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1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * This file contains the functions which manage clocksource drivers.
4 *
5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
6 */
7
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9
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
18#include "tick-internal.h"
19#include "timekeeping_internal.h"
20
21/**
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
28 *
29 * The function evaluates the shift/mult pair for the scaled math
30 * operations of clocksources and clockevents.
31 *
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.
35 *
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 chosing smaller mult and shift
42 * factors.
43 */
44void
45clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
46{
47 u64 tmp;
48 u32 sft, sftacc= 32;
49
50 /*
51 * Calculate the shift factor which is limiting the conversion
52 * range:
53 */
54 tmp = ((u64)maxsec * from) >> 32;
55 while (tmp) {
56 tmp >>=1;
57 sftacc--;
58 }
59
60 /*
61 * Find the conversion shift/mult pair which has the best
62 * accuracy and fits the maxsec conversion range:
63 */
64 for (sft = 32; sft > 0; sft--) {
65 tmp = (u64) to << sft;
66 tmp += from / 2;
67 do_div(tmp, from);
68 if ((tmp >> sftacc) == 0)
69 break;
70 }
71 *mult = tmp;
72 *shift = sft;
73}
74EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
75
76/*[Clocksource internal variables]---------
77 * curr_clocksource:
78 * currently selected clocksource.
79 * suspend_clocksource:
80 * used to calculate the suspend time.
81 * clocksource_list:
82 * linked list with the registered clocksources
83 * clocksource_mutex:
84 * protects manipulations to curr_clocksource and the clocksource_list
85 * override_name:
86 * Name of the user-specified clocksource.
87 */
88static struct clocksource *curr_clocksource;
89static struct clocksource *suspend_clocksource;
90static LIST_HEAD(clocksource_list);
91static DEFINE_MUTEX(clocksource_mutex);
92static char override_name[CS_NAME_LEN];
93static int finished_booting;
94static u64 suspend_start;
95
96#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
97static void clocksource_watchdog_work(struct work_struct *work);
98static void clocksource_select(void);
99
100static LIST_HEAD(watchdog_list);
101static struct clocksource *watchdog;
102static struct timer_list watchdog_timer;
103static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
104static DEFINE_SPINLOCK(watchdog_lock);
105static int watchdog_running;
106static atomic_t watchdog_reset_pending;
107
108static inline void clocksource_watchdog_lock(unsigned long *flags)
109{
110 spin_lock_irqsave(&watchdog_lock, *flags);
111}
112
113static inline void clocksource_watchdog_unlock(unsigned long *flags)
114{
115 spin_unlock_irqrestore(&watchdog_lock, *flags);
116}
117
118static int clocksource_watchdog_kthread(void *data);
119static void __clocksource_change_rating(struct clocksource *cs, int rating);
120
121/*
122 * Interval: 0.5sec Threshold: 0.0625s
123 */
124#define WATCHDOG_INTERVAL (HZ >> 1)
125#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
126
127static void clocksource_watchdog_work(struct work_struct *work)
128{
129 /*
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.
134 *
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
137 * kthread for this.
138 *
139 * If kthread_run fails the next watchdog scan over the
140 * watchdog_list will find the unstable clock again.
141 */
142 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
143}
144
145static void __clocksource_unstable(struct clocksource *cs)
146{
147 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
148 cs->flags |= CLOCK_SOURCE_UNSTABLE;
149
150 /*
151 * If the clocksource is registered clocksource_watchdog_kthread() will
152 * re-rate and re-select.
153 */
154 if (list_empty(&cs->list)) {
155 cs->rating = 0;
156 return;
157 }
158
159 if (cs->mark_unstable)
160 cs->mark_unstable(cs);
161
162 /* kick clocksource_watchdog_kthread() */
163 if (finished_booting)
164 schedule_work(&watchdog_work);
165}
166
167/**
168 * clocksource_mark_unstable - mark clocksource unstable via watchdog
169 * @cs: clocksource to be marked unstable
170 *
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.
173 */
174void clocksource_mark_unstable(struct clocksource *cs)
175{
176 unsigned long flags;
177
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);
183 }
184 spin_unlock_irqrestore(&watchdog_lock, flags);
185}
186
187static void clocksource_watchdog(struct timer_list *unused)
188{
189 struct clocksource *cs;
190 u64 csnow, wdnow, cslast, wdlast, delta;
191 int64_t wd_nsec, cs_nsec;
192 int next_cpu, reset_pending;
193
194 spin_lock(&watchdog_lock);
195 if (!watchdog_running)
196 goto out;
197
198 reset_pending = atomic_read(&watchdog_reset_pending);
199
200 list_for_each_entry(cs, &watchdog_list, wd_list) {
201
202 /* Clocksource already marked unstable? */
203 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
204 if (finished_booting)
205 schedule_work(&watchdog_work);
206 continue;
207 }
208
209 local_irq_disable();
210 csnow = cs->read(cs);
211 wdnow = watchdog->read(watchdog);
212 local_irq_enable();
213
214 /* Clocksource initialized ? */
215 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
216 atomic_read(&watchdog_reset_pending)) {
217 cs->flags |= CLOCK_SOURCE_WATCHDOG;
218 cs->wd_last = wdnow;
219 cs->cs_last = csnow;
220 continue;
221 }
222
223 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
224 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
225 watchdog->shift);
226
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;
231 cs->cs_last = csnow;
232 cs->wd_last = wdnow;
233
234 if (atomic_read(&watchdog_reset_pending))
235 continue;
236
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);
246 continue;
247 }
248
249 if (cs == curr_clocksource && cs->tick_stable)
250 cs->tick_stable(cs);
251
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;
257
258 /*
259 * clocksource_done_booting() will sort it if
260 * finished_booting is not set yet.
261 */
262 if (!finished_booting)
263 continue;
264
265 /*
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
271 * that change.
272 */
273 if (cs != curr_clocksource) {
274 cs->flags |= CLOCK_SOURCE_RESELECT;
275 schedule_work(&watchdog_work);
276 } else {
277 tick_clock_notify();
278 }
279 }
280 }
281
282 /*
283 * We only clear the watchdog_reset_pending, when we did a
284 * full cycle through all clocksources.
285 */
286 if (reset_pending)
287 atomic_dec(&watchdog_reset_pending);
288
289 /*
290 * Cycle through CPUs to check if the CPUs stay synchronized
291 * to each other.
292 */
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);
296 watchdog_timer.expires += WATCHDOG_INTERVAL;
297 add_timer_on(&watchdog_timer, next_cpu);
298out:
299 spin_unlock(&watchdog_lock);
300}
301
302static inline void clocksource_start_watchdog(void)
303{
304 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
305 return;
306 timer_setup(&watchdog_timer, clocksource_watchdog, 0);
307 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
308 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
309 watchdog_running = 1;
310}
311
312static inline void clocksource_stop_watchdog(void)
313{
314 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
315 return;
316 del_timer(&watchdog_timer);
317 watchdog_running = 0;
318}
319
320static inline void clocksource_reset_watchdog(void)
321{
322 struct clocksource *cs;
323
324 list_for_each_entry(cs, &watchdog_list, wd_list)
325 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
326}
327
328static void clocksource_resume_watchdog(void)
329{
330 atomic_inc(&watchdog_reset_pending);
331}
332
333static void clocksource_enqueue_watchdog(struct clocksource *cs)
334{
335 INIT_LIST_HEAD(&cs->wd_list);
336
337 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
338 /* cs is a clocksource to be watched. */
339 list_add(&cs->wd_list, &watchdog_list);
340 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
341 } else {
342 /* cs is a watchdog. */
343 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
344 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
345 }
346}
347
348static void clocksource_select_watchdog(bool fallback)
349{
350 struct clocksource *cs, *old_wd;
351 unsigned long flags;
352
353 spin_lock_irqsave(&watchdog_lock, flags);
354 /* save current watchdog */
355 old_wd = watchdog;
356 if (fallback)
357 watchdog = NULL;
358
359 list_for_each_entry(cs, &clocksource_list, list) {
360 /* cs is a clocksource to be watched. */
361 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
362 continue;
363
364 /* Skip current if we were requested for a fallback. */
365 if (fallback && cs == old_wd)
366 continue;
367
368 /* Pick the best watchdog. */
369 if (!watchdog || cs->rating > watchdog->rating)
370 watchdog = cs;
371 }
372 /* If we failed to find a fallback restore the old one. */
373 if (!watchdog)
374 watchdog = old_wd;
375
376 /* If we changed the watchdog we need to reset cycles. */
377 if (watchdog != old_wd)
378 clocksource_reset_watchdog();
379
380 /* Check if the watchdog timer needs to be started. */
381 clocksource_start_watchdog();
382 spin_unlock_irqrestore(&watchdog_lock, flags);
383}
384
385static void clocksource_dequeue_watchdog(struct clocksource *cs)
386{
387 if (cs != watchdog) {
388 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
389 /* cs is a watched clocksource. */
390 list_del_init(&cs->wd_list);
391 /* Check if the watchdog timer needs to be stopped. */
392 clocksource_stop_watchdog();
393 }
394 }
395}
396
397static int __clocksource_watchdog_kthread(void)
398{
399 struct clocksource *cs, *tmp;
400 unsigned long flags;
401 int select = 0;
402
403 spin_lock_irqsave(&watchdog_lock, flags);
404 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
405 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
406 list_del_init(&cs->wd_list);
407 __clocksource_change_rating(cs, 0);
408 select = 1;
409 }
410 if (cs->flags & CLOCK_SOURCE_RESELECT) {
411 cs->flags &= ~CLOCK_SOURCE_RESELECT;
412 select = 1;
413 }
414 }
415 /* Check if the watchdog timer needs to be stopped. */
416 clocksource_stop_watchdog();
417 spin_unlock_irqrestore(&watchdog_lock, flags);
418
419 return select;
420}
421
422static int clocksource_watchdog_kthread(void *data)
423{
424 mutex_lock(&clocksource_mutex);
425 if (__clocksource_watchdog_kthread())
426 clocksource_select();
427 mutex_unlock(&clocksource_mutex);
428 return 0;
429}
430
431static bool clocksource_is_watchdog(struct clocksource *cs)
432{
433 return cs == watchdog;
434}
435
436#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
437
438static void clocksource_enqueue_watchdog(struct clocksource *cs)
439{
440 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
441 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
442}
443
444static void clocksource_select_watchdog(bool fallback) { }
445static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
446static inline void clocksource_resume_watchdog(void) { }
447static inline int __clocksource_watchdog_kthread(void) { return 0; }
448static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
449void clocksource_mark_unstable(struct clocksource *cs) { }
450
451static inline void clocksource_watchdog_lock(unsigned long *flags) { }
452static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
453
454#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
455
456static bool clocksource_is_suspend(struct clocksource *cs)
457{
458 return cs == suspend_clocksource;
459}
460
461static void __clocksource_suspend_select(struct clocksource *cs)
462{
463 /*
464 * Skip the clocksource which will be stopped in suspend state.
