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1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * This file contains the functions which manage clocksource drivers.
4 *
5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
6 */
7
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9
10#include <linux/device.h>
11#include <linux/clocksource.h>
12#include <linux/init.h>
13#include <linux/module.h>
14#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
15#include <linux/tick.h>
16#include <linux/kthread.h>
17#include <linux/prandom.h>
18#include <linux/cpu.h>
19
20#include "tick-internal.h"
21#include "timekeeping_internal.h"
22
23/**
24 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
25 * @mult: pointer to mult variable
26 * @shift: pointer to shift variable
27 * @from: frequency to convert from
28 * @to: frequency to convert to
29 * @maxsec: guaranteed runtime conversion range in seconds
30 *
31 * The function evaluates the shift/mult pair for the scaled math
32 * operations of clocksources and clockevents.
33 *
34 * @to and @from are frequency values in HZ. For clock sources @to is
35 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
36 * event @to is the counter frequency and @from is NSEC_PER_SEC.
37 *
38 * The @maxsec conversion range argument controls the time frame in
39 * seconds which must be covered by the runtime conversion with the
40 * calculated mult and shift factors. This guarantees that no 64bit
41 * overflow happens when the input value of the conversion is
42 * multiplied with the calculated mult factor. Larger ranges may
43 * reduce the conversion accuracy by choosing smaller mult and shift
44 * factors.
45 */
46void
47clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
48{
49 u64 tmp;
50 u32 sft, sftacc= 32;
51
52 /*
53 * Calculate the shift factor which is limiting the conversion
54 * range:
55 */
56 tmp = ((u64)maxsec * from) >> 32;
57 while (tmp) {
58 tmp >>=1;
59 sftacc--;
60 }
61
62 /*
63 * Find the conversion shift/mult pair which has the best
64 * accuracy and fits the maxsec conversion range:
65 */
66 for (sft = 32; sft > 0; sft--) {
67 tmp = (u64) to << sft;
68 tmp += from / 2;
69 do_div(tmp, from);
70 if ((tmp >> sftacc) == 0)
71 break;
72 }
73 *mult = tmp;
74 *shift = sft;
75}
76EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
77
78/*[Clocksource internal variables]---------
79 * curr_clocksource:
80 * currently selected clocksource.
81 * suspend_clocksource:
82 * used to calculate the suspend time.
83 * clocksource_list:
84 * linked list with the registered clocksources
85 * clocksource_mutex:
86 * protects manipulations to curr_clocksource and the clocksource_list
87 * override_name:
88 * Name of the user-specified clocksource.
89 */
90static struct clocksource *curr_clocksource;
91static struct clocksource *suspend_clocksource;
92static LIST_HEAD(clocksource_list);
93static DEFINE_MUTEX(clocksource_mutex);
94static char override_name[CS_NAME_LEN];
95static int finished_booting;
96static u64 suspend_start;
97
98/*
99 * Threshold: 0.0312s, when doubled: 0.0625s.
100 * Also a default for cs->uncertainty_margin when registering clocks.
101 */
102#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)
103
104/*
105 * Maximum permissible delay between two readouts of the watchdog
106 * clocksource surrounding a read of the clocksource being validated.
107 * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as
108 * a lower bound for cs->uncertainty_margin values when registering clocks.
109 */
110#ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
111#define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
112#else
113#define MAX_SKEW_USEC 100
114#endif
115
116#define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
117
118#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
119static void clocksource_watchdog_work(struct work_struct *work);
120static void clocksource_select(void);
121
122static LIST_HEAD(watchdog_list);
123static struct clocksource *watchdog;
124static struct timer_list watchdog_timer;
125static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
126static DEFINE_SPINLOCK(watchdog_lock);
127static int watchdog_running;
128static atomic_t watchdog_reset_pending;
129
130static inline void clocksource_watchdog_lock(unsigned long *flags)
131{
132 spin_lock_irqsave(&watchdog_lock, *flags);
133}
134
135static inline void clocksource_watchdog_unlock(unsigned long *flags)
136{
137 spin_unlock_irqrestore(&watchdog_lock, *flags);
138}
139
140static int clocksource_watchdog_kthread(void *data);
141static void __clocksource_change_rating(struct clocksource *cs, int rating);
142
143/*
144 * Interval: 0.5sec.
145 */
146#define WATCHDOG_INTERVAL (HZ >> 1)
147
148static void clocksource_watchdog_work(struct work_struct *work)
149{
150 /*
151 * We cannot directly run clocksource_watchdog_kthread() here, because
152 * clocksource_select() calls timekeeping_notify() which uses
153 * stop_machine(). One cannot use stop_machine() from a workqueue() due
154 * lock inversions wrt CPU hotplug.
155 *
156 * Also, we only ever run this work once or twice during the lifetime
157 * of the kernel, so there is no point in creating a more permanent
158 * kthread for this.
159 *
160 * If kthread_run fails the next watchdog scan over the
161 * watchdog_list will find the unstable clock again.
162 */
163 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
164}
165
166static void __clocksource_unstable(struct clocksource *cs)
167{
168 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
169 cs->flags |= CLOCK_SOURCE_UNSTABLE;
170
171 /*
172 * If the clocksource is registered clocksource_watchdog_kthread() will
173 * re-rate and re-select.
174 */
175 if (list_empty(&cs->list)) {
176 cs->rating = 0;
177 return;
178 }
179
180 if (cs->mark_unstable)
181 cs->mark_unstable(cs);
182
183 /* kick clocksource_watchdog_kthread() */
184 if (finished_booting)
185 schedule_work(&watchdog_work);
186}
187
188/**
189 * clocksource_mark_unstable - mark clocksource unstable via watchdog
190 * @cs: clocksource to be marked unstable
191 *
192 * This function is called by the x86 TSC code to mark clocksources as unstable;
193 * it defers demotion and re-selection to a kthread.
