1 // SPDX-License-Identifier: GPL-2.0+
3 * This file contains the functions which manage clocksource drivers.
5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10 #include <linux/device.h>
11 #include <linux/clocksource.h>
12 #include <linux/init.h>
13 #include <linux/module.h>
14 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
15 #include <linux/tick.h>
16 #include <linux/kthread.h>
17 #include <linux/prandom.h>
18 #include <linux/cpu.h>
20 #include "tick-internal.h"
21 #include "timekeeping_internal.h"
24 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
25 * @mult: pointer to mult variable
26 * @shift: pointer to shift variable
27 * @from: frequency to convert from
28 * @to: frequency to convert to
29 * @maxsec: guaranteed runtime conversion range in seconds
31 * The function evaluates the shift/mult pair for the scaled math
32 * operations of clocksources and clockevents.
34 * @to and @from are frequency values in HZ. For clock sources @to is
35 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
36 * event @to is the counter frequency and @from is NSEC_PER_SEC.
38 * The @maxsec conversion range argument controls the time frame in
39 * seconds which must be covered by the runtime conversion with the
40 * calculated mult and shift factors. This guarantees that no 64bit
41 * overflow happens when the input value of the conversion is
42 * multiplied with the calculated mult factor. Larger ranges may
43 * reduce the conversion accuracy by choosing smaller mult and shift
47 clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
53 * Calculate the shift factor which is limiting the conversion
56 tmp = ((u64)maxsec * from) >> 32;
63 * Find the conversion shift/mult pair which has the best
64 * accuracy and fits the maxsec conversion range:
66 for (sft = 32; sft > 0; sft--) {
67 tmp = (u64) to << sft;
70 if ((tmp >> sftacc) == 0)
76 EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
78 /*[Clocksource internal variables]---------
80 * currently selected clocksource.
81 * suspend_clocksource:
82 * used to calculate the suspend time.
84 * linked list with the registered clocksources
86 * protects manipulations to curr_clocksource and the clocksource_list
88 * Name of the user-specified clocksource.
90 static struct clocksource *curr_clocksource;
91 static struct clocksource *suspend_clocksource;
92 static LIST_HEAD(clocksource_list);
93 static DEFINE_MUTEX(clocksource_mutex);
94 static char override_name[CS_NAME_LEN];
95 static int finished_booting;
96 static u64 suspend_start;
101 #define WATCHDOG_INTERVAL (HZ >> 1)
102 #define WATCHDOG_INTERVAL_MAX_NS ((2 * WATCHDOG_INTERVAL) * (NSEC_PER_SEC / HZ))
105 * Threshold: 0.0312s, when doubled: 0.0625s.
106 * Also a default for cs->uncertainty_margin when registering clocks.
108 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)
111 * Maximum permissible delay between two readouts of the watchdog
112 * clocksource surrounding a read of the clocksource being validated.
113 * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as
114 * a lower bound for cs->uncertainty_margin values when registering clocks.
116 * The default of 500 parts per million is based on NTP's limits.
117 * If a clocksource is good enough for NTP, it is good enough for us!
119 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
120 #define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
122 #define MAX_SKEW_USEC (125 * WATCHDOG_INTERVAL / HZ)
125 #define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
127 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
128 static void clocksource_watchdog_work(struct work_struct *work);
129 static void clocksource_select(void);
131 static LIST_HEAD(watchdog_list);
132 static struct clocksource *watchdog;
133 static struct timer_list watchdog_timer;
134 static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
135 static DEFINE_SPINLOCK(watchdog_lock);
136 static int watchdog_running;
137 static atomic_t watchdog_reset_pending;
138 static int64_t watchdog_max_interval;
140 static inline void clocksource_watchdog_lock(unsigned long *flags)
142 spin_lock_irqsave(&watchdog_lock, *flags);
145 static inline void clocksource_watchdog_unlock(unsigned long *flags)
147 spin_unlock_irqrestore(&watchdog_lock, *flags);
150 static int clocksource_watchdog_kthread(void *data);
151 static void __clocksource_change_rating(struct clocksource *cs, int rating);
153 static void clocksource_watchdog_work(struct work_struct *work)
156 * We cannot directly run clocksource_watchdog_kthread() here, because
157 * clocksource_select() calls timekeeping_notify() which uses
158 * stop_machine(). One cannot use stop_machine() from a workqueue() due
159 * lock inversions wrt CPU hotplug.
161 * Also, we only ever run this work once or twice during the lifetime
162 * of the kernel, so there is no point in creating a more permanent
165 * If kthread_run fails the next watchdog scan over the
166 * watchdog_list will find the unstable clock again.
168 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
171 static void __clocksource_unstable(struct clocksource *cs)
173 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
174 cs->flags |= CLOCK_SOURCE_UNSTABLE;
177 * If the clocksource is registered clocksource_watchdog_kthread() will
178 * re-rate and re-select.
