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>
18 #include "tick-internal.h"
19 #include "timekeeping_internal.h"
22 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
23 * @mult: pointer to mult variable
24 * @shift: pointer to shift variable
25 * @from: frequency to convert from
26 * @to: frequency to convert to
27 * @maxsec: guaranteed runtime conversion range in seconds
29 * The function evaluates the shift/mult pair for the scaled math
30 * operations of clocksources and clockevents.
32 * @to and @from are frequency values in HZ. For clock sources @to is
33 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
34 * event @to is the counter frequency and @from is NSEC_PER_SEC.
36 * The @maxsec conversion range argument controls the time frame in
37 * seconds which must be covered by the runtime conversion with the
38 * calculated mult and shift factors. This guarantees that no 64bit
39 * overflow happens when the input value of the conversion is
40 * multiplied with the calculated mult factor. Larger ranges may
41 * reduce the conversion accuracy by choosing smaller mult and shift
45 clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
51 * Calculate the shift factor which is limiting the conversion
54 tmp = ((u64)maxsec * from) >> 32;
61 * Find the conversion shift/mult pair which has the best
62 * accuracy and fits the maxsec conversion range:
64 for (sft = 32; sft > 0; sft--) {
65 tmp = (u64) to << sft;
68 if ((tmp >> sftacc) == 0)
74 EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
76 /*[Clocksource internal variables]---------
78 * currently selected clocksource.
79 * suspend_clocksource:
80 * used to calculate the suspend time.
82 * linked list with the registered clocksources
84 * protects manipulations to curr_clocksource and the clocksource_list
86 * Name of the user-specified clocksource.
88 static struct clocksource *curr_clocksource;
89 static struct clocksource *suspend_clocksource;
90 static LIST_HEAD(clocksource_list);
91 static DEFINE_MUTEX(clocksource_mutex);
92 static char override_name[CS_NAME_LEN];
93 static int finished_booting;
94 static u64 suspend_start;
96 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
97 static void clocksource_watchdog_work(struct work_struct *work);
98 static void clocksource_select(void);
100 static LIST_HEAD(watchdog_list);
101 static struct clocksource *watchdog;
102 static struct timer_list watchdog_timer;
103 static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
104 static DEFINE_SPINLOCK(watchdog_lock);
105 static int watchdog_running;
106 static atomic_t watchdog_reset_pending;
108 static inline void clocksource_watchdog_lock(unsigned long *flags)
110 spin_lock_irqsave(&watchdog_lock, *flags);
113 static inline void clocksource_watchdog_unlock(unsigned long *flags)
115 spin_unlock_irqrestore(&watchdog_lock, *flags);
118 static int clocksource_watchdog_kthread(void *data);
119 static void __clocksource_change_rating(struct clocksource *cs, int rating);
122 * Interval: 0.5sec Threshold: 0.0625s
124 #define WATCHDOG_INTERVAL (HZ >> 1)
125 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
127 static void clocksource_watchdog_work(struct work_struct *work)
130 * We cannot directly run clocksource_watchdog_kthread() here, because
131 * clocksource_select() calls timekeeping_notify() which uses
132 * stop_machine(). One cannot use stop_machine() from a workqueue() due
133 * lock inversions wrt CPU hotplug.
135 * Also, we only ever run this work once or twice during the lifetime
136 * of the kernel, so there is no point in creating a more permanent
139 * If kthread_run fails the next watchdog scan over the
140 * watchdog_list will find the unstable clock again.
142 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
145 static void __clocksource_unstable(struct clocksource *cs)
147 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
148 cs->flags |= CLOCK_SOURCE_UNSTABLE;
151 * If the clocksource is registered clocksource_watchdog_kthread() will
152 * re-rate and re-select.
154 if (list_empty(&cs->list)) {
159 if (cs->mark_unstable)
160 cs->mark_unstable(cs);
162 /* kick clocksource_watchdog_kthread() */
163 if (finished_booting)
164 schedule_work(&watchdog_work);
168 * clocksource_mark_unstable - mark clocksource unstable via watchdog
169 * @cs: clocksource to be marked unstable
171 * This function is called by the x86 TSC code to mark clocksources as unstable;
172 * it defers demotion and re-selection to a kthread.
