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;
99 * Threshold: 0.0312s, when doubled: 0.0625s.
100 * Also a default for cs->uncertainty_margin when registering clocks.
102 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)
105 * Maximum permissible delay between two readouts of the watchdog
106 * clocksource surrounding a read of the clocksource being validated.
107 * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as
108 * a lower bound for cs->uncertainty_margin values when registering clocks.
110 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
111 #define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
113 #define MAX_SKEW_USEC 100
116 #define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
118 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
119 static void clocksource_watchdog_work(struct work_struct *work);
120 static void clocksource_select(void);
122 static LIST_HEAD(watchdog_list);
123 static struct clocksource *watchdog;
124 static struct timer_list watchdog_timer;
125 static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
126 static DEFINE_SPINLOCK(watchdog_lock);
127 static int watchdog_running;
128 static atomic_t watchdog_reset_pending;
130 static inline void clocksource_watchdog_lock(unsigned long *flags)
132 spin_lock_irqsave(&watchdog_lock, *flags);
135 static inline void clocksource_watchdog_unlock(unsigned long *flags)
137 spin_unlock_irqrestore(&watchdog_lock, *flags);
140 static int clocksource_watchdog_kthread(void *data);
141 static void __clocksource_change_rating(struct clocksource *cs, int rating);
146 #define WATCHDOG_INTERVAL (HZ >> 1)
148 static void clocksource_watchdog_work(struct work_struct *work)
151 * We cannot directly run clocksource_watchdog_kthread() here, because
152 * clocksource_select() calls timekeeping_notify() which uses
153 * stop_machine(). One cannot use stop_machine() from a workqueue() due
154 * lock inversions wrt CPU hotplug.
156 * Also, we only ever run this work once or twice during the lifetime
157 * of the kernel, so there is no point in creating a more permanent
160 * If kthread_run fails the next watchdog scan over the
161 * watchdog_list will find the unstable clock again.
163 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
166 static void __clocksource_unstable(struct clocksource *cs)
168 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
169 cs->flags |= CLOCK_SOURCE_UNSTABLE;
172 * If the clocksource is registered clocksource_watchdog_kthread() will
173 * re-rate and re-select.
175 if (list_empty(&cs->list)) {
180 if (cs->mark_unstable)
181 cs->mark_unstable(cs);
183 /* kick clocksource_watchdog_kthread() */
184 if (finished_booting)
185 schedule_work(&watchdog_work);
189 * clocksource_mark_unstable - mark clocksource unstable via watchdog
190 * @cs: clocksource to be marked unstable
192 * This function is called by the x86 TSC code to mark clocksources as unstable;
193 * it defers demotion and re-selection to a kthread.
195 void clocksource_mark_unstable(struct clocksource *cs)
199 spin_lock_irqsave(&watchdog_lock, flags);
200 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
201 if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
202 list_add(&cs->wd_list, &watchdog_list);
203 __clocksource_unstable(cs);
205 spin_unlock_irqrestore(&watchdog_lock, flags);
208 ulong max_cswd_read_retries = 2;
209 module_param(max_cswd_read_retries, ulong, 0644);
210 EXPORT_SYMBOL_GPL(max_cswd_read_retries);
211 static int verify_n_cpus = 8;
212 module_param(verify_n_cpus, int, 0644);
214 enum wd_read_status {
220 static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
222 unsigned int nretries;
223 u64 wd_end, wd_end2, wd_delta;
224 int64_t wd_delay, wd_seq_delay;
226 for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) {
228 *wdnow = watchdog->read(watchdog);
229 *csnow = cs->read(cs);
230 wd_end = watchdog->read(watchdog);
231 wd_end2 = watchdog->read(watchdog);
234 wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
235 wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult,
237 if (wd_delay <= WATCHDOG_MAX_SKEW) {
238 if (nretries > 1 || nretries >= max_cswd_read_retries) {
239 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
240 smp_processor_id(), watchdog->name, nretries);
242 return WD_READ_SUCCESS;
246 * Now compute delay in consecutive watchdog read to see if
247 * there is too much external interferences that cause
248 * significant delay in reading both clocksource and watchdog.
