projects/linux·blob v6.13 · refs

1534 lines · 43.8 KiB

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 ([email protected])
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(end, start, cs->mask, cs->max_raw_delta);
28
29 if (likely(delta < cs->max_cycles))
30 return clocksource_cyc2ns(delta, cs->mult, cs->shift);
31
32 return mul_u64_u32_shr(delta, cs->mult, 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 unspecifed 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(&watchdog_lock, *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(&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(&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(&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(&cs->list) && list_empty(&cs->wd_list))
238 list_add(&cs->wd_list, &watchdog_list);
239 __clocksource_unstable(cs);
240 }
241 spin_unlock_irqrestore(&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 = 2 * 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(watchdog, *wdnow, 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(watchdog, wd_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) {
314 /* Check all of the CPUs. */
315 cpumask_copy(&cpus_chosen, cpu_online_mask);
316 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
317 return;
318 }
319
320 /* If no checking desired, or no other CPU to check, leave. */
321 cpumask_clear(&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_first(cpu_online_mask);
327 if (cpu == smp_processor_id())
328 cpu = cpumask_next(cpu, cpu_online_mask);
329 if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
330 return;
331 cpumask_set_cpu(cpu, &cpus_chosen);
332
333 /* Force a sane value for the boot parameter. */
334 if (n > nr_cpu_ids)
335 n = nr_cpu_ids;
336
337 /*
338 * Randomly select the specified number of CPUs. If the same
339 * CPU is selected multiple times, that CPU is checked only once,
340 * and no replacement CPU is selected. This gracefully handles
341 * situations where verify_n_cpus is greater than the number of
342 * CPUs that are currently online.
343 */
344 for (i = 1; i < n; i++) {
345 cpu = get_random_u32_below(nr_cpu_ids);
346 cpu = cpumask_next(cpu - 1, cpu_online_mask);
347 if (cpu >= nr_cpu_ids)
348 cpu = cpumask_first(cpu_online_mask);
349 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
350 cpumask_set_cpu(cpu, &cpus_chosen);
351 }
352
353 /* Don't verify ourselves. */
354 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
355}
356
357static void clocksource_verify_one_cpu(void *csin)
358{
359 struct clocksource *cs = (struct clocksource *)csin;
360
361 csnow_mid = cs->read(cs);
362}
363
364void clocksource_verify_percpu(struct clocksource *cs)
365{
366 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
367 u64 csnow_begin, csnow_end;
368 int cpu, testcpu;
369 s64 delta;
370
371 if (verify_n_cpus == 0)
372 return;
373 cpumask_clear(&cpus_ahead);
374 cpumask_clear(&cpus_behind);
375 cpus_read_lock();
376 preempt_disable();
377 clocksource_verify_choose_cpus();
378 if (cpumask_empty(&cpus_chosen)) {
379 preempt_enable();
380 cpus_read_unlock();
381 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
382 return;
383 }
384 testcpu = smp_processor_id();
385 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
386 for_each_cpu(cpu, &cpus_chosen) {
387 if (cpu == testcpu)
388 continue;
389 csnow_begin = cs->read(cs);
390 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
391 csnow_end = cs->read(cs);
392 delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
393 if (delta < 0)
394 cpumask_set_cpu(cpu, &cpus_behind);
395 delta = (csnow_end - csnow_mid) & cs->mask;
396 if (delta < 0)
397 cpumask_set_cpu(cpu, &cpus_ahead);
398 cs_nsec = cycles_to_nsec_safe(cs, csnow_begin, csnow_end);
399 if (cs_nsec > cs_nsec_max)
400 cs_nsec_max = cs_nsec;
401 if (cs_nsec < cs_nsec_min)
402 cs_nsec_min = cs_nsec;
403 }
404 preempt_enable();
405 cpus_read_unlock();
406 if (!cpumask_empty(&cpus_ahead))
407 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
408 cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
409 if (!cpumask_empty(&cpus_behind))
410 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n",
411 cpumask_pr_args(&cpus_behind), testcpu, cs->name);
412 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
413 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n",
414 testcpu, cs_nsec_min, cs_nsec_max, cs->name);
415}
416EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
417
418static inline void clocksource_reset_watchdog(void)
419{
420 struct clocksource *cs;
421
422 list_for_each_entry(cs, &watchdog_list, wd_list)
423 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
424}
425
426
427static void clocksource_watchdog(struct timer_list *unused)
428{
429 int64_t wd_nsec, cs_nsec, interval;
430 u64 csnow, wdnow, cslast, wdlast;
431 int next_cpu, reset_pending;
432 struct clocksource *cs;
433 enum wd_read_status read_ret;
434 unsigned long extra_wait = 0;
435 u32 md;
436
437 spin_lock(&watchdog_lock);
438 if (!watchdog_running)
439 goto out;
440
441 reset_pending = atomic_read(&watchdog_reset_pending);
442
443 list_for_each_entry(cs, &watchdog_list, wd_list) {
444
445 /* Clocksource already marked unstable? */
446 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
447 if (finished_booting)
448 schedule_work(&watchdog_work);
449 continue;
450 }
451
452 read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
453
454 if (read_ret == WD_READ_UNSTABLE) {
455 /* Clock readout unreliable, so give it up. */
456 __clocksource_unstable(cs);
457 continue;
458 }
459
460 /*
461 * When WD_READ_SKIP is returned, it means the system is likely
462 * under very heavy load, where the latency of reading
463 * watchdog/clocksource is very big, and affect the accuracy of
464 * watchdog check. So give system some space and suspend the
465 * watchdog check for 5 minutes.