180 if (list_empty(&cs->list)) {
185 if (cs->mark_unstable)
186 cs->mark_unstable(cs);
188 /* kick clocksource_watchdog_kthread() */
189 if (finished_booting)
190 schedule_work(&watchdog_work);
194 * clocksource_mark_unstable - mark clocksource unstable via watchdog
195 * @cs: clocksource to be marked unstable
197 * This function is called by the x86 TSC code to mark clocksources as unstable;
198 * it defers demotion and re-selection to a kthread.
200 void clocksource_mark_unstable(struct clocksource *cs)
204 spin_lock_irqsave(&watchdog_lock, flags);
205 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
206 if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
207 list_add(&cs->wd_list, &watchdog_list);
208 __clocksource_unstable(cs);
210 spin_unlock_irqrestore(&watchdog_lock, flags);
213 ulong max_cswd_read_retries = 2;
214 module_param(max_cswd_read_retries, ulong, 0644);
215 EXPORT_SYMBOL_GPL(max_cswd_read_retries);
216 static int verify_n_cpus = 8;
217 module_param(verify_n_cpus, int, 0644);
219 enum wd_read_status {
225 static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
227 unsigned int nretries;
228 u64 wd_end, wd_end2, wd_delta;
229 int64_t wd_delay, wd_seq_delay;
231 for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) {
233 *wdnow = watchdog->read(watchdog);
234 *csnow = cs->read(cs);
235 wd_end = watchdog->read(watchdog);
236 wd_end2 = watchdog->read(watchdog);
239 wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
240 wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult,
242 if (wd_delay <= WATCHDOG_MAX_SKEW) {
243 if (nretries > 1 || nretries >= max_cswd_read_retries) {
244 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
245 smp_processor_id(), watchdog->name, nretries);
247 return WD_READ_SUCCESS;
251 * Now compute delay in consecutive watchdog read to see if
252 * there is too much external interferences that cause
253 * significant delay in reading both clocksource and watchdog.
255 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2,
256 * report system busy, reinit the watchdog and skip the current
259 wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask);
260 wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift);
261 if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
265 pr_warn("timekeeping watchdog on CPU%d: wd-%s-wd excessive read-back delay of %lldns vs. limit of %ldns, wd-wd read-back delay only %lldns, attempt %d, marking %s unstable\n",
266 smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name);
267 return WD_READ_UNSTABLE;
270 pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
271 smp_processor_id(), watchdog->name, wd_seq_delay);
272 pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
277 static u64 csnow_mid;
278 static cpumask_t cpus_ahead;
279 static cpumask_t cpus_behind;
280 static cpumask_t cpus_chosen;
282 static void clocksource_verify_choose_cpus(void)
284 int cpu, i, n = verify_n_cpus;
287 /* Check all of the CPUs. */
288 cpumask_copy(&cpus_chosen, cpu_online_mask);
289 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
293 /* If no checking desired, or no other CPU to check, leave. */
294 cpumask_clear(&cpus_chosen);
295 if (n == 0 || num_online_cpus() <= 1)
298 /* Make sure to select at least one CPU other than the current CPU. */
299 cpu = cpumask_first(cpu_online_mask);
300 if (cpu == smp_processor_id())
301 cpu = cpumask_next(cpu, cpu_online_mask);
302 if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
304 cpumask_set_cpu(cpu, &cpus_chosen);
306 /* Force a sane value for the boot parameter. */
311 * Randomly select the specified number of CPUs. If the same
312 * CPU is selected multiple times, that CPU is checked only once,
313 * and no replacement CPU is selected. This gracefully handles
314 * situations where verify_n_cpus is greater than the number of
315 * CPUs that are currently online.
