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1/*
2 * linux/kernel/time/clocksource.c
3 *
4 * This file contains the functions which manage clocksource drivers.
5 *
6 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
17 *
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
21 *
22 * TODO WishList:
23 * o Allow clocksource drivers to be unregistered
24 */
25
26#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
27
28#include <linux/device.h>
29#include <linux/clocksource.h>
30#include <linux/init.h>
31#include <linux/module.h>
32#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
33#include <linux/tick.h>
34#include <linux/kthread.h>
35
36#include "tick-internal.h"
37#include "timekeeping_internal.h"
38
39/**
40 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
41 * @mult: pointer to mult variable
42 * @shift: pointer to shift variable
43 * @from: frequency to convert from
44 * @to: frequency to convert to
45 * @maxsec: guaranteed runtime conversion range in seconds
46 *
47 * The function evaluates the shift/mult pair for the scaled math
48 * operations of clocksources and clockevents.
49 *
50 * @to and @from are frequency values in HZ. For clock sources @to is
51 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
52 * event @to is the counter frequency and @from is NSEC_PER_SEC.
53 *
54 * The @maxsec conversion range argument controls the time frame in
55 * seconds which must be covered by the runtime conversion with the
56 * calculated mult and shift factors. This guarantees that no 64bit
57 * overflow happens when the input value of the conversion is
58 * multiplied with the calculated mult factor. Larger ranges may
59 * reduce the conversion accuracy by chosing smaller mult and shift
60 * factors.
61 */
62void
63clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
64{
65 u64 tmp;
66 u32 sft, sftacc= 32;
67
68 /*
69 * Calculate the shift factor which is limiting the conversion
70 * range:
71 */
72 tmp = ((u64)maxsec * from) >> 32;
73 while (tmp) {
74 tmp >>=1;
75 sftacc--;
76 }
77
78 /*
79 * Find the conversion shift/mult pair which has the best
80 * accuracy and fits the maxsec conversion range:
81 */
82 for (sft = 32; sft > 0; sft--) {
83 tmp = (u64) to << sft;
84 tmp += from / 2;
85 do_div(tmp, from);
86 if ((tmp >> sftacc) == 0)
87 break;
88 }
89 *mult = tmp;
90 *shift = sft;
91}
92
93/*[Clocksource internal variables]---------
94 * curr_clocksource:
95 * currently selected clocksource.
96 * clocksource_list:
97 * linked list with the registered clocksources
98 * clocksource_mutex:
99 * protects manipulations to curr_clocksource and the clocksource_list
100 * override_name:
101 * Name of the user-specified clocksource.
102 */
103static struct clocksource *curr_clocksource;
104static LIST_HEAD(clocksource_list);
105static DEFINE_MUTEX(clocksource_mutex);
106static char override_name[CS_NAME_LEN];
107static int finished_booting;
108
109#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
110static void clocksource_watchdog_work(struct work_struct *work);
111static void clocksource_select(void);
112
113static LIST_HEAD(watchdog_list);
114static struct clocksource *watchdog;
115static struct timer_list watchdog_timer;
116static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
117static DEFINE_SPINLOCK(watchdog_lock);
118static int watchdog_running;
119static atomic_t watchdog_reset_pending;
120
121static int clocksource_watchdog_kthread(void *data);
122static void __clocksource_change_rating(struct clocksource *cs, int rating);
123
124/*
125 * Interval: 0.5sec Threshold: 0.0625s
126 */
127#define WATCHDOG_INTERVAL (HZ >> 1)
128#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
129
130static void clocksource_watchdog_work(struct work_struct *work)
131{
132 /*
133 * If kthread_run fails the next watchdog scan over the
134 * watchdog_list will find the unstable clock again.
135 */
136 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
137}
138
139static void __clocksource_unstable(struct clocksource *cs)
140{
141 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
142 cs->flags |= CLOCK_SOURCE_UNSTABLE;
143 if (finished_booting)
144 schedule_work(&watchdog_work);
145}
146
147/**
148 * clocksource_mark_unstable - mark clocksource unstable via watchdog
149 * @cs: clocksource to be marked unstable
150 *
151 * This function is called instead of clocksource_change_rating from
152 * cpu hotplug code to avoid a deadlock between the clocksource mutex
153 * and the cpu hotplug mutex. It defers the update of the clocksource
154 * to the watchdog thread.
155 */
156void clocksource_mark_unstable(struct clocksource *cs)
157{
158 unsigned long flags;
159
160 spin_lock_irqsave(&watchdog_lock, flags);
161 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
162 if (list_empty(&cs->wd_list))
163 list_add(&cs->wd_list, &watchdog_list);
164 __clocksource_unstable(cs);
165 }
166 spin_unlock_irqrestore(&watchdog_lock, flags);
167}
168
169static void clocksource_watchdog(unsigned long data)
170{
171 struct clocksource *cs;
172 cycle_t csnow, wdnow, cslast, wdlast, delta;
173 int64_t wd_nsec, cs_nsec;
174 int next_cpu, reset_pending;
175
176 spin_lock(&watchdog_lock);
177 if (!watchdog_running)
178 goto out;
179
180 reset_pending = atomic_read(&watchdog_reset_pending);
181
182 list_for_each_entry(cs, &watchdog_list, wd_list) {
183
184 /* Clocksource already marked unstable? */
185 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
186 if (finished_booting)
187 schedule_work(&watchdog_work);
188 continue;
189 }
190
191 local_irq_disable();
192 csnow = cs->read(cs);
193 wdnow = watchdog->read(watchdog);
194 local_irq_enable();
195
196 /* Clocksource initialized ? */
197 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
198 atomic_read(&watchdog_reset_pending)) {
199 cs->flags |= CLOCK_SOURCE_WATCHDOG;
200 cs->wd_last = wdnow;
201 cs->cs_last = csnow;
202 continue;
203 }
204
205 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
206 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
207 watchdog->shift);
208
209 delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
210 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
211 wdlast = cs->wd_last; /* save these in case we print them */
212 cslast = cs->cs_last;
213 cs->cs_last = csnow;
214 cs->wd_last = wdnow;
215
216 if (atomic_read(&watchdog_reset_pending))
217 continue;
218
219 /* Check the deviation from the watchdog clocksource. */
220 if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
221 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
222 smp_processor_id(), cs->name);
223 pr_warn(" '%s' wd_now: %llx wd_last: %llx mask: %llx\n",
224 watchdog->name, wdnow, wdlast, watchdog->mask);
225 pr_warn(" '%s' cs_now: %llx cs_last: %llx mask: %llx\n",
226 cs->name, csnow, cslast, cs->mask);
227 __clocksource_unstable(cs);
228 continue;
229 }
230
231 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
232 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
233 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
234 /* Mark it valid for high-res. */
235 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
236
237 /*
238 * clocksource_done_booting() will sort it if
239 * finished_booting is not set yet.
240 */
241 if (!finished_booting)
242 continue;
243
244 /*
245 * If this is not the current clocksource let
246 * the watchdog thread reselect it. Due to the
247 * change to high res this clocksource might
248 * be preferred now. If it is the current
249 * clocksource let the tick code know about
250 * that change.
251 */
252 if (cs != curr_clocksource) {
253 cs->flags |= CLOCK_SOURCE_RESELECT;
254 schedule_work(&watchdog_work);
255 } else {
256 tick_clock_notify();
257 }
258 }
259 }
260
261 /*
262 * We only clear the watchdog_reset_pending, when we did a
263 * full cycle through all clocksources.
264 */
265 if (reset_pending)
266 atomic_dec(&watchdog_reset_pending);
267
268 /*
269 * Cycle through CPUs to check if the CPUs stay synchronized
270 * to each other.