466 */
467 if (read_ret == WD_READ_SKIP) {
468 /*
469 * As the watchdog timer will be suspended, and
470 * cs->last could keep unchanged for 5 minutes, reset
471 * the counters.
472 */
473 clocksource_reset_watchdog();
474 extra_wait = HZ * 300;
475 break;
476 }
477
478 /* Clocksource initialized ? */
479 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
480 atomic_read(&watchdog_reset_pending)) {
481 cs->flags |= CLOCK_SOURCE_WATCHDOG;
482 cs->wd_last = wdnow;
483 cs->cs_last = csnow;
484 continue;
485 }
486
487 wd_nsec = cycles_to_nsec_safe(watchdog, cs->wd_last, wdnow);
488 cs_nsec = cycles_to_nsec_safe(cs, cs->cs_last, csnow);
489 wdlast = cs->wd_last; /* save these in case we print them */
490 cslast = cs->cs_last;
491 cs->cs_last = csnow;
492 cs->wd_last = wdnow;
493
494 if (atomic_read(&watchdog_reset_pending))
495 continue;
496
497 /*
498 * The processing of timer softirqs can get delayed (usually
499 * on account of ksoftirqd not getting to run in a timely
500 * manner), which causes the watchdog interval to stretch.
501 * Skew detection may fail for longer watchdog intervals
502 * on account of fixed margins being used.
503 * Some clocksources, e.g. acpi_pm, cannot tolerate
504 * watchdog intervals longer than a few seconds.
505 */
506 interval = max(cs_nsec, wd_nsec);
507 if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) {
508 if (system_state > SYSTEM_SCHEDULING &&
509 interval > 2 * watchdog_max_interval) {
510 watchdog_max_interval = interval;
511 pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n",
512 cs_nsec, wd_nsec);
513 }
514 watchdog_timer.expires = jiffies;
515 continue;
516 }
517
518 /* Check the deviation from the watchdog clocksource. */
519 md = cs->uncertainty_margin + watchdog->uncertainty_margin;
520 if (abs(cs_nsec - wd_nsec) > md) {
521 s64 cs_wd_msec;
522 s64 wd_msec;
523 u32 wd_rem;
524
525 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
526 smp_processor_id(), cs->name);
527 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
528 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
529 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
530 cs->name, cs_nsec, csnow, cslast, cs->mask);
531 cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem);
532 wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem);
533 pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n",
534 cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec);
535 if (curr_clocksource == cs)
536 pr_warn(" '%s' is current clocksource.\n", cs->name);
537 else if (curr_clocksource)
538 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
539 else
540 pr_warn(" No current clocksource.\n");
541 __clocksource_unstable(cs);
542 continue;
543 }
544
545 if (cs == curr_clocksource && cs->tick_stable)
546 cs->tick_stable(cs);
547
548 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
549 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
550 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
551 /* Mark it valid for high-res. */
552 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
553
554 /*
555 * clocksource_done_booting() will sort it if
556 * finished_booting is not set yet.
557 */
558 if (!finished_booting)
559 continue;
560
561 /*
562 * If this is not the current clocksource let
563 * the watchdog thread reselect it. Due to the
564 * change to high res this clocksource might
565 * be preferred now. If it is the current
566 * clocksource let the tick code know about
567 * that change.
568 */
569 if (cs != curr_clocksource) {
570 cs->flags |= CLOCK_SOURCE_RESELECT;
571 schedule_work(&watchdog_work);
572 } else {
573 tick_clock_notify();
574 }
575 }
576 }
577
578 /*
579 * We only clear the watchdog_reset_pending, when we did a
580 * full cycle through all clocksources.
581 */
582 if (reset_pending)
583 atomic_dec(&watchdog_reset_pending);
584
585 /*
586 * Cycle through CPUs to check if the CPUs stay synchronized
587 * to each other.