465 */
466 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
467 return;
468
469 /*
470 * The nonstop clocksource can be selected as the suspend clocksource to
471 * calculate the suspend time, so it should not supply suspend/resume
472 * interfaces to suspend the nonstop clocksource when system suspends.
473 */
474 if (cs->suspend || cs->resume) {
475 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
476 cs->name);
477 }
478
479 /* Pick the best rating. */
480 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
481 suspend_clocksource = cs;
482}
483
484/**
485 * clocksource_suspend_select - Select the best clocksource for suspend timing
486 * @fallback: if select a fallback clocksource
487 */
488static void clocksource_suspend_select(bool fallback)
489{
490 struct clocksource *cs, *old_suspend;
491
492 old_suspend = suspend_clocksource;
493 if (fallback)
494 suspend_clocksource = NULL;
495
496 list_for_each_entry(cs, &clocksource_list, list) {
497 /* Skip current if we were requested for a fallback. */
498 if (fallback && cs == old_suspend)
499 continue;
500
501 __clocksource_suspend_select(cs);
502 }
503}
504
505/**
506 * clocksource_start_suspend_timing - Start measuring the suspend timing
507 * @cs: current clocksource from timekeeping
508 * @start_cycles: current cycles from timekeeping
509 *
510 * This function will save the start cycle values of suspend timer to calculate
511 * the suspend time when resuming system.
512 *
513 * This function is called late in the suspend process from timekeeping_suspend(),
514 * that means processes are freezed, non-boot cpus and interrupts are disabled
515 * now. It is therefore possible to start the suspend timer without taking the
516 * clocksource mutex.
517 */
518void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
519{
520 if (!suspend_clocksource)
521 return;
522
523 /*
524 * If current clocksource is the suspend timer, we should use the
525 * tkr_mono.cycle_last value as suspend_start to avoid same reading
526 * from suspend timer.
527 */
528 if (clocksource_is_suspend(cs)) {
529 suspend_start = start_cycles;
530 return;
531 }
532
533 if (suspend_clocksource->enable &&
534 suspend_clocksource->enable(suspend_clocksource)) {
535 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
536 return;
537 }
538
539 suspend_start = suspend_clocksource->read(suspend_clocksource);
540}
541
542/**
543 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
544 * @cs: current clocksource from timekeeping
545 * @cycle_now: current cycles from timekeeping
546 *
547 * This function will calculate the suspend time from suspend timer.
548 *
549 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
550 *
551 * This function is called early in the resume process from timekeeping_resume(),
552 * that means there is only one cpu, no processes are running and the interrupts
553 * are disabled. It is therefore possible to stop the suspend timer without
554 * taking the clocksource mutex.
555 */
556u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
557{
558 u64 now, delta, nsec = 0;
559
560 if (!suspend_clocksource)
561 return 0;
562
563 /*
564 * If current clocksource is the suspend timer, we should use the
565 * tkr_mono.cycle_last value from timekeeping as current cycle to
566 * avoid same reading from suspend timer.
567 */
568 if (clocksource_is_suspend(cs))
569 now = cycle_now;
570 else
571 now = suspend_clocksource->read(suspend_clocksource);
572
573 if (now > suspend_start) {
574 delta = clocksource_delta(now, suspend_start,
575 suspend_clocksource->mask);
576 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
577 suspend_clocksource->shift);
578 }
579
580 /*
581 * Disable the suspend timer to save power if current clocksource is
582 * not the suspend timer.
583 */
584 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
585 suspend_clocksource->disable(suspend_clocksource);
586
587 return nsec;
588}
589
590/**
591 * clocksource_suspend - suspend the clocksource(s)
592 */
593void clocksource_suspend(void)
594{
595 struct clocksource *cs;
596
597 list_for_each_entry_reverse(cs, &clocksource_list, list)
598 if (cs->suspend)
599 cs->suspend(cs);
600}
601
602/**
603 * clocksource_resume - resume the clocksource(s)
604 */
605void clocksource_resume(void)
606{
607 struct clocksource *cs;
608
609 list_for_each_entry(cs, &clocksource_list, list)
610 if (cs->resume)
611 cs->resume(cs);
612
613 clocksource_resume_watchdog();
614}
615
616/**
617 * clocksource_touch_watchdog - Update watchdog
618 *
619 * Update the watchdog after exception contexts such as kgdb so as not
620 * to incorrectly trip the watchdog. This might fail when the kernel
621 * was stopped in code which holds watchdog_lock.
622 */
623void clocksource_touch_watchdog(void)
624{
625 clocksource_resume_watchdog();
626}
627
628/**
629 * clocksource_max_adjustment- Returns max adjustment amount
630 * @cs: Pointer to clocksource
631 *
632 */
633static u32 clocksource_max_adjustment(struct clocksource *cs)
634{
635 u64 ret;
636 /*
637 * We won't try to correct for more than 11% adjustments (110,000 ppm),
638 */
639 ret = (u64)cs->mult * 11;
640 do_div(ret,100);
641 return (u32)ret;
642}
643
644/**
645 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
646 * @mult: cycle to nanosecond multiplier
647 * @shift: cycle to nanosecond divisor (power of two)
648 * @maxadj: maximum adjustment value to mult (~11%)
649 * @mask: bitmask for two's complement subtraction of non 64 bit counters
650 * @max_cyc: maximum cycle value before potential overflow (does not include
651 * any safety margin)
652 *
653 * NOTE: This function includes a safety margin of 50%, in other words, we
654 * return half the number of nanoseconds the hardware counter can technically
655 * cover. This is done so that we can potentially detect problems caused by
656 * delayed timers or bad hardware, which might result in time intervals that
657 * are larger than what the math used can handle without overflows.
658 */
659u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
660{
661 u64 max_nsecs, max_cycles;
662
663 /*
664 * Calculate the maximum number of cycles that we can pass to the
665 * cyc2ns() function without overflowing a 64-bit result.
666 */
667 max_cycles = ULLONG_MAX;
668 do_div(max_cycles, mult+maxadj);
669
670 /*
671 * The actual maximum number of cycles we can defer the clocksource is
672 * determined by the minimum of max_cycles and mask.
673 * Note: Here we subtract the maxadj to make sure we don't sleep for
674 * too long if there's a large negative adjustment.
675 */
676 max_cycles = min(max_cycles, mask);
677 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
678
679 /* return the max_cycles value as well if requested */
680 if (max_cyc)
681 *max_cyc = max_cycles;
682
683 /* Return 50% of the actual maximum, so we can detect bad values */
684 max_nsecs >>= 1;
685
686 return max_nsecs;
687}
688
689/**
690 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
691 * @cs: Pointer to clocksource to be updated
692 *
693 */
694static inline void clocksource_update_max_deferment(struct clocksource *cs)
695{
696 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
697 cs->maxadj, cs->mask,
698 &cs->max_cycles);
699}
700
701#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
702
703static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
704{
705 struct clocksource *cs;
706
707 if (!finished_booting || list_empty(&clocksource_list))
708 return NULL;
709
710 /*
711 * We pick the clocksource with the highest rating. If oneshot
712 * mode is active, we pick the highres valid clocksource with
713 * the best rating.
714 */
715 list_for_each_entry(cs, &clocksource_list, list) {
716 if (skipcur && cs == curr_clocksource)
717 continue;
718 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
719 continue;
720 return cs;
721 }
722 return NULL;
723}
724
725static void __clocksource_select(bool skipcur)
726{
727 bool oneshot = tick_oneshot_mode_active();
728 struct clocksource *best, *cs;
729
730 /* Find the best suitable clocksource */
731 best = clocksource_find_best(oneshot, skipcur);
732 if (!best)
733 return;
734
735 if (!strlen(override_name))
736 goto found;
737
738 /* Check for the override clocksource. */
739 list_for_each_entry(cs, &clocksource_list, list) {
740 if (skipcur && cs == curr_clocksource)
741 continue;
742 if (strcmp(cs->name, override_name) != 0)
743 continue;
744 /*
745 * Check to make sure we don't switch to a non-highres
746 * capable clocksource if the tick code is in oneshot
747 * mode (highres or nohz)
748 */
749 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
750 /* Override clocksource cannot be used. */
751 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
752 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
753 cs->name);
754 override_name[0] = 0;
755 } else {
756 /*
757 * The override cannot be currently verified.
758 * Deferring to let the watchdog check.