271 */
272 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
273 if (next_cpu >= nr_cpu_ids)
274 next_cpu = cpumask_first(cpu_online_mask);
275 watchdog_timer.expires += WATCHDOG_INTERVAL;
276 add_timer_on(&watchdog_timer, next_cpu);
277out:
278 spin_unlock(&watchdog_lock);
279}
280
281static inline void clocksource_start_watchdog(void)
282{
283 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
284 return;
285 init_timer(&watchdog_timer);
286 watchdog_timer.function = clocksource_watchdog;
287 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
288 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
289 watchdog_running = 1;
290}
291
292static inline void clocksource_stop_watchdog(void)
293{
294 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
295 return;
296 del_timer(&watchdog_timer);
297 watchdog_running = 0;
298}
299
300static inline void clocksource_reset_watchdog(void)
301{
302 struct clocksource *cs;
303
304 list_for_each_entry(cs, &watchdog_list, wd_list)
305 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
306}
307
308static void clocksource_resume_watchdog(void)
309{
310 atomic_inc(&watchdog_reset_pending);
311}
312
313static void clocksource_enqueue_watchdog(struct clocksource *cs)
314{
315 unsigned long flags;
316
317 spin_lock_irqsave(&watchdog_lock, flags);
318 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
319 /* cs is a clocksource to be watched. */
320 list_add(&cs->wd_list, &watchdog_list);
321 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
322 } else {
323 /* cs is a watchdog. */
324 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
325 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
326 }
327 spin_unlock_irqrestore(&watchdog_lock, flags);
328}
329
330static void clocksource_select_watchdog(bool fallback)
331{
332 struct clocksource *cs, *old_wd;
333 unsigned long flags;
334
335 spin_lock_irqsave(&watchdog_lock, flags);
336 /* save current watchdog */
337 old_wd = watchdog;
338 if (fallback)
339 watchdog = NULL;
340
341 list_for_each_entry(cs, &clocksource_list, list) {
342 /* cs is a clocksource to be watched. */
343 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
344 continue;
345
346 /* Skip current if we were requested for a fallback. */
347 if (fallback && cs == old_wd)
348 continue;
349
350 /* Pick the best watchdog. */
351 if (!watchdog || cs->rating > watchdog->rating)
352 watchdog = cs;
353 }
354 /* If we failed to find a fallback restore the old one. */
355 if (!watchdog)
356 watchdog = old_wd;
357
358 /* If we changed the watchdog we need to reset cycles. */
359 if (watchdog != old_wd)
360 clocksource_reset_watchdog();
361
362 /* Check if the watchdog timer needs to be started. */
363 clocksource_start_watchdog();
364 spin_unlock_irqrestore(&watchdog_lock, flags);
365}
366
367static void clocksource_dequeue_watchdog(struct clocksource *cs)
368{
369 unsigned long flags;
370
371 spin_lock_irqsave(&watchdog_lock, flags);
372 if (cs != watchdog) {
373 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
374 /* cs is a watched clocksource. */
375 list_del_init(&cs->wd_list);
376 /* Check if the watchdog timer needs to be stopped. */
377 clocksource_stop_watchdog();
378 }
379 }
380 spin_unlock_irqrestore(&watchdog_lock, flags);
381}
382
383static int __clocksource_watchdog_kthread(void)
384{
385 struct clocksource *cs, *tmp;
386 unsigned long flags;
387 LIST_HEAD(unstable);
388 int select = 0;
389
390 spin_lock_irqsave(&watchdog_lock, flags);
391 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
392 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
393 list_del_init(&cs->wd_list);
394 list_add(&cs->wd_list, &unstable);
395 select = 1;
396 }
397 if (cs->flags & CLOCK_SOURCE_RESELECT) {
398 cs->flags &= ~CLOCK_SOURCE_RESELECT;
399 select = 1;
400 }
401 }
402 /* Check if the watchdog timer needs to be stopped. */
403 clocksource_stop_watchdog();
404 spin_unlock_irqrestore(&watchdog_lock, flags);
405
406 /* Needs to be done outside of watchdog lock */
407 list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
408 list_del_init(&cs->wd_list);
409 __clocksource_change_rating(cs, 0);
410 }
411 return select;
412}
413
414static int clocksource_watchdog_kthread(void *data)
415{
416 mutex_lock(&clocksource_mutex);
417 if (__clocksource_watchdog_kthread())
418 clocksource_select();
419 mutex_unlock(&clocksource_mutex);
420 return 0;
421}
422
423static bool clocksource_is_watchdog(struct clocksource *cs)
424{
425 return cs == watchdog;
426}
427
428#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
429
430static void clocksource_enqueue_watchdog(struct clocksource *cs)
431{
432 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
433 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
434}
435
436static void clocksource_select_watchdog(bool fallback) { }
437static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
438static inline void clocksource_resume_watchdog(void) { }
439static inline int __clocksource_watchdog_kthread(void) { return 0; }
440static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
441void clocksource_mark_unstable(struct clocksource *cs) { }
442
443#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
444
445/**
446 * clocksource_suspend - suspend the clocksource(s)
447 */
448void clocksource_suspend(void)
449{
450 struct clocksource *cs;
451
452 list_for_each_entry_reverse(cs, &clocksource_list, list)
453 if (cs->suspend)
454 cs->suspend(cs);
455}
456
457/**
458 * clocksource_resume - resume the clocksource(s)
459 */
460void clocksource_resume(void)
461{
462 struct clocksource *cs;
463
464 list_for_each_entry(cs, &clocksource_list, list)
465 if (cs->resume)
466 cs->resume(cs);
467
468 clocksource_resume_watchdog();
469}
470
471/**
472 * clocksource_touch_watchdog - Update watchdog
473 *
474 * Update the watchdog after exception contexts such as kgdb so as not
475 * to incorrectly trip the watchdog. This might fail when the kernel
476 * was stopped in code which holds watchdog_lock.
477 */
478void clocksource_touch_watchdog(void)
479{
480 clocksource_resume_watchdog();
481}
482
483/**
484 * clocksource_max_adjustment- Returns max adjustment amount
485 * @cs: Pointer to clocksource
486 *
487 */
488static u32 clocksource_max_adjustment(struct clocksource *cs)
489{
490 u64 ret;
491 /*
492 * We won't try to correct for more than 11% adjustments (110,000 ppm),
493 */
494 ret = (u64)cs->mult * 11;
495 do_div(ret,100);
496 return (u32)ret;
497}
498
499/**
500 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
501 * @mult: cycle to nanosecond multiplier
502 * @shift: cycle to nanosecond divisor (power of two)
503 * @maxadj: maximum adjustment value to mult (~11%)
504 * @mask: bitmask for two's complement subtraction of non 64 bit counters
505 * @max_cyc: maximum cycle value before potential overflow (does not include
506 * any safety margin)
507 *
508 * NOTE: This function includes a safety margin of 50%, in other words, we
509 * return half the number of nanoseconds the hardware counter can technically
510 * cover. This is done so that we can potentially detect problems caused by
511 * delayed timers or bad hardware, which might result in time intervals that
512 * are larger than what the math used can handle without overflows.
513 */
514u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
515{
516 u64 max_nsecs, max_cycles;
517
518 /*
519 * Calculate the maximum number of cycles that we can pass to the
520 * cyc2ns() function without overflowing a 64-bit result.
521 */
522 max_cycles = ULLONG_MAX;
523 do_div(max_cycles, mult+maxadj);
524
525 /*
526 * The actual maximum number of cycles we can defer the clocksource is
527 * determined by the minimum of max_cycles and mask.