317 for (i = 1; i < n; i++) {
318 cpu = get_random_u32_below(nr_cpu_ids);
319 cpu = cpumask_next(cpu - 1, cpu_online_mask);
320 if (cpu >= nr_cpu_ids)
321 cpu = cpumask_first(cpu_online_mask);
322 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
323 cpumask_set_cpu(cpu, &cpus_chosen);
326 /* Don't verify ourselves. */
327 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
330 static void clocksource_verify_one_cpu(void *csin)
332 struct clocksource *cs = (struct clocksource *)csin;
334 csnow_mid = cs->read(cs);
337 void clocksource_verify_percpu(struct clocksource *cs)
339 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
340 u64 csnow_begin, csnow_end;
344 if (verify_n_cpus == 0)
346 cpumask_clear(&cpus_ahead);
347 cpumask_clear(&cpus_behind);
350 clocksource_verify_choose_cpus();
351 if (cpumask_empty(&cpus_chosen)) {
354 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
357 testcpu = smp_processor_id();
358 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
359 for_each_cpu(cpu, &cpus_chosen) {
362 csnow_begin = cs->read(cs);
363 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
364 csnow_end = cs->read(cs);
365 delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
367 cpumask_set_cpu(cpu, &cpus_behind);
368 delta = (csnow_end - csnow_mid) & cs->mask;
370 cpumask_set_cpu(cpu, &cpus_ahead);
371 delta = clocksource_delta(csnow_end, csnow_begin, cs->mask);
372 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
373 if (cs_nsec > cs_nsec_max)
374 cs_nsec_max = cs_nsec;
375 if (cs_nsec < cs_nsec_min)
376 cs_nsec_min = cs_nsec;
380 if (!cpumask_empty(&cpus_ahead))
381 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
382 cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
383 if (!cpumask_empty(&cpus_behind))
384 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n",
385 cpumask_pr_args(&cpus_behind), testcpu, cs->name);
386 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
387 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n",
388 testcpu, cs_nsec_min, cs_nsec_max, cs->name);
390 EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
392 static inline void clocksource_reset_watchdog(void)
394 struct clocksource *cs;
396 list_for_each_entry(cs, &watchdog_list, wd_list)
397 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
401 static void clocksource_watchdog(struct timer_list *unused)
403 u64 csnow, wdnow, cslast, wdlast, delta;
404 int64_t wd_nsec, cs_nsec, interval;
405 int next_cpu, reset_pending;
406 struct clocksource *cs;
407 enum wd_read_status read_ret;
408 unsigned long extra_wait = 0;
411 spin_lock(&watchdog_lock);
412 if (!watchdog_running)
415 reset_pending = atomic_read(&watchdog_reset_pending);
417 list_for_each_entry(cs, &watchdog_list, wd_list) {
419 /* Clocksource already marked unstable? */
420 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
421 if (finished_booting)
422 schedule_work(&watchdog_work);
426 read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
428 if (read_ret == WD_READ_UNSTABLE) {
429 /* Clock readout unreliable, so give it up. */
430 __clocksource_unstable(cs);
435 * When WD_READ_SKIP is returned, it means the system is likely
436 * under very heavy load, where the latency of reading
437 * watchdog/clocksource is very big, and affect the accuracy of
438 * watchdog check. So give system some space and suspend the
439 * watchdog check for 5 minutes.
441 if (read_ret == WD_READ_SKIP) {
443 * As the watchdog timer will be suspended, and
444 * cs->last could keep unchanged for 5 minutes, reset
447 clocksource_reset_watchdog();
448 extra_wait = HZ * 300;
452 /* Clocksource initialized ? */
453 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
454 atomic_read(&watchdog_reset_pending)) {
455 cs->flags |= CLOCK_SOURCE_WATCHDOG;
461 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
462 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
465 delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
466 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
467 wdlast = cs->wd_last; /* save these in case we print them */
468 cslast = cs->cs_last;
472 if (atomic_read(&watchdog_reset_pending))
476 * The processing of timer softirqs can get delayed (usually
477 * on account of ksoftirqd not getting to run in a timely
478 * manner), which causes the watchdog interval to stretch.
479 * Skew detection may fail for longer watchdog intervals
480 * on account of fixed margins being used.
481 * Some clocksources, e.g. acpi_pm, cannot tolerate
482 * watchdog intervals longer than a few seconds.
484 interval = max(cs_nsec, wd_nsec);
485 if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) {
486 if (system_state > SYSTEM_SCHEDULING &&
487 interval > 2 * watchdog_max_interval) {
488 watchdog_max_interval = interval;
489 pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n",
492 watchdog_timer.expires = jiffies;
496 /* Check the deviation from the watchdog clocksource. */
497 md = cs->uncertainty_margin + watchdog->uncertainty_margin;
498 if (abs(cs_nsec - wd_nsec) > md) {
503 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
504 smp_processor_id(), cs->name);
505 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
506 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
507 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
508 cs->name, cs_nsec, csnow, cslast, cs->mask);
509 cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem);
510 wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem);
511 pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n",
512 cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec);
513 if (curr_clocksource == cs)
514 pr_warn(" '%s' is current clocksource.\n", cs->name);
515 else if (curr_clocksource)
516 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
518 pr_warn(" No current clocksource.\n");
519 __clocksource_unstable(cs);
523 if (cs == curr_clocksource && cs->tick_stable)
526 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
527 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
528 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
529 /* Mark it valid for high-res. */
530 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
533 * clocksource_done_booting() will sort it if
534 * finished_booting is not set yet.