759 */
760 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
761 cs->name);
762 }
763 } else
764 /* Override clocksource can be used. */
765 best = cs;
766 break;
767 }
768
769found:
770 if (curr_clocksource != best && !timekeeping_notify(best)) {
771 pr_info("Switched to clocksource %s\n", best->name);
772 curr_clocksource = best;
773 }
774}
775
776/**
777 * clocksource_select - Select the best clocksource available
778 *
779 * Private function. Must hold clocksource_mutex when called.
780 *
781 * Select the clocksource with the best rating, or the clocksource,
782 * which is selected by userspace override.
783 */
784static void clocksource_select(void)
785{
786 __clocksource_select(false);
787}
788
789static void clocksource_select_fallback(void)
790{
791 __clocksource_select(true);
792}
793
794#else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
795static inline void clocksource_select(void) { }
796static inline void clocksource_select_fallback(void) { }
797
798#endif
799
800/*
801 * clocksource_done_booting - Called near the end of core bootup
802 *
803 * Hack to avoid lots of clocksource churn at boot time.
804 * We use fs_initcall because we want this to start before
805 * device_initcall but after subsys_initcall.
806 */
807static int __init clocksource_done_booting(void)
808{
809 mutex_lock(&clocksource_mutex);
810 curr_clocksource = clocksource_default_clock();
811 finished_booting = 1;
812 /*
813 * Run the watchdog first to eliminate unstable clock sources
814 */
815 __clocksource_watchdog_kthread();
816 clocksource_select();
817 mutex_unlock(&clocksource_mutex);
818 return 0;
819}
820fs_initcall(clocksource_done_booting);
821
822/*
823 * Enqueue the clocksource sorted by rating
824 */
825static void clocksource_enqueue(struct clocksource *cs)
826{
827 struct list_head *entry = &clocksource_list;
828 struct clocksource *tmp;
829
830 list_for_each_entry(tmp, &clocksource_list, list) {
831 /* Keep track of the place, where to insert */
832 if (tmp->rating < cs->rating)
833 break;
834 entry = &tmp->list;
835 }
836 list_add(&cs->list, entry);
837}
838
839/**
840 * __clocksource_update_freq_scale - Used update clocksource with new freq
841 * @cs: clocksource to be registered
842 * @scale: Scale factor multiplied against freq to get clocksource hz
843 * @freq: clocksource frequency (cycles per second) divided by scale
844 *
845 * This should only be called from the clocksource->enable() method.
846 *
847 * This *SHOULD NOT* be called directly! Please use the
848 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
849 * functions.
850 */
851void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
852{
853 u64 sec;
854
855 /*
856 * Default clocksources are *special* and self-define their mult/shift.
857 * But, you're not special, so you should specify a freq value.
858 */
859 if (freq) {
860 /*
861 * Calc the maximum number of seconds which we can run before
862 * wrapping around. For clocksources which have a mask > 32-bit
863 * we need to limit the max sleep time to have a good
864 * conversion precision. 10 minutes is still a reasonable
865 * amount. That results in a shift value of 24 for a
866 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
867 * ~ 0.06ppm granularity for NTP.
868 */
869 sec = cs->mask;
870 do_div(sec, freq);
871 do_div(sec, scale);
872 if (!sec)
873 sec = 1;
874 else if (sec > 600 && cs->mask > UINT_MAX)
875 sec = 600;
876
877 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
878 NSEC_PER_SEC / scale, sec * scale);
879 }
880 /*
881 * Ensure clocksources that have large 'mult' values don't overflow
882 * when adjusted.
883 */
884 cs->maxadj = clocksource_max_adjustment(cs);
885 while (freq && ((cs->mult + cs->maxadj < cs->mult)
886 || (cs->mult - cs->maxadj > cs->mult))) {
887 cs->mult >>= 1;
888 cs->shift--;
889 cs->maxadj = clocksource_max_adjustment(cs);
890 }
891
892 /*
893 * Only warn for *special* clocksources that self-define
894 * their mult/shift values and don't specify a freq.
895 */
896 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
897 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
898 cs->name);
899
900 clocksource_update_max_deferment(cs);
901
902 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
903 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
904}
905EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
906
907/**
908 * __clocksource_register_scale - Used to install new clocksources
909 * @cs: clocksource to be registered
910 * @scale: Scale factor multiplied against freq to get clocksource hz
911 * @freq: clocksource frequency (cycles per second) divided by scale
912 *
913 * Returns -EBUSY if registration fails, zero otherwise.
914 *
915 * This *SHOULD NOT* be called directly! Please use the
916 * clocksource_register_hz() or clocksource_register_khz helper functions.
917 */
918int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
919{
920 unsigned long flags;
921
922 clocksource_arch_init(cs);
923
924 /* Initialize mult/shift and max_idle_ns */
925 __clocksource_update_freq_scale(cs, scale, freq);
926
927 /* Add clocksource to the clocksource list */
928 mutex_lock(&clocksource_mutex);
929
930 clocksource_watchdog_lock(&flags);
931 clocksource_enqueue(cs);
932 clocksource_enqueue_watchdog(cs);
933 clocksource_watchdog_unlock(&flags);
934
935 clocksource_select();
936 clocksource_select_watchdog(false);
937 __clocksource_suspend_select(cs);
938 mutex_unlock(&clocksource_mutex);
939 return 0;
940}
941EXPORT_SYMBOL_GPL(__clocksource_register_scale);
942
943static void __clocksource_change_rating(struct clocksource *cs, int rating)
944{
945 list_del(&cs->list);
946 cs->rating = rating;
947 clocksource_enqueue(cs);
948}
949
950/**
951 * clocksource_change_rating - Change the rating of a registered clocksource
952 * @cs: clocksource to be changed
953 * @rating: new rating
954 */
955void clocksource_change_rating(struct clocksource *cs, int rating)
956{
957 unsigned long flags;
958
959 mutex_lock(&clocksource_mutex);
960 clocksource_watchdog_lock(&flags);
961 __clocksource_change_rating(cs, rating);
962 clocksource_watchdog_unlock(&flags);
963
964 clocksource_select();
965 clocksource_select_watchdog(false);
966 clocksource_suspend_select(false);
967 mutex_unlock(&clocksource_mutex);
968}
969EXPORT_SYMBOL(clocksource_change_rating);
970
971/*
972 * Unbind clocksource @cs. Called with clocksource_mutex held
973 */
974static int clocksource_unbind(struct clocksource *cs)
975{
976 unsigned long flags;
977
978 if (clocksource_is_watchdog(cs)) {
979 /* Select and try to install a replacement watchdog. */
980 clocksource_select_watchdog(true);
981 if (clocksource_is_watchdog(cs))
982 return -EBUSY;
983 }
984
985 if (cs == curr_clocksource) {
986 /* Select and try to install a replacement clock source */
987 clocksource_select_fallback();
988 if (curr_clocksource == cs)
989 return -EBUSY;
990 }
991
992 if (clocksource_is_suspend(cs)) {
993 /*
994 * Select and try to install a replacement suspend clocksource.
995 * If no replacement suspend clocksource, we will just let the
996 * clocksource go and have no suspend clocksource.
997 */
998 clocksource_suspend_select(true);
999 }
1000
1001 clocksource_watchdog_lock(&flags);
1002 clocksource_dequeue_watchdog(cs);
1003 list_del_init(&cs->list);
1004 clocksource_watchdog_unlock(&flags);
1005
1006 return 0;
1007}
1008
1009/**
1010 * clocksource_unregister - remove a registered clocksource
1011 * @cs: clocksource to be unregistered
1012 */
1013int clocksource_unregister(struct clocksource *cs)
1014{
1015 int ret = 0;
1016
1017 mutex_lock(&clocksource_mutex);
1018 if (!list_empty(&cs->list))
1019 ret = clocksource_unbind(cs);
1020 mutex_unlock(&clocksource_mutex);
1021 return ret;
1022}
1023EXPORT_SYMBOL(clocksource_unregister);
1024
1025#ifdef CONFIG_SYSFS
1026/**
1027 * current_clocksource_show - sysfs interface for current clocksource
1028 * @dev: unused
1029 * @attr: unused
1030 * @buf: char buffer to be filled with clocksource list
1031 *
1032 * Provides sysfs interface for listing current clocksource.
1033 */
1034static ssize_t current_clocksource_show(struct device *dev,
1035 struct device_attribute *attr,
1036 char *buf)
1037{
1038 ssize_t count = 0;
1039
1040 mutex_lock(&clocksource_mutex);
1041 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
1042 mutex_unlock(&clocksource_mutex);
1043
1044 return count;
1045}
1046
1047ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1048{
1049 size_t ret = cnt;
1050
1051 /* strings from sysfs write are not 0 terminated! */
1052 if (!cnt || cnt >= CS_NAME_LEN)
1053 return -EINVAL;
1054
1055 /* strip of \n: */
1056 if (buf[cnt-1] == '\n')
1057 cnt--;
1058 if (cnt > 0)
1059 memcpy(dst, buf, cnt);
1060 dst[cnt] = 0;
1061 return ret;
1062}
1063
1064/**
1065 * current_clocksource_store - interface for manually overriding clocksource
1066 * @dev: unused
1067 * @attr: unused
1068 * @buf: name of override clocksource
1069 * @count: length of buffer
1070 *
1071 * Takes input from sysfs interface for manually overriding the default
1072 * clocksource selection.
1073 */
1074static ssize_t current_clocksource_store(struct device *dev,
1075 struct device_attribute *attr,
1076 const char *buf, size_t count)
1077{
1078 ssize_t ret;
1079
1080 mutex_lock(&clocksource_mutex);
1081
1082 ret = sysfs_get_uname(buf, override_name, count);
1083 if (ret >= 0)
1084 clocksource_select();
1085
1086 mutex_unlock(&clocksource_mutex);
1087
1088 return ret;
1089}
1090static DEVICE_ATTR_RW(current_clocksource);
1091
1092/**
1093 * unbind_clocksource_store - interface for manually unbinding clocksource
1094 * @dev: unused
1095 * @attr: unused
1096 * @buf: unused
1097 * @count: length of buffer
1098 *
1099 * Takes input from sysfs interface for manually unbinding a clocksource.