588 */
589 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
590 if (next_cpu >= nr_cpu_ids)
591 next_cpu = cpumask_first(cpu_online_mask);
592
593 /*
594 * Arm timer if not already pending: could race with concurrent
595 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
596 */
597 if (!timer_pending(&watchdog_timer)) {
598 watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait;
599 add_timer_on(&watchdog_timer, next_cpu);
600 }
601out:
602 spin_unlock(&watchdog_lock);
603}
604
605static inline void clocksource_start_watchdog(void)
606{
607 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
608 return;
609 timer_setup(&watchdog_timer, clocksource_watchdog, 0);
610 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
611 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
612 watchdog_running = 1;
613}
614
615static inline void clocksource_stop_watchdog(void)
616{
617 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
618 return;
619 del_timer(&watchdog_timer);
620 watchdog_running = 0;
621}
622
623static void clocksource_resume_watchdog(void)
624{
625 atomic_inc(&watchdog_reset_pending);
626}
627
628static void clocksource_enqueue_watchdog(struct clocksource *cs)
629{
630 INIT_LIST_HEAD(&cs->wd_list);
631
632 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
633 /* cs is a clocksource to be watched. */
634 list_add(&cs->wd_list, &watchdog_list);
635 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
636 } else {
637 /* cs is a watchdog. */
638 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
639 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
640 }
641}
642
643static void clocksource_select_watchdog(bool fallback)
644{
645 struct clocksource *cs, *old_wd;
646 unsigned long flags;
647
648 spin_lock_irqsave(&watchdog_lock, flags);
649 /* save current watchdog */
650 old_wd = watchdog;
651 if (fallback)
652 watchdog = NULL;
653
654 list_for_each_entry(cs, &clocksource_list, list) {
655 /* cs is a clocksource to be watched. */
656 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
657 continue;
658
659 /* Skip current if we were requested for a fallback. */
660 if (fallback && cs == old_wd)
661 continue;
662
663 /* Pick the best watchdog. */
664 if (!watchdog || cs->rating > watchdog->rating)
665 watchdog = cs;
666 }
667 /* If we failed to find a fallback restore the old one. */
668 if (!watchdog)
669 watchdog = old_wd;
670
671 /* If we changed the watchdog we need to reset cycles. */
672 if (watchdog != old_wd)
673 clocksource_reset_watchdog();
674
675 /* Check if the watchdog timer needs to be started. */
676 clocksource_start_watchdog();
677 spin_unlock_irqrestore(&watchdog_lock, flags);
678}
679
680static void clocksource_dequeue_watchdog(struct clocksource *cs)
681{
682 if (cs != watchdog) {
683 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
684 /* cs is a watched clocksource. */
685 list_del_init(&cs->wd_list);
686 /* Check if the watchdog timer needs to be stopped. */
687 clocksource_stop_watchdog();
688 }
689 }
690}
691
692static int __clocksource_watchdog_kthread(void)
693{
694 struct clocksource *cs, *tmp;
695 unsigned long flags;
696 int select = 0;
697
698 /* Do any required per-CPU skew verification. */
699 if (curr_clocksource &&
700 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
701 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
702 clocksource_verify_percpu(curr_clocksource);
703
704 spin_lock_irqsave(&watchdog_lock, flags);
705 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
706 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
707 list_del_init(&cs->wd_list);
708 clocksource_change_rating(cs, 0);
709 select = 1;
710 }
711 if (cs->flags & CLOCK_SOURCE_RESELECT) {
712 cs->flags &= ~CLOCK_SOURCE_RESELECT;
713 select = 1;
714 }
715 }
716 /* Check if the watchdog timer needs to be stopped. */
717 clocksource_stop_watchdog();
718 spin_unlock_irqrestore(&watchdog_lock, flags);
719
720 return select;
721}
722
723static int clocksource_watchdog_kthread(void *data)
724{
725 mutex_lock(&clocksource_mutex);
726 if (__clocksource_watchdog_kthread())
727 clocksource_select();
728 mutex_unlock(&clocksource_mutex);
729 return 0;
730}
731
732static bool clocksource_is_watchdog(struct clocksource *cs)
733{
734 return cs == watchdog;
735}
736
737#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
738
739static void clocksource_enqueue_watchdog(struct clocksource *cs)
740{
741 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
742 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
743}
744
745static void clocksource_select_watchdog(bool fallback) { }
746static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
747static inline void clocksource_resume_watchdog(void) { }
748static inline int __clocksource_watchdog_kthread(void) { return 0; }
749static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
750void clocksource_mark_unstable(struct clocksource *cs) { }
751
752static inline void clocksource_watchdog_lock(unsigned long *flags) { }
753static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
754
755#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
756
757static bool clocksource_is_suspend(struct clocksource *cs)
758{
759 return cs == suspend_clocksource;
760}
761
762static void __clocksource_suspend_select(struct clocksource *cs)
763{
764 /*
765 * Skip the clocksource which will be stopped in suspend state.