536 if (!finished_booting)
540 * If this is not the current clocksource let
541 * the watchdog thread reselect it. Due to the
542 * change to high res this clocksource might
543 * be preferred now. If it is the current
544 * clocksource let the tick code know about
547 if (cs != curr_clocksource) {
548 cs->flags |= CLOCK_SOURCE_RESELECT;
549 schedule_work(&watchdog_work);
557 * We only clear the watchdog_reset_pending, when we did a
558 * full cycle through all clocksources.
561 atomic_dec(&watchdog_reset_pending);
564 * Cycle through CPUs to check if the CPUs stay synchronized
567 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
568 if (next_cpu >= nr_cpu_ids)
569 next_cpu = cpumask_first(cpu_online_mask);
572 * Arm timer if not already pending: could race with concurrent
573 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
575 if (!timer_pending(&watchdog_timer)) {
576 watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait;
577 add_timer_on(&watchdog_timer, next_cpu);
580 spin_unlock(&watchdog_lock);
583 static inline void clocksource_start_watchdog(void)
585 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
587 timer_setup(&watchdog_timer, clocksource_watchdog, 0);
588 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
589 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
590 watchdog_running = 1;
593 static inline void clocksource_stop_watchdog(void)
595 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
597 del_timer(&watchdog_timer);
598 watchdog_running = 0;
601 static void clocksource_resume_watchdog(void)
603 atomic_inc(&watchdog_reset_pending);
606 static void clocksource_enqueue_watchdog(struct clocksource *cs)
608 INIT_LIST_HEAD(&cs->wd_list);
610 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
611 /* cs is a clocksource to be watched. */
612 list_add(&cs->wd_list, &watchdog_list);
613 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
615 /* cs is a watchdog. */
616 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
617 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
621 static void clocksource_select_watchdog(bool fallback)
623 struct clocksource *cs, *old_wd;
626 spin_lock_irqsave(&watchdog_lock, flags);
627 /* save current watchdog */
632 list_for_each_entry(cs, &clocksource_list, list) {
633 /* cs is a clocksource to be watched. */
634 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
637 /* Skip current if we were requested for a fallback. */
638 if (fallback && cs == old_wd)
641 /* Pick the best watchdog. */
642 if (!watchdog || cs->rating > watchdog->rating)
645 /* If we failed to find a fallback restore the old one. */
649 /* If we changed the watchdog we need to reset cycles. */
650 if (watchdog != old_wd)
651 clocksource_reset_watchdog();
653 /* Check if the watchdog timer needs to be started. */
654 clocksource_start_watchdog();
655 spin_unlock_irqrestore(&watchdog_lock, flags);
658 static void clocksource_dequeue_watchdog(struct clocksource *cs)
660 if (cs != watchdog) {
661 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
662 /* cs is a watched clocksource. */
663 list_del_init(&cs->wd_list);
664 /* Check if the watchdog timer needs to be stopped. */
665 clocksource_stop_watchdog();
670 static int __clocksource_watchdog_kthread(void)
672 struct clocksource *cs, *tmp;
676 /* Do any required per-CPU skew verification. */
677 if (curr_clocksource &&
678 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
679 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
680 clocksource_verify_percpu(curr_clocksource);
682 spin_lock_irqsave(&watchdog_lock, flags);
683 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
684 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
685 list_del_init(&cs->wd_list);
686 __clocksource_change_rating(cs, 0);
689 if (cs->flags & CLOCK_SOURCE_RESELECT) {
690 cs->flags &= ~CLOCK_SOURCE_RESELECT;
694 /* Check if the watchdog timer needs to be stopped. */
695 clocksource_stop_watchdog();
696 spin_unlock_irqrestore(&watchdog_lock, flags);
701 static int clocksource_watchdog_kthread(void *data)
703 mutex_lock(&clocksource_mutex);
704 if (__clocksource_watchdog_kthread())
705 clocksource_select();
706 mutex_unlock(&clocksource_mutex);
710 static bool clocksource_is_watchdog(struct clocksource *cs)
712 return cs == watchdog;
715 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
717 static void clocksource_enqueue_watchdog(struct clocksource *cs)
719 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
720 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
723 static void clocksource_select_watchdog(bool fallback) { }
724 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
725 static inline void clocksource_resume_watchdog(void) { }
726 static inline int __clocksource_watchdog_kthread(void) { return 0; }
727 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
728 void clocksource_mark_unstable(struct clocksource *cs) { }
730 static inline void clocksource_watchdog_lock(unsigned long *flags) { }
731 static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
733 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
735 static bool clocksource_is_suspend(struct clocksource *cs)
737 return cs == suspend_clocksource;
740 static void __clocksource_suspend_select(struct clocksource *cs)
743 * Skip the clocksource which will be stopped in suspend state.
745 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
749 * The nonstop clocksource can be selected as the suspend clocksource to
750 * calculate the suspend time, so it should not supply suspend/resume
751 * interfaces to suspend the nonstop clocksource when system suspends.