1100 */
1101static ssize_t unbind_clocksource_store(struct device *dev,
1102 struct device_attribute *attr,
1103 const char *buf, size_t count)
1104{
1105 struct clocksource *cs;
1106 char name[CS_NAME_LEN];
1107 ssize_t ret;
1108
1109 ret = sysfs_get_uname(buf, name, count);
1110 if (ret < 0)
1111 return ret;
1112
1113 ret = -ENODEV;
1114 mutex_lock(&clocksource_mutex);
1115 list_for_each_entry(cs, &clocksource_list, list) {
1116 if (strcmp(cs->name, name))
1117 continue;
1118 ret = clocksource_unbind(cs);
1119 break;
1120 }
1121 mutex_unlock(&clocksource_mutex);
1122
1123 return ret ? ret : count;
1124}
1125static DEVICE_ATTR_WO(unbind_clocksource);
1126
1127/**
1128 * available_clocksource_show - sysfs interface for listing clocksource
1129 * @dev: unused
1130 * @attr: unused
1131 * @buf: char buffer to be filled with clocksource list
1132 *
1133 * Provides sysfs interface for listing registered clocksources
1134 */
1135static ssize_t available_clocksource_show(struct device *dev,
1136 struct device_attribute *attr,
1137 char *buf)
1138{
1139 struct clocksource *src;
1140 ssize_t count = 0;
1141
1142 mutex_lock(&clocksource_mutex);
1143 list_for_each_entry(src, &clocksource_list, list) {
1144 /*
1145 * Don't show non-HRES clocksource if the tick code is
1146 * in one shot mode (highres=on or nohz=on)
1147 */
1148 if (!tick_oneshot_mode_active() ||
1149 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1150 count += snprintf(buf + count,
1151 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1152 "%s ", src->name);
1153 }
1154 mutex_unlock(&clocksource_mutex);
1155
1156 count += snprintf(buf + count,
1157 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1158
1159 return count;
1160}
1161static DEVICE_ATTR_RO(available_clocksource);
1162
1163static struct attribute *clocksource_attrs[] = {
1164 &dev_attr_current_clocksource.attr,
1165 &dev_attr_unbind_clocksource.attr,
1166 &dev_attr_available_clocksource.attr,
1167 NULL
1168};
1169ATTRIBUTE_GROUPS(clocksource);
1170
1171static struct bus_type clocksource_subsys = {
1172 .name = "clocksource",
1173 .dev_name = "clocksource",
1174};
1175
1176static struct device device_clocksource = {
1177 .id = 0,
1178 .bus = &clocksource_subsys,
1179 .groups = clocksource_groups,
1180};
1181
1182static int __init init_clocksource_sysfs(void)
1183{
1184 int error = subsys_system_register(&clocksource_subsys, NULL);
1185
1186 if (!error)
1187 error = device_register(&device_clocksource);
1188
1189 return error;
1190}
1191
1192device_initcall(init_clocksource_sysfs);
1193#endif /* CONFIG_SYSFS */
1194
1195/**
1196 * boot_override_clocksource - boot clock override
1197 * @str: override name
1198 *
1199 * Takes a clocksource= boot argument and uses it
1200 * as the clocksource override name.
1201 */
1202static int __init boot_override_clocksource(char* str)
1203{
1204 mutex_lock(&clocksource_mutex);
1205 if (str)
1206 strlcpy(override_name, str, sizeof(override_name));
1207 mutex_unlock(&clocksource_mutex);
1208 return 1;
1209}
1210
1211__setup("clocksource=", boot_override_clocksource);
1212
1213/**
1214 * boot_override_clock - Compatibility layer for deprecated boot option
1215 * @str: override name
1216 *
1217 * DEPRECATED! Takes a clock= boot argument and uses it
1218 * as the clocksource override name
1219 */
1220static int __init boot_override_clock(char* str)
1221{
1222 if (!strcmp(str, "pmtmr")) {
1223 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1224 return boot_override_clocksource("acpi_pm");
1225 }
1226 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1227 return boot_override_clocksource(str);
1228}
1229
1230__setup("clock=", boot_override_clock);
1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * This file contains the functions which manage clocksource drivers.
4 *
5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
6 */
7
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9
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>
19
20#include "tick-internal.h"
21#include "timekeeping_internal.h"
22
23/**
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
30 *
31 * The function evaluates the shift/mult pair for the scaled math
32 * operations of clocksources and clockevents.
33 *
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.
37 *
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
44 * factors.
45 */
46void
47clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
48{
49 u64 tmp;
50 u32 sft, sftacc= 32;
51
52 /*
53 * Calculate the shift factor which is limiting the conversion
54 * range:
55 */
56 tmp = ((u64)maxsec * from) >> 32;
57 while (tmp) {
58 tmp >>=1;
59 sftacc--;
60 }
61
62 /*
63 * Find the conversion shift/mult pair which has the best
64 * accuracy and fits the maxsec conversion range:
65 */
66 for (sft = 32; sft > 0; sft--) {
67 tmp = (u64) to << sft;
68 tmp += from / 2;
69 do_div(tmp, from);
70 if ((tmp >> sftacc) == 0)
71 break;
72 }
73 *mult = tmp;
74 *shift = sft;
75}
76EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
77
78/*[Clocksource internal variables]---------
79 * curr_clocksource:
80 * currently selected clocksource.
81 * suspend_clocksource:
82 * used to calculate the suspend time.
83 * clocksource_list:
84 * linked list with the registered clocksources
85 * clocksource_mutex:
86 * protects manipulations to curr_clocksource and the clocksource_list
87 * override_name:
88 * Name of the user-specified clocksource.
89 */
90static struct clocksource *curr_clocksource;
91static struct clocksource *suspend_clocksource;
92static LIST_HEAD(clocksource_list);
93static DEFINE_MUTEX(clocksource_mutex);
94static char override_name[CS_NAME_LEN];
95static int finished_booting;
96static u64 suspend_start;
97
98/*
99 * Interval: 0.5sec.
100 */
101#define WATCHDOG_INTERVAL (HZ >> 1)
102#define WATCHDOG_INTERVAL_MAX_NS ((2 * WATCHDOG_INTERVAL) * (NSEC_PER_SEC / HZ))
103
104/*
105 * Threshold: 0.0312s, when doubled: 0.0625s.
106 * Also a default for cs->uncertainty_margin when registering clocks.
107 */
108#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)
109
110/*
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.
115 *
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!
118 */
119#ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
120#define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
121#else
122#define MAX_SKEW_USEC (125 * WATCHDOG_INTERVAL / HZ)
123#endif
124
125#define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
126
127#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
128static void clocksource_watchdog_work(struct work_struct *work);
129static void clocksource_select(void);
130
131static LIST_HEAD(watchdog_list);
132static struct clocksource *watchdog;
133static struct timer_list watchdog_timer;
134static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
135static DEFINE_SPINLOCK(watchdog_lock);
136static int watchdog_running;
137static atomic_t watchdog_reset_pending;
138static int64_t watchdog_max_interval;
139
140static inline void clocksource_watchdog_lock(unsigned long *flags)
141{
142 spin_lock_irqsave(&watchdog_lock, *flags);
143}
144
145static inline void clocksource_watchdog_unlock(unsigned long *flags)
146{
147 spin_unlock_irqrestore(&watchdog_lock, *flags);
148}
149
150static int clocksource_watchdog_kthread(void *data);
151static void __clocksource_change_rating(struct clocksource *cs, int rating);
152
153static void clocksource_watchdog_work(struct work_struct *work)
154{
155 /*
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.
160 *
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
163 * kthread for this.
164 *
165 * If kthread_run fails the next watchdog scan over the
166 * watchdog_list will find the unstable clock again.
167 */
168 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
169}
170
171static void __clocksource_unstable(struct clocksource *cs)
172{
173 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
174 cs->flags |= CLOCK_SOURCE_UNSTABLE;
175
176 /*
177 * If the clocksource is registered clocksource_watchdog_kthread() will
178 * re-rate and re-select.
179 */
180 if (list_empty(&cs->list)) {
181 cs->rating = 0;
182 return;
183 }
184
185 if (cs->mark_unstable)
186 cs->mark_unstable(cs);
187
188 /* kick clocksource_watchdog_kthread() */
189 if (finished_booting)
190 schedule_work(&watchdog_work);
191}
192
193/**
194 * clocksource_mark_unstable - mark clocksource unstable via watchdog
195 * @cs: clocksource to be marked unstable
196 *
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.
199 */
200void clocksource_mark_unstable(struct clocksource *cs)
201{
202 unsigned long flags;
203
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);
209 }
210 spin_unlock_irqrestore(&watchdog_lock, flags);
211}
212
213static int verify_n_cpus = 8;
214module_param(verify_n_cpus, int, 0644);
215
216enum wd_read_status {
217 WD_READ_SUCCESS,
218 WD_READ_UNSTABLE,
219 WD_READ_SKIP
220};
221
222static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
223{
224 unsigned int nretries, max_retries;
225 u64 wd_end, wd_end2, wd_delta;
226 int64_t wd_delay, wd_seq_delay;
227
228 max_retries = clocksource_get_max_watchdog_retry();
229 for (nretries = 0; nretries <= max_retries; nretries++) {
230 local_irq_disable();
231 *wdnow = watchdog->read(watchdog);
232 *csnow = cs->read(cs);
233 wd_end = watchdog->read(watchdog);
234 wd_end2 = watchdog->read(watchdog);
235 local_irq_enable();
236
237 wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
238 wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult,
239 watchdog->shift);
240 if (wd_delay <= WATCHDOG_MAX_SKEW) {
241 if (nretries > 1 || nretries >= max_retries) {
242 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
243 smp_processor_id(), watchdog->name, nretries);
244 }
245 return WD_READ_SUCCESS;
246 }
247
248 /*
249 * Now compute delay in consecutive watchdog read to see if
250 * there is too much external interferences that cause
251 * significant delay in reading both clocksource and watchdog.