528 * Note: Here we subtract the maxadj to make sure we don't sleep for
529 * too long if there's a large negative adjustment.
530 */
531 max_cycles = min(max_cycles, mask);
532 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
533
534 /* return the max_cycles value as well if requested */
535 if (max_cyc)
536 *max_cyc = max_cycles;
537
538 /* Return 50% of the actual maximum, so we can detect bad values */
539 max_nsecs >>= 1;
540
541 return max_nsecs;
542}
543
544/**
545 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
546 * @cs: Pointer to clocksource to be updated
547 *
548 */
549static inline void clocksource_update_max_deferment(struct clocksource *cs)
550{
551 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
552 cs->maxadj, cs->mask,
553 &cs->max_cycles);
554}
555
556#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
557
558static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
559{
560 struct clocksource *cs;
561
562 if (!finished_booting || list_empty(&clocksource_list))
563 return NULL;
564
565 /*
566 * We pick the clocksource with the highest rating. If oneshot
567 * mode is active, we pick the highres valid clocksource with
568 * the best rating.
569 */
570 list_for_each_entry(cs, &clocksource_list, list) {
571 if (skipcur && cs == curr_clocksource)
572 continue;
573 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
574 continue;
575 return cs;
576 }
577 return NULL;
578}
579
580static void __clocksource_select(bool skipcur)
581{
582 bool oneshot = tick_oneshot_mode_active();
583 struct clocksource *best, *cs;
584
585 /* Find the best suitable clocksource */
586 best = clocksource_find_best(oneshot, skipcur);
587 if (!best)
588 return;
589
590 /* Check for the override clocksource. */
591 list_for_each_entry(cs, &clocksource_list, list) {
592 if (skipcur && cs == curr_clocksource)
593 continue;
594 if (strcmp(cs->name, override_name) != 0)
595 continue;
596 /*
597 * Check to make sure we don't switch to a non-highres
598 * capable clocksource if the tick code is in oneshot
599 * mode (highres or nohz)
600 */
601 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
602 /* Override clocksource cannot be used. */
603 pr_warn("Override clocksource %s is not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
604 cs->name);
605 override_name[0] = 0;
606 } else
607 /* Override clocksource can be used. */
608 best = cs;
609 break;
610 }
611
612 if (curr_clocksource != best && !timekeeping_notify(best)) {
613 pr_info("Switched to clocksource %s\n", best->name);
614 curr_clocksource = best;
615 }
616}
617
618/**
619 * clocksource_select - Select the best clocksource available
620 *
621 * Private function. Must hold clocksource_mutex when called.
622 *
623 * Select the clocksource with the best rating, or the clocksource,
624 * which is selected by userspace override.
625 */
626static void clocksource_select(void)
627{
628 __clocksource_select(false);
629}
630
631static void clocksource_select_fallback(void)
632{
633 __clocksource_select(true);
634}
635
636#else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
637static inline void clocksource_select(void) { }
638static inline void clocksource_select_fallback(void) { }
639
640#endif
641
642/*
643 * clocksource_done_booting - Called near the end of core bootup
644 *
645 * Hack to avoid lots of clocksource churn at boot time.
646 * We use fs_initcall because we want this to start before
647 * device_initcall but after subsys_initcall.
648 */
649static int __init clocksource_done_booting(void)
650{
651 mutex_lock(&clocksource_mutex);
652 curr_clocksource = clocksource_default_clock();
653 finished_booting = 1;
654 /*
655 * Run the watchdog first to eliminate unstable clock sources
656 */
657 __clocksource_watchdog_kthread();
658 clocksource_select();
659 mutex_unlock(&clocksource_mutex);
660 return 0;
661}
662fs_initcall(clocksource_done_booting);
663
664/*
665 * Enqueue the clocksource sorted by rating
666 */
667static void clocksource_enqueue(struct clocksource *cs)
668{
669 struct list_head *entry = &clocksource_list;
670 struct clocksource *tmp;
671
672 list_for_each_entry(tmp, &clocksource_list, list)
673 /* Keep track of the place, where to insert */
674 if (tmp->rating >= cs->rating)
675 entry = &tmp->list;
676 list_add(&cs->list, entry);
677}
678
679/**
680 * __clocksource_update_freq_scale - Used update clocksource with new freq
681 * @cs: clocksource to be registered
682 * @scale: Scale factor multiplied against freq to get clocksource hz
683 * @freq: clocksource frequency (cycles per second) divided by scale
684 *
685 * This should only be called from the clocksource->enable() method.
686 *
687 * This *SHOULD NOT* be called directly! Please use the
688 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
689 * functions.
690 */
691void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
692{
693 u64 sec;
694
695 /*
696 * Default clocksources are *special* and self-define their mult/shift.
697 * But, you're not special, so you should specify a freq value.
698 */
699 if (freq) {
700 /*
701 * Calc the maximum number of seconds which we can run before
702 * wrapping around. For clocksources which have a mask > 32-bit
703 * we need to limit the max sleep time to have a good
704 * conversion precision. 10 minutes is still a reasonable
705 * amount. That results in a shift value of 24 for a
706 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
707 * ~ 0.06ppm granularity for NTP.
708 */
709 sec = cs->mask;
710 do_div(sec, freq);
711 do_div(sec, scale);
712 if (!sec)
713 sec = 1;
714 else if (sec > 600 && cs->mask > UINT_MAX)
715 sec = 600;
716
717 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
718 NSEC_PER_SEC / scale, sec * scale);
719 }
720 /*
721 * Ensure clocksources that have large 'mult' values don't overflow
722 * when adjusted.
723 */
724 cs->maxadj = clocksource_max_adjustment(cs);
725 while (freq && ((cs->mult + cs->maxadj < cs->mult)
726 || (cs->mult - cs->maxadj > cs->mult))) {
727 cs->mult >>= 1;
728 cs->shift--;
729 cs->maxadj = clocksource_max_adjustment(cs);
730 }
731
732 /*
733 * Only warn for *special* clocksources that self-define
734 * their mult/shift values and don't specify a freq.
735 */
736 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
737 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
738 cs->name);
739
740 clocksource_update_max_deferment(cs);
741
742 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
743 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
744}
745EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
746
747/**
748 * __clocksource_register_scale - Used to install new clocksources
749 * @cs: clocksource to be registered
750 * @scale: Scale factor multiplied against freq to get clocksource hz
751 * @freq: clocksource frequency (cycles per second) divided by scale
752 *
753 * Returns -EBUSY if registration fails, zero otherwise.
754 *
755 * This *SHOULD NOT* be called directly! Please use the
756 * clocksource_register_hz() or clocksource_register_khz helper functions.