174 void clocksource_mark_unstable(struct clocksource *cs)
178 spin_lock_irqsave(&watchdog_lock, flags);
179 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
180 if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
181 list_add(&cs->wd_list, &watchdog_list);
182 __clocksource_unstable(cs);
184 spin_unlock_irqrestore(&watchdog_lock, flags);
187 static void clocksource_watchdog(struct timer_list *unused)
189 struct clocksource *cs;
190 u64 csnow, wdnow, cslast, wdlast, delta;
191 int64_t wd_nsec, cs_nsec;
192 int next_cpu, reset_pending;
194 spin_lock(&watchdog_lock);
195 if (!watchdog_running)
198 reset_pending = atomic_read(&watchdog_reset_pending);
200 list_for_each_entry(cs, &watchdog_list, wd_list) {
202 /* Clocksource already marked unstable? */
203 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
204 if (finished_booting)
205 schedule_work(&watchdog_work);
210 csnow = cs->read(cs);
211 wdnow = watchdog->read(watchdog);
214 /* Clocksource initialized ? */
215 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
216 atomic_read(&watchdog_reset_pending)) {
217 cs->flags |= CLOCK_SOURCE_WATCHDOG;
223 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
224 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
227 delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
228 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
229 wdlast = cs->wd_last; /* save these in case we print them */
230 cslast = cs->cs_last;
234 if (atomic_read(&watchdog_reset_pending))
237 /* Check the deviation from the watchdog clocksource. */
238 if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
239 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
240 smp_processor_id(), cs->name);
241 pr_warn(" '%s' wd_now: %llx wd_last: %llx mask: %llx\n",
242 watchdog->name, wdnow, wdlast, watchdog->mask);
243 pr_warn(" '%s' cs_now: %llx cs_last: %llx mask: %llx\n",
244 cs->name, csnow, cslast, cs->mask);
245 __clocksource_unstable(cs);
249 if (cs == curr_clocksource && cs->tick_stable)
252 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
253 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
254 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
255 /* Mark it valid for high-res. */
256 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
259 * clocksource_done_booting() will sort it if
260 * finished_booting is not set yet.
262 if (!finished_booting)
266 * If this is not the current clocksource let
267 * the watchdog thread reselect it. Due to the
268 * change to high res this clocksource might
269 * be preferred now. If it is the current
270 * clocksource let the tick code know about
273 if (cs != curr_clocksource) {
274 cs->flags |= CLOCK_SOURCE_RESELECT;
275 schedule_work(&watchdog_work);
283 * We only clear the watchdog_reset_pending, when we did a
284 * full cycle through all clocksources.
287 atomic_dec(&watchdog_reset_pending);
290 * Cycle through CPUs to check if the CPUs stay synchronized
293 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
294 if (next_cpu >= nr_cpu_ids)
295 next_cpu = cpumask_first(cpu_online_mask);
298 * Arm timer if not already pending: could race with concurrent
299 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
301 if (!timer_pending(&watchdog_timer)) {
302 watchdog_timer.expires += WATCHDOG_INTERVAL;
303 add_timer_on(&watchdog_timer, next_cpu);
306 spin_unlock(&watchdog_lock);
309 static inline void clocksource_start_watchdog(void)
311 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
313 timer_setup(&watchdog_timer, clocksource_watchdog, 0);
314 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
315 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
316 watchdog_running = 1;
319 static inline void clocksource_stop_watchdog(void)
321 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
323 del_timer(&watchdog_timer);
324 watchdog_running = 0;
327 static inline void clocksource_reset_watchdog(void)
329 struct clocksource *cs;
331 list_for_each_entry(cs, &watchdog_list, wd_list)
332 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
335 static void clocksource_resume_watchdog(void)
337 atomic_inc(&watchdog_reset_pending);
340 static void clocksource_enqueue_watchdog(struct clocksource *cs)
342 INIT_LIST_HEAD(&cs->wd_list);
344 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
345 /* cs is a clocksource to be watched. */
346 list_add(&cs->wd_list, &watchdog_list);
347 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
349 /* cs is a watchdog. */
350 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
351 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
355 static void clocksource_select_watchdog(bool fallback)
357 struct clocksource *cs, *old_wd;
360 spin_lock_irqsave(&watchdog_lock, flags);