250 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2,
251 * report system busy, reinit the watchdog and skip the current
254 wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask);
255 wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift);
256 if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
260 pr_warn("timekeeping watchdog on CPU%d: %s read-back delay of %lldns, attempt %d, marking unstable\n",
261 smp_processor_id(), watchdog->name, wd_delay, nretries);
262 return WD_READ_UNSTABLE;
265 pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
266 smp_processor_id(), watchdog->name, wd_seq_delay);
267 pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
272 static u64 csnow_mid;
273 static cpumask_t cpus_ahead;
274 static cpumask_t cpus_behind;
275 static cpumask_t cpus_chosen;
277 static void clocksource_verify_choose_cpus(void)
279 int cpu, i, n = verify_n_cpus;
282 /* Check all of the CPUs. */
283 cpumask_copy(&cpus_chosen, cpu_online_mask);
284 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
288 /* If no checking desired, or no other CPU to check, leave. */
289 cpumask_clear(&cpus_chosen);
290 if (n == 0 || num_online_cpus() <= 1)
293 /* Make sure to select at least one CPU other than the current CPU. */
294 cpu = cpumask_first(cpu_online_mask);
295 if (cpu == smp_processor_id())
296 cpu = cpumask_next(cpu, cpu_online_mask);
297 if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
299 cpumask_set_cpu(cpu, &cpus_chosen);
301 /* Force a sane value for the boot parameter. */
306 * Randomly select the specified number of CPUs. If the same
307 * CPU is selected multiple times, that CPU is checked only once,
308 * and no replacement CPU is selected. This gracefully handles
309 * situations where verify_n_cpus is greater than the number of
310 * CPUs that are currently online.
312 for (i = 1; i < n; i++) {
313 cpu = get_random_u32_below(nr_cpu_ids);
314 cpu = cpumask_next(cpu - 1, cpu_online_mask);
315 if (cpu >= nr_cpu_ids)
316 cpu = cpumask_first(cpu_online_mask);
317 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
318 cpumask_set_cpu(cpu, &cpus_chosen);
321 /* Don't verify ourselves. */
322 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
325 static void clocksource_verify_one_cpu(void *csin)
327 struct clocksource *cs = (struct clocksource *)csin;
329 csnow_mid = cs->read(cs);
332 void clocksource_verify_percpu(struct clocksource *cs)
334 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
335 u64 csnow_begin, csnow_end;
339 if (verify_n_cpus == 0)
341 cpumask_clear(&cpus_ahead);
342 cpumask_clear(&cpus_behind);
345 clocksource_verify_choose_cpus();
346 if (cpumask_empty(&cpus_chosen)) {
349 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
352 testcpu = smp_processor_id();
353 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
354 for_each_cpu(cpu, &cpus_chosen) {
357 csnow_begin = cs->read(cs);
358 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
359 csnow_end = cs->read(cs);
360 delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
362 cpumask_set_cpu(cpu, &cpus_behind);
363 delta = (csnow_end - csnow_mid) & cs->mask;
365 cpumask_set_cpu(cpu, &cpus_ahead);
366 delta = clocksource_delta(csnow_end, csnow_begin, cs->mask);
367 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
368 if (cs_nsec > cs_nsec_max)
369 cs_nsec_max = cs_nsec;
370 if (cs_nsec < cs_nsec_min)
371 cs_nsec_min = cs_nsec;
375 if (!cpumask_empty(&cpus_ahead))
376 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
377 cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
378 if (!cpumask_empty(&cpus_behind))
379 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n",
380 cpumask_pr_args(&cpus_behind), testcpu, cs->name);
381 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
382 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n",
383 testcpu, cs_nsec_min, cs_nsec_max, cs->name);
385 EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
387 static void clocksource_watchdog(struct timer_list *unused)
389 u64 csnow, wdnow, cslast, wdlast, delta;
390 int next_cpu, reset_pending;
391 int64_t wd_nsec, cs_nsec;
392 struct clocksource *cs;
393 enum wd_read_status read_ret;
396 spin_lock(&watchdog_lock);
397 if (!watchdog_running)
400 reset_pending = atomic_read(&watchdog_reset_pending);
402 list_for_each_entry(cs, &watchdog_list, wd_list) {
404 /* Clocksource already marked unstable? */
405 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
406 if (finished_booting)
407 schedule_work(&watchdog_work);
411 read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
413 if (read_ret != WD_READ_SUCCESS) {
414 if (read_ret == WD_READ_UNSTABLE)
415 /* Clock readout unreliable, so give it up. */
416 __clocksource_unstable(cs);
420 /* Clocksource initialized ? */