194 */
195void clocksource_mark_unstable(struct clocksource *cs)
196{
197 unsigned long flags;
198
199 spin_lock_irqsave(&watchdog_lock, flags);
200 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
201 if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
202 list_add(&cs->wd_list, &watchdog_list);
203 __clocksource_unstable(cs);
204 }
205 spin_unlock_irqrestore(&watchdog_lock, flags);
206}
207
208ulong max_cswd_read_retries = 2;
209module_param(max_cswd_read_retries, ulong, 0644);
210EXPORT_SYMBOL_GPL(max_cswd_read_retries);
211static int verify_n_cpus = 8;
212module_param(verify_n_cpus, int, 0644);
213
214enum wd_read_status {
215 WD_READ_SUCCESS,
216 WD_READ_UNSTABLE,
217 WD_READ_SKIP
218};
219
220static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
221{
222 unsigned int nretries;
223 u64 wd_end, wd_end2, wd_delta;
224 int64_t wd_delay, wd_seq_delay;
225
226 for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) {
227 local_irq_disable();
228 *wdnow = watchdog->read(watchdog);
229 *csnow = cs->read(cs);
230 wd_end = watchdog->read(watchdog);
231 wd_end2 = watchdog->read(watchdog);
232 local_irq_enable();
233
234 wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
235 wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult,
236 watchdog->shift);
237 if (wd_delay <= WATCHDOG_MAX_SKEW) {
238 if (nretries > 1 || nretries >= max_cswd_read_retries) {
239 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
240 smp_processor_id(), watchdog->name, nretries);
241 }
242 return WD_READ_SUCCESS;
243 }
244
245 /*
246 * Now compute delay in consecutive watchdog read to see if
247 * there is too much external interferences that cause
248 * significant delay in reading both clocksource and watchdog.
249 *
250 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2,
251 * report system busy, reinit the watchdog and skip the current
252 * watchdog test.
253 */
254 wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask);
255 wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift);
256 if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
257 goto skip_test;
258 }
259
260 pr_warn("timekeeping watchdog on CPU%d: %s read-back delay of %lldns, attempt %d, marking unstable\n",
261 smp_processor_id(), watchdog->name, wd_delay, nretries);
262 return WD_READ_UNSTABLE;
263
264skip_test:
265 pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
266 smp_processor_id(), watchdog->name, wd_seq_delay);
267 pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
268 cs->name, wd_delay);
269 return WD_READ_SKIP;
270}
271
272static u64 csnow_mid;
273static cpumask_t cpus_ahead;
274static cpumask_t cpus_behind;
275static cpumask_t cpus_chosen;
276
277static void clocksource_verify_choose_cpus(void)
278{
279 int cpu, i, n = verify_n_cpus;
280
281 if (n < 0) {
282 /* Check all of the CPUs. */
283 cpumask_copy(&cpus_chosen, cpu_online_mask);
284 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
285 return;
286 }
287
288 /* If no checking desired, or no other CPU to check, leave. */
289 cpumask_clear(&cpus_chosen);
290 if (n == 0 || num_online_cpus() <= 1)
291 return;
292
293 /* Make sure to select at least one CPU other than the current CPU. */
294 cpu = cpumask_first(cpu_online_mask);
295 if (cpu == smp_processor_id())
296 cpu = cpumask_next(cpu, cpu_online_mask);
297 if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
298 return;
299 cpumask_set_cpu(cpu, &cpus_chosen);
300
301 /* Force a sane value for the boot parameter. */
302 if (n > nr_cpu_ids)
303 n = nr_cpu_ids;
304
305 /*
306 * Randomly select the specified number of CPUs. If the same
307 * CPU is selected multiple times, that CPU is checked only once,
308 * and no replacement CPU is selected. This gracefully handles
309 * situations where verify_n_cpus is greater than the number of
310 * CPUs that are currently online.