753 if (cs->suspend || cs->resume) {
754 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
758 /* Pick the best rating. */
759 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
760 suspend_clocksource = cs;
764 * clocksource_suspend_select - Select the best clocksource for suspend timing
765 * @fallback: if select a fallback clocksource
767 static void clocksource_suspend_select(bool fallback)
769 struct clocksource *cs, *old_suspend;
771 old_suspend = suspend_clocksource;
773 suspend_clocksource = NULL;
775 list_for_each_entry(cs, &clocksource_list, list) {
776 /* Skip current if we were requested for a fallback. */
777 if (fallback && cs == old_suspend)
780 __clocksource_suspend_select(cs);
785 * clocksource_start_suspend_timing - Start measuring the suspend timing
786 * @cs: current clocksource from timekeeping
787 * @start_cycles: current cycles from timekeeping
789 * This function will save the start cycle values of suspend timer to calculate
790 * the suspend time when resuming system.
792 * This function is called late in the suspend process from timekeeping_suspend(),
793 * that means processes are frozen, non-boot cpus and interrupts are disabled
794 * now. It is therefore possible to start the suspend timer without taking the
797 void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
799 if (!suspend_clocksource)
803 * If current clocksource is the suspend timer, we should use the
804 * tkr_mono.cycle_last value as suspend_start to avoid same reading
805 * from suspend timer.
807 if (clocksource_is_suspend(cs)) {
808 suspend_start = start_cycles;
812 if (suspend_clocksource->enable &&
813 suspend_clocksource->enable(suspend_clocksource)) {
814 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
818 suspend_start = suspend_clocksource->read(suspend_clocksource);
822 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
823 * @cs: current clocksource from timekeeping
824 * @cycle_now: current cycles from timekeeping
826 * This function will calculate the suspend time from suspend timer.
828 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
830 * This function is called early in the resume process from timekeeping_resume(),
831 * that means there is only one cpu, no processes are running and the interrupts
832 * are disabled. It is therefore possible to stop the suspend timer without
833 * taking the clocksource mutex.
835 u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
837 u64 now, delta, nsec = 0;
839 if (!suspend_clocksource)
843 * If current clocksource is the suspend timer, we should use the
844 * tkr_mono.cycle_last value from timekeeping as current cycle to
845 * avoid same reading from suspend timer.
847 if (clocksource_is_suspend(cs))
850 now = suspend_clocksource->read(suspend_clocksource);
852 if (now > suspend_start) {
853 delta = clocksource_delta(now, suspend_start,
854 suspend_clocksource->mask);
855 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
856 suspend_clocksource->shift);
860 * Disable the suspend timer to save power if current clocksource is
861 * not the suspend timer.
863 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
864 suspend_clocksource->disable(suspend_clocksource);
870 * clocksource_suspend - suspend the clocksource(s)
872 void clocksource_suspend(void)
874 struct clocksource *cs;
876 list_for_each_entry_reverse(cs, &clocksource_list, list)
882 * clocksource_resume - resume the clocksource(s)
884 void clocksource_resume(void)
886 struct clocksource *cs;
888 list_for_each_entry(cs, &clocksource_list, list)
892 clocksource_resume_watchdog();
896 * clocksource_touch_watchdog - Update watchdog
898 * Update the watchdog after exception contexts such as kgdb so as not
899 * to incorrectly trip the watchdog. This might fail when the kernel
900 * was stopped in code which holds watchdog_lock.
902 void clocksource_touch_watchdog(void)
904 clocksource_resume_watchdog();
908 * clocksource_max_adjustment- Returns max adjustment amount
909 * @cs: Pointer to clocksource
912 static u32 clocksource_max_adjustment(struct clocksource *cs)
916 * We won't try to correct for more than 11% adjustments (110,000 ppm),
918 ret = (u64)cs->mult * 11;
924 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
925 * @mult: cycle to nanosecond multiplier
926 * @shift: cycle to nanosecond divisor (power of two)
927 * @maxadj: maximum adjustment value to mult (~11%)
928 * @mask: bitmask for two's complement subtraction of non 64 bit counters
929 * @max_cyc: maximum cycle value before potential overflow (does not include
932 * NOTE: This function includes a safety margin of 50%, in other words, we
933 * return half the number of nanoseconds the hardware counter can technically
934 * cover. This is done so that we can potentially detect problems caused by
935 * delayed timers or bad hardware, which might result in time intervals that
936 * are larger than what the math used can handle without overflows.
938 u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
940 u64 max_nsecs, max_cycles;
943 * Calculate the maximum number of cycles that we can pass to the
944 * cyc2ns() function without overflowing a 64-bit result.