421 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
422 atomic_read(&watchdog_reset_pending)) {
423 cs->flags |= CLOCK_SOURCE_WATCHDOG;
429 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
430 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
433 delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
434 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
435 wdlast = cs->wd_last; /* save these in case we print them */
436 cslast = cs->cs_last;
440 if (atomic_read(&watchdog_reset_pending))
443 /* Check the deviation from the watchdog clocksource. */
444 md = cs->uncertainty_margin + watchdog->uncertainty_margin;
445 if (abs(cs_nsec - wd_nsec) > md) {
446 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
447 smp_processor_id(), cs->name);
448 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
449 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
450 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
451 cs->name, cs_nsec, csnow, cslast, cs->mask);
452 if (curr_clocksource == cs)
453 pr_warn(" '%s' is current clocksource.\n", cs->name);
454 else if (curr_clocksource)
455 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
457 pr_warn(" No current clocksource.\n");
458 __clocksource_unstable(cs);
462 if (cs == curr_clocksource && cs->tick_stable)
465 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
466 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
467 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
468 /* Mark it valid for high-res. */
469 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
472 * clocksource_done_booting() will sort it if
473 * finished_booting is not set yet.
475 if (!finished_booting)
479 * If this is not the current clocksource let
480 * the watchdog thread reselect it. Due to the
481 * change to high res this clocksource might
482 * be preferred now. If it is the current
483 * clocksource let the tick code know about
486 if (cs != curr_clocksource) {
487 cs->flags |= CLOCK_SOURCE_RESELECT;
488 schedule_work(&watchdog_work);
496 * We only clear the watchdog_reset_pending, when we did a
497 * full cycle through all clocksources.
500 atomic_dec(&watchdog_reset_pending);
503 * Cycle through CPUs to check if the CPUs stay synchronized
506 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
507 if (next_cpu >= nr_cpu_ids)
508 next_cpu = cpumask_first(cpu_online_mask);
511 * Arm timer if not already pending: could race with concurrent
512 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
514 if (!timer_pending(&watchdog_timer)) {
515 watchdog_timer.expires += WATCHDOG_INTERVAL;
516 add_timer_on(&watchdog_timer, next_cpu);
519 spin_unlock(&watchdog_lock);
522 static inline void clocksource_start_watchdog(void)
524 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
526 timer_setup(&watchdog_timer, clocksource_watchdog, 0);
527 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
528 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
529 watchdog_running = 1;
532 static inline void clocksource_stop_watchdog(void)
534 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
536 del_timer(&watchdog_timer);
537 watchdog_running = 0;
540 static inline void clocksource_reset_watchdog(void)
542 struct clocksource *cs;
544 list_for_each_entry(cs, &watchdog_list, wd_list)
545 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
548 static void clocksource_resume_watchdog(void)
550 atomic_inc(&watchdog_reset_pending);
553 static void clocksource_enqueue_watchdog(struct clocksource *cs)
555 INIT_LIST_HEAD(&cs->wd_list);
557 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
558 /* cs is a clocksource to be watched. */
559 list_add(&cs->wd_list, &watchdog_list);
560 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
562 /* cs is a watchdog. */
563 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
564 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
568 static void clocksource_select_watchdog(bool fallback)
570 struct clocksource *cs, *old_wd;
573 spin_lock_irqsave(&watchdog_lock, flags);
574 /* save current watchdog */
579 list_for_each_entry(cs, &clocksource_list, list) {
580 /* cs is a clocksource to be watched. */
581 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
584 /* Skip current if we were requested for a fallback. */
585 if (fallback && cs == old_wd)
588 /* Pick the best watchdog. */
589 if (!watchdog || cs->rating > watchdog->rating)
592 /* If we failed to find a fallback restore the old one. */
596 /* If we changed the watchdog we need to reset cycles. */
597 if (watchdog != old_wd)
598 clocksource_reset_watchdog();
600 /* Check if the watchdog timer needs to be started. */
601 clocksource_start_watchdog();
602 spin_unlock_irqrestore(&watchdog_lock, flags);