252 *
253 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2,
254 * report system busy, reinit the watchdog and skip the current
255 * watchdog test.
256 */
257 wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask);
258 wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift);
259 if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
260 goto skip_test;
261 }
262
263 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",
264 smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name);
265 return WD_READ_UNSTABLE;
266
267skip_test:
268 pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
269 smp_processor_id(), watchdog->name, wd_seq_delay);
270 pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
271 cs->name, wd_delay);
272 return WD_READ_SKIP;
273}
274
275static u64 csnow_mid;
276static cpumask_t cpus_ahead;
277static cpumask_t cpus_behind;
278static cpumask_t cpus_chosen;
279
280static void clocksource_verify_choose_cpus(void)
281{
282 int cpu, i, n = verify_n_cpus;
283
284 if (n < 0) {
285 /* Check all of the CPUs. */
286 cpumask_copy(&cpus_chosen, cpu_online_mask);
287 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
288 return;
289 }
290
291 /* If no checking desired, or no other CPU to check, leave. */
292 cpumask_clear(&cpus_chosen);
293 if (n == 0 || num_online_cpus() <= 1)
294 return;
295
296 /* Make sure to select at least one CPU other than the current CPU. */
297 cpu = cpumask_first(cpu_online_mask);
298 if (cpu == smp_processor_id())
299 cpu = cpumask_next(cpu, cpu_online_mask);
300 if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
301 return;
302 cpumask_set_cpu(cpu, &cpus_chosen);
303
304 /* Force a sane value for the boot parameter. */
305 if (n > nr_cpu_ids)
306 n = nr_cpu_ids;
307
308 /*
309 * Randomly select the specified number of CPUs. If the same
310 * CPU is selected multiple times, that CPU is checked only once,
311 * and no replacement CPU is selected. This gracefully handles
312 * situations where verify_n_cpus is greater than the number of
313 * CPUs that are currently online.
314 */
315 for (i = 1; i < n; i++) {
316 cpu = get_random_u32_below(nr_cpu_ids);
317 cpu = cpumask_next(cpu - 1, cpu_online_mask);
318 if (cpu >= nr_cpu_ids)
319 cpu = cpumask_first(cpu_online_mask);
320 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
321 cpumask_set_cpu(cpu, &cpus_chosen);
322 }
323
324 /* Don't verify ourselves. */
325 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
326}
327
328static void clocksource_verify_one_cpu(void *csin)
329{
330 struct clocksource *cs = (struct clocksource *)csin;
331
332 csnow_mid = cs->read(cs);
333}
334
335void clocksource_verify_percpu(struct clocksource *cs)
336{
337 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
338 u64 csnow_begin, csnow_end;
339 int cpu, testcpu;
340 s64 delta;
341
342 if (verify_n_cpus == 0)
343 return;
344 cpumask_clear(&cpus_ahead);
345 cpumask_clear(&cpus_behind);
346 cpus_read_lock();
347 preempt_disable();
348 clocksource_verify_choose_cpus();
349 if (cpumask_empty(&cpus_chosen)) {
350 preempt_enable();
351 cpus_read_unlock();
352 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
353 return;
354 }
355 testcpu = smp_processor_id();
356 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
357 for_each_cpu(cpu, &cpus_chosen) {
358 if (cpu == testcpu)
359 continue;
360 csnow_begin = cs->read(cs);
361 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
362 csnow_end = cs->read(cs);
363 delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
364 if (delta < 0)
365 cpumask_set_cpu(cpu, &cpus_behind);
366 delta = (csnow_end - csnow_mid) & cs->mask;
367 if (delta < 0)
368 cpumask_set_cpu(cpu, &cpus_ahead);
369 delta = clocksource_delta(csnow_end, csnow_begin, cs->mask);
370 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
371 if (cs_nsec > cs_nsec_max)
372 cs_nsec_max = cs_nsec;
373 if (cs_nsec < cs_nsec_min)
374 cs_nsec_min = cs_nsec;
375 }
376 preempt_enable();
377 cpus_read_unlock();
378 if (!cpumask_empty(&cpus_ahead))
379 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
380 cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
381 if (!cpumask_empty(&cpus_behind))
382 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n",
383 cpumask_pr_args(&cpus_behind), testcpu, cs->name);
384 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
385 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n",
386 testcpu, cs_nsec_min, cs_nsec_max, cs->name);
387}
388EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
389
390static inline void clocksource_reset_watchdog(void)
391{
392 struct clocksource *cs;
393
394 list_for_each_entry(cs, &watchdog_list, wd_list)
395 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
396}
397
398
399static void clocksource_watchdog(struct timer_list *unused)
400{
401 u64 csnow, wdnow, cslast, wdlast, delta;
402 int64_t wd_nsec, cs_nsec, interval;
403 int next_cpu, reset_pending;
404 struct clocksource *cs;
405 enum wd_read_status read_ret;
406 unsigned long extra_wait = 0;
407 u32 md;
408
409 spin_lock(&watchdog_lock);
410 if (!watchdog_running)
411 goto out;
412
413 reset_pending = atomic_read(&watchdog_reset_pending);
414
415 list_for_each_entry(cs, &watchdog_list, wd_list) {
416
417 /* Clocksource already marked unstable? */
418 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
419 if (finished_booting)
420 schedule_work(&watchdog_work);
421 continue;
422 }
423
424 read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
425
426 if (read_ret == WD_READ_UNSTABLE) {
427 /* Clock readout unreliable, so give it up. */
428 __clocksource_unstable(cs);
429 continue;
430 }
431
432 /*
433 * When WD_READ_SKIP is returned, it means the system is likely
434 * under very heavy load, where the latency of reading
435 * watchdog/clocksource is very big, and affect the accuracy of
436 * watchdog check. So give system some space and suspend the
437 * watchdog check for 5 minutes.
438 */
439 if (read_ret == WD_READ_SKIP) {
440 /*
441 * As the watchdog timer will be suspended, and
442 * cs->last could keep unchanged for 5 minutes, reset
443 * the counters.
444 */
445 clocksource_reset_watchdog();
446 extra_wait = HZ * 300;
447 break;
448 }
449
450 /* Clocksource initialized ? */
451 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
452 atomic_read(&watchdog_reset_pending)) {
453 cs->flags |= CLOCK_SOURCE_WATCHDOG;
454 cs->wd_last = wdnow;
455 cs->cs_last = csnow;
456 continue;
457 }
458
459 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
460 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
461 watchdog->shift);
462
463 delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
464 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
465 wdlast = cs->wd_last; /* save these in case we print them */
466 cslast = cs->cs_last;
467 cs->cs_last = csnow;
468 cs->wd_last = wdnow;
469
470 if (atomic_read(&watchdog_reset_pending))
471 continue;
472
473 /*
474 * The processing of timer softirqs can get delayed (usually
475 * on account of ksoftirqd not getting to run in a timely
476 * manner), which causes the watchdog interval to stretch.
477 * Skew detection may fail for longer watchdog intervals
478 * on account of fixed margins being used.
479 * Some clocksources, e.g. acpi_pm, cannot tolerate
480 * watchdog intervals longer than a few seconds.
481 */
482 interval = max(cs_nsec, wd_nsec);
483 if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) {
484 if (system_state > SYSTEM_SCHEDULING &&
485 interval > 2 * watchdog_max_interval) {
486 watchdog_max_interval = interval;
487 pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n",
488 cs_nsec, wd_nsec);
489 }
490 watchdog_timer.expires = jiffies;
491 continue;
492 }
493
494 /* Check the deviation from the watchdog clocksource. */
495 md = cs->uncertainty_margin + watchdog->uncertainty_margin;
496 if (abs(cs_nsec - wd_nsec) > md) {
497 s64 cs_wd_msec;
498 s64 wd_msec;
499 u32 wd_rem;
500
501 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
502 smp_processor_id(), cs->name);
503 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
504 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
505 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
506 cs->name, cs_nsec, csnow, cslast, cs->mask);
507 cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem);
508 wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem);
509 pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n",
510 cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec);
511 if (curr_clocksource == cs)
512 pr_warn(" '%s' is current clocksource.\n", cs->name);
513 else if (curr_clocksource)
514 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
515 else
516 pr_warn(" No current clocksource.\n");
517 __clocksource_unstable(cs);
518 continue;
519 }
520
521 if (cs == curr_clocksource && cs->tick_stable)
522 cs->tick_stable(cs);
523
524 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
525 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
526 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
527 /* Mark it valid for high-res. */
528 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
529
530 /*
531 * clocksource_done_booting() will sort it if
532 * finished_booting is not set yet.
533 */
534 if (!finished_booting)
535 continue;
536
537 /*
538 * If this is not the current clocksource let
539 * the watchdog thread reselect it. Due to the
540 * change to high res this clocksource might
541 * be preferred now. If it is the current
542 * clocksource let the tick code know about
543 * that change.
544 */
545 if (cs != curr_clocksource) {
546 cs->flags |= CLOCK_SOURCE_RESELECT;
547 schedule_work(&watchdog_work);
548 } else {
549 tick_clock_notify();
550 }
551 }
552 }
553
554 /*
555 * We only clear the watchdog_reset_pending, when we did a
556 * full cycle through all clocksources.
