_RONLY;
332
333 switch (time_state) {
334 case TIME_OK:
335 start_timer:
336 sec = ts.tv_sec;
337 if (time_status & STA_INS) {
338 time_state = TIME_INS;
339 sec += 86400 - sec % 86400;
340 hrtimer_start(&leap_timer, ktime_set(sec, 0), HRTIMER_MODE_ABS);
341 } else if (time_status & STA_DEL) {
342 time_state = TIME_DEL;
343 sec += 86400 - (sec + 1) % 86400;
344 hrtimer_start(&leap_timer, ktime_set(sec, 0), HRTIMER_MODE_ABS);
345 }
346 break;
347 case TIME_INS:
348 case TIME_DEL:
349 time_state = TIME_OK;
350 goto start_timer;
351 break;
352 case TIME_WAIT:
353 if (!(time_status & (STA_INS | STA_DEL)))
354 time_state = TIME_OK;
355 break;
356 case TIME_OOP:
357 hrtimer_restart(&leap_timer);
358 break;
359 }
360 }
361
362 if (txc->modes & ADJ_NANO)
363 time_status |= STA_NANO;
364 if (txc->modes & ADJ_MICRO)
365 time_status &= ~STA_NANO;
366
367 if (txc->modes & ADJ_FREQUENCY) {
368 time_freq = (s64)txc->freq * PPM_SCALE;
369 time_freq = min(time_freq, MAXFREQ_SCALED);
370 time_freq = max(time_freq, -MAXFREQ_SCALED);
371 }
372
373 if (txc->modes & ADJ_MAXERROR)
374 time_maxerror = txc->maxerror;
375 if (txc->modes & ADJ_ESTERROR)
376 time_esterror = txc->esterror;
377
378 if (txc->modes & ADJ_TIMECONST) {
379 time_constant = txc->constant;
380 if (!(time_status & STA_NANO))
381 time_constant += 4;
382 time_constant = min(time_constant, (long)MAXTC);
383 time_constant = max(time_constant, 0l);
384 }
385
386 if (txc->modes & ADJ_TAI && txc->constant > 0)
387 time_tai = txc->constant;
388
389 if (txc->modes & ADJ_OFFSET)
390 ntp_update_offset(txc->offset);
391 if (txc->modes & ADJ_TICK)
392 tick_usec = txc->tick;
393
394 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
395 ntp_update_frequency();
396 }
397
398 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
399 NTP_SCALE_SHIFT);
400 if (!(time_status & STA_NANO))
401 txc->offset /= NSEC_PER_USEC;
402
403 adj_done:
404 result = time_state; /* mostly `TIME_OK' */
405 if (time_status & (STA_UNSYNC|STA_CLOCKERR))
406 result = TIME_ERROR;
407
408 txc->freq = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
409 (s64)PPM_SCALE_INV, NTP_SCALE_SHIFT);
410 txc->maxerror = time_maxerror;
411 txc->esterror = time_esterror;
412 txc->status = time_status;
413 txc->constant = time_constant;
414 txc->precision = 1;
415 txc->tolerance = MAXFREQ_SCALED / PPM_SCALE;
416 txc->tick = tick_usec;
417 txc->tai = time_tai;
418
419 /* PPS is not implemented, so these are zero */
420 txc->ppsfreq = 0;
421 txc->jitter = 0;
422 txc->shift = 0;
423 txc->stabil = 0;
424 txc->jitcnt = 0;
425 txc->calcnt = 0;
426 txc->errcnt = 0;
427 txc->stbcnt = 0;
428 write_sequnlock_irq(&xtime_lock);
429
430 txc->time.tv_sec = ts.tv_sec;
431 txc->time.tv_usec = ts.tv_nsec;
432 if (!(time_status & STA_NANO))
433 txc->time.tv_usec /= NSEC_PER_USEC;
434
435 notify_cmos_timer();
436
437 return result;
438 }
439
ntp_tick_adj_setup(char * str)440 static int __init ntp_tick_adj_setup(char *str)
441 {
442 ntp_tick_adj = simple_strtol(str, NULL, 0);
443 return 1;
444 }
445
446 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
447
ntp_init(void)448 void __init ntp_init(void)
449 {
450 ntp_clear();
451 hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
452 leap_timer.function = ntp_leap_second;
453 }
454