766 */
767 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
768 return;
769
770 /*
771 * The nonstop clocksource can be selected as the suspend clocksource to
772 * calculate the suspend time, so it should not supply suspend/resume
773 * interfaces to suspend the nonstop clocksource when system suspends.
774 */
775 if (cs->suspend || cs->resume) {
776 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
777 cs->name);
778 }
779
780 /* Pick the best rating. */
781 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
782 suspend_clocksource = cs;
783}
784
785/**
786 * clocksource_suspend_select - Select the best clocksource for suspend timing
787 * @fallback: if select a fallback clocksource
788 */
789static void clocksource_suspend_select(bool fallback)
790{
791 struct clocksource *cs, *old_suspend;
792
793 old_suspend = suspend_clocksource;
794 if (fallback)
795 suspend_clocksource = NULL;
796
797 list_for_each_entry(cs, &clocksource_list, list) {
798 /* Skip current if we were requested for a fallback. */
799 if (fallback && cs == old_suspend)
800 continue;
801
802 __clocksource_suspend_select(cs);
803 }
804}
805
806/**
807 * clocksource_start_suspend_timing - Start measuring the suspend timing
808 * @cs: current clocksource from timekeeping
809 * @start_cycles: current cycles from timekeeping
810 *
811 * This function will save the start cycle values of suspend timer to calculate
812 * the suspend time when resuming system.
813 *
814 * This function is called late in the suspend process from timekeeping_suspend(),
815 * that means processes are frozen, non-boot cpus and interrupts are disabled
816 * now. It is therefore possible to start the suspend timer without taking the
817 * clocksource mutex.
818 */
819void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
820{
821 if (!suspend_clocksource)
822 return;
823
824 /*
825 * If current clocksource is the suspend timer, we should use the
826 * tkr_mono.cycle_last value as suspend_start to avoid same reading
827 * from suspend timer.
828 */
829 if (clocksource_is_suspend(cs)) {
830 suspend_start = start_cycles;
831 return;
832 }
833
834 if (suspend_clocksource->enable &&
835 suspend_clocksource->enable(suspend_clocksource)) {
836 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
837 return;
838 }
839
840 suspend_start = suspend_clocksource->read(suspend_clocksource);
841}
842
843/**
844 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
845 * @cs: current clocksource from timekeeping
846 * @cycle_now: current cycles from timekeeping
847 *
848 * This function will calculate the suspend time from suspend timer.
849 *
850 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
851 *
852 * This function is called early in the resume process from timekeeping_resume(),
853 * that means there is only one cpu, no processes are running and the interrupts
854 * are disabled. It is therefore possible to stop the suspend timer without
855 * taking the clocksource mutex.
856 */
857u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
858{
859 u64 now, nsec = 0;
860
861 if (!suspend_clocksource)
862 return 0;
863
864 /*
865 * If current clocksource is the suspend timer, we should use the
866 * tkr_mono.cycle_last value from timekeeping as current cycle to
867 * avoid same reading from suspend timer.
868 */
869 if (clocksource_is_suspend(cs))
870 now = cycle_now;
871 else
872 now = suspend_clocksource->read(suspend_clocksource);
873
874 if (now > suspend_start)
875 nsec = cycles_to_nsec_safe(suspend_clocksource, suspend_start, now);
876
877 /*
878 * Disable the suspend timer to save power if current clocksource is
879 * not the suspend timer.
880 */
881 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
882 suspend_clocksource->disable(suspend_clocksource);
883
884 return nsec;
885}
886
887/**
888 * clocksource_suspend - suspend the clocksource(s)
889 */
890void clocksource_suspend(void)
891{
892 struct clocksource *cs;
893
894 list_for_each_entry_reverse(cs, &clocksource_list, list)
895 if (cs->suspend)
896 cs->suspend(cs);
897}
898
899/**
900 * clocksource_resume - resume the clocksource(s)
901 */
902void clocksource_resume(void)
903{
904 struct clocksource *cs;
905
906 list_for_each_entry(cs, &clocksource_list, list)
907 if (cs->resume)
908 cs->resume(cs);
909
910 clocksource_resume_watchdog();
911}
912
913/**
914 * clocksource_touch_watchdog - Update watchdog
915 *
916 * Update the watchdog after exception contexts such as kgdb so as not
917 * to incorrectly trip the watchdog. This might fail when the kernel
918 * was stopped in code which holds watchdog_lock.