757 */
758int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
759{
760
761 /* Initialize mult/shift and max_idle_ns */
762 __clocksource_update_freq_scale(cs, scale, freq);
763
764 /* Add clocksource to the clocksource list */
765 mutex_lock(&clocksource_mutex);
766 clocksource_enqueue(cs);
767 clocksource_enqueue_watchdog(cs);
768 clocksource_select();
769 clocksource_select_watchdog(false);
770 mutex_unlock(&clocksource_mutex);
771 return 0;
772}
773EXPORT_SYMBOL_GPL(__clocksource_register_scale);
774
775static void __clocksource_change_rating(struct clocksource *cs, int rating)
776{
777 list_del(&cs->list);
778 cs->rating = rating;
779 clocksource_enqueue(cs);
780}
781
782/**
783 * clocksource_change_rating - Change the rating of a registered clocksource
784 * @cs: clocksource to be changed
785 * @rating: new rating
786 */
787void clocksource_change_rating(struct clocksource *cs, int rating)
788{
789 mutex_lock(&clocksource_mutex);
790 __clocksource_change_rating(cs, rating);
791 clocksource_select();
792 clocksource_select_watchdog(false);
793 mutex_unlock(&clocksource_mutex);
794}
795EXPORT_SYMBOL(clocksource_change_rating);
796
797/*
798 * Unbind clocksource @cs. Called with clocksource_mutex held
799 */
800static int clocksource_unbind(struct clocksource *cs)
801{
802 if (clocksource_is_watchdog(cs)) {
803 /* Select and try to install a replacement watchdog. */
804 clocksource_select_watchdog(true);
805 if (clocksource_is_watchdog(cs))
806 return -EBUSY;
807 }
808
809 if (cs == curr_clocksource) {
810 /* Select and try to install a replacement clock source */
811 clocksource_select_fallback();
812 if (curr_clocksource == cs)
813 return -EBUSY;
814 }
815 clocksource_dequeue_watchdog(cs);
816 list_del_init(&cs->list);
817 return 0;
818}
819
820/**
821 * clocksource_unregister - remove a registered clocksource
822 * @cs: clocksource to be unregistered
823 */
824int clocksource_unregister(struct clocksource *cs)
825{
826 int ret = 0;
827
828 mutex_lock(&clocksource_mutex);
829 if (!list_empty(&cs->list))
830 ret = clocksource_unbind(cs);
831 mutex_unlock(&clocksource_mutex);
832 return ret;
833}
834EXPORT_SYMBOL(clocksource_unregister);
835
836#ifdef CONFIG_SYSFS
837/**
838 * sysfs_show_current_clocksources - sysfs interface for current clocksource
839 * @dev: unused
840 * @attr: unused
841 * @buf: char buffer to be filled with clocksource list
842 *
843 * Provides sysfs interface for listing current clocksource.
844 */
845static ssize_t
846sysfs_show_current_clocksources(struct device *dev,
847 struct device_attribute *attr, char *buf)
848{
849 ssize_t count = 0;
850
851 mutex_lock(&clocksource_mutex);
852 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
853 mutex_unlock(&clocksource_mutex);
854
855 return count;
856}
857
858ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
859{
860 size_t ret = cnt;
861
862 /* strings from sysfs write are not 0 terminated! */
863 if (!cnt || cnt >= CS_NAME_LEN)
864 return -EINVAL;
865
866 /* strip of \n: */
867 if (buf[cnt-1] == '\n')
868 cnt--;
869 if (cnt > 0)
870 memcpy(dst, buf, cnt);
871 dst[cnt] = 0;
872 return ret;
873}
874
875/**
876 * sysfs_override_clocksource - interface for manually overriding clocksource
877 * @dev: unused
878 * @attr: unused
879 * @buf: name of override clocksource
880 * @count: length of buffer
881 *
882 * Takes input from sysfs interface for manually overriding the default
883 * clocksource selection.
884 */
885static ssize_t sysfs_override_clocksource(struct device *dev,
886 struct device_attribute *attr,
887 const char *buf, size_t count)
888{
889 ssize_t ret;
890
891 mutex_lock(&clocksource_mutex);
892
893 ret = sysfs_get_uname(buf, override_name, count);
894 if (ret >= 0)
895 clocksource_select();
896
897 mutex_unlock(&clocksource_mutex);
898
899 return ret;
900}
901
902/**
903 * sysfs_unbind_current_clocksource - interface for manually unbinding clocksource
904 * @dev: unused
905 * @attr: unused
906 * @buf: unused
907 * @count: length of buffer
908 *
909 * Takes input from sysfs interface for manually unbinding a clocksource.
910 */
911static ssize_t sysfs_unbind_clocksource(struct device *dev,
912 struct device_attribute *attr,
913 const char *buf, size_t count)
914{
915 struct clocksource *cs;
916 char name[CS_NAME_LEN];
917 ssize_t ret;
918
919 ret = sysfs_get_uname(buf, name, count);
920 if (ret < 0)
921 return ret;
922
923 ret = -ENODEV;
924 mutex_lock(&clocksource_mutex);
925 list_for_each_entry(cs, &clocksource_list, list) {
926 if (strcmp(cs->name, name))
927 continue;
928 ret = clocksource_unbind(cs);
929 break;
930 }
931 mutex_unlock(&clocksource_mutex);
932
933 return ret ? ret : count;
934}
935
936/**
937 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
938 * @dev: unused
939 * @attr: unused
940 * @buf: char buffer to be filled with clocksource list
941 *
942 * Provides sysfs interface for listing registered clocksources
943 */
944static ssize_t
945sysfs_show_available_clocksources(struct device *dev,
946 struct device_attribute *attr,
947 char *buf)
948{
949 struct clocksource *src;
950 ssize_t count = 0;
951
952 mutex_lock(&clocksource_mutex);
953 list_for_each_entry(src, &clocksource_list, list) {
954 /*
955 * Don't show non-HRES clocksource if the tick code is
956 * in one shot mode (highres=on or nohz=on)
957 */
958 if (!tick_oneshot_mode_active() ||
959 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
960 count += snprintf(buf + count,
961 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
962 "%s ", src->name);
963 }
964 mutex_unlock(&clocksource_mutex);
965
966 count += snprintf(buf + count,
967 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
968
969 return count;
970}
971
972/*
973 * Sysfs setup bits:
974 */
975static DEVICE_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
976 sysfs_override_clocksource);
977
978static DEVICE_ATTR(unbind_clocksource, 0200, NULL, sysfs_unbind_clocksource);
979
980static DEVICE_ATTR(available_clocksource, 0444,
981 sysfs_show_available_clocksources, NULL);
982
983static struct bus_type clocksource_subsys = {
984 .name = "clocksource",
985 .dev_name = "clocksource",
986};
987
988static struct device device_clocksource = {
989 .id = 0,
990 .bus = &clocksource_subsys,
991};
992
993static int __init init_clocksource_sysfs(void)
994{
995 int error = subsys_system_register(&clocksource_subsys, NULL);
996
997 if (!error)
998 error = device_register(&device_clocksource);
999 if (!error)
1000 error = device_create_file(
1001 &device_clocksource,
1002 &dev_attr_current_clocksource);
1003 if (!error)
1004 error = device_create_file(&device_clocksource,
1005 &dev_attr_unbind_clocksource);
1006 if (!error)
1007 error = device_create_file(
1008 &device_clocksource,
1009 &dev_attr_available_clocksource);
1010 return error;
1011}
1012
1013device_initcall(init_clocksource_sysfs);
1014#endif /* CONFIG_SYSFS */
1015
1016/**
1017 * boot_override_clocksource - boot clock override
1018 * @str: override name
1019 *
1020 * Takes a clocksource= boot argument and uses it
1021 * as the clocksource override name.
1022 */
1023static int __init boot_override_clocksource(char* str)
1024{
1025 mutex_lock(&clocksource_mutex);
1026 if (str)
1027 strlcpy(override_name, str, sizeof(override_name));
1028 mutex_unlock(&clocksource_mutex);
1029 return 1;
1030}
1031
1032__setup("clocksource=", boot_override_clocksource);
1033
1034/**
1035 * boot_override_clock - Compatibility layer for deprecated boot option
1036 * @str: override name
1037 *
1038 * DEPRECATED! Takes a clock= boot argument and uses it
1039 * as the clocksource override name
1040 */
1041static int __init boot_override_clock(char* str)
1042{
1043 if (!strcmp(str, "pmtmr")) {
1044 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1045 return boot_override_clocksource("acpi_pm");
1046 }
1047 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1048 return boot_override_clocksource(str);
1049}
1050
1051__setup("clock=", boot_override_clock);
1/*
2 * linux/kernel/time/clocksource.c
3 *
4 * This file contains the functions which manage clocksource drivers.