557 */
558 if (reset_pending)
559 atomic_dec(&watchdog_reset_pending);
560
561 /*
562 * Cycle through CPUs to check if the CPUs stay synchronized
563 * to each other.
564 */
565 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
566 if (next_cpu >= nr_cpu_ids)
567 next_cpu = cpumask_first(cpu_online_mask);
568
569 /*
570 * Arm timer if not already pending: could race with concurrent
571 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
572 */
573 if (!timer_pending(&watchdog_timer)) {
574 watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait;
575 add_timer_on(&watchdog_timer, next_cpu);
576 }
577out:
578 spin_unlock(&watchdog_lock);
579}
580
581static inline void clocksource_start_watchdog(void)
582{
583 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
584 return;
585 timer_setup(&watchdog_timer, clocksource_watchdog, 0);
586 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
587 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
588 watchdog_running = 1;
589}
590
591static inline void clocksource_stop_watchdog(void)
592{
593 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
594 return;
595 del_timer(&watchdog_timer);
596 watchdog_running = 0;
597}
598
599static void clocksource_resume_watchdog(void)
600{
601 atomic_inc(&watchdog_reset_pending);
602}
603
604static void clocksource_enqueue_watchdog(struct clocksource *cs)
605{
606 INIT_LIST_HEAD(&cs->wd_list);
607
608 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
609 /* cs is a clocksource to be watched. */
610 list_add(&cs->wd_list, &watchdog_list);
611 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
612 } else {
613 /* cs is a watchdog. */
614 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
615 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
616 }
617}
618
619static void clocksource_select_watchdog(bool fallback)
620{
621 struct clocksource *cs, *old_wd;
622 unsigned long flags;
623
624 spin_lock_irqsave(&watchdog_lock, flags);
625 /* save current watchdog */
626 old_wd = watchdog;
627 if (fallback)
628 watchdog = NULL;
629
630 list_for_each_entry(cs, &clocksource_list, list) {
631 /* cs is a clocksource to be watched. */
632 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
633 continue;
634
635 /* Skip current if we were requested for a fallback. */
636 if (fallback && cs == old_wd)
637 continue;
638
639 /* Pick the best watchdog. */
640 if (!watchdog || cs->rating > watchdog->rating)
641 watchdog = cs;
642 }
643 /* If we failed to find a fallback restore the old one. */
644 if (!watchdog)
645 watchdog = old_wd;
646
647 /* If we changed the watchdog we need to reset cycles. */
648 if (watchdog != old_wd)
649 clocksource_reset_watchdog();
650
651 /* Check if the watchdog timer needs to be started. */
652 clocksource_start_watchdog();
653 spin_unlock_irqrestore(&watchdog_lock, flags);
654}
655
656static void clocksource_dequeue_watchdog(struct clocksource *cs)
657{
658 if (cs != watchdog) {
659 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
660 /* cs is a watched clocksource. */
661 list_del_init(&cs->wd_list);
662 /* Check if the watchdog timer needs to be stopped. */
663 clocksource_stop_watchdog();
664 }
665 }
666}
667
668static int __clocksource_watchdog_kthread(void)
669{
670 struct clocksource *cs, *tmp;
671 unsigned long flags;
672 int select = 0;
673
674 /* Do any required per-CPU skew verification. */
675 if (curr_clocksource &&
676 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
677 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
678 clocksource_verify_percpu(curr_clocksource);
679
680 spin_lock_irqsave(&watchdog_lock, flags);
681 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
682 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
683 list_del_init(&cs->wd_list);
684 __clocksource_change_rating(cs, 0);
685 select = 1;
686 }
687 if (cs->flags & CLOCK_SOURCE_RESELECT) {
688 cs->flags &= ~CLOCK_SOURCE_RESELECT;
689 select = 1;
690 }
691 }
692 /* Check if the watchdog timer needs to be stopped. */
693 clocksource_stop_watchdog();
694 spin_unlock_irqrestore(&watchdog_lock, flags);
695
696 return select;
697}
698
699static int clocksource_watchdog_kthread(void *data)
700{
701 mutex_lock(&clocksource_mutex);
702 if (__clocksource_watchdog_kthread())
703 clocksource_select();
704 mutex_unlock(&clocksource_mutex);
705 return 0;
706}
707
708static bool clocksource_is_watchdog(struct clocksource *cs)
709{
710 return cs == watchdog;
711}
712
713#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
714
715static void clocksource_enqueue_watchdog(struct clocksource *cs)
716{
717 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
718 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
719}
720
721static void clocksource_select_watchdog(bool fallback) { }
722static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
723static inline void clocksource_resume_watchdog(void) { }
724static inline int __clocksource_watchdog_kthread(void) { return 0; }
725static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
726void clocksource_mark_unstable(struct clocksource *cs) { }
727
728static inline void clocksource_watchdog_lock(unsigned long *flags) { }
729static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
730
731#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
732
733static bool clocksource_is_suspend(struct clocksource *cs)
734{
735 return cs == suspend_clocksource;
736}
737
738static void __clocksource_suspend_select(struct clocksource *cs)
739{
740 /*
741 * Skip the clocksource which will be stopped in suspend state.
742 */
743 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
744 return;
745
746 /*
747 * The nonstop clocksource can be selected as the suspend clocksource to
748 * calculate the suspend time, so it should not supply suspend/resume
749 * interfaces to suspend the nonstop clocksource when system suspends.
750 */
751 if (cs->suspend || cs->resume) {
752 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
753 cs->name);
754 }
755
756 /* Pick the best rating. */
757 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
758 suspend_clocksource = cs;
759}
760
761/**
762 * clocksource_suspend_select - Select the best clocksource for suspend timing
763 * @fallback: if select a fallback clocksource
764 */
765static void clocksource_suspend_select(bool fallback)
766{
767 struct clocksource *cs, *old_suspend;
768
769 old_suspend = suspend_clocksource;
770 if (fallback)
771 suspend_clocksource = NULL;
772
773 list_for_each_entry(cs, &clocksource_list, list) {
774 /* Skip current if we were requested for a fallback. */
775 if (fallback && cs == old_suspend)
776 continue;
777
778 __clocksource_suspend_select(cs);
779 }
780}
781
782/**
783 * clocksource_start_suspend_timing - Start measuring the suspend timing
784 * @cs: current clocksource from timekeeping
785 * @start_cycles: current cycles from timekeeping
786 *
787 * This function will save the start cycle values of suspend timer to calculate
788 * the suspend time when resuming system.
789 *
790 * This function is called late in the suspend process from timekeeping_suspend(),
791 * that means processes are frozen, non-boot cpus and interrupts are disabled
792 * now. It is therefore possible to start the suspend timer without taking the
793 * clocksource mutex.
794 */
795void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
796{
797 if (!suspend_clocksource)
798 return;
799
800 /*
801 * If current clocksource is the suspend timer, we should use the
802 * tkr_mono.cycle_last value as suspend_start to avoid same reading
803 * from suspend timer.
804 */
805 if (clocksource_is_suspend(cs)) {
806 suspend_start = start_cycles;
807 return;
808 }
809
810 if (suspend_clocksource->enable &&
811 suspend_clocksource->enable(suspend_clocksource)) {
812 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
813 return;
814 }
815
816 suspend_start = suspend_clocksource->read(suspend_clocksource);
817}
818
819/**
820 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
821 * @cs: current clocksource from timekeeping
822 * @cycle_now: current cycles from timekeeping
823 *
824 * This function will calculate the suspend time from suspend timer.
825 *
826 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
827 *
828 * This function is called early in the resume process from timekeeping_resume(),
829 * that means there is only one cpu, no processes are running and the interrupts
830 * are disabled. It is therefore possible to stop the suspend timer without
831 * taking the clocksource mutex.
832 */
833u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
834{
835 u64 now, delta, nsec = 0;
836
837 if (!suspend_clocksource)
838 return 0;
839
840 /*
841 * If current clocksource is the suspend timer, we should use the
842 * tkr_mono.cycle_last value from timekeeping as current cycle to
843 * avoid same reading from suspend timer.
844 */
845 if (clocksource_is_suspend(cs))
846 now = cycle_now;
847 else
848 now = suspend_clocksource->read(suspend_clocksource);
849
850 if (now > suspend_start) {
851 delta = clocksource_delta(now, suspend_start,
852 suspend_clocksource->mask);
853 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
854 suspend_clocksource->shift);
855 }
856
857 /*
858 * Disable the suspend timer to save power if current clocksource is
859 * not the suspend timer.
860 */
861 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
862 suspend_clocksource->disable(suspend_clocksource);
863
864 return nsec;
865}
866
867/**
868 * clocksource_suspend - suspend the clocksource(s)
869 */
870void clocksource_suspend(void)
871{
872 struct clocksource *cs;
873
874 list_for_each_entry_reverse(cs, &clocksource_list, list)
875 if (cs->suspend)
876 cs->suspend(cs);
877}
878
879/**
880 * clocksource_resume - resume the clocksource(s)
881 */
882void clocksource_resume(void)
883{
884 struct clocksource *cs;
885
886 list_for_each_entry(cs, &clocksource_list, list)
887 if (cs->resume)
888 cs->resume(cs);
889
890 clocksource_resume_watchdog();
891}
892
893/**
894 * clocksource_touch_watchdog - Update watchdog
895 *
896 * Update the watchdog after exception contexts such as kgdb so as not
897 * to incorrectly trip the watchdog. This might fail when the kernel
898 * was stopped in code which holds watchdog_lock.