946 max_cycles = ULLONG_MAX;
947 do_div(max_cycles, mult+maxadj);
950 * The actual maximum number of cycles we can defer the clocksource is
951 * determined by the minimum of max_cycles and mask.
952 * Note: Here we subtract the maxadj to make sure we don't sleep for
953 * too long if there's a large negative adjustment.
955 max_cycles = min(max_cycles, mask);
956 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
958 /* return the max_cycles value as well if requested */
960 *max_cyc = max_cycles;
962 /* Return 50% of the actual maximum, so we can detect bad values */
969 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
970 * @cs: Pointer to clocksource to be updated
973 static inline void clocksource_update_max_deferment(struct clocksource *cs)
975 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
976 cs->maxadj, cs->mask,
980 static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
982 struct clocksource *cs;
984 if (!finished_booting || list_empty(&clocksource_list))
988 * We pick the clocksource with the highest rating. If oneshot
989 * mode is active, we pick the highres valid clocksource with
992 list_for_each_entry(cs, &clocksource_list, list) {
993 if (skipcur && cs == curr_clocksource)
995 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1002 static void __clocksource_select(bool skipcur)
1004 bool oneshot = tick_oneshot_mode_active();
1005 struct clocksource *best, *cs;
1007 /* Find the best suitable clocksource */
1008 best = clocksource_find_best(oneshot, skipcur);
1012 if (!strlen(override_name))
1015 /* Check for the override clocksource. */
1016 list_for_each_entry(cs, &clocksource_list, list) {
1017 if (skipcur && cs == curr_clocksource)
1019 if (strcmp(cs->name, override_name) != 0)
1022 * Check to make sure we don't switch to a non-highres
1023 * capable clocksource if the tick code is in oneshot
1024 * mode (highres or nohz)
1026 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
1027 /* Override clocksource cannot be used. */
1028 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
1029 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
1031 override_name[0] = 0;
1034 * The override cannot be currently verified.
1035 * Deferring to let the watchdog check.
1037 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
1041 /* Override clocksource can be used. */
1047 if (curr_clocksource != best && !timekeeping_notify(best)) {
1048 pr_info("Switched to clocksource %s\n", best->name);
1049 curr_clocksource = best;
1054 * clocksource_select - Select the best clocksource available
1056 * Private function. Must hold clocksource_mutex when called.
1058 * Select the clocksource with the best rating, or the clocksource,
1059 * which is selected by userspace override.
1061 static void clocksource_select(void)
1063 __clocksource_select(false);
1066 static void clocksource_select_fallback(void)
1068 __clocksource_select(true);
1072 * clocksource_done_booting - Called near the end of core bootup
1074 * Hack to avoid lots of clocksource churn at boot time.
1075 * We use fs_initcall because we want this to start before
1076 * device_initcall but after subsys_initcall.
1078 static int __init clocksource_done_booting(void)
1080 mutex_lock(&clocksource_mutex);
1081 curr_clocksource = clocksource_default_clock();
1082 finished_booting = 1;
1084 * Run the watchdog first to eliminate unstable clock sources
1086 __clocksource_watchdog_kthread();
1087 clocksource_select();
1088 mutex_unlock(&clocksource_mutex);
1091 fs_initcall(clocksource_done_booting);
1094 * Enqueue the clocksource sorted by rating
1096 static void clocksource_enqueue(struct clocksource *cs)
1098 struct list_head *entry = &clocksource_list;
1099 struct clocksource *tmp;
1101 list_for_each_entry(tmp, &clocksource_list, list) {
1102 /* Keep track of the place, where to insert */
1103 if (tmp->rating < cs->rating)
1107 list_add(&cs->list, entry);
1111 * __clocksource_update_freq_scale - Used update clocksource with new freq
1112 * @cs: clocksource to be registered
1113 * @scale: Scale factor multiplied against freq to get clocksource hz
1114 * @freq: clocksource frequency (cycles per second) divided by scale
1116 * This should only be called from the clocksource->enable() method.
1118 * This *SHOULD NOT* be called directly! Please use the
1119 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
1122 void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1127 * Default clocksources are *special* and self-define their mult/shift.
1128 * But, you're not special, so you should specify a freq value.
1132 * Calc the maximum number of seconds which we can run before
1133 * wrapping around. For clocksources which have a mask > 32-bit
1134 * we need to limit the max sleep time to have a good
1135 * conversion precision. 10 minutes is still a reasonable
1136 * amount. That results in a shift value of 24 for a
1137 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1138 * ~ 0.06ppm granularity for NTP.
1145 else if (sec > 600 && cs->mask > UINT_MAX)
1148 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1149 NSEC_PER_SEC / scale, sec * scale);
1153 * If the uncertainty margin is not specified, calculate it.