5 *
6 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
17 *
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
21 *
22 * TODO WishList:
23 * o Allow clocksource drivers to be unregistered
24 */
25
26#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
27
28#include <linux/device.h>
29#include <linux/clocksource.h>
30#include <linux/init.h>
31#include <linux/module.h>
32#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
33#include <linux/tick.h>
34#include <linux/kthread.h>
35
36#include "tick-internal.h"
37#include "timekeeping_internal.h"
38
39/**
40 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
41 * @mult: pointer to mult variable
42 * @shift: pointer to shift variable
43 * @from: frequency to convert from
44 * @to: frequency to convert to
45 * @maxsec: guaranteed runtime conversion range in seconds
46 *
47 * The function evaluates the shift/mult pair for the scaled math
48 * operations of clocksources and clockevents.
49 *
50 * @to and @from are frequency values in HZ. For clock sources @to is
51 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
52 * event @to is the counter frequency and @from is NSEC_PER_SEC.
53 *
54 * The @maxsec conversion range argument controls the time frame in
55 * seconds which must be covered by the runtime conversion with the
56 * calculated mult and shift factors. This guarantees that no 64bit
57 * overflow happens when the input value of the conversion is
58 * multiplied with the calculated mult factor. Larger ranges may
59 * reduce the conversion accuracy by chosing smaller mult and shift
60 * factors.
61 */
62void
63clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
64{
65 u64 tmp;
66 u32 sft, sftacc= 32;
67
68 /*
69 * Calculate the shift factor which is limiting the conversion
70 * range:
71 */
72 tmp = ((u64)maxsec * from) >> 32;
73 while (tmp) {
74 tmp >>=1;
75 sftacc--;
76 }
77
78 /*
79 * Find the conversion shift/mult pair which has the best
80 * accuracy and fits the maxsec conversion range:
81 */
82 for (sft = 32; sft > 0; sft--) {
83 tmp = (u64) to << sft;
84 tmp += from / 2;
85 do_div(tmp, from);
86 if ((tmp >> sftacc) == 0)
87 break;
88 }
89 *mult = tmp;
90 *shift = sft;
91}
92EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
93
94/*[Clocksource internal variables]---------
95 * curr_clocksource:
96 * currently selected clocksource.
97 * clocksource_list:
98 * linked list with the registered clocksources
99 * clocksource_mutex:
100 * protects manipulations to curr_clocksource and the clocksource_list
101 * override_name:
102 * Name of the user-specified clocksource.
103 */
104static struct clocksource *curr_clocksource;
105static LIST_HEAD(clocksource_list);
106static DEFINE_MUTEX(clocksource_mutex);
107static char override_name[CS_NAME_LEN];
108static int finished_booting;
109
110#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
111static void clocksource_watchdog_work(struct work_struct *work);
112static void clocksource_select(void);
113
114static LIST_HEAD(watchdog_list);
115static struct clocksource *watchdog;
116static struct timer_list watchdog_timer;
117static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
118static DEFINE_SPINLOCK(watchdog_lock);
119static int watchdog_running;
120static atomic_t watchdog_reset_pending;
121
122static int clocksource_watchdog_kthread(void *data);
123static void __clocksource_change_rating(struct clocksource *cs, int rating);
124
125/*
126 * Interval: 0.5sec Threshold: 0.0625s
127 */
128#define WATCHDOG_INTERVAL (HZ >> 1)
129#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
130
131static void clocksource_watchdog_work(struct work_struct *work)
132{
133 /*
134 * If kthread_run fails the next watchdog scan over the
135 * watchdog_list will find the unstable clock again.
136 */
137 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
138}
139
140static void __clocksource_unstable(struct clocksource *cs)
141{
142 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
143 cs->flags |= CLOCK_SOURCE_UNSTABLE;
144 if (finished_booting)
145 schedule_work(&watchdog_work);
146}
147
148/**
149 * clocksource_mark_unstable - mark clocksource unstable via watchdog
150 * @cs: clocksource to be marked unstable
151 *
152 * This function is called instead of clocksource_change_rating from
153 * cpu hotplug code to avoid a deadlock between the clocksource mutex
154 * and the cpu hotplug mutex. It defers the update of the clocksource
155 * to the watchdog thread.
156 */
157void clocksource_mark_unstable(struct clocksource *cs)
158{
159 unsigned long flags;
160
161 spin_lock_irqsave(&watchdog_lock, flags);
162 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
163 if (list_empty(&cs->wd_list))
164 list_add(&cs->wd_list, &watchdog_list);
165 __clocksource_unstable(cs);
166 }
167 spin_unlock_irqrestore(&watchdog_lock, flags);
168}
169
170static void clocksource_watchdog(unsigned long data)
171{
172 struct clocksource *cs;
173 u64 csnow, wdnow, cslast, wdlast, delta;
174 int64_t wd_nsec, cs_nsec;
175 int next_cpu, reset_pending;
176
177 spin_lock(&watchdog_lock);
178 if (!watchdog_running)
179 goto out;
180
181 reset_pending = atomic_read(&watchdog_reset_pending);
182
183 list_for_each_entry(cs, &watchdog_list, wd_list) {
184
185 /* Clocksource already marked unstable? */
186 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
187 if (finished_booting)
188 schedule_work(&watchdog_work);
189 continue;
190 }
191
192 local_irq_disable();
193 csnow = cs->read(cs);
194 wdnow = watchdog->read(watchdog);
195 local_irq_enable();
196
197 /* Clocksource initialized ? */
198 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
199 atomic_read(&watchdog_reset_pending)) {
200 cs->flags |= CLOCK_SOURCE_WATCHDOG;
201 cs->wd_last = wdnow;
202 cs->cs_last = csnow;
203 continue;
204 }
205
206 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
207 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
208 watchdog->shift);
209
210 delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
211 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
212 wdlast = cs->wd_last; /* save these in case we print them */
213 cslast = cs->cs_last;
214 cs->cs_last = csnow;
215 cs->wd_last = wdnow;
216
217 if (atomic_read(&watchdog_reset_pending))
218 continue;
219
220 /* Check the deviation from the watchdog clocksource. */
221 if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
222 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
223 smp_processor_id(), cs->name);
224 pr_warn(" '%s' wd_now: %llx wd_last: %llx mask: %llx\n",
225 watchdog->name, wdnow, wdlast, watchdog->mask);
226 pr_warn(" '%s' cs_now: %llx cs_last: %llx mask: %llx\n",
227 cs->name, csnow, cslast, cs->mask);
228 __clocksource_unstable(cs);
229 continue;
230 }
231
232 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
233 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
234 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
235 /* Mark it valid for high-res. */
236 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
237
238 /*
239 * clocksource_done_booting() will sort it if
240 * finished_booting is not set yet.
241 */
242 if (!finished_booting)
243 continue;
244
245 /*
246 * If this is not the current clocksource let
247 * the watchdog thread reselect it. Due to the
248 * change to high res this clocksource might
249 * be preferred now. If it is the current
250 * clocksource let the tick code know about
251 * that change.
252 */
253 if (cs != curr_clocksource) {
254 cs->flags |= CLOCK_SOURCE_RESELECT;
255 schedule_work(&watchdog_work);
256 } else {
257 tick_clock_notify();
258 }
259 }
260 }
261
262 /*
263 * We only clear the watchdog_reset_pending, when we did a
264 * full cycle through all clocksources.
265 */
266 if (reset_pending)
267 atomic_dec(&watchdog_reset_pending);
268
269 /*
270 * Cycle through CPUs to check if the CPUs stay synchronized
271 * to each other.