311 */
312 for (i = 1; i < n; i++) {
313 cpu = get_random_u32_below(nr_cpu_ids);
314 cpu = cpumask_next(cpu - 1, cpu_online_mask);
315 if (cpu >= nr_cpu_ids)
316 cpu = cpumask_first(cpu_online_mask);
317 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
318 cpumask_set_cpu(cpu, &cpus_chosen);
319 }
320
321 /* Don't verify ourselves. */
322 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
323}
324
325static void clocksource_verify_one_cpu(void *csin)
326{
327 struct clocksource *cs = (struct clocksource *)csin;
328
329 csnow_mid = cs->read(cs);
330}
331
332void clocksource_verify_percpu(struct clocksource *cs)
333{
334 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
335 u64 csnow_begin, csnow_end;
336 int cpu, testcpu;
337 s64 delta;
338
339 if (verify_n_cpus == 0)
340 return;
341 cpumask_clear(&cpus_ahead);
342 cpumask_clear(&cpus_behind);
343 cpus_read_lock();
344 preempt_disable();
345 clocksource_verify_choose_cpus();
346 if (cpumask_empty(&cpus_chosen)) {
347 preempt_enable();
348 cpus_read_unlock();
349 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
350 return;
351 }
352 testcpu = smp_processor_id();
353 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
354 for_each_cpu(cpu, &cpus_chosen) {
355 if (cpu == testcpu)
356 continue;
357 csnow_begin = cs->read(cs);
358 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
359 csnow_end = cs->read(cs);
360 delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
361 if (delta < 0)
362 cpumask_set_cpu(cpu, &cpus_behind);
363 delta = (csnow_end - csnow_mid) & cs->mask;
364 if (delta < 0)
365 cpumask_set_cpu(cpu, &cpus_ahead);
366 delta = clocksource_delta(csnow_end, csnow_begin, cs->mask);
367 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
368 if (cs_nsec > cs_nsec_max)
369 cs_nsec_max = cs_nsec;
370 if (cs_nsec < cs_nsec_min)
371 cs_nsec_min = cs_nsec;
372 }
373 preempt_enable();
374 cpus_read_unlock();
375 if (!cpumask_empty(&cpus_ahead))
376 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
377 cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
378 if (!cpumask_empty(&cpus_behind))
379 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n",
380 cpumask_pr_args(&cpus_behind), testcpu, cs->name);
381 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
382 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n",
383 testcpu, cs_nsec_min, cs_nsec_max, cs->name);
384}
385EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
386
387static void clocksource_watchdog(struct timer_list *unused)
388{
389 u64 csnow, wdnow, cslast, wdlast, delta;
390 int next_cpu, reset_pending;
391 int64_t wd_nsec, cs_nsec;
392 struct clocksource *cs;
393 enum wd_read_status read_ret;
394 u32 md;
395
396 spin_lock(&watchdog_lock);
397 if (!watchdog_running)
398 goto out;
399
400 reset_pending = atomic_read(&watchdog_reset_pending);
401
402 list_for_each_entry(cs, &watchdog_list, wd_list) {
403
404 /* Clocksource already marked unstable? */
405 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
406 if (finished_booting)
407 schedule_work(&watchdog_work);
408 continue;
409 }
410
411 read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
412
413 if (read_ret != WD_READ_SUCCESS) {
414 if (read_ret == WD_READ_UNSTABLE)
415 /* Clock readout unreliable, so give it up. */
416 __clocksource_unstable(cs);
417 continue;
418 }
419
420 /* Clocksource initialized ? */
421 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
422 atomic_read(&watchdog_reset_pending)) {
423 cs->flags |= CLOCK_SOURCE_WATCHDOG;
424 cs->wd_last = wdnow;
425 cs->cs_last = csnow;
426 continue;
427 }
428
429 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
430 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
431 watchdog->shift);
432
433 delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
434 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
435 wdlast = cs->wd_last; /* save these in case we print them */
436 cslast = cs->cs_last;
437 cs->cs_last = csnow;
438 cs->wd_last = wdnow;
439
440 if (atomic_read(&watchdog_reset_pending))
441 continue;
442
443 /* Check the deviation from the watchdog clocksource. */
444 md = cs->uncertainty_margin + watchdog->uncertainty_margin;
445 if (abs(cs_nsec - wd_nsec) > md) {
446 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
447 smp_processor_id(), cs->name);
448 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
449 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
450 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
451 cs->name, cs_nsec, csnow, cslast, cs->mask);
452 if (curr_clocksource == cs)
453 pr_warn(" '%s' is current clocksource.\n", cs->name);
454 else if (curr_clocksource)
455 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
456 else
457 pr_warn(" No current clocksource.\n");
458 __clocksource_unstable(cs);
459 continue;
460 }
461
462 if (cs == curr_clocksource && cs->tick_stable)
463 cs->tick_stable(cs);
464
465 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
466 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
467 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
468 /* Mark it valid for high-res. */
469 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
470
471 /*
472 * clocksource_done_booting() will sort it if
473 * finished_booting is not set yet.
474 */
475 if (!finished_booting)
476 continue;
477
478 /*
479 * If this is not the current clocksource let
480 * the watchdog thread reselect it. Due to the
481 * change to high res this clocksource might
482 * be preferred now. If it is the current
483 * clocksource let the tick code know about
484 * that change.
485 */
486 if (cs != curr_clocksource) {
487 cs->flags |= CLOCK_SOURCE_RESELECT;
488 schedule_work(&watchdog_work);
489 } else {
490 tick_clock_notify();
491 }
492 }
493 }
494
495 /*
496 * We only clear the watchdog_reset_pending, when we did a
497 * full cycle through all clocksources.
498 */
499 if (reset_pending)
500 atomic_dec(&watchdog_reset_pending);
501
502 /*
503 * Cycle through CPUs to check if the CPUs stay synchronized
504 * to each other.
