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
23static void clocksource_enqueue(struct clocksource *cs);
24
25static noinline u64 cycles_to_nsec_safe(struct clocksource *cs, u64 start, u64 end)
26{
27 u64 delta = clocksource_delta(now: end, last: start, mask: cs->mask, max_delta: cs->max_raw_delta);
28
29 if (likely(delta < cs->max_cycles))
30 return clocksource_cyc2ns(cycles: delta, mult: cs->mult, shift: cs->shift);
31
32 return mul_u64_u32_shr(a: delta, mul: cs->mult, shift: cs->shift);
33}
34
35/**
36 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
37 * @mult: pointer to mult variable
38 * @shift: pointer to shift variable
39 * @from: frequency to convert from
40 * @to: frequency to convert to
41 * @maxsec: guaranteed runtime conversion range in seconds
42 *
43 * The function evaluates the shift/mult pair for the scaled math
44 * operations of clocksources and clockevents.
45 *
46 * @to and @from are frequency values in HZ. For clock sources @to is
47 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
48 * event @to is the counter frequency and @from is NSEC_PER_SEC.
49 *
50 * The @maxsec conversion range argument controls the time frame in
51 * seconds which must be covered by the runtime conversion with the
52 * calculated mult and shift factors. This guarantees that no 64bit
53 * overflow happens when the input value of the conversion is
54 * multiplied with the calculated mult factor. Larger ranges may
55 * reduce the conversion accuracy by choosing smaller mult and shift
56 * factors.
57 */
58void
59clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
60{
61 u64 tmp;
62 u32 sft, sftacc= 32;
63
64 /*
65 * Calculate the shift factor which is limiting the conversion
66 * range:
67 */
68 tmp = ((u64)maxsec * from) >> 32;
69 while (tmp) {
70 tmp >>=1;
71 sftacc--;
72 }
73
74 /*
75 * Find the conversion shift/mult pair which has the best
76 * accuracy and fits the maxsec conversion range:
77 */
78 for (sft = 32; sft > 0; sft--) {
79 tmp = (u64) to << sft;
80 tmp += from / 2;
81 do_div(tmp, from);
82 if ((tmp >> sftacc) == 0)
83 break;
84 }
85 *mult = tmp;
86 *shift = sft;
87}
88EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
89
90/*[Clocksource internal variables]---------
91 * curr_clocksource:
92 * currently selected clocksource.
93 * suspend_clocksource:
94 * used to calculate the suspend time.
95 * clocksource_list:
96 * linked list with the registered clocksources
97 * clocksource_mutex:
98 * protects manipulations to curr_clocksource and the clocksource_list
99 * override_name:
100 * Name of the user-specified clocksource.
101 */
102static struct clocksource *curr_clocksource;
103static struct clocksource *suspend_clocksource;
104static LIST_HEAD(clocksource_list);
105static DEFINE_MUTEX(clocksource_mutex);
106static char override_name[CS_NAME_LEN];
107static int finished_booting;
108static u64 suspend_start;
109
110/*
111 * Interval: 0.5sec.
112 */
113#define WATCHDOG_INTERVAL (HZ >> 1)
114#define WATCHDOG_INTERVAL_MAX_NS ((2 * WATCHDOG_INTERVAL) * (NSEC_PER_SEC / HZ))
115
116/*
117 * Threshold: 0.0312s, when doubled: 0.0625s.
118 */
119#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)
120
121/*
122 * Maximum permissible delay between two readouts of the watchdog
123 * clocksource surrounding a read of the clocksource being validated.
124 * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as
125 * a lower bound for cs->uncertainty_margin values when registering clocks.
126 *
127 * The default of 500 parts per million is based on NTP's limits.
128 * If a clocksource is good enough for NTP, it is good enough for us!
129 *
130 * In other words, by default, even if a clocksource is extremely
131 * precise (for example, with a sub-nanosecond period), the maximum
132 * permissible skew between the clocksource watchdog and the clocksource
133 * under test is not permitted to go below the 500ppm minimum defined
134 * by MAX_SKEW_USEC. This 500ppm minimum may be overridden using the
135 * CLOCKSOURCE_WATCHDOG_MAX_SKEW_US Kconfig option.
136 */
137#ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
138#define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
139#else
140#define MAX_SKEW_USEC (125 * WATCHDOG_INTERVAL / HZ)
141#endif
142
143/*
144 * Default for maximum permissible skew when cs->uncertainty_margin is
145 * not specified, and the lower bound even when cs->uncertainty_margin
146 * is specified. This is also the default that is used when registering
147 * clocks with unspecified cs->uncertainty_margin, so this macro is used
148 * even in CONFIG_CLOCKSOURCE_WATCHDOG=n kernels.
149 */
150#define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
151
152#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
153static void clocksource_watchdog_work(struct work_struct *work);
154static void clocksource_select(void);
155
156static LIST_HEAD(watchdog_list);
157static struct clocksource *watchdog;
158static struct timer_list watchdog_timer;
159static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
160static DEFINE_SPINLOCK(watchdog_lock);
161static int watchdog_running;
162static atomic_t watchdog_reset_pending;
163static int64_t watchdog_max_interval;
164
165static inline void clocksource_watchdog_lock(unsigned long *flags)
166{
167 spin_lock_irqsave(&watchdog_lock, *flags);
168}
169
170static inline void clocksource_watchdog_unlock(unsigned long *flags)
171{
172 spin_unlock_irqrestore(lock: &watchdog_lock, flags: *flags);
173}
174
175static int clocksource_watchdog_kthread(void *data);
176
177static void clocksource_watchdog_work(struct work_struct *work)
178{
179 /*
180 * We cannot directly run clocksource_watchdog_kthread() here, because
181 * clocksource_select() calls timekeeping_notify() which uses
182 * stop_machine(). One cannot use stop_machine() from a workqueue() due
183 * lock inversions wrt CPU hotplug.
184 *
185 * Also, we only ever run this work once or twice during the lifetime
186 * of the kernel, so there is no point in creating a more permanent
187 * kthread for this.
188 *
189 * If kthread_run fails the next watchdog scan over the
190 * watchdog_list will find the unstable clock again.