1154 * If both scale and freq are non-zero, calculate the clock
1155 * period, but bound below at 2*WATCHDOG_MAX_SKEW. However,
1156 * if either of scale or freq is zero, be very conservative and
1157 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the
1158 * uncertainty margin. Allow stupidly small uncertainty margins
1159 * to be specified by the caller for testing purposes, but warn
1160 * to discourage production use of this capability.
1162 if (scale && freq && !cs->uncertainty_margin) {
1163 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
1164 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
1165 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
1166 } else if (!cs->uncertainty_margin) {
1167 cs->uncertainty_margin = WATCHDOG_THRESHOLD;
1169 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
1172 * Ensure clocksources that have large 'mult' values don't overflow
1175 cs->maxadj = clocksource_max_adjustment(cs);
1176 while (freq && ((cs->mult + cs->maxadj < cs->mult)
1177 || (cs->mult - cs->maxadj > cs->mult))) {
1180 cs->maxadj = clocksource_max_adjustment(cs);
1184 * Only warn for *special* clocksources that self-define
1185 * their mult/shift values and don't specify a freq.
1187 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1188 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1191 clocksource_update_max_deferment(cs);
1193 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1194 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1196 EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
1199 * __clocksource_register_scale - Used to install new clocksources
1200 * @cs: clocksource to be registered
1201 * @scale: Scale factor multiplied against freq to get clocksource hz
1202 * @freq: clocksource frequency (cycles per second) divided by scale
1204 * Returns -EBUSY if registration fails, zero otherwise.
1206 * This *SHOULD NOT* be called directly! Please use the
1207 * clocksource_register_hz() or clocksource_register_khz helper functions.
1209 int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1211 unsigned long flags;
1213 clocksource_arch_init(cs);
1215 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1216 cs->id = CSID_GENERIC;
1217 if (cs->vdso_clock_mode < 0 ||
1218 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1219 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1220 cs->name, cs->vdso_clock_mode);
1221 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1224 /* Initialize mult/shift and max_idle_ns */
1225 __clocksource_update_freq_scale(cs, scale, freq);
1227 /* Add clocksource to the clocksource list */
1228 mutex_lock(&clocksource_mutex);
1230 clocksource_watchdog_lock(&flags);
1231 clocksource_enqueue(cs);
1232 clocksource_enqueue_watchdog(cs);
1233 clocksource_watchdog_unlock(&flags);
1235 clocksource_select();
1236 clocksource_select_watchdog(false);
1237 __clocksource_suspend_select(cs);
1238 mutex_unlock(&clocksource_mutex);
1241 EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1243 static void __clocksource_change_rating(struct clocksource *cs, int rating)
1245 list_del(&cs->list);
1246 cs->rating = rating;
1247 clocksource_enqueue(cs);
1251 * clocksource_change_rating - Change the rating of a registered clocksource
1252 * @cs: clocksource to be changed
1253 * @rating: new rating
1255 void clocksource_change_rating(struct clocksource *cs, int rating)
1257 unsigned long flags;
1259 mutex_lock(&clocksource_mutex);
1260 clocksource_watchdog_lock(&flags);
1261 __clocksource_change_rating(cs, rating);
1262 clocksource_watchdog_unlock(&flags);
1264 clocksource_select();
1265 clocksource_select_watchdog(false);
1266 clocksource_suspend_select(false);
1267 mutex_unlock(&clocksource_mutex);
1269 EXPORT_SYMBOL(clocksource_change_rating);
1272 * Unbind clocksource @cs. Called with clocksource_mutex held
1274 static int clocksource_unbind(struct clocksource *cs)
1276 unsigned long flags;
1278 if (clocksource_is_watchdog(cs)) {
1279 /* Select and try to install a replacement watchdog. */
1280 clocksource_select_watchdog(true);
1281 if (clocksource_is_watchdog(cs))
1285 if (cs == curr_clocksource) {
1286 /* Select and try to install a replacement clock source */
1287 clocksource_select_fallback();
1288 if (curr_clocksource == cs)
1292 if (clocksource_is_suspend(cs)) {
1294 * Select and try to install a replacement suspend clocksource.
1295 * If no replacement suspend clocksource, we will just let the
1296 * clocksource go and have no suspend clocksource.
1298 clocksource_suspend_select(true);
1301 clocksource_watchdog_lock(&flags);
1302 clocksource_dequeue_watchdog(cs);
1303 list_del_init(&cs->list);
1304 clocksource_watchdog_unlock(&flags);
1310 * clocksource_unregister - remove a registered clocksource
1311 * @cs: clocksource to be unregistered
1313 int clocksource_unregister(struct clocksource *cs)
1317 mutex_lock(&clocksource_mutex);
1318 if (!list_empty(&cs->list))
1319 ret = clocksource_unbind(cs);
1320 mutex_unlock(&clocksource_mutex);
1323 EXPORT_SYMBOL(clocksource_unregister);
1327 * current_clocksource_show - sysfs interface for current clocksource
1330 * @buf: char buffer to be filled with clocksource list
1332 * Provides sysfs interface for listing current clocksource.