505 */
506 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
507 if (next_cpu >= nr_cpu_ids)
508 next_cpu = cpumask_first(cpu_online_mask);
509
510 /*
511 * Arm timer if not already pending: could race with concurrent
512 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
513 */
514 if (!timer_pending(&watchdog_timer)) {
515 watchdog_timer.expires += WATCHDOG_INTERVAL;
516 add_timer_on(&watchdog_timer, next_cpu);
517 }
518out:
519 spin_unlock(&watchdog_lock);
520}
521
522static inline void clocksource_start_watchdog(void)
523{
524 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
525 return;
526 timer_setup(&watchdog_timer, clocksource_watchdog, 0);
527 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
528 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
529 watchdog_running = 1;
530}
531
532static inline void clocksource_stop_watchdog(void)
533{
534 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
535 return;
536 del_timer(&watchdog_timer);
537 watchdog_running = 0;
538}
539
540static inline void clocksource_reset_watchdog(void)
541{
542 struct clocksource *cs;
543
544 list_for_each_entry(cs, &watchdog_list, wd_list)
545 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
546}
547
548static void clocksource_resume_watchdog(void)
549{
550 atomic_inc(&watchdog_reset_pending);
551}
552
553static void clocksource_enqueue_watchdog(struct clocksource *cs)
554{
555 INIT_LIST_HEAD(&cs->wd_list);
556
557 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
558 /* cs is a clocksource to be watched. */
559 list_add(&cs->wd_list, &watchdog_list);
560 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
561 } else {
562 /* cs is a watchdog. */
563 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
564 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
565 }
566}
567
568static void clocksource_select_watchdog(bool fallback)
569{
570 struct clocksource *cs, *old_wd;
571 unsigned long flags;
572
573 spin_lock_irqsave(&watchdog_lock, flags);
574 /* save current watchdog */
575 old_wd = watchdog;
576 if (fallback)
577 watchdog = NULL;
578
579 list_for_each_entry(cs, &clocksource_list, list) {
580 /* cs is a clocksource to be watched. */
581 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
582 continue;
583
584 /* Skip current if we were requested for a fallback. */
585 if (fallback && cs == old_wd)
586 continue;
587
588 /* Pick the best watchdog. */
589 if (!watchdog || cs->rating > watchdog->rating)
590 watchdog = cs;
591 }
592 /* If we failed to find a fallback restore the old one. */
593 if (!watchdog)
594 watchdog = old_wd;
595
596 /* If we changed the watchdog we need to reset cycles. */
597 if (watchdog != old_wd)
598 clocksource_reset_watchdog();
599
600 /* Check if the watchdog timer needs to be started. */
601 clocksource_start_watchdog();
602 spin_unlock_irqrestore(&watchdog_lock, flags);
603}
604
605static void clocksource_dequeue_watchdog(struct clocksource *cs)
606{
607 if (cs != watchdog) {
608 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
609 /* cs is a watched clocksource. */
610 list_del_init(&cs->wd_list);
611 /* Check if the watchdog timer needs to be stopped. */
612 clocksource_stop_watchdog();
613 }
614 }
615}
616
617static int __clocksource_watchdog_kthread(void)
618{
619 struct clocksource *cs, *tmp;
620 unsigned long flags;
621 int select = 0;
622
623 /* Do any required per-CPU skew verification. */
624 if (curr_clocksource &&
625 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
626 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
627 clocksource_verify_percpu(curr_clocksource);
628
629 spin_lock_irqsave(&watchdog_lock, flags);
630 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
631 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
632 list_del_init(&cs->wd_list);
633 __clocksource_change_rating(cs, 0);
634 select = 1;
635 }
636 if (cs->flags & CLOCK_SOURCE_RESELECT) {
637 cs->flags &= ~CLOCK_SOURCE_RESELECT;
638 select = 1;
639 }
640 }
641 /* Check if the watchdog timer needs to be stopped. */
642 clocksource_stop_watchdog();
643 spin_unlock_irqrestore(&watchdog_lock, flags);
644
645 return select;
646}
647
648static int clocksource_watchdog_kthread(void *data)
649{
650 mutex_lock(&clocksource_mutex);
651 if (__clocksource_watchdog_kthread())
652 clocksource_select();
653 mutex_unlock(&clocksource_mutex);
654 return 0;
655}
656
657static bool clocksource_is_watchdog(struct clocksource *cs)
658{
659 return cs == watchdog;
660}
661
662#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
663
664static void clocksource_enqueue_watchdog(struct clocksource *cs)
665{
666 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
667 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
668}
669
670static void clocksource_select_watchdog(bool fallback) { }
671static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
672static inline void clocksource_resume_watchdog(void) { }
673static inline int __clocksource_watchdog_kthread(void) { return 0; }
674static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
675void clocksource_mark_unstable(struct clocksource *cs) { }
676
677static inline void clocksource_watchdog_lock(unsigned long *flags) { }
678static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
679
680#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
681
682static bool clocksource_is_suspend(struct clocksource *cs)
683{
684 return cs == suspend_clocksource;
685}
686
687static void __clocksource_suspend_select(struct clocksource *cs)
688{
689 /*
690 * Skip the clocksource which will be stopped in suspend state.
691 */
692 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
693 return;
694
695 /*
696 * The nonstop clocksource can be selected as the suspend clocksource to
697 * calculate the suspend time, so it should not supply suspend/resume
698 * interfaces to suspend the nonstop clocksource when system suspends.
699 */
700 if (cs->suspend || cs->resume) {
701 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
702 cs->name);
703 }
704
705 /* Pick the best rating. */
706 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
707 suspend_clocksource = cs;
708}
709
710/**
711 * clocksource_suspend_select - Select the best clocksource for suspend timing
712 * @fallback: if select a fallback clocksource
713 */
714static void clocksource_suspend_select(bool fallback)
715{
716 struct clocksource *cs, *old_suspend;
717
718 old_suspend = suspend_clocksource;
719 if (fallback)
720 suspend_clocksource = NULL;
721
722 list_for_each_entry(cs, &clocksource_list, list) {
723 /* Skip current if we were requested for a fallback. */
724 if (fallback && cs == old_suspend)
725 continue;
726
727 __clocksource_suspend_select(cs);
728 }
729}
730
731/**
732 * clocksource_start_suspend_timing - Start measuring the suspend timing
733 * @cs: current clocksource from timekeeping
734 * @start_cycles: current cycles from timekeeping
735 *
736 * This function will save the start cycle values of suspend timer to calculate
737 * the suspend time when resuming system.
738 *
739 * This function is called late in the suspend process from timekeeping_suspend(),
740 * that means processes are frozen, non-boot cpus and interrupts are disabled
741 * now. It is therefore possible to start the suspend timer without taking the
742 * clocksource mutex.