361 /* save current watchdog */
366 list_for_each_entry(cs, &clocksource_list, list) {
367 /* cs is a clocksource to be watched. */
368 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
371 /* Skip current if we were requested for a fallback. */
372 if (fallback && cs == old_wd)
375 /* Pick the best watchdog. */
376 if (!watchdog || cs->rating > watchdog->rating)
379 /* If we failed to find a fallback restore the old one. */
383 /* If we changed the watchdog we need to reset cycles. */
384 if (watchdog != old_wd)
385 clocksource_reset_watchdog();
387 /* Check if the watchdog timer needs to be started. */
388 clocksource_start_watchdog();
389 spin_unlock_irqrestore(&watchdog_lock, flags);
392 static void clocksource_dequeue_watchdog(struct clocksource *cs)
394 if (cs != watchdog) {
395 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
396 /* cs is a watched clocksource. */
397 list_del_init(&cs->wd_list);
398 /* Check if the watchdog timer needs to be stopped. */
399 clocksource_stop_watchdog();
404 static int __clocksource_watchdog_kthread(void)
406 struct clocksource *cs, *tmp;
410 spin_lock_irqsave(&watchdog_lock, flags);
411 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
412 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
413 list_del_init(&cs->wd_list);
414 __clocksource_change_rating(cs, 0);
417 if (cs->flags & CLOCK_SOURCE_RESELECT) {
418 cs->flags &= ~CLOCK_SOURCE_RESELECT;
422 /* Check if the watchdog timer needs to be stopped. */
423 clocksource_stop_watchdog();
424 spin_unlock_irqrestore(&watchdog_lock, flags);
429 static int clocksource_watchdog_kthread(void *data)
431 mutex_lock(&clocksource_mutex);
432 if (__clocksource_watchdog_kthread())
433 clocksource_select();
434 mutex_unlock(&clocksource_mutex);
438 static bool clocksource_is_watchdog(struct clocksource *cs)
440 return cs == watchdog;
443 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
445 static void clocksource_enqueue_watchdog(struct clocksource *cs)
447 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
448 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
451 static void clocksource_select_watchdog(bool fallback) { }
452 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
453 static inline void clocksource_resume_watchdog(void) { }
454 static inline int __clocksource_watchdog_kthread(void) { return 0; }
455 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
456 void clocksource_mark_unstable(struct clocksource *cs) { }
458 static inline void clocksource_watchdog_lock(unsigned long *flags) { }
459 static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
461 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
463 static bool clocksource_is_suspend(struct clocksource *cs)
465 return cs == suspend_clocksource;
468 static void __clocksource_suspend_select(struct clocksource *cs)
471 * Skip the clocksource which will be stopped in suspend state.
473 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
477 * The nonstop clocksource can be selected as the suspend clocksource to
478 * calculate the suspend time, so it should not supply suspend/resume
479 * interfaces to suspend the nonstop clocksource when system suspends.
481 if (cs->suspend || cs->resume) {
482 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
486 /* Pick the best rating. */
487 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
488 suspend_clocksource = cs;
492 * clocksource_suspend_select - Select the best clocksource for suspend timing
493 * @fallback: if select a fallback clocksource
495 static void clocksource_suspend_select(bool fallback)
497 struct clocksource *cs, *old_suspend;
499 old_suspend = suspend_clocksource;
501 suspend_clocksource = NULL;
503 list_for_each_entry(cs, &clocksource_list, list) {
504 /* Skip current if we were requested for a fallback. */
505 if (fallback && cs == old_suspend)
508 __clocksource_suspend_select(cs);
513 * clocksource_start_suspend_timing - Start measuring the suspend timing
514 * @cs: current clocksource from timekeeping
515 * @start_cycles: current cycles from timekeeping
517 * This function will save the start cycle values of suspend timer to calculate
518 * the suspend time when resuming system.
520 * This function is called late in the suspend process from timekeeping_suspend(),
521 * that means processes are frozen, non-boot cpus and interrupts are disabled
522 * now. It is therefore possible to start the suspend timer without taking the
525 void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
527 if (!suspend_clocksource)
531 * If current clocksource is the suspend timer, we should use the
532 * tkr_mono.cycle_last value as suspend_start to avoid same reading
533 * from suspend timer.