899 */
900void clocksource_touch_watchdog(void)
901{
902 clocksource_resume_watchdog();
903}
904
905/**
906 * clocksource_max_adjustment- Returns max adjustment amount
907 * @cs: Pointer to clocksource
908 *
909 */
910static u32 clocksource_max_adjustment(struct clocksource *cs)
911{
912 u64 ret;
913 /*
914 * We won't try to correct for more than 11% adjustments (110,000 ppm),
915 */
916 ret = (u64)cs->mult * 11;
917 do_div(ret,100);
918 return (u32)ret;
919}
920
921/**
922 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
923 * @mult: cycle to nanosecond multiplier
924 * @shift: cycle to nanosecond divisor (power of two)
925 * @maxadj: maximum adjustment value to mult (~11%)
926 * @mask: bitmask for two's complement subtraction of non 64 bit counters
927 * @max_cyc: maximum cycle value before potential overflow (does not include
928 * any safety margin)
929 *
930 * NOTE: This function includes a safety margin of 50%, in other words, we
931 * return half the number of nanoseconds the hardware counter can technically
932 * cover. This is done so that we can potentially detect problems caused by
933 * delayed timers or bad hardware, which might result in time intervals that
934 * are larger than what the math used can handle without overflows.
935 */
936u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
937{
938 u64 max_nsecs, max_cycles;
939
940 /*
941 * Calculate the maximum number of cycles that we can pass to the
942 * cyc2ns() function without overflowing a 64-bit result.
943 */
944 max_cycles = ULLONG_MAX;
945 do_div(max_cycles, mult+maxadj);
946
947 /*
948 * The actual maximum number of cycles we can defer the clocksource is
949 * determined by the minimum of max_cycles and mask.
950 * Note: Here we subtract the maxadj to make sure we don't sleep for
951 * too long if there's a large negative adjustment.
952 */
953 max_cycles = min(max_cycles, mask);
954 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
955
956 /* return the max_cycles value as well if requested */
957 if (max_cyc)
958 *max_cyc = max_cycles;
959
960 /* Return 50% of the actual maximum, so we can detect bad values */
961 max_nsecs >>= 1;
962
963 return max_nsecs;
964}
965
966/**
967 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
968 * @cs: Pointer to clocksource to be updated
969 *
970 */
971static inline void clocksource_update_max_deferment(struct clocksource *cs)
972{
973 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
974 cs->maxadj, cs->mask,
975 &cs->max_cycles);
976}
977
978static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
979{
980 struct clocksource *cs;
981
982 if (!finished_booting || list_empty(&clocksource_list))
983 return NULL;
984
985 /*
986 * We pick the clocksource with the highest rating. If oneshot
987 * mode is active, we pick the highres valid clocksource with
988 * the best rating.
989 */
990 list_for_each_entry(cs, &clocksource_list, list) {
991 if (skipcur && cs == curr_clocksource)
992 continue;
993 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
994 continue;
995 return cs;
996 }
997 return NULL;
998}
999
1000static void __clocksource_select(bool skipcur)
1001{
1002 bool oneshot = tick_oneshot_mode_active();
1003 struct clocksource *best, *cs;
1004
1005 /* Find the best suitable clocksource */
1006 best = clocksource_find_best(oneshot, skipcur);
1007 if (!best)
1008 return;
1009
1010 if (!strlen(override_name))
1011 goto found;
1012
1013 /* Check for the override clocksource. */
1014 list_for_each_entry(cs, &clocksource_list, list) {
1015 if (skipcur && cs == curr_clocksource)
1016 continue;
1017 if (strcmp(cs->name, override_name) != 0)
1018 continue;
1019 /*
1020 * Check to make sure we don't switch to a non-highres
1021 * capable clocksource if the tick code is in oneshot
1022 * mode (highres or nohz)
1023 */
1024 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
1025 /* Override clocksource cannot be used. */
1026 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
1027 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
1028 cs->name);
1029 override_name[0] = 0;
1030 } else {
1031 /*
1032 * The override cannot be currently verified.
1033 * Deferring to let the watchdog check.
1034 */
1035 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
1036 cs->name);
1037 }
1038 } else
1039 /* Override clocksource can be used. */
1040 best = cs;
1041 break;
1042 }
1043
1044found:
1045 if (curr_clocksource != best && !timekeeping_notify(best)) {
1046 pr_info("Switched to clocksource %s\n", best->name);
1047 curr_clocksource = best;
1048 }
1049}
1050
1051/**
1052 * clocksource_select - Select the best clocksource available
1053 *
1054 * Private function. Must hold clocksource_mutex when called.
1055 *
1056 * Select the clocksource with the best rating, or the clocksource,
1057 * which is selected by userspace override.
1058 */
1059static void clocksource_select(void)
1060{
1061 __clocksource_select(false);
1062}
1063
1064static void clocksource_select_fallback(void)
1065{
1066 __clocksource_select(true);
1067}
1068
1069/*
1070 * clocksource_done_booting - Called near the end of core bootup
1071 *
1072 * Hack to avoid lots of clocksource churn at boot time.
1073 * We use fs_initcall because we want this to start before
1074 * device_initcall but after subsys_initcall.
1075 */
1076static int __init clocksource_done_booting(void)
1077{
1078 mutex_lock(&clocksource_mutex);
1079 curr_clocksource = clocksource_default_clock();
1080 finished_booting = 1;
1081 /*
1082 * Run the watchdog first to eliminate unstable clock sources
1083 */
1084 __clocksource_watchdog_kthread();
1085 clocksource_select();
1086 mutex_unlock(&clocksource_mutex);
1087 return 0;
1088}
1089fs_initcall(clocksource_done_booting);
1090
1091/*
1092 * Enqueue the clocksource sorted by rating
1093 */
1094static void clocksource_enqueue(struct clocksource *cs)
1095{
1096 struct list_head *entry = &clocksource_list;
1097 struct clocksource *tmp;
1098
1099 list_for_each_entry(tmp, &clocksource_list, list) {
1100 /* Keep track of the place, where to insert */
1101 if (tmp->rating < cs->rating)
1102 break;
1103 entry = &tmp->list;
1104 }
1105 list_add(&cs->list, entry);
1106}
1107
1108/**
1109 * __clocksource_update_freq_scale - Used update clocksource with new freq
1110 * @cs: clocksource to be registered
1111 * @scale: Scale factor multiplied against freq to get clocksource hz
1112 * @freq: clocksource frequency (cycles per second) divided by scale
1113 *
1114 * This should only be called from the clocksource->enable() method.
1115 *
1116 * This *SHOULD NOT* be called directly! Please use the
1117 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
1118 * functions.
1119 */
1120void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1121{
1122 u64 sec;
1123
1124 /*
1125 * Default clocksources are *special* and self-define their mult/shift.
1126 * But, you're not special, so you should specify a freq value.
1127 */
1128 if (freq) {
1129 /*
1130 * Calc the maximum number of seconds which we can run before
1131 * wrapping around. For clocksources which have a mask > 32-bit
1132 * we need to limit the max sleep time to have a good
1133 * conversion precision. 10 minutes is still a reasonable
1134 * amount. That results in a shift value of 24 for a
1135 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1136 * ~ 0.06ppm granularity for NTP.
1137 */
1138 sec = cs->mask;
1139 do_div(sec, freq);
1140 do_div(sec, scale);
1141 if (!sec)
1142 sec = 1;
1143 else if (sec > 600 && cs->mask > UINT_MAX)
1144 sec = 600;
1145
1146 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1147 NSEC_PER_SEC / scale, sec * scale);
1148 }
1149
1150 /*
1151 * If the uncertainty margin is not specified, calculate it.
1152 * If both scale and freq are non-zero, calculate the clock
1153 * period, but bound below at 2*WATCHDOG_MAX_SKEW. However,
1154 * if either of scale or freq is zero, be very conservative and
1155 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the
1156 * uncertainty margin. Allow stupidly small uncertainty margins
1157 * to be specified by the caller for testing purposes, but warn
1158 * to discourage production use of this capability.
1159 */
1160 if (scale && freq && !cs->uncertainty_margin) {
1161 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
1162 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
1163 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
1164 } else if (!cs->uncertainty_margin) {
1165 cs->uncertainty_margin = WATCHDOG_THRESHOLD;
1166 }
1167 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
1168
1169 /*
1170 * Ensure clocksources that have large 'mult' values don't overflow
1171 * when adjusted.
1172 */
1173 cs->maxadj = clocksource_max_adjustment(cs);
1174 while (freq && ((cs->mult + cs->maxadj < cs->mult)
1175 || (cs->mult - cs->maxadj > cs->mult))) {
1176 cs->mult >>= 1;
1177 cs->shift--;
1178 cs->maxadj = clocksource_max_adjustment(cs);
1179 }
1180
1181 /*
1182 * Only warn for *special* clocksources that self-define
1183 * their mult/shift values and don't specify a freq.
1184 */
1185 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1186 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1187 cs->name);
1188
1189 clocksource_update_max_deferment(cs);
1190
1191 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1192 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1193}
1194EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
1195
1196/**
1197 * __clocksource_register_scale - Used to install new clocksources
1198 * @cs: clocksource to be registered
1199 * @scale: Scale factor multiplied against freq to get clocksource hz
1200 * @freq: clocksource frequency (cycles per second) divided by scale
1201 *
1202 * Returns -EBUSY if registration fails, zero otherwise.
1203 *
1204 * This *SHOULD NOT* be called directly! Please use the
1205 * clocksource_register_hz() or clocksource_register_khz helper functions.