743 */
744void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
745{
746 if (!suspend_clocksource)
747 return;
748
749 /*
750 * If current clocksource is the suspend timer, we should use the
751 * tkr_mono.cycle_last value as suspend_start to avoid same reading
752 * from suspend timer.
753 */
754 if (clocksource_is_suspend(cs)) {
755 suspend_start = start_cycles;
756 return;
757 }
758
759 if (suspend_clocksource->enable &&
760 suspend_clocksource->enable(suspend_clocksource)) {
761 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
762 return;
763 }
764
765 suspend_start = suspend_clocksource->read(suspend_clocksource);
766}
767
768/**
769 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
770 * @cs: current clocksource from timekeeping
771 * @cycle_now: current cycles from timekeeping
772 *
773 * This function will calculate the suspend time from suspend timer.
774 *
775 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
776 *
777 * This function is called early in the resume process from timekeeping_resume(),
778 * that means there is only one cpu, no processes are running and the interrupts
779 * are disabled. It is therefore possible to stop the suspend timer without
780 * taking the clocksource mutex.
781 */
782u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
783{
784 u64 now, delta, nsec = 0;
785
786 if (!suspend_clocksource)
787 return 0;
788
789 /*
790 * If current clocksource is the suspend timer, we should use the
791 * tkr_mono.cycle_last value from timekeeping as current cycle to
792 * avoid same reading from suspend timer.
793 */
794 if (clocksource_is_suspend(cs))
795 now = cycle_now;
796 else
797 now = suspend_clocksource->read(suspend_clocksource);
798
799 if (now > suspend_start) {
800 delta = clocksource_delta(now, suspend_start,
801 suspend_clocksource->mask);
802 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
803 suspend_clocksource->shift);
804 }
805
806 /*
807 * Disable the suspend timer to save power if current clocksource is
808 * not the suspend timer.
809 */
810 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
811 suspend_clocksource->disable(suspend_clocksource);
812
813 return nsec;
814}
815
816/**
817 * clocksource_suspend - suspend the clocksource(s)
818 */
819void clocksource_suspend(void)
820{
821 struct clocksource *cs;
822
823 list_for_each_entry_reverse(cs, &clocksource_list, list)
824 if (cs->suspend)
825 cs->suspend(cs);
826}
827
828/**
829 * clocksource_resume - resume the clocksource(s)
830 */
831void clocksource_resume(void)
832{
833 struct clocksource *cs;
834
835 list_for_each_entry(cs, &clocksource_list, list)
836 if (cs->resume)
837 cs->resume(cs);
838
839 clocksource_resume_watchdog();
840}
841
842/**
843 * clocksource_touch_watchdog - Update watchdog
844 *
845 * Update the watchdog after exception contexts such as kgdb so as not
846 * to incorrectly trip the watchdog. This might fail when the kernel
847 * was stopped in code which holds watchdog_lock.
848 */
849void clocksource_touch_watchdog(void)
850{
851 clocksource_resume_watchdog();
852}
853
854/**
855 * clocksource_max_adjustment- Returns max adjustment amount
856 * @cs: Pointer to clocksource
857 *
858 */
859static u32 clocksource_max_adjustment(struct clocksource *cs)
860{
861 u64 ret;
862 /*
863 * We won't try to correct for more than 11% adjustments (110,000 ppm),
864 */
865 ret = (u64)cs->mult * 11;
866 do_div(ret,100);
867 return (u32)ret;
868}
869
870/**
871 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
872 * @mult: cycle to nanosecond multiplier
873 * @shift: cycle to nanosecond divisor (power of two)
874 * @maxadj: maximum adjustment value to mult (~11%)
875 * @mask: bitmask for two's complement subtraction of non 64 bit counters
876 * @max_cyc: maximum cycle value before potential overflow (does not include
877 * any safety margin)
878 *
879 * NOTE: This function includes a safety margin of 50%, in other words, we
880 * return half the number of nanoseconds the hardware counter can technically
881 * cover. This is done so that we can potentially detect problems caused by
882 * delayed timers or bad hardware, which might result in time intervals that
883 * are larger than what the math used can handle without overflows.
884 */
885u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
886{
887 u64 max_nsecs, max_cycles;
888
889 /*
890 * Calculate the maximum number of cycles that we can pass to the
891 * cyc2ns() function without overflowing a 64-bit result.
892 */
893 max_cycles = ULLONG_MAX;
894 do_div(max_cycles, mult+maxadj);
895
896 /*
897 * The actual maximum number of cycles we can defer the clocksource is
898 * determined by the minimum of max_cycles and mask.
899 * Note: Here we subtract the maxadj to make sure we don't sleep for
900 * too long if there's a large negative adjustment.
901 */
902 max_cycles = min(max_cycles, mask);
903 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
904
905 /* return the max_cycles value as well if requested */
906 if (max_cyc)
907 *max_cyc = max_cycles;
908
909 /* Return 50% of the actual maximum, so we can detect bad values */
910 max_nsecs >>= 1;
911
912 return max_nsecs;
913}
914
915/**
916 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
917 * @cs: Pointer to clocksource to be updated
918 *
919 */
920static inline void clocksource_update_max_deferment(struct clocksource *cs)
921{
922 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
923 cs->maxadj, cs->mask,
924 &cs->max_cycles);
925}
926
927static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
928{
929 struct clocksource *cs;
930
931 if (!finished_booting || list_empty(&clocksource_list))
932 return NULL;
933
934 /*
935 * We pick the clocksource with the highest rating. If oneshot
936 * mode is active, we pick the highres valid clocksource with
937 * the best rating.