605 static void clocksource_dequeue_watchdog(struct clocksource *cs)
607 if (cs != watchdog) {
608 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
609 /* cs is a watched clocksource. */
610 list_del_init(&cs->wd_list);
611 /* Check if the watchdog timer needs to be stopped. */
612 clocksource_stop_watchdog();
617 static int __clocksource_watchdog_kthread(void)
619 struct clocksource *cs, *tmp;
623 /* Do any required per-CPU skew verification. */
624 if (curr_clocksource &&
625 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
626 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
627 clocksource_verify_percpu(curr_clocksource);
629 spin_lock_irqsave(&watchdog_lock, flags);
630 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
631 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
632 list_del_init(&cs->wd_list);
633 __clocksource_change_rating(cs, 0);
636 if (cs->flags & CLOCK_SOURCE_RESELECT) {
637 cs->flags &= ~CLOCK_SOURCE_RESELECT;
641 /* Check if the watchdog timer needs to be stopped. */
642 clocksource_stop_watchdog();
643 spin_unlock_irqrestore(&watchdog_lock, flags);
648 static int clocksource_watchdog_kthread(void *data)
650 mutex_lock(&clocksource_mutex);
651 if (__clocksource_watchdog_kthread())
652 clocksource_select();
653 mutex_unlock(&clocksource_mutex);
657 static bool clocksource_is_watchdog(struct clocksource *cs)
659 return cs == watchdog;
662 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
664 static void clocksource_enqueue_watchdog(struct clocksource *cs)
666 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
667 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
670 static void clocksource_select_watchdog(bool fallback) { }
671 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
672 static inline void clocksource_resume_watchdog(void) { }
673 static inline int __clocksource_watchdog_kthread(void) { return 0; }
674 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
675 void clocksource_mark_unstable(struct clocksource *cs) { }
677 static inline void clocksource_watchdog_lock(unsigned long *flags) { }
678 static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
680 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
682 static bool clocksource_is_suspend(struct clocksource *cs)
684 return cs == suspend_clocksource;
687 static void __clocksource_suspend_select(struct clocksource *cs)
690 * Skip the clocksource which will be stopped in suspend state.
692 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
696 * The nonstop clocksource can be selected as the suspend clocksource to
697 * calculate the suspend time, so it should not supply suspend/resume
698 * interfaces to suspend the nonstop clocksource when system suspends.
700 if (cs->suspend || cs->resume) {
701 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
705 /* Pick the best rating. */
706 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
707 suspend_clocksource = cs;
711 * clocksource_suspend_select - Select the best clocksource for suspend timing
712 * @fallback: if select a fallback clocksource
714 static void clocksource_suspend_select(bool fallback)
716 struct clocksource *cs, *old_suspend;
718 old_suspend = suspend_clocksource;
720 suspend_clocksource = NULL;
722 list_for_each_entry(cs, &clocksource_list, list) {
723 /* Skip current if we were requested for a fallback. */
724 if (fallback && cs == old_suspend)
727 __clocksource_suspend_select(cs);
732 * clocksource_start_suspend_timing - Start measuring the suspend timing
733 * @cs: current clocksource from timekeeping
734 * @start_cycles: current cycles from timekeeping
736 * This function will save the start cycle values of suspend timer to calculate
737 * the suspend time when resuming system.
739 * This function is called late in the suspend process from timekeeping_suspend(),
740 * that means processes are frozen, non-boot cpus and interrupts are disabled
741 * now. It is therefore possible to start the suspend timer without taking the
744 void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
746 if (!suspend_clocksource)
750 * If current clocksource is the suspend timer, we should use the
751 * tkr_mono.cycle_last value as suspend_start to avoid same reading
752 * from suspend timer.
754 if (clocksource_is_suspend(cs)) {
755 suspend_start = start_cycles;
759 if (suspend_clocksource->enable &&
760 suspend_clocksource->enable(suspend_clocksource)) {
761 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
765 suspend_start = suspend_clocksource->read(suspend_clocksource);
769 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
770 * @cs: current clocksource from timekeeping
771 * @cycle_now: current cycles from timekeeping
773 * This function will calculate the suspend time from suspend timer.