1206 */
1207int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1208{
1209 unsigned long flags;
1210
1211 clocksource_arch_init(cs);
1212
1213 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1214 cs->id = CSID_GENERIC;
1215 if (cs->vdso_clock_mode < 0 ||
1216 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1217 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1218 cs->name, cs->vdso_clock_mode);
1219 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1220 }
1221
1222 /* Initialize mult/shift and max_idle_ns */
1223 __clocksource_update_freq_scale(cs, scale, freq);
1224
1225 /* Add clocksource to the clocksource list */
1226 mutex_lock(&clocksource_mutex);
1227
1228 clocksource_watchdog_lock(&flags);
1229 clocksource_enqueue(cs);
1230 clocksource_enqueue_watchdog(cs);
1231 clocksource_watchdog_unlock(&flags);
1232
1233 clocksource_select();
1234 clocksource_select_watchdog(false);
1235 __clocksource_suspend_select(cs);
1236 mutex_unlock(&clocksource_mutex);
1237 return 0;
1238}
1239EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1240
1241static void __clocksource_change_rating(struct clocksource *cs, int rating)
1242{
1243 list_del(&cs->list);
1244 cs->rating = rating;
1245 clocksource_enqueue(cs);
1246}
1247
1248/**
1249 * clocksource_change_rating - Change the rating of a registered clocksource
1250 * @cs: clocksource to be changed
1251 * @rating: new rating
1252 */
1253void clocksource_change_rating(struct clocksource *cs, int rating)
1254{
1255 unsigned long flags;
1256
1257 mutex_lock(&clocksource_mutex);
1258 clocksource_watchdog_lock(&flags);
1259 __clocksource_change_rating(cs, rating);
1260 clocksource_watchdog_unlock(&flags);
1261
1262 clocksource_select();
1263 clocksource_select_watchdog(false);
1264 clocksource_suspend_select(false);
1265 mutex_unlock(&clocksource_mutex);
1266}
1267EXPORT_SYMBOL(clocksource_change_rating);
1268
1269/*
1270 * Unbind clocksource @cs. Called with clocksource_mutex held
1271 */
1272static int clocksource_unbind(struct clocksource *cs)
1273{
1274 unsigned long flags;
1275
1276 if (clocksource_is_watchdog(cs)) {
1277 /* Select and try to install a replacement watchdog. */
1278 clocksource_select_watchdog(true);
1279 if (clocksource_is_watchdog(cs))
1280 return -EBUSY;
1281 }
1282
1283 if (cs == curr_clocksource) {
1284 /* Select and try to install a replacement clock source */
1285 clocksource_select_fallback();
1286 if (curr_clocksource == cs)
1287 return -EBUSY;
1288 }
1289
1290 if (clocksource_is_suspend(cs)) {
1291 /*
1292 * Select and try to install a replacement suspend clocksource.
1293 * If no replacement suspend clocksource, we will just let the
1294 * clocksource go and have no suspend clocksource.
1295 */
1296 clocksource_suspend_select(true);
1297 }
1298
1299 clocksource_watchdog_lock(&flags);
1300 clocksource_dequeue_watchdog(cs);
1301 list_del_init(&cs->list);
1302 clocksource_watchdog_unlock(&flags);
1303
1304 return 0;
1305}
1306
1307/**
1308 * clocksource_unregister - remove a registered clocksource
1309 * @cs: clocksource to be unregistered
1310 */
1311int clocksource_unregister(struct clocksource *cs)
1312{
1313 int ret = 0;
1314
1315 mutex_lock(&clocksource_mutex);
1316 if (!list_empty(&cs->list))
1317 ret = clocksource_unbind(cs);
1318 mutex_unlock(&clocksource_mutex);
1319 return ret;
1320}
1321EXPORT_SYMBOL(clocksource_unregister);
1322
1323#ifdef CONFIG_SYSFS
1324/**
1325 * current_clocksource_show - sysfs interface for current clocksource
1326 * @dev: unused
1327 * @attr: unused
1328 * @buf: char buffer to be filled with clocksource list
1329 *
1330 * Provides sysfs interface for listing current clocksource.
1331 */
1332static ssize_t current_clocksource_show(struct device *dev,
1333 struct device_attribute *attr,
1334 char *buf)
1335{
1336 ssize_t count = 0;
1337
1338 mutex_lock(&clocksource_mutex);
1339 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
1340 mutex_unlock(&clocksource_mutex);
1341
1342 return count;
1343}
1344
1345ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1346{
1347 size_t ret = cnt;
1348
1349 /* strings from sysfs write are not 0 terminated! */
1350 if (!cnt || cnt >= CS_NAME_LEN)
1351 return -EINVAL;
1352
1353 /* strip of \n: */
1354 if (buf[cnt-1] == '\n')
1355 cnt--;
1356 if (cnt > 0)
1357 memcpy(dst, buf, cnt);
1358 dst[cnt] = 0;
1359 return ret;
1360}
1361
1362/**
1363 * current_clocksource_store - interface for manually overriding clocksource
1364 * @dev: unused
1365 * @attr: unused
1366 * @buf: name of override clocksource
1367 * @count: length of buffer
1368 *
1369 * Takes input from sysfs interface for manually overriding the default
1370 * clocksource selection.
1371 */
1372static ssize_t current_clocksource_store(struct device *dev,
1373 struct device_attribute *attr,
1374 const char *buf, size_t count)
1375{
1376 ssize_t ret;
1377
1378 mutex_lock(&clocksource_mutex);
1379
1380 ret = sysfs_get_uname(buf, override_name, count);
1381 if (ret >= 0)
1382 clocksource_select();
1383
1384 mutex_unlock(&clocksource_mutex);
1385
1386 return ret;
1387}
1388static DEVICE_ATTR_RW(current_clocksource);
1389
1390/**
1391 * unbind_clocksource_store - interface for manually unbinding clocksource
1392 * @dev: unused
1393 * @attr: unused
1394 * @buf: unused
1395 * @count: length of buffer
1396 *
1397 * Takes input from sysfs interface for manually unbinding a clocksource.
1398 */
1399static ssize_t unbind_clocksource_store(struct device *dev,
1400 struct device_attribute *attr,
1401 const char *buf, size_t count)
1402{
1403 struct clocksource *cs;
1404 char name[CS_NAME_LEN];
1405 ssize_t ret;
1406
1407 ret = sysfs_get_uname(buf, name, count);
1408 if (ret < 0)
1409 return ret;
1410
1411 ret = -ENODEV;
1412 mutex_lock(&clocksource_mutex);
1413 list_for_each_entry(cs, &clocksource_list, list) {
1414 if (strcmp(cs->name, name))
1415 continue;
1416 ret = clocksource_unbind(cs);
1417 break;
1418 }
1419 mutex_unlock(&clocksource_mutex);
1420
1421 return ret ? ret : count;
1422}
1423static DEVICE_ATTR_WO(unbind_clocksource);
1424
1425/**
1426 * available_clocksource_show - sysfs interface for listing clocksource
1427 * @dev: unused
1428 * @attr: unused
1429 * @buf: char buffer to be filled with clocksource list
1430 *
1431 * Provides sysfs interface for listing registered clocksources
1432 */
1433static ssize_t available_clocksource_show(struct device *dev,
1434 struct device_attribute *attr,
1435 char *buf)
1436{
1437 struct clocksource *src;
1438 ssize_t count = 0;
1439
1440 mutex_lock(&clocksource_mutex);
1441 list_for_each_entry(src, &clocksource_list, list) {
1442 /*
1443 * Don't show non-HRES clocksource if the tick code is
1444 * in one shot mode (highres=on or nohz=on)
1445 */
1446 if (!tick_oneshot_mode_active() ||
1447 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1448 count += snprintf(buf + count,
1449 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1450 "%s ", src->name);
1451 }
1452 mutex_unlock(&clocksource_mutex);
1453
1454 count += snprintf(buf + count,
1455 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1456
1457 return count;
1458}
1459static DEVICE_ATTR_RO(available_clocksource);
1460
1461static struct attribute *clocksource_attrs[] = {
1462 &dev_attr_current_clocksource.attr,
1463 &dev_attr_unbind_clocksource.attr,
1464 &dev_attr_available_clocksource.attr,
1465 NULL
1466};
1467ATTRIBUTE_GROUPS(clocksource);
1468
1469static const struct bus_type clocksource_subsys = {
1470 .name = "clocksource",
1471 .dev_name = "clocksource",
1472};
1473
1474static struct device device_clocksource = {
1475 .id = 0,
1476 .bus = &clocksource_subsys,
1477 .groups = clocksource_groups,
1478};
1479
1480static int __init init_clocksource_sysfs(void)
1481{
1482 int error = subsys_system_register(&clocksource_subsys, NULL);
1483
1484 if (!error)
1485 error = device_register(&device_clocksource);
1486
1487 return error;
1488}
1489
1490device_initcall(init_clocksource_sysfs);
1491#endif /* CONFIG_SYSFS */
1492
1493/**
1494 * boot_override_clocksource - boot clock override
1495 * @str: override name
1496 *
1497 * Takes a clocksource= boot argument and uses it
1498 * as the clocksource override name.
1499 */
1500static int __init boot_override_clocksource(char* str)
1501{
1502 mutex_lock(&clocksource_mutex);
1503 if (str)
1504 strscpy(override_name, str, sizeof(override_name));
1505 mutex_unlock(&clocksource_mutex);
1506 return 1;
1507}
1508
1509__setup("clocksource=", boot_override_clocksource);
1510
1511/**
1512 * boot_override_clock - Compatibility layer for deprecated boot option
1513 * @str: override name
1514 *
1515 * DEPRECATED! Takes a clock= boot argument and uses it
1516 * as the clocksource override name
1517 */
1518static int __init boot_override_clock(char* str)
1519{
1520 if (!strcmp(str, "pmtmr")) {
1521 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1522 return boot_override_clocksource("acpi_pm");
1523 }
1524 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1525 return boot_override_clocksource(str);
1526}
1527
1528__setup("clock=", boot_override_clock);