938 */
939 list_for_each_entry(cs, &clocksource_list, list) {
940 if (skipcur && cs == curr_clocksource)
941 continue;
942 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
943 continue;
944 return cs;
945 }
946 return NULL;
947}
948
949static void __clocksource_select(bool skipcur)
950{
951 bool oneshot = tick_oneshot_mode_active();
952 struct clocksource *best, *cs;
953
954 /* Find the best suitable clocksource */
955 best = clocksource_find_best(oneshot, skipcur);
956 if (!best)
957 return;
958
959 if (!strlen(override_name))
960 goto found;
961
962 /* Check for the override clocksource. */
963 list_for_each_entry(cs, &clocksource_list, list) {
964 if (skipcur && cs == curr_clocksource)
965 continue;
966 if (strcmp(cs->name, override_name) != 0)
967 continue;
968 /*
969 * Check to make sure we don't switch to a non-highres
970 * capable clocksource if the tick code is in oneshot
971 * mode (highres or nohz)
972 */
973 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
974 /* Override clocksource cannot be used. */
975 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
976 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
977 cs->name);
978 override_name[0] = 0;
979 } else {
980 /*
981 * The override cannot be currently verified.
982 * Deferring to let the watchdog check.
983 */
984 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
985 cs->name);
986 }
987 } else
988 /* Override clocksource can be used. */
989 best = cs;
990 break;
991 }
992
993found:
994 if (curr_clocksource != best && !timekeeping_notify(best)) {
995 pr_info("Switched to clocksource %s\n", best->name);
996 curr_clocksource = best;
997 }
998}
999
1000/**
1001 * clocksource_select - Select the best clocksource available
1002 *
1003 * Private function. Must hold clocksource_mutex when called.
1004 *
1005 * Select the clocksource with the best rating, or the clocksource,
1006 * which is selected by userspace override.
1007 */
1008static void clocksource_select(void)
1009{
1010 __clocksource_select(false);
1011}
1012
1013static void clocksource_select_fallback(void)
1014{
1015 __clocksource_select(true);
1016}
1017
1018/*
1019 * clocksource_done_booting - Called near the end of core bootup
1020 *
1021 * Hack to avoid lots of clocksource churn at boot time.
1022 * We use fs_initcall because we want this to start before
1023 * device_initcall but after subsys_initcall.
1024 */
1025static int __init clocksource_done_booting(void)
1026{
1027 mutex_lock(&clocksource_mutex);
1028 curr_clocksource = clocksource_default_clock();
1029 finished_booting = 1;
1030 /*
1031 * Run the watchdog first to eliminate unstable clock sources
1032 */
1033 __clocksource_watchdog_kthread();
1034 clocksource_select();
1035 mutex_unlock(&clocksource_mutex);
1036 return 0;
1037}
1038fs_initcall(clocksource_done_booting);
1039
1040/*
1041 * Enqueue the clocksource sorted by rating
1042 */
1043static void clocksource_enqueue(struct clocksource *cs)
1044{
1045 struct list_head *entry = &clocksource_list;
1046 struct clocksource *tmp;
1047
1048 list_for_each_entry(tmp, &clocksource_list, list) {
1049 /* Keep track of the place, where to insert */
1050 if (tmp->rating < cs->rating)
1051 break;
1052 entry = &tmp->list;
1053 }
1054 list_add(&cs->list, entry);
1055}
1056
1057/**
1058 * __clocksource_update_freq_scale - Used update clocksource with new freq
1059 * @cs: clocksource to be registered
1060 * @scale: Scale factor multiplied against freq to get clocksource hz
1061 * @freq: clocksource frequency (cycles per second) divided by scale
1062 *
1063 * This should only be called from the clocksource->enable() method.
1064 *
1065 * This *SHOULD NOT* be called directly! Please use the
1066 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
1067 * functions.
1068 */
1069void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1070{
1071 u64 sec;
1072
1073 /*
1074 * Default clocksources are *special* and self-define their mult/shift.
1075 * But, you're not special, so you should specify a freq value.
1076 */
1077 if (freq) {
1078 /*
1079 * Calc the maximum number of seconds which we can run before
1080 * wrapping around. For clocksources which have a mask > 32-bit
1081 * we need to limit the max sleep time to have a good
1082 * conversion precision. 10 minutes is still a reasonable
1083 * amount. That results in a shift value of 24 for a
1084 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1085 * ~ 0.06ppm granularity for NTP.
1086 */
1087 sec = cs->mask;
1088 do_div(sec, freq);
1089 do_div(sec, scale);
1090 if (!sec)
1091 sec = 1;
1092 else if (sec > 600 && cs->mask > UINT_MAX)
1093 sec = 600;
1094
1095 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1096 NSEC_PER_SEC / scale, sec * scale);
1097 }
1098
1099 /*
1100 * If the uncertainty margin is not specified, calculate it.
1101 * If both scale and freq are non-zero, calculate the clock
1102 * period, but bound below at 2*WATCHDOG_MAX_SKEW. However,
1103 * if either of scale or freq is zero, be very conservative and
1104 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the
1105 * uncertainty margin. Allow stupidly small uncertainty margins
1106 * to be specified by the caller for testing purposes, but warn
1107 * to discourage production use of this capability.
1108 */
1109 if (scale && freq && !cs->uncertainty_margin) {
1110 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
1111 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
1112 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
1113 } else if (!cs->uncertainty_margin) {
1114 cs->uncertainty_margin = WATCHDOG_THRESHOLD;
1115 }
1116 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
1117
1118 /*
1119 * Ensure clocksources that have large 'mult' values don't overflow
1120 * when adjusted.