919 */
920void clocksource_touch_watchdog(void)
921{
922 clocksource_resume_watchdog();
923}
924
925/**
926 * clocksource_max_adjustment- Returns max adjustment amount
927 * @cs: Pointer to clocksource
928 *
929 */
930static u32 clocksource_max_adjustment(struct clocksource *cs)
931{
932 u64 ret;
933 /*
934 * We won't try to correct for more than 11% adjustments (110,000 ppm),
935 */
936 ret = (u64)cs->mult * 11;
937 do_div(ret,100);
938 return (u32)ret;
939}
940
941/**
942 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
943 * @mult: cycle to nanosecond multiplier
944 * @shift: cycle to nanosecond divisor (power of two)
945 * @maxadj: maximum adjustment value to mult (~11%)
946 * @mask: bitmask for two's complement subtraction of non 64 bit counters
947 * @max_cyc: maximum cycle value before potential overflow (does not include
948 * any safety margin)
949 *
950 * NOTE: This function includes a safety margin of 50%, in other words, we
951 * return half the number of nanoseconds the hardware counter can technically
952 * cover. This is done so that we can potentially detect problems caused by
953 * delayed timers or bad hardware, which might result in time intervals that
954 * are larger than what the math used can handle without overflows.
955 */
956u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
957{
958 u64 max_nsecs, max_cycles;
959
960 /*
961 * Calculate the maximum number of cycles that we can pass to the
962 * cyc2ns() function without overflowing a 64-bit result.
963 */
964 max_cycles = ULLONG_MAX;
965 do_div(max_cycles, mult+maxadj);
966
967 /*
968 * The actual maximum number of cycles we can defer the clocksource is
969 * determined by the minimum of max_cycles and mask.
970 * Note: Here we subtract the maxadj to make sure we don't sleep for
971 * too long if there's a large negative adjustment.
972 */
973 max_cycles = min(max_cycles, mask);
974 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
975
976 /* return the max_cycles value as well if requested */
977 if (max_cyc)
978 *max_cyc = max_cycles;
979
980 /* Return 50% of the actual maximum, so we can detect bad values */
981 max_nsecs >>= 1;
982
983 return max_nsecs;
984}
985
986/**
987 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
988 * @cs: Pointer to clocksource to be updated
989 *
990 */
991static inline void clocksource_update_max_deferment(struct clocksource *cs)
992{
993 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
994 cs->maxadj, cs->mask,
995 &cs->max_cycles);
996
997 /*
998 * Threshold for detecting negative motion in clocksource_delta().
999 *
1000 * Allow for 0.875 of the counter width so that overly long idle
1001 * sleeps, which go slightly over mask/2, do not trigger the
1002 * negative motion detection.
1003 */
1004 cs->max_raw_delta = (cs->mask >> 1) + (cs->mask >> 2) + (cs->mask >> 3);
1005}
1006
1007static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
1008{
1009 struct clocksource *cs;
1010
1011 if (!finished_booting || list_empty(&clocksource_list))
1012 return NULL;
1013
1014 /*
1015 * We pick the clocksource with the highest rating. If oneshot
1016 * mode is active, we pick the highres valid clocksource with
1017 * the best rating.
1018 */
1019 list_for_each_entry(cs, &clocksource_list, list) {
1020 if (skipcur && cs == curr_clocksource)
1021 continue;
1022 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1023 continue;
1024 return cs;
1025 }
1026 return NULL;
1027}
1028
1029static void __clocksource_select(bool skipcur)
1030{
1031 bool oneshot = tick_oneshot_mode_active();
1032 struct clocksource *best, *cs;
1033
1034 /* Find the best suitable clocksource */
1035 best = clocksource_find_best(oneshot, skipcur);
1036 if (!best)
1037 return;
1038
1039 if (!strlen(override_name))
1040 goto found;
1041
1042 /* Check for the override clocksource. */
1043 list_for_each_entry(cs, &clocksource_list, list) {
1044 if (skipcur && cs == curr_clocksource)
1045 continue;
1046 if (strcmp(cs->name, override_name) != 0)
1047 continue;
1048 /*
1049 * Check to make sure we don't switch to a non-highres
1050 * capable clocksource if the tick code is in oneshot
1051 * mode (highres or nohz)
1052 */
1053 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
1054 /* Override clocksource cannot be used. */
1055 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
1056 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
1057 cs->name);
1058 override_name[0] = 0;
1059 } else {
1060 /*
1061 * The override cannot be currently verified.
1062 * Deferring to let the watchdog check.
1063 */
1064 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
1065 cs->name);
1066 }
1067 } else
1068 /* Override clocksource can be used. */
1069 best = cs;
1070 break;
1071 }
1072
1073found:
1074 if (curr_clocksource != best && !timekeeping_notify(best)) {
1075 pr_info("Switched to clocksource %s\n", best->name);
1076 curr_clocksource = best;
1077 }
1078}
1079
1080/**
1081 * clocksource_select - Select the best clocksource available
1082 *
1083 * Private function. Must hold clocksource_mutex when called.
1084 *
1085 * Select the clocksource with the best rating, or the clocksource,
1086 * which is selected by userspace override.