535 if (clocksource_is_suspend(cs)) {
536 suspend_start = start_cycles;
540 if (suspend_clocksource->enable &&
541 suspend_clocksource->enable(suspend_clocksource)) {
542 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
546 suspend_start = suspend_clocksource->read(suspend_clocksource);
550 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
551 * @cs: current clocksource from timekeeping
552 * @cycle_now: current cycles from timekeeping
554 * This function will calculate the suspend time from suspend timer.
556 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
558 * This function is called early in the resume process from timekeeping_resume(),
559 * that means there is only one cpu, no processes are running and the interrupts
560 * are disabled. It is therefore possible to stop the suspend timer without
561 * taking the clocksource mutex.
563 u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
565 u64 now, delta, nsec = 0;
567 if (!suspend_clocksource)
571 * If current clocksource is the suspend timer, we should use the
572 * tkr_mono.cycle_last value from timekeeping as current cycle to
573 * avoid same reading from suspend timer.
575 if (clocksource_is_suspend(cs))
578 now = suspend_clocksource->read(suspend_clocksource);
580 if (now > suspend_start) {
581 delta = clocksource_delta(now, suspend_start,
582 suspend_clocksource->mask);
583 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
584 suspend_clocksource->shift);
588 * Disable the suspend timer to save power if current clocksource is
589 * not the suspend timer.
591 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
592 suspend_clocksource->disable(suspend_clocksource);
598 * clocksource_suspend - suspend the clocksource(s)
600 void clocksource_suspend(void)
602 struct clocksource *cs;
604 list_for_each_entry_reverse(cs, &clocksource_list, list)
610 * clocksource_resume - resume the clocksource(s)
612 void clocksource_resume(void)
614 struct clocksource *cs;
616 list_for_each_entry(cs, &clocksource_list, list)
620 clocksource_resume_watchdog();
624 * clocksource_touch_watchdog - Update watchdog
626 * Update the watchdog after exception contexts such as kgdb so as not
627 * to incorrectly trip the watchdog. This might fail when the kernel
628 * was stopped in code which holds watchdog_lock.
630 void clocksource_touch_watchdog(void)
632 clocksource_resume_watchdog();
636 * clocksource_max_adjustment- Returns max adjustment amount
637 * @cs: Pointer to clocksource
640 static u32 clocksource_max_adjustment(struct clocksource *cs)
644 * We won't try to correct for more than 11% adjustments (110,000 ppm),
646 ret = (u64)cs->mult * 11;
652 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
653 * @mult: cycle to nanosecond multiplier
654 * @shift: cycle to nanosecond divisor (power of two)
655 * @maxadj: maximum adjustment value to mult (~11%)
656 * @mask: bitmask for two's complement subtraction of non 64 bit counters
657 * @max_cyc: maximum cycle value before potential overflow (does not include
660 * NOTE: This function includes a safety margin of 50%, in other words, we
661 * return half the number of nanoseconds the hardware counter can technically
662 * cover. This is done so that we can potentially detect problems caused by
663 * delayed timers or bad hardware, which might result in time intervals that
664 * are larger than what the math used can handle without overflows.
666 u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
668 u64 max_nsecs, max_cycles;
671 * Calculate the maximum number of cycles that we can pass to the
672 * cyc2ns() function without overflowing a 64-bit result.
674 max_cycles = ULLONG_MAX;
675 do_div(max_cycles, mult+maxadj);
678 * The actual maximum number of cycles we can defer the clocksource is
679 * determined by the minimum of max_cycles and mask.
680 * Note: Here we subtract the maxadj to make sure we don't sleep for
681 * too long if there's a large negative adjustment.