1121 */
1122 cs->maxadj = clocksource_max_adjustment(cs);
1123 while (freq && ((cs->mult + cs->maxadj < cs->mult)
1124 || (cs->mult - cs->maxadj > cs->mult))) {
1125 cs->mult >>= 1;
1126 cs->shift--;
1127 cs->maxadj = clocksource_max_adjustment(cs);
1128 }
1129
1130 /*
1131 * Only warn for *special* clocksources that self-define
1132 * their mult/shift values and don't specify a freq.
1133 */
1134 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1135 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1136 cs->name);
1137
1138 clocksource_update_max_deferment(cs);
1139
1140 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1141 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1142}
1143EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
1144
1145/**
1146 * __clocksource_register_scale - Used to install new clocksources
1147 * @cs: clocksource to be registered
1148 * @scale: Scale factor multiplied against freq to get clocksource hz
1149 * @freq: clocksource frequency (cycles per second) divided by scale
1150 *
1151 * Returns -EBUSY if registration fails, zero otherwise.
1152 *
1153 * This *SHOULD NOT* be called directly! Please use the
1154 * clocksource_register_hz() or clocksource_register_khz helper functions.
1155 */
1156int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1157{
1158 unsigned long flags;
1159
1160 clocksource_arch_init(cs);
1161
1162 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1163 cs->id = CSID_GENERIC;
1164 if (cs->vdso_clock_mode < 0 ||
1165 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1166 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1167 cs->name, cs->vdso_clock_mode);
1168 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1169 }
1170
1171 /* Initialize mult/shift and max_idle_ns */
1172 __clocksource_update_freq_scale(cs, scale, freq);
1173
1174 /* Add clocksource to the clocksource list */
1175 mutex_lock(&clocksource_mutex);
1176
1177 clocksource_watchdog_lock(&flags);
1178 clocksource_enqueue(cs);
1179 clocksource_enqueue_watchdog(cs);
1180 clocksource_watchdog_unlock(&flags);
1181
1182 clocksource_select();
1183 clocksource_select_watchdog(false);
1184 __clocksource_suspend_select(cs);
1185 mutex_unlock(&clocksource_mutex);
1186 return 0;
1187}
1188EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1189
1190static void __clocksource_change_rating(struct clocksource *cs, int rating)
1191{
1192 list_del(&cs->list);
1193 cs->rating = rating;
1194 clocksource_enqueue(cs);
1195}
1196
1197/**
1198 * clocksource_change_rating - Change the rating of a registered clocksource
1199 * @cs: clocksource to be changed
1200 * @rating: new rating
1201 */
1202void clocksource_change_rating(struct clocksource *cs, int rating)
1203{
1204 unsigned long flags;
1205
1206 mutex_lock(&clocksource_mutex);
1207 clocksource_watchdog_lock(&flags);
1208 __clocksource_change_rating(cs, rating);
1209 clocksource_watchdog_unlock(&flags);
1210
1211 clocksource_select();
1212 clocksource_select_watchdog(false);
1213 clocksource_suspend_select(false);
1214 mutex_unlock(&clocksource_mutex);
1215}
1216EXPORT_SYMBOL(clocksource_change_rating);
1217
1218/*
1219 * Unbind clocksource @cs. Called with clocksource_mutex held
1220 */
1221static int clocksource_unbind(struct clocksource *cs)
1222{
1223 unsigned long flags;
1224
1225 if (clocksource_is_watchdog(cs)) {
1226 /* Select and try to install a replacement watchdog. */
1227 clocksource_select_watchdog(true);
1228 if (clocksource_is_watchdog(cs))
1229 return -EBUSY;
1230 }
1231
1232 if (cs == curr_clocksource) {
1233 /* Select and try to install a replacement clock source */
1234 clocksource_select_fallback();
1235 if (curr_clocksource == cs)
1236 return -EBUSY;
1237 }
1238
1239 if (clocksource_is_suspend(cs)) {
1240 /*
1241 * Select and try to install a replacement suspend clocksource.
1242 * If no replacement suspend clocksource, we will just let the
1243 * clocksource go and have no suspend clocksource.
1244 */
1245 clocksource_suspend_select(true);
1246 }
1247
1248 clocksource_watchdog_lock(&flags);
1249 clocksource_dequeue_watchdog(cs);
1250 list_del_init(&cs->list);
1251 clocksource_watchdog_unlock(&flags);
1252
1253 return 0;
1254}
1255
1256/**
1257 * clocksource_unregister - remove a registered clocksource
1258 * @cs: clocksource to be unregistered
1259 */
1260int clocksource_unregister(struct clocksource *cs)
1261{
1262 int ret = 0;
1263
1264 mutex_lock(&clocksource_mutex);
1265 if (!list_empty(&cs->list))
1266 ret = clocksource_unbind(cs);
1267 mutex_unlock(&clocksource_mutex);
1268 return ret;
1269}
1270EXPORT_SYMBOL(clocksource_unregister);
1271
1272#ifdef CONFIG_SYSFS
1273/**
1274 * current_clocksource_show - sysfs interface for current clocksource
1275 * @dev: unused
1276 * @attr: unused
1277 * @buf: char buffer to be filled with clocksource list
1278 *
1279 * Provides sysfs interface for listing current clocksource.