775 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
777 * This function is called early in the resume process from timekeeping_resume(),
778 * that means there is only one cpu, no processes are running and the interrupts
779 * are disabled. It is therefore possible to stop the suspend timer without
780 * taking the clocksource mutex.
782 u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
784 u64 now, delta, nsec = 0;
786 if (!suspend_clocksource)
790 * If current clocksource is the suspend timer, we should use the
791 * tkr_mono.cycle_last value from timekeeping as current cycle to
792 * avoid same reading from suspend timer.
794 if (clocksource_is_suspend(cs))
797 now = suspend_clocksource->read(suspend_clocksource);
799 if (now > suspend_start) {
800 delta = clocksource_delta(now, suspend_start,
801 suspend_clocksource->mask);
802 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
803 suspend_clocksource->shift);
807 * Disable the suspend timer to save power if current clocksource is
808 * not the suspend timer.
810 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
811 suspend_clocksource->disable(suspend_clocksource);
817 * clocksource_suspend - suspend the clocksource(s)
819 void clocksource_suspend(void)
821 struct clocksource *cs;
823 list_for_each_entry_reverse(cs, &clocksource_list, list)
829 * clocksource_resume - resume the clocksource(s)
831 void clocksource_resume(void)
833 struct clocksource *cs;
835 list_for_each_entry(cs, &clocksource_list, list)
839 clocksource_resume_watchdog();
843 * clocksource_touch_watchdog - Update watchdog
845 * Update the watchdog after exception contexts such as kgdb so as not
846 * to incorrectly trip the watchdog. This might fail when the kernel
847 * was stopped in code which holds watchdog_lock.
849 void clocksource_touch_watchdog(void)
851 clocksource_resume_watchdog();
855 * clocksource_max_adjustment- Returns max adjustment amount
856 * @cs: Pointer to clocksource
859 static u32 clocksource_max_adjustment(struct clocksource *cs)
863 * We won't try to correct for more than 11% adjustments (110,000 ppm),
865 ret = (u64)cs->mult * 11;
871 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
872 * @mult: cycle to nanosecond multiplier
873 * @shift: cycle to nanosecond divisor (power of two)
874 * @maxadj: maximum adjustment value to mult (~11%)
875 * @mask: bitmask for two's complement subtraction of non 64 bit counters
876 * @max_cyc: maximum cycle value before potential overflow (does not include
879 * NOTE: This function includes a safety margin of 50%, in other words, we
880 * return half the number of nanoseconds the hardware counter can technically
881 * cover. This is done so that we can potentially detect problems caused by
882 * delayed timers or bad hardware, which might result in time intervals that
883 * are larger than what the math used can handle without overflows.
885 u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
887 u64 max_nsecs, max_cycles;
890 * Calculate the maximum number of cycles that we can pass to the
891 * cyc2ns() function without overflowing a 64-bit result.
893 max_cycles = ULLONG_MAX;
894 do_div(max_cycles, mult+maxadj);
897 * The actual maximum number of cycles we can defer the clocksource is
898 * determined by the minimum of max_cycles and mask.
899 * Note: Here we subtract the maxadj to make sure we don't sleep for
900 * too long if there's a large negative adjustment.
902 max_cycles = min(max_cycles, mask);
903 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
905 /* return the max_cycles value as well if requested */
907 *max_cyc = max_cycles;
909 /* Return 50% of the actual maximum, so we can detect bad values */
916 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
917 * @cs: Pointer to clocksource to be updated
920 static inline void clocksource_update_max_deferment(struct clocksource *cs)
922 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
923 cs->maxadj, cs->mask,
927 static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
929 struct clocksource *cs;
931 if (!finished_booting || list_empty(&clocksource_list))
935 * We pick the clocksource with the highest rating. If oneshot
936 * mode is active, we pick the highres valid clocksource with
939 list_for_each_entry(cs, &clocksource_list, list) {
940 if (skipcur && cs == curr_clocksource)
942 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
949 static void __clocksource_select(bool skipcur)
951 bool oneshot = tick_oneshot_mode_active();
952 struct clocksource *best, *cs;
954 /* Find the best suitable clocksource */
955 best = clocksource_find_best(oneshot, skipcur);
959 if (!strlen(override_name))
962 /* Check for the override clocksource. */
963 list_for_each_entry(cs, &clocksource_list, list) {
964 if (skipcur && cs == curr_clocksource)
966 if (strcmp(cs->name, override_name) != 0)
969 * Check to make sure we don't switch to a non-highres
970 * capable clocksource if the tick code is in oneshot
971 * mode (highres or nohz)
973 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
974 /* Override clocksource cannot be used. */
975 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
976 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
978 override_name[0] = 0;
981 * The override cannot be currently verified.