191 */
192 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
193}
194
195static void clocksource_change_rating(struct clocksource *cs, int rating)
196{
197 list_del(entry: &cs->list);
198 cs->rating = rating;
199 clocksource_enqueue(cs);
200}
201
202static void __clocksource_unstable(struct clocksource *cs)
203{
204 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
205 cs->flags |= CLOCK_SOURCE_UNSTABLE;
206
207 /*
208 * If the clocksource is registered clocksource_watchdog_kthread() will
209 * re-rate and re-select.
210 */
211 if (list_empty(head: &cs->list)) {
212 cs->rating = 0;
213 return;
214 }
215
216 if (cs->mark_unstable)
217 cs->mark_unstable(cs);
218
219 /* kick clocksource_watchdog_kthread() */
220 if (finished_booting)
221 schedule_work(work: &watchdog_work);
222}
223
224/**
225 * clocksource_mark_unstable - mark clocksource unstable via watchdog
226 * @cs: clocksource to be marked unstable
227 *
228 * This function is called by the x86 TSC code to mark clocksources as unstable;
229 * it defers demotion and re-selection to a kthread.
230 */
231void clocksource_mark_unstable(struct clocksource *cs)
232{
233 unsigned long flags;
234
235 spin_lock_irqsave(&watchdog_lock, flags);
236 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
237 if (!list_empty(head: &cs->list) && list_empty(head: &cs->wd_list))
238 list_add(new: &cs->wd_list, head: &watchdog_list);
239 __clocksource_unstable(cs);
240 }
241 spin_unlock_irqrestore(lock: &watchdog_lock, flags);
242}
243
244static int verify_n_cpus = 8;
245module_param(verify_n_cpus, int, 0644);
246
247enum wd_read_status {
248 WD_READ_SUCCESS,
249 WD_READ_UNSTABLE,
250 WD_READ_SKIP
251};
252
253static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
254{
255 int64_t md = watchdog->uncertainty_margin;
256 unsigned int nretries, max_retries;
257 int64_t wd_delay, wd_seq_delay;
258 u64 wd_end, wd_end2;
259
260 max_retries = clocksource_get_max_watchdog_retry();
261 for (nretries = 0; nretries <= max_retries; nretries++) {
262 local_irq_disable();
263 *wdnow = watchdog->read(watchdog);
264 *csnow = cs->read(cs);
265 wd_end = watchdog->read(watchdog);
266 wd_end2 = watchdog->read(watchdog);
267 local_irq_enable();
268
269 wd_delay = cycles_to_nsec_safe(cs: watchdog, start: *wdnow, end: wd_end);
270 if (wd_delay <= md + cs->uncertainty_margin) {
271 if (nretries > 1 && nretries >= max_retries) {
272 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
273 smp_processor_id(), watchdog->name, nretries);
274 }
275 return WD_READ_SUCCESS;
276 }
277
278 /*
279 * Now compute delay in consecutive watchdog read to see if
280 * there is too much external interferences that cause
281 * significant delay in reading both clocksource and watchdog.
282 *
283 * If consecutive WD read-back delay > md, report
284 * system busy, reinit the watchdog and skip the current
285 * watchdog test.
286 */
287 wd_seq_delay = cycles_to_nsec_safe(cs: watchdog, start: wd_end, end: wd_end2);
288 if (wd_seq_delay > md)
289 goto skip_test;
290 }
291
292 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",
293 smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name);
294 return WD_READ_UNSTABLE;
295
296skip_test:
297 pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
298 smp_processor_id(), watchdog->name, wd_seq_delay);
299 pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
300 cs->name, wd_delay);
301 return WD_READ_SKIP;
302}
303
304static u64 csnow_mid;
305static cpumask_t cpus_ahead;
306static cpumask_t cpus_behind;
307static cpumask_t cpus_chosen;
308
309static void clocksource_verify_choose_cpus(void)
310{
311 int cpu, i, n = verify_n_cpus;
312
313 if (n < 0 || n >= num_online_cpus()) {
314 /* Check all of the CPUs. */
315 cpumask_copy(dstp: &cpus_chosen, cpu_online_mask);
316 cpumask_clear_cpu(smp_processor_id(), dstp: &cpus_chosen);
317 return;
318 }
319
320 /* If no checking desired, or no other CPU to check, leave. */
321 cpumask_clear(dstp: &cpus_chosen);
322 if (n == 0 || num_online_cpus() <= 1)
323 return;
324
325 /* Make sure to select at least one CPU other than the current CPU. */
326 cpu = cpumask_any_but(cpu_online_mask, smp_processor_id());
327 if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
328 return;
329 cpumask_set_cpu(cpu, dstp: &cpus_chosen);
330
331 /* Force a sane value for the boot parameter. */
332 if (n > nr_cpu_ids)
333 n = nr_cpu_ids;
334
335 /*
336 * Randomly select the specified number of CPUs. If the same
337 * CPU is selected multiple times, that CPU is checked only once,
338 * and no replacement CPU is selected. This gracefully handles
339 * situations where verify_n_cpus is greater than the number of
340 * CPUs that are currently online.