683 max_cycles = min(max_cycles, mask);
684 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
686 /* return the max_cycles value as well if requested */
688 *max_cyc = max_cycles;
690 /* Return 50% of the actual maximum, so we can detect bad values */
697 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
698 * @cs: Pointer to clocksource to be updated
701 static inline void clocksource_update_max_deferment(struct clocksource *cs)
703 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
704 cs->maxadj, cs->mask,
708 static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
710 struct clocksource *cs;
712 if (!finished_booting || list_empty(&clocksource_list))
716 * We pick the clocksource with the highest rating. If oneshot
717 * mode is active, we pick the highres valid clocksource with
720 list_for_each_entry(cs, &clocksource_list, list) {
721 if (skipcur && cs == curr_clocksource)
723 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
730 static void __clocksource_select(bool skipcur)
732 bool oneshot = tick_oneshot_mode_active();
733 struct clocksource *best, *cs;
735 /* Find the best suitable clocksource */
736 best = clocksource_find_best(oneshot, skipcur);
740 if (!strlen(override_name))
743 /* Check for the override clocksource. */
744 list_for_each_entry(cs, &clocksource_list, list) {
745 if (skipcur && cs == curr_clocksource)
747 if (strcmp(cs->name, override_name) != 0)
750 * Check to make sure we don't switch to a non-highres
751 * capable clocksource if the tick code is in oneshot
752 * mode (highres or nohz)
754 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
755 /* Override clocksource cannot be used. */
756 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
757 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
759 override_name[0] = 0;
762 * The override cannot be currently verified.
763 * Deferring to let the watchdog check.
765 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
769 /* Override clocksource can be used. */
775 if (curr_clocksource != best && !timekeeping_notify(best)) {
776 pr_info("Switched to clocksource %s\n", best->name);
777 curr_clocksource = best;
782 * clocksource_select - Select the best clocksource available
784 * Private function. Must hold clocksource_mutex when called.
786 * Select the clocksource with the best rating, or the clocksource,
787 * which is selected by userspace override.
789 static void clocksource_select(void)
791 __clocksource_select(false);
794 static void clocksource_select_fallback(void)
796 __clocksource_select(true);
800 * clocksource_done_booting - Called near the end of core bootup
802 * Hack to avoid lots of clocksource churn at boot time.
803 * We use fs_initcall because we want this to start before
804 * device_initcall but after subsys_initcall.
806 static int __init clocksource_done_booting(void)
808 mutex_lock(&clocksource_mutex);
809 curr_clocksource = clocksource_default_clock();
810 finished_booting = 1;
812 * Run the watchdog first to eliminate unstable clock sources
814 __clocksource_watchdog_kthread();
815 clocksource_select();
816 mutex_unlock(&clocksource_mutex);
819 fs_initcall(clocksource_done_booting);
822 * Enqueue the clocksource sorted by rating
824 static void clocksource_enqueue(struct clocksource *cs)
826 struct list_head *entry = &clocksource_list;
827 struct clocksource *tmp;
829 list_for_each_entry(tmp, &clocksource_list, list) {
830 /* Keep track of the place, where to insert */
831 if (tmp->rating < cs->rating)
835 list_add(&cs->list, entry);
839 * __clocksource_update_freq_scale - Used update clocksource with new freq
840 * @cs: clocksource to be registered
841 * @scale: Scale factor multiplied against freq to get clocksource hz
842 * @freq: clocksource frequency (cycles per second) divided by scale
844 * This should only be called from the clocksource->enable() method.
846 * This *SHOULD NOT* be called directly! Please use the
847 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
850 void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
855 * Default clocksources are *special* and self-define their mult/shift.
856 * But, you're not special, so you should specify a freq value.
860 * Calc the maximum number of seconds which we can run before
861 * wrapping around. For clocksources which have a mask > 32-bit
862 * we need to limit the max sleep time to have a good
863 * conversion precision. 10 minutes is still a reasonable
864 * amount. That results in a shift value of 24 for a
865 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
866 * ~ 0.06ppm granularity for NTP.
873 else if (sec > 600 && cs->mask > UINT_MAX)
876 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
877 NSEC_PER_SEC / scale, sec * scale);
880 * Ensure clocksources that have large 'mult' values don't overflow
883 cs->maxadj = clocksource_max_adjustment(cs);
884 while (freq && ((cs->mult + cs->maxadj < cs->mult)
885 || (cs->mult - cs->maxadj > cs->mult))) {
888 cs->maxadj = clocksource_max_adjustment(cs);
892 * Only warn for *special* clocksources that self-define
893 * their mult/shift values and don't specify a freq.