982 * Deferring to let the watchdog check.
984 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
988 /* Override clocksource can be used. */
994 if (curr_clocksource != best && !timekeeping_notify(best)) {
995 pr_info("Switched to clocksource %s\n", best->name);
996 curr_clocksource = best;
1001 * clocksource_select - Select the best clocksource available
1003 * Private function. Must hold clocksource_mutex when called.
1005 * Select the clocksource with the best rating, or the clocksource,
1006 * which is selected by userspace override.
1008 static void clocksource_select(void)
1010 __clocksource_select(false);
1013 static void clocksource_select_fallback(void)
1015 __clocksource_select(true);
1019 * clocksource_done_booting - Called near the end of core bootup
1021 * Hack to avoid lots of clocksource churn at boot time.
1022 * We use fs_initcall because we want this to start before
1023 * device_initcall but after subsys_initcall.
1025 static int __init clocksource_done_booting(void)
1027 mutex_lock(&clocksource_mutex);
1028 curr_clocksource = clocksource_default_clock();
1029 finished_booting = 1;
1031 * Run the watchdog first to eliminate unstable clock sources
1033 __clocksource_watchdog_kthread();
1034 clocksource_select();
1035 mutex_unlock(&clocksource_mutex);
1038 fs_initcall(clocksource_done_booting);
1041 * Enqueue the clocksource sorted by rating
1043 static void clocksource_enqueue(struct clocksource *cs)
1045 struct list_head *entry = &clocksource_list;
1046 struct clocksource *tmp;
1048 list_for_each_entry(tmp, &clocksource_list, list) {
1049 /* Keep track of the place, where to insert */
1050 if (tmp->rating < cs->rating)
1054 list_add(&cs->list, entry);
1058 * __clocksource_update_freq_scale - Used update clocksource with new freq
1059 * @cs: clocksource to be registered
1060 * @scale: Scale factor multiplied against freq to get clocksource hz
1061 * @freq: clocksource frequency (cycles per second) divided by scale
1063 * This should only be called from the clocksource->enable() method.
1065 * This *SHOULD NOT* be called directly! Please use the
1066 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
1069 void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1074 * Default clocksources are *special* and self-define their mult/shift.
1075 * But, you're not special, so you should specify a freq value.
1079 * Calc the maximum number of seconds which we can run before
1080 * wrapping around. For clocksources which have a mask > 32-bit
1081 * we need to limit the max sleep time to have a good
1082 * conversion precision. 10 minutes is still a reasonable
1083 * amount. That results in a shift value of 24 for a
1084 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1085 * ~ 0.06ppm granularity for NTP.
1092 else if (sec > 600 && cs->mask > UINT_MAX)
1095 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1096 NSEC_PER_SEC / scale, sec * scale);
1100 * If the uncertainty margin is not specified, calculate it.
1101 * If both scale and freq are non-zero, calculate the clock
1102 * period, but bound below at 2*WATCHDOG_MAX_SKEW. However,
1103 * if either of scale or freq is zero, be very conservative and
1104 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the
1105 * uncertainty margin. Allow stupidly small uncertainty margins
1106 * to be specified by the caller for testing purposes, but warn
1107 * to discourage production use of this capability.
1109 if (scale && freq && !cs->uncertainty_margin) {
1110 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
1111 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
1112 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
1113 } else if (!cs->uncertainty_margin) {
1114 cs->uncertainty_margin = WATCHDOG_THRESHOLD;
1116 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
1119 * Ensure clocksources that have large 'mult' values don't overflow
1122 cs->maxadj = clocksource_max_adjustment(cs);
1123 while (freq && ((cs->mult + cs->maxadj < cs->mult)
1124 || (cs->mult - cs->maxadj > cs->mult))) {
1127 cs->maxadj = clocksource_max_adjustment(cs);
1131 * Only warn for *special* clocksources that self-define
1132 * their mult/shift values and don't specify a freq.