341 */
342 for (i = 1; i < n; i++) {
343 cpu = cpumask_random(cpu_online_mask);
344 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
345 cpumask_set_cpu(cpu, dstp: &cpus_chosen);
346 }
347
348 /* Don't verify ourselves. */
349 cpumask_clear_cpu(smp_processor_id(), dstp: &cpus_chosen);
350}
351
352static void clocksource_verify_one_cpu(void *csin)
353{
354 struct clocksource *cs = (struct clocksource *)csin;
355
356 csnow_mid = cs->read(cs);
357}
358
359void clocksource_verify_percpu(struct clocksource *cs)
360{
361 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
362 u64 csnow_begin, csnow_end;
363 int cpu, testcpu;
364 s64 delta;
365
366 if (verify_n_cpus == 0)
367 return;
368 cpumask_clear(dstp: &cpus_ahead);
369 cpumask_clear(dstp: &cpus_behind);
370 cpus_read_lock();
371 migrate_disable();
372 clocksource_verify_choose_cpus();
373 if (cpumask_empty(srcp: &cpus_chosen)) {
374 migrate_enable();
375 cpus_read_unlock();
376 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
377 return;
378 }
379 testcpu = smp_processor_id();
380 pr_info("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n",
381 cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
382 preempt_disable();
383 for_each_cpu(cpu, &cpus_chosen) {
384 if (cpu == testcpu)
385 continue;
386 csnow_begin = cs->read(cs);
387 smp_call_function_single(cpuid: cpu, func: clocksource_verify_one_cpu, info: cs, wait: 1);
388 csnow_end = cs->read(cs);
389 delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
390 if (delta < 0)
391 cpumask_set_cpu(cpu, dstp: &cpus_behind);
392 delta = (csnow_end - csnow_mid) & cs->mask;
393 if (delta < 0)
394 cpumask_set_cpu(cpu, dstp: &cpus_ahead);
395 cs_nsec = cycles_to_nsec_safe(cs, start: csnow_begin, end: csnow_end);
396 if (cs_nsec > cs_nsec_max)
397 cs_nsec_max = cs_nsec;
398 if (cs_nsec < cs_nsec_min)
399 cs_nsec_min = cs_nsec;
400 }
401 preempt_enable();
402 migrate_enable();
403 cpus_read_unlock();
404 if (!cpumask_empty(srcp: &cpus_ahead))
405 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
406 cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
407 if (!cpumask_empty(srcp: &cpus_behind))
408 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n",
409 cpumask_pr_args(&cpus_behind), testcpu, cs->name);
410 pr_info(" CPU %d check durations %lldns - %lldns for clocksource %s.\n",
411 testcpu, cs_nsec_min, cs_nsec_max, cs->name);
412}
413EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
414
415static inline void clocksource_reset_watchdog(void)
416{
417 struct clocksource *cs;
418
419 list_for_each_entry(cs, &watchdog_list, wd_list)
420 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
421}
422
423
424static void clocksource_watchdog(struct timer_list *unused)
425{
426 int64_t wd_nsec, cs_nsec, interval;
427 u64 csnow, wdnow, cslast, wdlast;
428 int next_cpu, reset_pending;
429 struct clocksource *cs;
430 enum wd_read_status read_ret;
431 unsigned long extra_wait = 0;
432 u32 md;
433
434 spin_lock(lock: &watchdog_lock);
435 if (!watchdog_running)
436 goto out;
437
438 reset_pending = atomic_read(v: &watchdog_reset_pending);
439
440 list_for_each_entry(cs, &watchdog_list, wd_list) {
441
442 /* Clocksource already marked unstable? */
443 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
444 if (finished_booting)
445 schedule_work(work: &watchdog_work);
446 continue;
447 }
448
449 read_ret = cs_watchdog_read(cs, csnow: &csnow, wdnow: &wdnow);
450
451 if (read_ret == WD_READ_UNSTABLE) {
452 /* Clock readout unreliable, so give it up. */
453 __clocksource_unstable(cs);
454 continue;
455 }
456
457 /*
458 * When WD_READ_SKIP is returned, it means the system is likely
459 * under very heavy load, where the latency of reading
460 * watchdog/clocksource is very big, and affect the accuracy of
461 * watchdog check. So give system some space and suspend the
462 * watchdog check for 5 minutes.
463 */
464 if (read_ret == WD_READ_SKIP) {
465 /*
466 * As the watchdog timer will be suspended, and
467 * cs->last could keep unchanged for 5 minutes, reset
468 * the counters.
469 */
470 clocksource_reset_watchdog();
471 extra_wait = HZ * 300;
472 break;
473 }
474
475 /* Clocksource initialized ? */
476 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
477 atomic_read(v: &watchdog_reset_pending)) {
478 cs->flags |= CLOCK_SOURCE_WATCHDOG;
479 cs->wd_last = wdnow;
480 cs->cs_last = csnow;
481 continue;
482 }
483
484 wd_nsec = cycles_to_nsec_safe(cs: watchdog, start: cs->wd_last, end: wdnow);
485 cs_nsec = cycles_to_nsec_safe(cs, start: cs->cs_last, end: csnow);
486 wdlast = cs->wd_last; /* save these in case we print them */
487 cslast = cs->cs_last;
488 cs->cs_last = csnow;
489 cs->wd_last = wdnow;
490
491 if (atomic_read(v: &watchdog_reset_pending))
492 continue;
493
494 /*
495 * The processing of timer softirqs can get delayed (usually
496 * on account of ksoftirqd not getting to run in a timely
497 * manner), which causes the watchdog interval to stretch.
498 * Skew detection may fail for longer watchdog intervals
499 * on account of fixed margins being used.
500 * Some clocksources, e.g. acpi_pm, cannot tolerate
501 * watchdog intervals longer than a few seconds.
502 */
503 interval = max(cs_nsec, wd_nsec);
504 if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) {
505 if (system_state > SYSTEM_SCHEDULING &&
506 interval > 2 * watchdog_max_interval) {
507 watchdog_max_interval = interval;
508 pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n",
509 cs_nsec, wd_nsec);
510 }
511 watchdog_timer.expires = jiffies;
512 continue;
513 }
514
515 /* Check the deviation from the watchdog clocksource. */
516 md = cs->uncertainty_margin + watchdog->uncertainty_margin;
517 if (abs(cs_nsec - wd_nsec) > md) {
518 s64 cs_wd_msec;
519 s64 wd_msec;
520 u32 wd_rem;
521
522 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
523 smp_processor_id(), cs->name);
524 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
525 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
526 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
527 cs->name, cs_nsec, csnow, cslast, cs->mask);
528 cs_wd_msec = div_s64_rem(dividend: cs_nsec - wd_nsec, divisor: 1000 * 1000, remainder: &wd_rem);
529 wd_msec = div_s64_rem(dividend: wd_nsec, divisor: 1000 * 1000, remainder: &wd_rem);
530 pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n",
531 cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec);
532 if (curr_clocksource == cs)
533 pr_warn(" '%s' is current clocksource.\n", cs->name);
534 else if (curr_clocksource)
535 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
536 else
537 pr_warn(" No current clocksource.\n");
538 __clocksource_unstable(cs);
539 continue;
540 }
541
542 if (cs == curr_clocksource && cs->tick_stable)
543 cs->tick_stable(cs);
544
545 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
546 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
547 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
548 /* Mark it valid for high-res. */
549 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
550
551 /*
552 * clocksource_done_booting() will sort it if
553 * finished_booting is not set yet.