272 */
273 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
274 if (next_cpu >= nr_cpu_ids)
275 next_cpu = cpumask_first(cpu_online_mask);
276 watchdog_timer.expires += WATCHDOG_INTERVAL;
277 add_timer_on(&watchdog_timer, next_cpu);
278out:
279 spin_unlock(&watchdog_lock);
280}
281
282static inline void clocksource_start_watchdog(void)
283{
284 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
285 return;
286 init_timer(&watchdog_timer);
287 watchdog_timer.function = clocksource_watchdog;
288 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
289 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
290 watchdog_running = 1;
291}
292
293static inline void clocksource_stop_watchdog(void)
294{
295 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
296 return;
297 del_timer(&watchdog_timer);
298 watchdog_running = 0;
299}
300
301static inline void clocksource_reset_watchdog(void)
302{
303 struct clocksource *cs;
304
305 list_for_each_entry(cs, &watchdog_list, wd_list)
306 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
307}
308
309static void clocksource_resume_watchdog(void)
310{
311 atomic_inc(&watchdog_reset_pending);
312}
313
314static void clocksource_enqueue_watchdog(struct clocksource *cs)
315{
316 unsigned long flags;
317
318 spin_lock_irqsave(&watchdog_lock, flags);
319 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
320 /* cs is a clocksource to be watched. */
321 list_add(&cs->wd_list, &watchdog_list);
322 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
323 } else {
324 /* cs is a watchdog. */
325 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
326 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
327 }
328 spin_unlock_irqrestore(&watchdog_lock, flags);
329}
330
331static void clocksource_select_watchdog(bool fallback)
332{
333 struct clocksource *cs, *old_wd;
334 unsigned long flags;
335
336 spin_lock_irqsave(&watchdog_lock, flags);
337 /* save current watchdog */
338 old_wd = watchdog;
339 if (fallback)
340 watchdog = NULL;
341
342 list_for_each_entry(cs, &clocksource_list, list) {
343 /* cs is a clocksource to be watched. */
344 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
345 continue;
346
347 /* Skip current if we were requested for a fallback. */
348 if (fallback && cs == old_wd)
349 continue;
350
351 /* Pick the best watchdog. */
352 if (!watchdog || cs->rating > watchdog->rating)
353 watchdog = cs;
354 }
355 /* If we failed to find a fallback restore the old one. */
356 if (!watchdog)
357 watchdog = old_wd;
358
359 /* If we changed the watchdog we need to reset cycles. */
360 if (watchdog != old_wd)
361 clocksource_reset_watchdog();
362
363 /* Check if the watchdog timer needs to be started. */
364 clocksource_start_watchdog();
365 spin_unlock_irqrestore(&watchdog_lock, flags);
366}
367
368static void clocksource_dequeue_watchdog(struct clocksource *cs)
369{
370 unsigned long flags;
371
372 spin_lock_irqsave(&watchdog_lock, flags);
373 if (cs != watchdog) {
374 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
375 /* cs is a watched clocksource. */
376 list_del_init(&cs->wd_list);
377 /* Check if the watchdog timer needs to be stopped. */
378 clocksource_stop_watchdog();
379 }
380 }
381 spin_unlock_irqrestore(&watchdog_lock, flags);
382}
383
384static int __clocksource_watchdog_kthread(void)
385{
386 struct clocksource *cs, *tmp;
387 unsigned long flags;
388 LIST_HEAD(unstable);
389 int select = 0;
390
391 spin_lock_irqsave(&watchdog_lock, flags);
392 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
393 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
394 list_del_init(&cs->wd_list);
395 list_add(&cs->wd_list, &unstable);
396 select = 1;
397 }
398 if (cs->flags & CLOCK_SOURCE_RESELECT) {
399 cs->flags &= ~CLOCK_SOURCE_RESELECT;
400 select = 1;
401 }
402 }
403 /* Check if the watchdog timer needs to be stopped. */
404 clocksource_stop_watchdog();
405 spin_unlock_irqrestore(&watchdog_lock, flags);
406
407 /* Needs to be done outside of watchdog lock */
408 list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
409 list_del_init(&cs->wd_list);
410 __clocksource_change_rating(cs, 0);
411 }
412 return select;
413}
414
415static int clocksource_watchdog_kthread(void *data)
416{
417 mutex_lock(&clocksource_mutex);
418 if (__clocksource_watchdog_kthread())
419 clocksource_select();
420 mutex_unlock(&clocksource_mutex);
421 return 0;
422}
423
424static bool clocksource_is_watchdog(struct clocksource *cs)
425{
426 return cs == watchdog;
427}
428
429#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
430
431static void clocksource_enqueue_watchdog(struct clocksource *cs)
432{
433 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
434 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
435}
436
437static void clocksource_select_watchdog(bool fallback) { }
438static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
439static inline void clocksource_resume_watchdog(void) { }
440static inline int __clocksource_watchdog_kthread(void) { return 0; }
441static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
442void clocksource_mark_unstable(struct clocksource *cs) { }
443
444#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
445
446/**
447 * clocksource_suspend - suspend the clocksource(s)
448 */
449void clocksource_suspend(void)
450{
451 struct clocksource *cs;
452
453 list_for_each_entry_reverse(cs, &clocksource_list, list)
454 if (cs->suspend)
455 cs->suspend(cs);
456}
457
458/**
459 * clocksource_resume - resume the clocksource(s)
460 */
461void clocksource_resume(void)
462{
463 struct clocksource *cs;
464
465 list_for_each_entry(cs, &clocksource_list, list)
466 if (cs->resume)
467 cs->resume(cs);
468
469 clocksource_resume_watchdog();
470}
471
472/**
473 * clocksource_touch_watchdog - Update watchdog
474 *
475 * Update the watchdog after exception contexts such as kgdb so as not
476 * to incorrectly trip the watchdog. This might fail when the kernel
477 * was stopped in code which holds watchdog_lock.
478 */
479void clocksource_touch_watchdog(void)
480{
481 clocksource_resume_watchdog();
482}
483
484/**
485 * clocksource_max_adjustment- Returns max adjustment amount
486 * @cs: Pointer to clocksource
487 *
488 */
489static u32 clocksource_max_adjustment(struct clocksource *cs)
490{
491 u64 ret;
492 /*
493 * We won't try to correct for more than 11% adjustments (110,000 ppm),
494 */
495 ret = (u64)cs->mult * 11;
496 do_div(ret,100);
497 return (u32)ret;
498}
499
500/**
501 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
502 * @mult: cycle to nanosecond multiplier
503 * @shift: cycle to nanosecond divisor (power of two)
504 * @maxadj: maximum adjustment value to mult (~11%)
505 * @mask: bitmask for two's complement subtraction of non 64 bit counters
506 * @max_cyc: maximum cycle value before potential overflow (does not include
507 * any safety margin)
508 *
509 * NOTE: This function includes a safety margin of 50%, in other words, we
510 * return half the number of nanoseconds the hardware counter can technically
511 * cover. This is done so that we can potentially detect problems caused by
512 * delayed timers or bad hardware, which might result in time intervals that
513 * are larger than what the math used can handle without overflows.
514 */
515u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
516{
517 u64 max_nsecs, max_cycles;
518
519 /*
520 * Calculate the maximum number of cycles that we can pass to the
521 * cyc2ns() function without overflowing a 64-bit result.
522 */
523 max_cycles = ULLONG_MAX;
524 do_div(max_cycles, mult+maxadj);
525
526 /*
527 * The actual maximum number of cycles we can defer the clocksource is
528 * determined by the minimum of max_cycles and mask.
529 * Note: Here we subtract the maxadj to make sure we don't sleep for
530 * too long if there's a large negative adjustment.