1134 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1135 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1138 clocksource_update_max_deferment(cs);
1140 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1141 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1143 EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
1146 * __clocksource_register_scale - Used to install new clocksources
1147 * @cs: clocksource to be registered
1148 * @scale: Scale factor multiplied against freq to get clocksource hz
1149 * @freq: clocksource frequency (cycles per second) divided by scale
1151 * Returns -EBUSY if registration fails, zero otherwise.
1153 * This *SHOULD NOT* be called directly! Please use the
1154 * clocksource_register_hz() or clocksource_register_khz helper functions.
1156 int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1158 unsigned long flags;
1160 clocksource_arch_init(cs);
1162 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1163 cs->id = CSID_GENERIC;
1164 if (cs->vdso_clock_mode < 0 ||
1165 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1166 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1167 cs->name, cs->vdso_clock_mode);
1168 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1171 /* Initialize mult/shift and max_idle_ns */
1172 __clocksource_update_freq_scale(cs, scale, freq);
1174 /* Add clocksource to the clocksource list */
1175 mutex_lock(&clocksource_mutex);
1177 clocksource_watchdog_lock(&flags);
1178 clocksource_enqueue(cs);
1179 clocksource_enqueue_watchdog(cs);
1180 clocksource_watchdog_unlock(&flags);
1182 clocksource_select();
1183 clocksource_select_watchdog(false);
1184 __clocksource_suspend_select(cs);
1185 mutex_unlock(&clocksource_mutex);
1188 EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1190 static void __clocksource_change_rating(struct clocksource *cs, int rating)
1192 list_del(&cs->list);
1193 cs->rating = rating;
1194 clocksource_enqueue(cs);
1198 * clocksource_change_rating - Change the rating of a registered clocksource
1199 * @cs: clocksource to be changed
1200 * @rating: new rating
1202 void clocksource_change_rating(struct clocksource *cs, int rating)
1204 unsigned long flags;
1206 mutex_lock(&clocksource_mutex);
1207 clocksource_watchdog_lock(&flags);
1208 __clocksource_change_rating(cs, rating);
1209 clocksource_watchdog_unlock(&flags);
1211 clocksource_select();
1212 clocksource_select_watchdog(false);
1213 clocksource_suspend_select(false);
1214 mutex_unlock(&clocksource_mutex);
1216 EXPORT_SYMBOL(clocksource_change_rating);
1219 * Unbind clocksource @cs. Called with clocksource_mutex held
1221 static int clocksource_unbind(struct clocksource *cs)
1223 unsigned long flags;
1225 if (clocksource_is_watchdog(cs)) {
1226 /* Select and try to install a replacement watchdog. */
1227 clocksource_select_watchdog(true);
1228 if (clocksource_is_watchdog(cs))
1232 if (cs == curr_clocksource) {
1233 /* Select and try to install a replacement clock source */
1234 clocksource_select_fallback();
1235 if (curr_clocksource == cs)
1239 if (clocksource_is_suspend(cs)) {
1241 * Select and try to install a replacement suspend clocksource.
1242 * If no replacement suspend clocksource, we will just let the
1243 * clocksource go and have no suspend clocksource.
1245 clocksource_suspend_select(true);
1248 clocksource_watchdog_lock(&flags);
1249 clocksource_dequeue_watchdog(cs);
1250 list_del_init(&cs->list);
1251 clocksource_watchdog_unlock(&flags);
1257 * clocksource_unregister - remove a registered clocksource
1258 * @cs: clocksource to be unregistered
1260 int clocksource_unregister(struct clocksource *cs)
1264 mutex_lock(&clocksource_mutex);
1265 if (!list_empty(&cs->list))
1266 ret = clocksource_unbind(cs);
1267 mutex_unlock(&clocksource_mutex);
1270 EXPORT_SYMBOL(clocksource_unregister);
1274 * current_clocksource_show - sysfs interface for current clocksource
1277 * @buf: char buffer to be filled with clocksource list
1279 * Provides sysfs interface for listing current clocksource.