1087 */
1088static void clocksource_select(void)
1089{
1090 __clocksource_select(false);
1091}
1092
1093static void clocksource_select_fallback(void)
1094{
1095 __clocksource_select(true);
1096}
1097
1098/*
1099 * clocksource_done_booting - Called near the end of core bootup
1100 *
1101 * Hack to avoid lots of clocksource churn at boot time.
1102 * We use fs_initcall because we want this to start before
1103 * device_initcall but after subsys_initcall.
1104 */
1105static int __init clocksource_done_booting(void)
1106{
1107 mutex_lock(&clocksource_mutex);
1108 curr_clocksource = clocksource_default_clock();
1109 finished_booting = 1;
1110 /*
1111 * Run the watchdog first to eliminate unstable clock sources
1112 */
1113 __clocksource_watchdog_kthread();
1114 clocksource_select();
1115 mutex_unlock(&clocksource_mutex);
1116 return 0;
1117}
1118fs_initcall(clocksource_done_booting);
1119
1120/*
1121 * Enqueue the clocksource sorted by rating
1122 */
1123static void clocksource_enqueue(struct clocksource *cs)
1124{
1125 struct list_head *entry = &clocksource_list;
1126 struct clocksource *tmp;
1127
1128 list_for_each_entry(tmp, &clocksource_list, list) {
1129 /* Keep track of the place, where to insert */
1130 if (tmp->rating < cs->rating)
1131 break;
1132 entry = &tmp->list;
1133 }
1134 list_add(&cs->list, entry);
1135}
1136
1137/**
1138 * __clocksource_update_freq_scale - Used update clocksource with new freq
1139 * @cs: clocksource to be registered
1140 * @scale: Scale factor multiplied against freq to get clocksource hz
1141 * @freq: clocksource frequency (cycles per second) divided by scale
1142 *
1143 * This should only be called from the clocksource->enable() method.
1144 *
1145 * This *SHOULD NOT* be called directly! Please use the
1146 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
1147 * functions.
1148 */
1149void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1150{
1151 u64 sec;
1152
1153 /*
1154 * Default clocksources are *special* and self-define their mult/shift.
1155 * But, you're not special, so you should specify a freq value.
1156 */
1157 if (freq) {
1158 /*
1159 * Calc the maximum number of seconds which we can run before
1160 * wrapping around. For clocksources which have a mask > 32-bit
1161 * we need to limit the max sleep time to have a good
1162 * conversion precision. 10 minutes is still a reasonable
1163 * amount. That results in a shift value of 24 for a
1164 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1165 * ~ 0.06ppm granularity for NTP.
1166 */
1167 sec = cs->mask;
1168 do_div(sec, freq);
1169 do_div(sec, scale);
1170 if (!sec)
1171 sec = 1;
1172 else if (sec > 600 && cs->mask > UINT_MAX)
1173 sec = 600;
1174
1175 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1176 NSEC_PER_SEC / scale, sec * scale);
1177 }
1178
1179 /*
1180 * If the uncertainty margin is not specified, calculate it. If
1181 * both scale and freq are non-zero, calculate the clock period, but
1182 * bound below at 2*WATCHDOG_MAX_SKEW, that is, 500ppm by default.
1183 * However, if either of scale or freq is zero, be very conservative
1184 * and take the tens-of-milliseconds WATCHDOG_THRESHOLD value
1185 * for the uncertainty margin. Allow stupidly small uncertainty
1186 * margins to be specified by the caller for testing purposes,
1187 * but warn to discourage production use of this capability.
1188 *
1189 * Bottom line: The sum of the uncertainty margins of the
1190 * watchdog clocksource and the clocksource under test will be at
1191 * least 500ppm by default. For more information, please see the
1192 * comment preceding CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US above.
1193 */
1194 if (scale && freq && !cs->uncertainty_margin) {
1195 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
1196 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
1197 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
1198 } else if (!cs->uncertainty_margin) {
1199 cs->uncertainty_margin = WATCHDOG_THRESHOLD;
1200 }
1201 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
1202
1203 /*
1204 * Ensure clocksources that have large 'mult' values don't overflow
1205 * when adjusted.
1206 */
1207 cs->maxadj = clocksource_max_adjustment(cs);
1208 while (freq && ((cs->mult + cs->maxadj < cs->mult)
1209 || (cs->mult - cs->maxadj > cs->mult))) {
1210 cs->mult >>= 1;
1211 cs->shift--;
1212 cs->maxadj = clocksource_max_adjustment(cs);
1213 }
1214
1215 /*
1216 * Only warn for *special* clocksources that self-define
1217 * their mult/shift values and don't specify a freq.
1218 */
1219 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1220 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1221 cs->name);
1222
1223 clocksource_update_max_deferment(cs);
1224
1225 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1226 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1227}
1228EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
1229
1230/**
1231 * __clocksource_register_scale - Used to install new clocksources
1232 * @cs: clocksource to be registered
1233 * @scale: Scale factor multiplied against freq to get clocksource hz
1234 * @freq: clocksource frequency (cycles per second) divided by scale
1235 *
1236 * Returns -EBUSY if registration fails, zero otherwise.