531 */
532 max_cycles = min(max_cycles, mask);
533 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
534
535 /* return the max_cycles value as well if requested */
536 if (max_cyc)
537 *max_cyc = max_cycles;
538
539 /* Return 50% of the actual maximum, so we can detect bad values */
540 max_nsecs >>= 1;
541
542 return max_nsecs;
543}
544
545/**
546 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
547 * @cs: Pointer to clocksource to be updated
548 *
549 */
550static inline void clocksource_update_max_deferment(struct clocksource *cs)
551{
552 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
553 cs->maxadj, cs->mask,
554 &cs->max_cycles);
555}
556
557#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
558
559static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
560{
561 struct clocksource *cs;
562
563 if (!finished_booting || list_empty(&clocksource_list))
564 return NULL;
565
566 /*
567 * We pick the clocksource with the highest rating. If oneshot
568 * mode is active, we pick the highres valid clocksource with
569 * the best rating.
570 */
571 list_for_each_entry(cs, &clocksource_list, list) {
572 if (skipcur && cs == curr_clocksource)
573 continue;
574 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
575 continue;
576 return cs;
577 }
578 return NULL;
579}
580
581static void __clocksource_select(bool skipcur)
582{
583 bool oneshot = tick_oneshot_mode_active();
584 struct clocksource *best, *cs;
585
586 /* Find the best suitable clocksource */
587 best = clocksource_find_best(oneshot, skipcur);
588 if (!best)
589 return;
590
591 /* Check for the override clocksource. */
592 list_for_each_entry(cs, &clocksource_list, list) {
593 if (skipcur && cs == curr_clocksource)
594 continue;
595 if (strcmp(cs->name, override_name) != 0)
596 continue;
597 /*
598 * Check to make sure we don't switch to a non-highres
599 * capable clocksource if the tick code is in oneshot
600 * mode (highres or nohz)
601 */
602 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
603 /* Override clocksource cannot be used. */
604 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
605 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
606 cs->name);
607 override_name[0] = 0;
608 } else {
609 /*
610 * The override cannot be currently verified.
611 * Deferring to let the watchdog check.
612 */
613 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
614 cs->name);
615 }
616 } else
617 /* Override clocksource can be used. */
618 best = cs;
619 break;
620 }
621
622 if (curr_clocksource != best && !timekeeping_notify(best)) {
623 pr_info("Switched to clocksource %s\n", best->name);
624 curr_clocksource = best;
625 }
626}
627
628/**
629 * clocksource_select - Select the best clocksource available
630 *
631 * Private function. Must hold clocksource_mutex when called.
632 *
633 * Select the clocksource with the best rating, or the clocksource,
634 * which is selected by userspace override.
635 */
636static void clocksource_select(void)
637{
638 __clocksource_select(false);
639}
640
641static void clocksource_select_fallback(void)
642{
643 __clocksource_select(true);
644}
645
646#else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
647static inline void clocksource_select(void) { }
648static inline void clocksource_select_fallback(void) { }
649
650#endif
651
652/*
653 * clocksource_done_booting - Called near the end of core bootup
654 *
655 * Hack to avoid lots of clocksource churn at boot time.
656 * We use fs_initcall because we want this to start before
657 * device_initcall but after subsys_initcall.
658 */
659static int __init clocksource_done_booting(void)
660{
661 mutex_lock(&clocksource_mutex);
662 curr_clocksource = clocksource_default_clock();
663 finished_booting = 1;
664 /*
665 * Run the watchdog first to eliminate unstable clock sources
666 */
667 __clocksource_watchdog_kthread();
668 clocksource_select();
669 mutex_unlock(&clocksource_mutex);
670 return 0;
671}
672fs_initcall(clocksource_done_booting);
673
674/*
675 * Enqueue the clocksource sorted by rating
676 */
677static void clocksource_enqueue(struct clocksource *cs)
678{
679 struct list_head *entry = &clocksource_list;
680 struct clocksource *tmp;
681
682 list_for_each_entry(tmp, &clocksource_list, list) {
683 /* Keep track of the place, where to insert */
684 if (tmp->rating < cs->rating)
685 break;
686 entry = &tmp->list;
687 }
688 list_add(&cs->list, entry);
689}
690
691/**
692 * __clocksource_update_freq_scale - Used update clocksource with new freq
693 * @cs: clocksource to be registered
694 * @scale: Scale factor multiplied against freq to get clocksource hz
695 * @freq: clocksource frequency (cycles per second) divided by scale
696 *
697 * This should only be called from the clocksource->enable() method.
698 *
699 * This *SHOULD NOT* be called directly! Please use the
700 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
701 * functions.
702 */
703void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
704{
705 u64 sec;
706
707 /*
708 * Default clocksources are *special* and self-define their mult/shift.
709 * But, you're not special, so you should specify a freq value.
710 */
711 if (freq) {
712 /*
713 * Calc the maximum number of seconds which we can run before
714 * wrapping around. For clocksources which have a mask > 32-bit
715 * we need to limit the max sleep time to have a good
716 * conversion precision. 10 minutes is still a reasonable
717 * amount. That results in a shift value of 24 for a
718 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
719 * ~ 0.06ppm granularity for NTP.
720 */
721 sec = cs->mask;
722 do_div(sec, freq);
723 do_div(sec, scale);
724 if (!sec)
725 sec = 1;
726 else if (sec > 600 && cs->mask > UINT_MAX)
727 sec = 600;
728
729 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
730 NSEC_PER_SEC / scale, sec * scale);
731 }
732 /*
733 * Ensure clocksources that have large 'mult' values don't overflow
734 * when adjusted.
735 */
736 cs->maxadj = clocksource_max_adjustment(cs);
737 while (freq && ((cs->mult + cs->maxadj < cs->mult)
738 || (cs->mult - cs->maxadj > cs->mult))) {
739 cs->mult >>= 1;
740 cs->shift--;
741 cs->maxadj = clocksource_max_adjustment(cs);
742 }
743
744 /*
745 * Only warn for *special* clocksources that self-define
746 * their mult/shift values and don't specify a freq.
747 */
748 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
749 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
750 cs->name);
751
752 clocksource_update_max_deferment(cs);
753
754 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
755 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
756}
757EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
758
759/**
760 * __clocksource_register_scale - Used to install new clocksources
761 * @cs: clocksource to be registered
762 * @scale: Scale factor multiplied against freq to get clocksource hz
763 * @freq: clocksource frequency (cycles per second) divided by scale
764 *
765 * Returns -EBUSY if registration fails, zero otherwise.
766 *
767 * This *SHOULD NOT* be called directly! Please use the
768 * clocksource_register_hz() or clocksource_register_khz helper functions.