554 */
555 if (!finished_booting)
556 continue;
557
558 /*
559 * If this is not the current clocksource let
560 * the watchdog thread reselect it. Due to the
561 * change to high res this clocksource might
562 * be preferred now. If it is the current
563 * clocksource let the tick code know about
564 * that change.
565 */
566 if (cs != curr_clocksource) {
567 cs->flags |= CLOCK_SOURCE_RESELECT;
568 schedule_work(work: &watchdog_work);
569 } else {
570 tick_clock_notify();
571 }
572 }
573 }
574
575 /*
576 * We only clear the watchdog_reset_pending, when we did a
577 * full cycle through all clocksources.
578 */
579 if (reset_pending)
580 atomic_dec(v: &watchdog_reset_pending);
581
582 /*
583 * Cycle through CPUs to check if the CPUs stay synchronized
584 * to each other.
585 */
586 next_cpu = cpumask_next_wrap(raw_smp_processor_id(), cpu_online_mask);
587
588 /*
589 * Arm timer if not already pending: could race with concurrent
590 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
591 */
592 if (!timer_pending(timer: &watchdog_timer)) {
593 watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait;
594 add_timer_on(timer: &watchdog_timer, cpu: next_cpu);
595 }
596out:
597 spin_unlock(lock: &watchdog_lock);
598}
599
600static inline void clocksource_start_watchdog(void)
601{
602 if (watchdog_running || !watchdog || list_empty(head: &watchdog_list))
603 return;
604 timer_setup(&watchdog_timer, clocksource_watchdog, 0);
605 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
606 add_timer_on(timer: &watchdog_timer, cpu: cpumask_first(cpu_online_mask));
607 watchdog_running = 1;
608}
609
610static inline void clocksource_stop_watchdog(void)
611{
612 if (!watchdog_running || (watchdog && !list_empty(head: &watchdog_list)))
613 return;
614 timer_delete(timer: &watchdog_timer);
615 watchdog_running = 0;
616}
617
618static void clocksource_resume_watchdog(void)
619{
620 atomic_inc(v: &watchdog_reset_pending);
621}
622
623static void clocksource_enqueue_watchdog(struct clocksource *cs)
624{
625 INIT_LIST_HEAD(list: &cs->wd_list);
626
627 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
628 /* cs is a clocksource to be watched. */
629 list_add(new: &cs->wd_list, head: &watchdog_list);
630 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
631 } else {
632 /* cs is a watchdog. */
633 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
634 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
635 }
636}
637
638static void clocksource_select_watchdog(bool fallback)
639{
640 struct clocksource *cs, *old_wd;
641 unsigned long flags;
642
643 spin_lock_irqsave(&watchdog_lock, flags);
644 /* save current watchdog */
645 old_wd = watchdog;
646 if (fallback)
647 watchdog = NULL;
648
649 list_for_each_entry(cs, &clocksource_list, list) {
650 /* cs is a clocksource to be watched. */
651 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
652 continue;
653
654 /* Skip current if we were requested for a fallback. */
655 if (fallback && cs == old_wd)
656 continue;
657
658 /* Pick the best watchdog. */
659 if (!watchdog || cs->rating > watchdog->rating)
660 watchdog = cs;
661 }
662 /* If we failed to find a fallback restore the old one. */
663 if (!watchdog)
664 watchdog = old_wd;
665
666 /* If we changed the watchdog we need to reset cycles. */
667 if (watchdog != old_wd)
668 clocksource_reset_watchdog();
669
670 /* Check if the watchdog timer needs to be started. */
671 clocksource_start_watchdog();
672 spin_unlock_irqrestore(lock: &watchdog_lock, flags);
673}
674
675static void clocksource_dequeue_watchdog(struct clocksource *cs)
676{
677 if (cs != watchdog) {
678 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
679 /* cs is a watched clocksource. */
680 list_del_init(entry: &cs->wd_list);
681 /* Check if the watchdog timer needs to be stopped. */
682 clocksource_stop_watchdog();
683 }
684 }
685}
686
687static int __clocksource_watchdog_kthread(void)
688{
689 struct clocksource *cs, *tmp;
690 unsigned long flags;
691 int select = 0;
692
693 /* Do any required per-CPU skew verification. */
694 if (curr_clocksource &&
695 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
696 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
697 clocksource_verify_percpu(curr_clocksource);
698
699 spin_lock_irqsave(&watchdog_lock, flags);
700 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
701 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
702 list_del_init(entry: &cs->wd_list);
703 clocksource_change_rating(cs, rating: 0);
704 select = 1;
705 }
706 if (cs->flags & CLOCK_SOURCE_RESELECT) {
707 cs->flags &= ~CLOCK_SOURCE_RESELECT;
708 select = 1;
709 }
710 }
711 /* Check if the watchdog timer needs to be stopped. */
712 clocksource_stop_watchdog();
713 spin_unlock_irqrestore(lock: &watchdog_lock, flags);
714
715 return select;
716}
717
718static int clocksource_watchdog_kthread(void *data)
719{
720 mutex_lock(&clocksource_mutex);
721 if (__clocksource_watchdog_kthread())
722 clocksource_select();
723 mutex_unlock(lock: &clocksource_mutex);
724 return 0;
725}
726
727static bool clocksource_is_watchdog(struct clocksource *cs)
728{
729 return cs == watchdog;
730}
731
732#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
733
734static void clocksource_enqueue_watchdog(struct clocksource *cs)
735{
736 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
737 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
738}
739
740static void clocksource_select_watchdog(bool fallback) { }
741static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
742static inline void clocksource_resume_watchdog(void) { }
743static inline int __clocksource_watchdog_kthread(void) { return 0; }
744static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
745void clocksource_mark_unstable(struct clocksource *cs) { }
746
747static inline void clocksource_watchdog_lock(unsigned long *flags) { }
748static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
749
750#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
751
752static bool clocksource_is_suspend(struct clocksource *cs)
753{
754 return cs == suspend_clocksource;
755}
756
757static void __clocksource_suspend_select(struct clocksource *cs)
758{
759 /*
760 * Skip the clocksource which will be stopped in suspend state.