1237 *
1238 * This *SHOULD NOT* be called directly! Please use the
1239 * clocksource_register_hz() or clocksource_register_khz helper functions.
1240 */
1241int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1242{
1243 unsigned long flags;
1244
1245 clocksource_arch_init(cs);
1246
1247 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1248 cs->id = CSID_GENERIC;
1249 if (cs->vdso_clock_mode < 0 ||
1250 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1251 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1252 cs->name, cs->vdso_clock_mode);
1253 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1254 }
1255
1256 /* Initialize mult/shift and max_idle_ns */
1257 __clocksource_update_freq_scale(cs, scale, freq);
1258
1259 /* Add clocksource to the clocksource list */
1260 mutex_lock(&clocksource_mutex);
1261
1262 clocksource_watchdog_lock(&flags);
1263 clocksource_enqueue(cs);
1264 clocksource_enqueue_watchdog(cs);
1265 clocksource_watchdog_unlock(&flags);
1266
1267 clocksource_select();
1268 clocksource_select_watchdog(false);
1269 __clocksource_suspend_select(cs);
1270 mutex_unlock(&clocksource_mutex);
1271 return 0;
1272}
1273EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1274
1275/*
1276 * Unbind clocksource @cs. Called with clocksource_mutex held
1277 */
1278static int clocksource_unbind(struct clocksource *cs)
1279{
1280 unsigned long flags;
1281
1282 if (clocksource_is_watchdog(cs)) {
1283 /* Select and try to install a replacement watchdog. */
1284 clocksource_select_watchdog(true);
1285 if (clocksource_is_watchdog(cs))
1286 return -EBUSY;
1287 }
1288
1289 if (cs == curr_clocksource) {
1290 /* Select and try to install a replacement clock source */
1291 clocksource_select_fallback();
1292 if (curr_clocksource == cs)
1293 return -EBUSY;
1294 }
1295
1296 if (clocksource_is_suspend(cs)) {
1297 /*
1298 * Select and try to install a replacement suspend clocksource.
1299 * If no replacement suspend clocksource, we will just let the
1300 * clocksource go and have no suspend clocksource.
1301 */
1302 clocksource_suspend_select(true);
1303 }
1304
1305 clocksource_watchdog_lock(&flags);
1306 clocksource_dequeue_watchdog(cs);
1307 list_del_init(&cs->list);
1308 clocksource_watchdog_unlock(&flags);
1309
1310 return 0;
1311}
1312
1313/**
1314 * clocksource_unregister - remove a registered clocksource
1315 * @cs: clocksource to be unregistered
1316 */
1317int clocksource_unregister(struct clocksource *cs)
1318{
1319 int ret = 0;
1320
1321 mutex_lock(&clocksource_mutex);
1322 if (!list_empty(&cs->list))
1323 ret = clocksource_unbind(cs);
1324 mutex_unlock(&clocksource_mutex);
1325 return ret;
1326}
1327EXPORT_SYMBOL(clocksource_unregister);
1328
1329#ifdef CONFIG_SYSFS
1330/**
1331 * current_clocksource_show - sysfs interface for current clocksource
1332 * @dev: unused
1333 * @attr: unused
1334 * @buf: char buffer to be filled with clocksource list
1335 *
1336 * Provides sysfs interface for listing current clocksource.
1337 */
1338static ssize_t current_clocksource_show(struct device *dev,
1339 struct device_attribute *attr,
1340 char *buf)
1341{
1342 ssize_t count = 0;
1343
1344 mutex_lock(&clocksource_mutex);
1345 count = sysfs_emit(buf, "%s\n", curr_clocksource->name);
1346 mutex_unlock(&clocksource_mutex);
1347
1348 return count;
1349}
1350
1351ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1352{
1353 size_t ret = cnt;
1354
1355 /* strings from sysfs write are not 0 terminated! */
1356 if (!cnt || cnt >= CS_NAME_LEN)
1357 return -EINVAL;
1358
1359 /* strip of \n: */
1360 if (buf[cnt-1] == '\n')
1361 cnt--;
1362 if (cnt > 0)
1363 memcpy(dst, buf, cnt);
1364 dst[cnt] = 0;
1365 return ret;
1366}
1367
1368/**
1369 * current_clocksource_store - interface for manually overriding clocksource
1370 * @dev: unused
1371 * @attr: unused
1372 * @buf: name of override clocksource
1373 * @count: length of buffer
1374 *
1375 * Takes input from sysfs interface for manually overriding the default
1376 * clocksource selection.