1334 static ssize_t current_clocksource_show(struct device *dev,
1335 struct device_attribute *attr,
1340 mutex_lock(&clocksource_mutex);
1341 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
1342 mutex_unlock(&clocksource_mutex);
1347 ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1351 /* strings from sysfs write are not 0 terminated! */
1352 if (!cnt || cnt >= CS_NAME_LEN)
1356 if (buf[cnt-1] == '\n')
1359 memcpy(dst, buf, cnt);
1365 * current_clocksource_store - interface for manually overriding clocksource
1368 * @buf: name of override clocksource
1369 * @count: length of buffer
1371 * Takes input from sysfs interface for manually overriding the default
1372 * clocksource selection.
1374 static ssize_t current_clocksource_store(struct device *dev,
1375 struct device_attribute *attr,
1376 const char *buf, size_t count)
1380 mutex_lock(&clocksource_mutex);
1382 ret = sysfs_get_uname(buf, override_name, count);
1384 clocksource_select();
1386 mutex_unlock(&clocksource_mutex);
1390 static DEVICE_ATTR_RW(current_clocksource);
1393 * unbind_clocksource_store - interface for manually unbinding clocksource
1397 * @count: length of buffer
1399 * Takes input from sysfs interface for manually unbinding a clocksource.
1401 static ssize_t unbind_clocksource_store(struct device *dev,
1402 struct device_attribute *attr,
1403 const char *buf, size_t count)
1405 struct clocksource *cs;
1406 char name[CS_NAME_LEN];
1409 ret = sysfs_get_uname(buf, name, count);
1414 mutex_lock(&clocksource_mutex);
1415 list_for_each_entry(cs, &clocksource_list, list) {
1416 if (strcmp(cs->name, name))
1418 ret = clocksource_unbind(cs);
1421 mutex_unlock(&clocksource_mutex);
1423 return ret ? ret : count;
1425 static DEVICE_ATTR_WO(unbind_clocksource);
1428 * available_clocksource_show - sysfs interface for listing clocksource
1431 * @buf: char buffer to be filled with clocksource list
1433 * Provides sysfs interface for listing registered clocksources
1435 static ssize_t available_clocksource_show(struct device *dev,
1436 struct device_attribute *attr,
1439 struct clocksource *src;
1442 mutex_lock(&clocksource_mutex);
1443 list_for_each_entry(src, &clocksource_list, list) {
1445 * Don't show non-HRES clocksource if the tick code is
1446 * in one shot mode (highres=on or nohz=on)
1448 if (!tick_oneshot_mode_active() ||
1449 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1450 count += snprintf(buf + count,
1451 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1454 mutex_unlock(&clocksource_mutex);
1456 count += snprintf(buf + count,
1457 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1461 static DEVICE_ATTR_RO(available_clocksource);
1463 static struct attribute *clocksource_attrs[] = {
1464 &dev_attr_current_clocksource.attr,
1465 &dev_attr_unbind_clocksource.attr,
1466 &dev_attr_available_clocksource.attr,
1469 ATTRIBUTE_GROUPS(clocksource);
1471 static struct bus_type clocksource_subsys = {
1472 .name = "clocksource",
1473 .dev_name = "clocksource",
1476 static struct device device_clocksource = {
1478 .bus = &clocksource_subsys,
1479 .groups = clocksource_groups,
1482 static int __init init_clocksource_sysfs(void)
1484 int error = subsys_system_register(&clocksource_subsys, NULL);
1487 error = device_register(&device_clocksource);
1492 device_initcall(init_clocksource_sysfs);
1493 #endif /* CONFIG_SYSFS */
1496 * boot_override_clocksource - boot clock override
1497 * @str: override name
1499 * Takes a clocksource= boot argument and uses it
1500 * as the clocksource override name.
1502 static int __init boot_override_clocksource(char* str)
1504 mutex_lock(&clocksource_mutex);
1506 strscpy(override_name, str, sizeof(override_name));
1507 mutex_unlock(&clocksource_mutex);
1511 __setup("clocksource=", boot_override_clocksource);
1514 * boot_override_clock - Compatibility layer for deprecated boot option
1515 * @str: override name
1517 * DEPRECATED! Takes a clock= boot argument and uses it
1518 * as the clocksource override name
1520 static int __init boot_override_clock(char* str)
1522 if (!strcmp(str, "pmtmr")) {
1523 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1524 return boot_override_clocksource("acpi_pm");
1526 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1527 return boot_override_clocksource(str);
1530 __setup("clock=", boot_override_clock);