895 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
896 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
899 clocksource_update_max_deferment(cs);
901 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
902 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
904 EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
907 * __clocksource_register_scale - Used to install new clocksources
908 * @cs: clocksource to be registered
909 * @scale: Scale factor multiplied against freq to get clocksource hz
910 * @freq: clocksource frequency (cycles per second) divided by scale
912 * Returns -EBUSY if registration fails, zero otherwise.
914 * This *SHOULD NOT* be called directly! Please use the
915 * clocksource_register_hz() or clocksource_register_khz helper functions.
917 int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
921 clocksource_arch_init(cs);
923 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
924 cs->id = CSID_GENERIC;
925 if (cs->vdso_clock_mode < 0 ||
926 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
927 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
928 cs->name, cs->vdso_clock_mode);
929 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
932 /* Initialize mult/shift and max_idle_ns */
933 __clocksource_update_freq_scale(cs, scale, freq);
935 /* Add clocksource to the clocksource list */
936 mutex_lock(&clocksource_mutex);
938 clocksource_watchdog_lock(&flags);
939 clocksource_enqueue(cs);
940 clocksource_enqueue_watchdog(cs);
941 clocksource_watchdog_unlock(&flags);
943 clocksource_select();
944 clocksource_select_watchdog(false);
945 __clocksource_suspend_select(cs);
946 mutex_unlock(&clocksource_mutex);
949 EXPORT_SYMBOL_GPL(__clocksource_register_scale);
951 static void __clocksource_change_rating(struct clocksource *cs, int rating)
955 clocksource_enqueue(cs);
959 * clocksource_change_rating - Change the rating of a registered clocksource
960 * @cs: clocksource to be changed
961 * @rating: new rating
963 void clocksource_change_rating(struct clocksource *cs, int rating)
967 mutex_lock(&clocksource_mutex);
968 clocksource_watchdog_lock(&flags);
969 __clocksource_change_rating(cs, rating);
970 clocksource_watchdog_unlock(&flags);
972 clocksource_select();
973 clocksource_select_watchdog(false);
974 clocksource_suspend_select(false);
975 mutex_unlock(&clocksource_mutex);
977 EXPORT_SYMBOL(clocksource_change_rating);
980 * Unbind clocksource @cs. Called with clocksource_mutex held
982 static int clocksource_unbind(struct clocksource *cs)
986 if (clocksource_is_watchdog(cs)) {
987 /* Select and try to install a replacement watchdog. */
988 clocksource_select_watchdog(true);
989 if (clocksource_is_watchdog(cs))
993 if (cs == curr_clocksource) {
994 /* Select and try to install a replacement clock source */
995 clocksource_select_fallback();
996 if (curr_clocksource == cs)
1000 if (clocksource_is_suspend(cs)) {
1002 * Select and try to install a replacement suspend clocksource.
1003 * If no replacement suspend clocksource, we will just let the
1004 * clocksource go and have no suspend clocksource.
1006 clocksource_suspend_select(true);
1009 clocksource_watchdog_lock(&flags);
1010 clocksource_dequeue_watchdog(cs);
1011 list_del_init(&cs->list);
1012 clocksource_watchdog_unlock(&flags);
1018 * clocksource_unregister - remove a registered clocksource
1019 * @cs: clocksource to be unregistered
1021 int clocksource_unregister(struct clocksource *cs)
1025 mutex_lock(&clocksource_mutex);
1026 if (!list_empty(&cs->list))
1027 ret = clocksource_unbind(cs);
1028 mutex_unlock(&clocksource_mutex);
1031 EXPORT_SYMBOL(clocksource_unregister);
1035 * current_clocksource_show - sysfs interface for current clocksource
1038 * @buf: char buffer to be filled with clocksource list
1040 * Provides sysfs interface for listing current clocksource.