1281 static ssize_t current_clocksource_show(struct device *dev,
1282 struct device_attribute *attr,
1287 mutex_lock(&clocksource_mutex);
1288 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
1289 mutex_unlock(&clocksource_mutex);
1294 ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1298 /* strings from sysfs write are not 0 terminated! */
1299 if (!cnt || cnt >= CS_NAME_LEN)
1303 if (buf[cnt-1] == '\n')
1306 memcpy(dst, buf, cnt);
1312 * current_clocksource_store - interface for manually overriding clocksource
1315 * @buf: name of override clocksource
1316 * @count: length of buffer
1318 * Takes input from sysfs interface for manually overriding the default
1319 * clocksource selection.
1321 static ssize_t current_clocksource_store(struct device *dev,
1322 struct device_attribute *attr,
1323 const char *buf, size_t count)
1327 mutex_lock(&clocksource_mutex);
1329 ret = sysfs_get_uname(buf, override_name, count);
1331 clocksource_select();
1333 mutex_unlock(&clocksource_mutex);
1337 static DEVICE_ATTR_RW(current_clocksource);
1340 * unbind_clocksource_store - interface for manually unbinding clocksource
1344 * @count: length of buffer
1346 * Takes input from sysfs interface for manually unbinding a clocksource.
1348 static ssize_t unbind_clocksource_store(struct device *dev,
1349 struct device_attribute *attr,
1350 const char *buf, size_t count)
1352 struct clocksource *cs;
1353 char name[CS_NAME_LEN];
1356 ret = sysfs_get_uname(buf, name, count);
1361 mutex_lock(&clocksource_mutex);
1362 list_for_each_entry(cs, &clocksource_list, list) {
1363 if (strcmp(cs->name, name))
1365 ret = clocksource_unbind(cs);
1368 mutex_unlock(&clocksource_mutex);
1370 return ret ? ret : count;
1372 static DEVICE_ATTR_WO(unbind_clocksource);
1375 * available_clocksource_show - sysfs interface for listing clocksource
1378 * @buf: char buffer to be filled with clocksource list
1380 * Provides sysfs interface for listing registered clocksources
1382 static ssize_t available_clocksource_show(struct device *dev,
1383 struct device_attribute *attr,
1386 struct clocksource *src;
1389 mutex_lock(&clocksource_mutex);
1390 list_for_each_entry(src, &clocksource_list, list) {
1392 * Don't show non-HRES clocksource if the tick code is
1393 * in one shot mode (highres=on or nohz=on)
1395 if (!tick_oneshot_mode_active() ||
1396 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1397 count += snprintf(buf + count,
1398 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1401 mutex_unlock(&clocksource_mutex);
1403 count += snprintf(buf + count,
1404 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1408 static DEVICE_ATTR_RO(available_clocksource);
1410 static struct attribute *clocksource_attrs[] = {
1411 &dev_attr_current_clocksource.attr,
1412 &dev_attr_unbind_clocksource.attr,
1413 &dev_attr_available_clocksource.attr,
1416 ATTRIBUTE_GROUPS(clocksource);
1418 static struct bus_type clocksource_subsys = {
1419 .name = "clocksource",
1420 .dev_name = "clocksource",
1423 static struct device device_clocksource = {
1425 .bus = &clocksource_subsys,
1426 .groups = clocksource_groups,
1429 static int __init init_clocksource_sysfs(void)
1431 int error = subsys_system_register(&clocksource_subsys, NULL);
1434 error = device_register(&device_clocksource);
1439 device_initcall(init_clocksource_sysfs);
1440 #endif /* CONFIG_SYSFS */
1443 * boot_override_clocksource - boot clock override
1444 * @str: override name
1446 * Takes a clocksource= boot argument and uses it
1447 * as the clocksource override name.
1449 static int __init boot_override_clocksource(char* str)
1451 mutex_lock(&clocksource_mutex);
1453 strlcpy(override_name, str, sizeof(override_name));
1454 mutex_unlock(&clocksource_mutex);
1458 __setup("clocksource=", boot_override_clocksource);
1461 * boot_override_clock - Compatibility layer for deprecated boot option
1462 * @str: override name
1464 * DEPRECATED! Takes a clock= boot argument and uses it
1465 * as the clocksource override name
1467 static int __init boot_override_clock(char* str)
1469 if (!strcmp(str, "pmtmr")) {
1470 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1471 return boot_override_clocksource("acpi_pm");
1473 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1474 return boot_override_clocksource(str);
1477 __setup("clock=", boot_override_clock);