761 */
762 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
763 return;
764
765 /*
766 * The nonstop clocksource can be selected as the suspend clocksource to
767 * calculate the suspend time, so it should not supply suspend/resume
768 * interfaces to suspend the nonstop clocksource when system suspends.
769 */
770 if (cs->suspend || cs->resume) {
771 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
772 cs->name);
773 }
774
775 /* Pick the best rating. */
776 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
777 suspend_clocksource = cs;
778}
779
780/**
781 * clocksource_suspend_select - Select the best clocksource for suspend timing
782 * @fallback: if select a fallback clocksource
783 */
784static void clocksource_suspend_select(bool fallback)
785{
786 struct clocksource *cs, *old_suspend;
787
788 old_suspend = suspend_clocksource;
789 if (fallback)
790 suspend_clocksource = NULL;
791
792 list_for_each_entry(cs, &clocksource_list, list) {
793 /* Skip current if we were requested for a fallback. */
794 if (fallback && cs == old_suspend)
795 continue;
796
797 __clocksource_suspend_select(cs);
798 }
799}
800
801/**
802 * clocksource_start_suspend_timing - Start measuring the suspend timing
803 * @cs: current clocksource from timekeeping
804 * @start_cycles: current cycles from timekeeping
805 *
806 * This function will save the start cycle values of suspend timer to calculate
807 * the suspend time when resuming system.
808 *
809 * This function is called late in the suspend process from timekeeping_suspend(),
810 * that means processes are frozen, non-boot cpus and interrupts are disabled
811 * now. It is therefore possible to start the suspend timer without taking the
812 * clocksource mutex.
813 */
814void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
815{
816 if (!suspend_clocksource)
817 return;
818
819 /*
820 * If current clocksource is the suspend timer, we should use the
821 * tkr_mono.cycle_last value as suspend_start to avoid same reading
822 * from suspend timer.
823 */
824 if (clocksource_is_suspend(cs)) {
825 suspend_start = start_cycles;
826 return;
827 }
828
829 if (suspend_clocksource->enable &&
830 suspend_clocksource->enable(suspend_clocksource)) {
831 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
832 return;
833 }
834
835 suspend_start = suspend_clocksource->read(suspend_clocksource);
836}
837
838/**
839 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
840 * @cs: current clocksource from timekeeping
841 * @cycle_now: current cycles from timekeeping
842 *
843 * This function will calculate the suspend time from suspend timer.
844 *
845 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
846 *
847 * This function is called early in the resume process from timekeeping_resume(),
848 * that means there is only one cpu, no processes are running and the interrupts
849 * are disabled. It is therefore possible to stop the suspend timer without
850 * taking the clocksource mutex.
851 */
852u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
853{
854 u64 now, nsec = 0;
855
856 if (!suspend_clocksource)
857 return 0;
858
859 /*
860 * If current clocksource is the suspend timer, we should use the
861 * tkr_mono.cycle_last value from timekeeping as current cycle to
862 * avoid same reading from suspend timer.
863 */
864 if (clocksource_is_suspend(cs))
865 now = cycle_now;
866 else
867 now = suspend_clocksource->read(suspend_clocksource);
868
869 if (now > suspend_start)
870 nsec = cycles_to_nsec_safe(cs: suspend_clocksource, start: suspend_start, end: now);
871
872 /*
873 * Disable the suspend timer to save power if current clocksource is
874 * not the suspend timer.
875 */
876 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
877 suspend_clocksource->disable(suspend_clocksource);
878
879 return nsec;
880}
881
882/**
883 * clocksource_suspend - suspend the clocksource(s)
884 */
885void clocksource_suspend(void)
886{
887 struct clocksource *cs;
888
889 list_for_each_entry_reverse(cs, &clocksource_list, list)
890 if (cs->suspend)
891 cs->suspend(cs);
892}
893
894/**
895 * clocksource_resume - resume the clocksource(s)
896 */
897void clocksource_resume(void)
898{
899 struct clocksource *cs;
900
901 list_for_each_entry(cs, &clocksource_list, list)
902 if (cs->resume)
903 cs->resume(cs);
904
905 clocksource_resume_watchdog();
906}
907
908/**
909 * clocksource_touch_watchdog - Update watchdog
910 *
911 * Update the watchdog after exception contexts such as kgdb so as not
912 * to incorrectly trip the watchdog. This might fail when the kernel
913 * was stopped in code which holds watchdog_lock.
914 */
915void clocksource_touch_watchdog(void)
916{
917 clocksource_resume_watchdog();
918}
919
920/**
921 * clocksource_max_adjustment- Returns max adjustment amount
922 * @cs: Pointer to clocksource
923 *
924 */
925static u32 clocksource_max_adjustment(struct clocksource *cs)
926{
927 u64 ret;
928 /*
929 * We won't try to correct for more than 11% adjustments (110,000 ppm),
930 */
931 ret = (u64)cs->mult * 11;
932 do_div(ret,100);
933 return (u32)ret;
934}
935
936/**
937 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
938 * @mult: cycle to nanosecond multiplier
939 * @shift: cycle to nanosecond divisor (power of two)
940 * @maxadj: maximum adjustment value to mult (~11%)
941 * @mask: bitmask for two's complement subtraction of non 64 bit counters
942 * @max_cyc: maximum cycle value before potential overflow (does not include
943 * any safety margin)
944 *
945 * NOTE: This function includes a safety margin of 50%, in other words, we
946 * return half the number of nanoseconds the hardware counter can technically
947 * cover. This is done so that we can potentially detect problems caused by
948 * delayed timers or bad hardware, which might result in time intervals that
949 * are larger than what the math used can handle without overflows.
950 */
951u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
952{
953 u64 max_nsecs, max_cycles;
954
955 /*
956 * Calculate the maximum number of cycles that we can pass to the
957 * cyc2ns() function without overflowing a 64-bit result.
958 */
959 max_cycles = ULLONG_MAX;
960 do_div(max_cycles, mult+maxadj);
961
962 /*
963 * The actual maximum number of cycles we can defer the clocksource is
964 * determined by the minimum of max_cycles and mask.