769 */
770int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
771{
772
773 /* Initialize mult/shift and max_idle_ns */
774 __clocksource_update_freq_scale(cs, scale, freq);
775
776 /* Add clocksource to the clocksource list */
777 mutex_lock(&clocksource_mutex);
778 clocksource_enqueue(cs);
779 clocksource_enqueue_watchdog(cs);
780 clocksource_select();
781 clocksource_select_watchdog(false);
782 mutex_unlock(&clocksource_mutex);
783 return 0;
784}
785EXPORT_SYMBOL_GPL(__clocksource_register_scale);
786
787static void __clocksource_change_rating(struct clocksource *cs, int rating)
788{
789 list_del(&cs->list);
790 cs->rating = rating;
791 clocksource_enqueue(cs);
792}
793
794/**
795 * clocksource_change_rating - Change the rating of a registered clocksource
796 * @cs: clocksource to be changed
797 * @rating: new rating
798 */
799void clocksource_change_rating(struct clocksource *cs, int rating)
800{
801 mutex_lock(&clocksource_mutex);
802 __clocksource_change_rating(cs, rating);
803 clocksource_select();
804 clocksource_select_watchdog(false);
805 mutex_unlock(&clocksource_mutex);
806}
807EXPORT_SYMBOL(clocksource_change_rating);
808
809/*
810 * Unbind clocksource @cs. Called with clocksource_mutex held
811 */
812static int clocksource_unbind(struct clocksource *cs)
813{
814 if (clocksource_is_watchdog(cs)) {
815 /* Select and try to install a replacement watchdog. */
816 clocksource_select_watchdog(true);
817 if (clocksource_is_watchdog(cs))
818 return -EBUSY;
819 }
820
821 if (cs == curr_clocksource) {
822 /* Select and try to install a replacement clock source */
823 clocksource_select_fallback();
824 if (curr_clocksource == cs)
825 return -EBUSY;
826 }
827 clocksource_dequeue_watchdog(cs);
828 list_del_init(&cs->list);
829 return 0;
830}
831
832/**
833 * clocksource_unregister - remove a registered clocksource
834 * @cs: clocksource to be unregistered
835 */
836int clocksource_unregister(struct clocksource *cs)
837{
838 int ret = 0;
839
840 mutex_lock(&clocksource_mutex);
841 if (!list_empty(&cs->list))
842 ret = clocksource_unbind(cs);
843 mutex_unlock(&clocksource_mutex);
844 return ret;
845}
846EXPORT_SYMBOL(clocksource_unregister);
847
848#ifdef CONFIG_SYSFS
849/**
850 * sysfs_show_current_clocksources - sysfs interface for current clocksource
851 * @dev: unused
852 * @attr: unused
853 * @buf: char buffer to be filled with clocksource list
854 *
855 * Provides sysfs interface for listing current clocksource.
856 */
857static ssize_t
858sysfs_show_current_clocksources(struct device *dev,
859 struct device_attribute *attr, char *buf)
860{
861 ssize_t count = 0;
862
863 mutex_lock(&clocksource_mutex);
864 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
865 mutex_unlock(&clocksource_mutex);
866
867 return count;
868}
869
870ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
871{
872 size_t ret = cnt;
873
874 /* strings from sysfs write are not 0 terminated! */
875 if (!cnt || cnt >= CS_NAME_LEN)
876 return -EINVAL;
877
878 /* strip of \n: */
879 if (buf[cnt-1] == '\n')
880 cnt--;
881 if (cnt > 0)
882 memcpy(dst, buf, cnt);
883 dst[cnt] = 0;
884 return ret;
885}
886
887/**
888 * sysfs_override_clocksource - interface for manually overriding clocksource
889 * @dev: unused
890 * @attr: unused
891 * @buf: name of override clocksource
892 * @count: length of buffer
893 *
894 * Takes input from sysfs interface for manually overriding the default
895 * clocksource selection.
896 */
897static ssize_t sysfs_override_clocksource(struct device *dev,
898 struct device_attribute *attr,
899 const char *buf, size_t count)
900{
901 ssize_t ret;
902
903 mutex_lock(&clocksource_mutex);
904
905 ret = sysfs_get_uname(buf, override_name, count);
906 if (ret >= 0)
907 clocksource_select();
908
909 mutex_unlock(&clocksource_mutex);
910
911 return ret;
912}
913
914/**
915 * sysfs_unbind_current_clocksource - interface for manually unbinding clocksource
916 * @dev: unused
917 * @attr: unused
918 * @buf: unused
919 * @count: length of buffer
920 *
921 * Takes input from sysfs interface for manually unbinding a clocksource.
922 */
923static ssize_t sysfs_unbind_clocksource(struct device *dev,
924 struct device_attribute *attr,
925 const char *buf, size_t count)
926{
927 struct clocksource *cs;
928 char name[CS_NAME_LEN];
929 ssize_t ret;
930
931 ret = sysfs_get_uname(buf, name, count);
932 if (ret < 0)
933 return ret;
934
935 ret = -ENODEV;
936 mutex_lock(&clocksource_mutex);
937 list_for_each_entry(cs, &clocksource_list, list) {
938 if (strcmp(cs->name, name))
939 continue;
940 ret = clocksource_unbind(cs);
941 break;
942 }
943 mutex_unlock(&clocksource_mutex);
944
945 return ret ? ret : count;
946}
947
948/**
949 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
950 * @dev: unused
951 * @attr: unused
952 * @buf: char buffer to be filled with clocksource list
953 *
954 * Provides sysfs interface for listing registered clocksources
955 */
956static ssize_t
957sysfs_show_available_clocksources(struct device *dev,
958 struct device_attribute *attr,
959 char *buf)
960{
961 struct clocksource *src;
962 ssize_t count = 0;
963
964 mutex_lock(&clocksource_mutex);
965 list_for_each_entry(src, &clocksource_list, list) {
966 /*
967 * Don't show non-HRES clocksource if the tick code is
968 * in one shot mode (highres=on or nohz=on)
969 */
970 if (!tick_oneshot_mode_active() ||
971 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
972 count += snprintf(buf + count,
973 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
974 "%s ", src->name);
975 }
976 mutex_unlock(&clocksource_mutex);
977
978 count += snprintf(buf + count,
979 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
980
981 return count;
982}
983
984/*
985 * Sysfs setup bits:
986 */
987static DEVICE_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
988 sysfs_override_clocksource);
989
990static DEVICE_ATTR(unbind_clocksource, 0200, NULL, sysfs_unbind_clocksource);
991
992static DEVICE_ATTR(available_clocksource, 0444,
993 sysfs_show_available_clocksources, NULL);
994
995static struct bus_type clocksource_subsys = {
996 .name = "clocksource",
997 .dev_name = "clocksource",
998};
999
1000static struct device device_clocksource = {
1001 .id = 0,
1002 .bus = &clocksource_subsys,
1003};
1004
1005static int __init init_clocksource_sysfs(void)
1006{
1007 int error = subsys_system_register(&clocksource_subsys, NULL);
1008
1009 if (!error)
1010 error = device_register(&device_clocksource);
1011 if (!error)
1012 error = device_create_file(
1013 &device_clocksource,
1014 &dev_attr_current_clocksource);
1015 if (!error)
1016 error = device_create_file(&device_clocksource,
1017 &dev_attr_unbind_clocksource);
1018 if (!error)
1019 error = device_create_file(
1020 &device_clocksource,
1021 &dev_attr_available_clocksource);
1022 return error;
1023}
1024
1025device_initcall(init_clocksource_sysfs);
1026#endif /* CONFIG_SYSFS */
1027
1028/**
1029 * boot_override_clocksource - boot clock override
1030 * @str: override name
1031 *
1032 * Takes a clocksource= boot argument and uses it
1033 * as the clocksource override name.
1034 */
1035static int __init boot_override_clocksource(char* str)
1036{
1037 mutex_lock(&clocksource_mutex);
1038 if (str)
1039 strlcpy(override_name, str, sizeof(override_name));
1040 mutex_unlock(&clocksource_mutex);
1041 return 1;
1042}
1043
1044__setup("clocksource=", boot_override_clocksource);
1045
1046/**
1047 * boot_override_clock - Compatibility layer for deprecated boot option
1048 * @str: override name
1049 *
1050 * DEPRECATED! Takes a clock= boot argument and uses it
1051 * as the clocksource override name
1052 */
1053static int __init boot_override_clock(char* str)
1054{
1055 if (!strcmp(str, "pmtmr")) {
1056 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1057 return boot_override_clocksource("acpi_pm");
1058 }
1059 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1060 return boot_override_clocksource(str);
1061}
1062
1063__setup("clock=", boot_override_clock);