1377 */
1378static ssize_t current_clocksource_store(struct device *dev,
1379 struct device_attribute *attr,
1380 const char *buf, size_t count)
1381{
1382 ssize_t ret;
1383
1384 mutex_lock(&clocksource_mutex);
1385
1386 ret = sysfs_get_uname(buf, override_name, count);
1387 if (ret >= 0)
1388 clocksource_select();
1389
1390 mutex_unlock(&clocksource_mutex);
1391
1392 return ret;
1393}
1394static DEVICE_ATTR_RW(current_clocksource);
1395
1396/**
1397 * unbind_clocksource_store - interface for manually unbinding clocksource
1398 * @dev: unused
1399 * @attr: unused
1400 * @buf: unused
1401 * @count: length of buffer
1402 *
1403 * Takes input from sysfs interface for manually unbinding a clocksource.
1404 */
1405static ssize_t unbind_clocksource_store(struct device *dev,
1406 struct device_attribute *attr,
1407 const char *buf, size_t count)
1408{
1409 struct clocksource *cs;
1410 char name[CS_NAME_LEN];
1411 ssize_t ret;
1412
1413 ret = sysfs_get_uname(buf, name, count);
1414 if (ret < 0)
1415 return ret;
1416
1417 ret = -ENODEV;
1418 mutex_lock(&clocksource_mutex);
1419 list_for_each_entry(cs, &clocksource_list, list) {
1420 if (strcmp(cs->name, name))
1421 continue;
1422 ret = clocksource_unbind(cs);
1423 break;
1424 }
1425 mutex_unlock(&clocksource_mutex);
1426
1427 return ret ? ret : count;
1428}
1429static DEVICE_ATTR_WO(unbind_clocksource);
1430
1431/**
1432 * available_clocksource_show - sysfs interface for listing clocksource
1433 * @dev: unused
1434 * @attr: unused
1435 * @buf: char buffer to be filled with clocksource list
1436 *
1437 * Provides sysfs interface for listing registered clocksources
1438 */
1439static ssize_t available_clocksource_show(struct device *dev,
1440 struct device_attribute *attr,
1441 char *buf)
1442{
1443 struct clocksource *src;
1444 ssize_t count = 0;
1445
1446 mutex_lock(&clocksource_mutex);
1447 list_for_each_entry(src, &clocksource_list, list) {
1448 /*
1449 * Don't show non-HRES clocksource if the tick code is
1450 * in one shot mode (highres=on or nohz=on)
1451 */
1452 if (!tick_oneshot_mode_active() ||
1453 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1454 count += snprintf(buf + count,
1455 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1456 "%s ", src->name);
1457 }
1458 mutex_unlock(&clocksource_mutex);
1459
1460 count += snprintf(buf + count,
1461 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1462
1463 return count;
1464}
1465static DEVICE_ATTR_RO(available_clocksource);
1466
1467static struct attribute *clocksource_attrs[] = {
1468 &dev_attr_current_clocksource.attr,
1469 &dev_attr_unbind_clocksource.attr,
1470 &dev_attr_available_clocksource.attr,
1471 NULL
1472};
1473ATTRIBUTE_GROUPS(clocksource);
1474
1475static const struct bus_type clocksource_subsys = {
1476 .name = "clocksource",
1477 .dev_name = "clocksource",
1478};
1479
1480static struct device device_clocksource = {
1481 .id = 0,
1482 .bus = &clocksource_subsys,
1483 .groups = clocksource_groups,
1484};
1485
1486static int __init init_clocksource_sysfs(void)
1487{
1488 int error = subsys_system_register(&clocksource_subsys, NULL);
1489
1490 if (!error)
1491 error = device_register(&device_clocksource);
1492
1493 return error;
1494}
1495
1496device_initcall(init_clocksource_sysfs);
1497#endif /* CONFIG_SYSFS */
1498
1499/**
1500 * boot_override_clocksource - boot clock override
1501 * @str: override name
1502 *
1503 * Takes a clocksource= boot argument and uses it
1504 * as the clocksource override name.
1505 */
1506static int __init boot_override_clocksource(char* str)
1507{
1508 mutex_lock(&clocksource_mutex);
1509 if (str)
1510 strscpy(override_name, str, sizeof(override_name));
1511 mutex_unlock(&clocksource_mutex);
1512 return 1;
1513}
1514
1515__setup("clocksource=", boot_override_clocksource);
1516
1517/**
1518 * boot_override_clock - Compatibility layer for deprecated boot option
1519 * @str: override name
1520 *
1521 * DEPRECATED! Takes a clock= boot argument and uses it
1522 * as the clocksource override name
1523 */
1524static int __init boot_override_clock(char* str)
1525{
1526 if (!strcmp(str, "pmtmr")) {
1527 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1528 return boot_override_clocksource("acpi_pm");
1529 }
1530 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1531 return boot_override_clocksource(str);
1532}
1533
1534__setup("clock=", boot_override_clock);