965 * Note: Here we subtract the maxadj to make sure we don't sleep for
966 * too long if there's a large negative adjustment.
967 */
968 max_cycles = min(max_cycles, mask);
969 max_nsecs = clocksource_cyc2ns(cycles: max_cycles, mult: mult - maxadj, shift);
970
971 /* return the max_cycles value as well if requested */
972 if (max_cyc)
973 *max_cyc = max_cycles;
974
975 /* Return 50% of the actual maximum, so we can detect bad values */
976 max_nsecs >>= 1;
977
978 return max_nsecs;
979}
980
981/**
982 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
983 * @cs: Pointer to clocksource to be updated
984 *
985 */
986static inline void clocksource_update_max_deferment(struct clocksource *cs)
987{
988 cs->max_idle_ns = clocks_calc_max_nsecs(mult: cs->mult, shift: cs->shift,
989 maxadj: cs->maxadj, mask: cs->mask,
990 max_cyc: &cs->max_cycles);
991
992 /*
993 * Threshold for detecting negative motion in clocksource_delta().
994 *
995 * Allow for 0.875 of the counter width so that overly long idle
996 * sleeps, which go slightly over mask/2, do not trigger the
997 * negative motion detection.
998 */
999 cs->max_raw_delta = (cs->mask >> 1) + (cs->mask >> 2) + (cs->mask >> 3);
1000}
1001
1002static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
1003{
1004 struct clocksource *cs;
1005
1006 if (!finished_booting || list_empty(head: &clocksource_list))
1007 return NULL;
1008
1009 /*
1010 * We pick the clocksource with the highest rating. If oneshot
1011 * mode is active, we pick the highres valid clocksource with
1012 * the best rating.
1013 */
1014 list_for_each_entry(cs, &clocksource_list, list) {
1015 if (skipcur && cs == curr_clocksource)
1016 continue;
1017 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1018 continue;
1019 return cs;
1020 }
1021 return NULL;
1022}
1023
1024static void __clocksource_select(bool skipcur)
1025{
1026 bool oneshot = tick_oneshot_mode_active();
1027 struct clocksource *best, *cs;
1028
1029 /* Find the best suitable clocksource */
1030 best = clocksource_find_best(oneshot, skipcur);
1031 if (!best)
1032 return;
1033
1034 if (!strlen(override_name))
1035 goto found;
1036
1037 /* Check for the override clocksource. */
1038 list_for_each_entry(cs, &clocksource_list, list) {
1039 if (skipcur && cs == curr_clocksource)
1040 continue;
1041 if (strcmp(cs->name, override_name) != 0)
1042 continue;
1043 /*
1044 * Check to make sure we don't switch to a non-highres
1045 * capable clocksource if the tick code is in oneshot
1046 * mode (highres or nohz)
1047 */
1048 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
1049 /* Override clocksource cannot be used. */
1050 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
1051 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
1052 cs->name);
1053 override_name[0] = 0;
1054 } else {
1055 /*
1056 * The override cannot be currently verified.
1057 * Deferring to let the watchdog check.
1058 */
1059 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
1060 cs->name);
1061 }
1062 } else
1063 /* Override clocksource can be used. */
1064 best = cs;
1065 break;
1066 }
1067
1068found:
1069 if (curr_clocksource != best && !timekeeping_notify(clock: best)) {
1070 pr_info("Switched to clocksource %s\n", best->name);
1071 curr_clocksource = best;
1072 }
1073}
1074
1075/**
1076 * clocksource_select - Select the best clocksource available
1077 *
1078 * Private function. Must hold clocksource_mutex when called.
1079 *
1080 * Select the clocksource with the best rating, or the clocksource,
1081 * which is selected by userspace override.
1082 */
1083static void clocksource_select(void)
1084{
1085 __clocksource_select(skipcur: false);
1086}
1087
1088static void clocksource_select_fallback(void)
1089{
1090 __clocksource_select(skipcur: true);
1091}
1092
1093/*
1094 * clocksource_done_booting - Called near the end of core bootup
1095 *
1096 * Hack to avoid lots of clocksource churn at boot time.
1097 * We use fs_initcall because we want this to start before
1098 * device_initcall but after subsys_initcall.
1099 */
1100static int __init clocksource_done_booting(void)
1101{
1102 mutex_lock(&clocksource_mutex);
1103 curr_clocksource = clocksource_default_clock();
1104 finished_booting = 1;
1105 /*
1106 * Run the watchdog first to eliminate unstable clock sources
1107 */
1108 __clocksource_watchdog_kthread();
1109 clocksource_select();
1110 mutex_unlock(lock: &clocksource_mutex);
1111 return 0;
1112}
1113fs_initcall(clocksource_done_booting);
1114
1115/*
1116 * Enqueue the clocksource sorted by rating
1117 */
1118static void clocksource_enqueue(struct clocksource *cs)
1119{
1120 struct list_head *entry = &clocksource_list;
1121 struct clocksource *tmp;
1122
1123 list_for_each_entry(tmp, &clocksource_list, list) {
1124 /* Keep track of the place, where to insert */
1125 if (tmp->rating < cs->rating)
1126 break;
1127 entry = &tmp->list;
1128 }
1129 list_add(new: &cs->list, head: entry);
1130}
1131
1132/**
1133 * __clocksource_update_freq_scale - Used update clocksource with new freq
1134 * @cs: clocksource to be registered
1135 * @scale: Scale factor multiplied against freq to get clocksource hz
1136 * @freq: clocksource frequency (cycles per second) divided by scale
1137 *
1138 * This should only be called from the clocksource->enable() method.
1139 *
1140 * This *SHOULD NOT* be called directly! Please use the
1141 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
1142 * functions.
1143 */
1144void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1145{
1146 u64 sec;
1147
1148 /*
1149 * Default clocksources are *special* and self-define their mult/shift.
1150 * But, you're not special, so you should specify a freq value.
1151 */
1152 if (freq) {
1153 /*
1154 * Calc the maximum number of seconds which we can run before
1155 * wrapping around. For clocksources which have a mask > 32-bit
1156 * we need to limit the max sleep time to have a good
1157 * conversion precision. 10 minutes is still a reasonable
1158 * amount. That results in a shift value of 24 for a
1159 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1160 * ~ 0.06ppm granularity for NTP.