1042 static ssize_t current_clocksource_show(struct device *dev,
1043 struct device_attribute *attr,
1048 mutex_lock(&clocksource_mutex);
1049 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
1050 mutex_unlock(&clocksource_mutex);
1055 ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1059 /* strings from sysfs write are not 0 terminated! */
1060 if (!cnt || cnt >= CS_NAME_LEN)
1064 if (buf[cnt-1] == '\n')
1067 memcpy(dst, buf, cnt);
1073 * current_clocksource_store - interface for manually overriding clocksource
1076 * @buf: name of override clocksource
1077 * @count: length of buffer
1079 * Takes input from sysfs interface for manually overriding the default
1080 * clocksource selection.
1082 static ssize_t current_clocksource_store(struct device *dev,
1083 struct device_attribute *attr,
1084 const char *buf, size_t count)
1088 mutex_lock(&clocksource_mutex);
1090 ret = sysfs_get_uname(buf, override_name, count);
1092 clocksource_select();
1094 mutex_unlock(&clocksource_mutex);
1098 static DEVICE_ATTR_RW(current_clocksource);
1101 * unbind_clocksource_store - interface for manually unbinding clocksource
1105 * @count: length of buffer
1107 * Takes input from sysfs interface for manually unbinding a clocksource.
1109 static ssize_t unbind_clocksource_store(struct device *dev,
1110 struct device_attribute *attr,
1111 const char *buf, size_t count)
1113 struct clocksource *cs;
1114 char name[CS_NAME_LEN];
1117 ret = sysfs_get_uname(buf, name, count);
1122 mutex_lock(&clocksource_mutex);
1123 list_for_each_entry(cs, &clocksource_list, list) {
1124 if (strcmp(cs->name, name))
1126 ret = clocksource_unbind(cs);
1129 mutex_unlock(&clocksource_mutex);
1131 return ret ? ret : count;
1133 static DEVICE_ATTR_WO(unbind_clocksource);
1136 * available_clocksource_show - sysfs interface for listing clocksource
1139 * @buf: char buffer to be filled with clocksource list
1141 * Provides sysfs interface for listing registered clocksources
1143 static ssize_t available_clocksource_show(struct device *dev,
1144 struct device_attribute *attr,
1147 struct clocksource *src;
1150 mutex_lock(&clocksource_mutex);
1151 list_for_each_entry(src, &clocksource_list, list) {
1153 * Don't show non-HRES clocksource if the tick code is
1154 * in one shot mode (highres=on or nohz=on)
1156 if (!tick_oneshot_mode_active() ||
1157 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1158 count += snprintf(buf + count,
1159 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1162 mutex_unlock(&clocksource_mutex);
1164 count += snprintf(buf + count,
1165 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1169 static DEVICE_ATTR_RO(available_clocksource);
1171 static struct attribute *clocksource_attrs[] = {
1172 &dev_attr_current_clocksource.attr,
1173 &dev_attr_unbind_clocksource.attr,
1174 &dev_attr_available_clocksource.attr,
1177 ATTRIBUTE_GROUPS(clocksource);
1179 static struct bus_type clocksource_subsys = {
1180 .name = "clocksource",
1181 .dev_name = "clocksource",
1184 static struct device device_clocksource = {
1186 .bus = &clocksource_subsys,
1187 .groups = clocksource_groups,
1190 static int __init init_clocksource_sysfs(void)
1192 int error = subsys_system_register(&clocksource_subsys, NULL);
1195 error = device_register(&device_clocksource);
1200 device_initcall(init_clocksource_sysfs);
1201 #endif /* CONFIG_SYSFS */
1204 * boot_override_clocksource - boot clock override
1205 * @str: override name
1207 * Takes a clocksource= boot argument and uses it
1208 * as the clocksource override name.
1210 static int __init boot_override_clocksource(char* str)
1212 mutex_lock(&clocksource_mutex);
1214 strlcpy(override_name, str, sizeof(override_name));
1215 mutex_unlock(&clocksource_mutex);
1219 __setup("clocksource=", boot_override_clocksource);
1222 * boot_override_clock - Compatibility layer for deprecated boot option
1223 * @str: override name
1225 * DEPRECATED! Takes a clock= boot argument and uses it
1226 * as the clocksource override name
1228 static int __init boot_override_clock(char* str)
1230 if (!strcmp(str, "pmtmr")) {
1231 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1232 return boot_override_clocksource("acpi_pm");
1234 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1235 return boot_override_clocksource(str);
1238 __setup("clock=", boot_override_clock);