1161 */
1162 sec = cs->mask;
1163 do_div(sec, freq);
1164 do_div(sec, scale);
1165 if (!sec)
1166 sec = 1;
1167 else if (sec > 600 && cs->mask > UINT_MAX)
1168 sec = 600;
1169
1170 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1171 NSEC_PER_SEC / scale, sec * scale);
1172 }
1173
1174 /*
1175 * If the uncertainty margin is not specified, calculate it. If
1176 * both scale and freq are non-zero, calculate the clock period, but
1177 * bound below at 2*WATCHDOG_MAX_SKEW, that is, 500ppm by default.
1178 * However, if either of scale or freq is zero, be very conservative
1179 * and take the tens-of-milliseconds WATCHDOG_THRESHOLD value
1180 * for the uncertainty margin. Allow stupidly small uncertainty
1181 * margins to be specified by the caller for testing purposes,
1182 * but warn to discourage production use of this capability.
1183 *
1184 * Bottom line: The sum of the uncertainty margins of the
1185 * watchdog clocksource and the clocksource under test will be at
1186 * least 500ppm by default. For more information, please see the
1187 * comment preceding CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US above.
1188 */
1189 if (scale && freq && !cs->uncertainty_margin) {
1190 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
1191 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
1192 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
1193 } else if (!cs->uncertainty_margin) {
1194 cs->uncertainty_margin = WATCHDOG_THRESHOLD;
1195 }
1196 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
1197
1198 /*
1199 * Ensure clocksources that have large 'mult' values don't overflow
1200 * when adjusted.
1201 */
1202 cs->maxadj = clocksource_max_adjustment(cs);
1203 while (freq && ((cs->mult + cs->maxadj < cs->mult)
1204 || (cs->mult - cs->maxadj > cs->mult))) {
1205 cs->mult >>= 1;
1206 cs->shift--;
1207 cs->maxadj = clocksource_max_adjustment(cs);
1208 }
1209
1210 /*
1211 * Only warn for *special* clocksources that self-define
1212 * their mult/shift values and don't specify a freq.
1213 */
1214 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1215 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1216 cs->name);
1217
1218 clocksource_update_max_deferment(cs);
1219
1220 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1221 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1222}
1223EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
1224
1225/**
1226 * __clocksource_register_scale - Used to install new clocksources
1227 * @cs: clocksource to be registered
1228 * @scale: Scale factor multiplied against freq to get clocksource hz
1229 * @freq: clocksource frequency (cycles per second) divided by scale
1230 *
1231 * Returns -EBUSY if registration fails, zero otherwise.
1232 *
1233 * This *SHOULD NOT* be called directly! Please use the
1234 * clocksource_register_hz() or clocksource_register_khz helper functions.
1235 */
1236int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1237{
1238 unsigned long flags;
1239
1240 clocksource_arch_init(cs);
1241
1242 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1243 cs->id = CSID_GENERIC;
1244 if (cs->vdso_clock_mode < 0 ||
1245 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1246 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1247 cs->name, cs->vdso_clock_mode);
1248 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1249 }
1250
1251 /* Initialize mult/shift and max_idle_ns */
1252 __clocksource_update_freq_scale(cs, scale, freq);
1253
1254 /* Add clocksource to the clocksource list */
1255 mutex_lock(&clocksource_mutex);
1256
1257 clocksource_watchdog_lock(flags: &flags);
1258 clocksource_enqueue(cs);
1259 clocksource_enqueue_watchdog(cs);
1260 clocksource_watchdog_unlock(flags: &flags);
1261
1262 clocksource_select();
1263 clocksource_select_watchdog(fallback: false);
1264 __clocksource_suspend_select(cs);
1265 mutex_unlock(lock: &clocksource_mutex);
1266 return 0;
1267}
1268EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1269
1270/*
1271 * Unbind clocksource @cs. Called with clocksource_mutex held
1272 */
1273static int clocksource_unbind(struct clocksource *cs)
1274{
1275 unsigned long flags;
1276
1277 if (clocksource_is_watchdog(cs)) {
1278 /* Select and try to install a replacement watchdog. */
1279 clocksource_select_watchdog(fallback: true);
1280 if (clocksource_is_watchdog(cs))
1281 return -EBUSY;
1282 }
1283
1284 if (cs == curr_clocksource) {
1285 /* Select and try to install a replacement clock source */
1286 clocksource_select_fallback();
1287 if (curr_clocksource == cs)
1288 return -EBUSY;
1289 }
1290
1291 if (clocksource_is_suspend(cs)) {
1292 /*
1293 * Select and try to install a replacement suspend clocksource.
1294 * If no replacement suspend clocksource, we will just let the
1295 * clocksource go and have no suspend clocksource.
1296 */
1297 clocksource_suspend_select(fallback: true);
1298 }
1299
1300 clocksource_watchdog_lock(flags: &flags);
1301 clocksource_dequeue_watchdog(cs);
1302 list_del_init(entry: &cs->list);
1303 clocksource_watchdog_unlock(flags: &flags);
1304
1305 return 0;
1306}
1307
1308/**
1309 * clocksource_unregister - remove a registered clocksource
1310 * @cs: clocksource to be unregistered
1311 */
1312int clocksource_unregister(struct clocksource *cs)
1313{
1314 int ret = 0;
1315
1316 mutex_lock(&clocksource_mutex);
1317 if (!list_empty(head: &cs->list))
1318 ret = clocksource_unbind(cs);
1319 mutex_unlock(lock: &clocksource_mutex);
1320 return ret;
1321}
1322EXPORT_SYMBOL(clocksource_unregister);
1323
1324#ifdef CONFIG_SYSFS
1325/**
1326 * current_clocksource_show - sysfs interface for current clocksource
1327 * @dev: unused
1328 * @attr: unused
1329 * @buf: char buffer to be filled with clocksource list
1330 *
1331 * Provides sysfs interface for listing current clocksource.
1332 */
1333static ssize_t current_clocksource_show(struct device *dev,
1334 struct device_attribute *attr,
1335 char *buf)
1336{
1337 ssize_t count = 0;
1338
1339 mutex_lock(&clocksource_mutex);
1340 count = sysfs_emit(buf, fmt: "%s\n", curr_clocksource->name);
1341 mutex_unlock(lock: &clocksource_mutex);
1342
1343 return count;
1344}
1345
1346ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1347{
1348 size_t ret = cnt;
1349
1350 /* strings from sysfs write are not 0 terminated! */
1351 if (!cnt || cnt >= CS_NAME_LEN)
1352 return -EINVAL;
1353
1354 /* strip of \n: */
1355 if (buf[cnt-1] == '\n')
1356 cnt--;
1357 if (cnt > 0)
1358 memcpy(dst, buf, cnt);
1359 dst[cnt] = 0;
1360 return ret;
1361}
1362
1363/**
1364 * current_clocksource_store - interface for manually overriding clocksource
1365 * @dev: unused
1366 * @attr: unused
1367 * @buf: name of override clocksource
1368 * @count: length of buffer
1369 *
1370 * Takes input from sysfs interface for manually overriding the default
1371 * clocksource selection.
1372 */
1373static ssize_t current_clocksource_store(struct device *dev,
1374 struct device_attribute *attr,
1375 const char *buf, size_t count)
1376{
1377 ssize_t ret;
1378
1379 mutex_lock(&clocksource_mutex);
1380
1381 ret = sysfs_get_uname(buf, dst: override_name, cnt: count);
1382 if (ret >= 0)
1383 clocksource_select();
1384
1385 mutex_unlock(lock: &clocksource_mutex);
1386
1387 return ret;
1388}
1389static DEVICE_ATTR_RW(current_clocksource);
1390
1391/**
1392 * unbind_clocksource_store - interface for manually unbinding clocksource
1393 * @dev: unused
1394 * @attr: unused
1395 * @buf: unused
1396 * @count: length of buffer
1397 *
1398 * Takes input from sysfs interface for manually unbinding a clocksource.
1399 */
1400static ssize_t unbind_clocksource_store(struct device *dev,
1401 struct device_attribute *attr,
1402 const char *buf, size_t count)
1403{
1404 struct clocksource *cs;
1405 char name[CS_NAME_LEN];
1406 ssize_t ret;
1407
1408 ret = sysfs_get_uname(buf, dst: name, cnt: count);
1409 if (ret < 0)
1410 return ret;
1411
1412 ret = -ENODEV;
1413 mutex_lock(&clocksource_mutex);
1414 list_for_each_entry(cs, &clocksource_list, list) {
1415 if (strcmp(cs->name, name))
1416 continue;
1417 ret = clocksource_unbind(cs);
1418 break;
1419 }
1420 mutex_unlock(lock: &clocksource_mutex);
1421
1422 return ret ? ret : count;
1423}
1424static DEVICE_ATTR_WO(unbind_clocksource);
1425
1426/**
1427 * available_clocksource_show - sysfs interface for listing clocksource
1428 * @dev: unused
1429 * @attr: unused
1430 * @buf: char buffer to be filled with clocksource list
1431 *
1432 * Provides sysfs interface for listing registered clocksources
1433 */
1434static ssize_t available_clocksource_show(struct device *dev,
1435 struct device_attribute *attr,
1436 char *buf)
1437{
1438 struct clocksource *src;
1439 ssize_t count = 0;
1440
1441 mutex_lock(&clocksource_mutex);
1442 list_for_each_entry(src, &clocksource_list, list) {
1443 /*
1444 * Don't show non-HRES clocksource if the tick code is
1445 * in one shot mode (highres=on or nohz=on)
1446 */
1447 if (!tick_oneshot_mode_active() ||
1448 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1449 count += snprintf(buf: buf + count,
1450 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1451 fmt: "%s ", src->name);
1452 }
1453 mutex_unlock(lock: &clocksource_mutex);
1454
1455 count += snprintf(buf: buf + count,
1456 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), fmt: "\n");
1457
1458 return count;
1459}
1460static DEVICE_ATTR_RO(available_clocksource);
1461
1462static struct attribute *clocksource_attrs[] = {
1463 &dev_attr_current_clocksource.attr,
1464 &dev_attr_unbind_clocksource.attr,
1465 &dev_attr_available_clocksource.attr,
1466 NULL
1467};
1468ATTRIBUTE_GROUPS(clocksource);
1469
1470static const struct bus_type clocksource_subsys = {
1471 .name = "clocksource",
1472 .dev_name = "clocksource",
1473};
1474
1475static struct device device_clocksource = {
1476 .id = 0,
1477 .bus = &clocksource_subsys,
1478 .groups = clocksource_groups,
1479};
1480
1481static int __init init_clocksource_sysfs(void)
1482{
1483 int error = subsys_system_register(subsys: &clocksource_subsys, NULL);
1484
1485 if (!error)
1486 error = device_register(dev: &device_clocksource);
1487
1488 return error;
1489}
1490
1491device_initcall(init_clocksource_sysfs);
1492#endif /* CONFIG_SYSFS */
1493
1494/**
1495 * boot_override_clocksource - boot clock override
1496 * @str: override name
1497 *
1498 * Takes a clocksource= boot argument and uses it
1499 * as the clocksource override name.
1500 */
1501static int __init boot_override_clocksource(char* str)
1502{
1503 mutex_lock(&clocksource_mutex);
1504 if (str)
1505 strscpy(override_name, str);
1506 mutex_unlock(lock: &clocksource_mutex);
1507 return 1;
1508}
1509
1510__setup("clocksource=", boot_override_clocksource);
1511
1512/**
1513 * boot_override_clock - Compatibility layer for deprecated boot option
1514 * @str: override name
1515 *
1516 * DEPRECATED! Takes a clock= boot argument and uses it
1517 * as the clocksource override name
1518 */
1519static int __init boot_override_clock(char* str)
1520{
1521 if (!strcmp(str, "pmtmr")) {
1522 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1523 return boot_override_clocksource(str: "acpi_pm");
1524 }
1525 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1526 return boot_override_clocksource(str);
1527}
1528
1529__setup("clock=", boot_override_clock);
1530

source code of linux/kernel/time/clocksource.c