1280 */
1281static ssize_t current_clocksource_show(struct device *dev,
1282 struct device_attribute *attr,
1283 char *buf)
1284{
1285 ssize_t count = 0;
1286
1287 mutex_lock(&clocksource_mutex);
1288 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
1289 mutex_unlock(&clocksource_mutex);
1290
1291 return count;
1292}
1293
1294ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1295{
1296 size_t ret = cnt;
1297
1298 /* strings from sysfs write are not 0 terminated! */
1299 if (!cnt || cnt >= CS_NAME_LEN)
1300 return -EINVAL;
1301
1302 /* strip of \n: */
1303 if (buf[cnt-1] == '\n')
1304 cnt--;
1305 if (cnt > 0)
1306 memcpy(dst, buf, cnt);
1307 dst[cnt] = 0;
1308 return ret;
1309}
1310
1311/**
1312 * current_clocksource_store - interface for manually overriding clocksource
1313 * @dev: unused
1314 * @attr: unused
1315 * @buf: name of override clocksource
1316 * @count: length of buffer
1317 *
1318 * Takes input from sysfs interface for manually overriding the default
1319 * clocksource selection.
1320 */
1321static ssize_t current_clocksource_store(struct device *dev,
1322 struct device_attribute *attr,
1323 const char *buf, size_t count)
1324{
1325 ssize_t ret;
1326
1327 mutex_lock(&clocksource_mutex);
1328
1329 ret = sysfs_get_uname(buf, override_name, count);
1330 if (ret >= 0)
1331 clocksource_select();
1332
1333 mutex_unlock(&clocksource_mutex);
1334
1335 return ret;
1336}
1337static DEVICE_ATTR_RW(current_clocksource);
1338
1339/**
1340 * unbind_clocksource_store - interface for manually unbinding clocksource
1341 * @dev: unused
1342 * @attr: unused
1343 * @buf: unused
1344 * @count: length of buffer
1345 *
1346 * Takes input from sysfs interface for manually unbinding a clocksource.
1347 */
1348static ssize_t unbind_clocksource_store(struct device *dev,
1349 struct device_attribute *attr,
1350 const char *buf, size_t count)
1351{
1352 struct clocksource *cs;
1353 char name[CS_NAME_LEN];
1354 ssize_t ret;
1355
1356 ret = sysfs_get_uname(buf, name, count);
1357 if (ret < 0)
1358 return ret;
1359
1360 ret = -ENODEV;
1361 mutex_lock(&clocksource_mutex);
1362 list_for_each_entry(cs, &clocksource_list, list) {
1363 if (strcmp(cs->name, name))
1364 continue;
1365 ret = clocksource_unbind(cs);
1366 break;
1367 }
1368 mutex_unlock(&clocksource_mutex);
1369
1370 return ret ? ret : count;
1371}
1372static DEVICE_ATTR_WO(unbind_clocksource);
1373
1374/**
1375 * available_clocksource_show - sysfs interface for listing clocksource
1376 * @dev: unused
1377 * @attr: unused
1378 * @buf: char buffer to be filled with clocksource list
1379 *
1380 * Provides sysfs interface for listing registered clocksources
1381 */
1382static ssize_t available_clocksource_show(struct device *dev,
1383 struct device_attribute *attr,
1384 char *buf)
1385{
1386 struct clocksource *src;
1387 ssize_t count = 0;
1388
1389 mutex_lock(&clocksource_mutex);
1390 list_for_each_entry(src, &clocksource_list, list) {
1391 /*
1392 * Don't show non-HRES clocksource if the tick code is
1393 * in one shot mode (highres=on or nohz=on)
1394 */
1395 if (!tick_oneshot_mode_active() ||
1396 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1397 count += snprintf(buf + count,
1398 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1399 "%s ", src->name);
1400 }
1401 mutex_unlock(&clocksource_mutex);
1402
1403 count += snprintf(buf + count,
1404 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1405
1406 return count;
1407}
1408static DEVICE_ATTR_RO(available_clocksource);
1409
1410static struct attribute *clocksource_attrs[] = {
1411 &dev_attr_current_clocksource.attr,
1412 &dev_attr_unbind_clocksource.attr,
1413 &dev_attr_available_clocksource.attr,
1414 NULL
1415};
1416ATTRIBUTE_GROUPS(clocksource);
1417
1418static struct bus_type clocksource_subsys = {
1419 .name = "clocksource",
1420 .dev_name = "clocksource",
1421};
1422
1423static struct device device_clocksource = {
1424 .id = 0,
1425 .bus = &clocksource_subsys,
1426 .groups = clocksource_groups,
1427};
1428
1429static int __init init_clocksource_sysfs(void)
1430{
1431 int error = subsys_system_register(&clocksource_subsys, NULL);
1432
1433 if (!error)
1434 error = device_register(&device_clocksource);
1435
1436 return error;
1437}
1438
1439device_initcall(init_clocksource_sysfs);
1440#endif /* CONFIG_SYSFS */
1441
1442/**
1443 * boot_override_clocksource - boot clock override
1444 * @str: override name
1445 *
1446 * Takes a clocksource= boot argument and uses it
1447 * as the clocksource override name.
1448 */
1449static int __init boot_override_clocksource(char* str)
1450{
1451 mutex_lock(&clocksource_mutex);
1452 if (str)
1453 strlcpy(override_name, str, sizeof(override_name));
1454 mutex_unlock(&clocksource_mutex);
1455 return 1;
1456}
1457
1458__setup("clocksource=", boot_override_clocksource);
1459
1460/**
1461 * boot_override_clock - Compatibility layer for deprecated boot option
1462 * @str: override name
1463 *
1464 * DEPRECATED! Takes a clock= boot argument and uses it
1465 * as the clocksource override name
1466 */
1467static int __init boot_override_clock(char* str)
1468{
1469 if (!strcmp(str, "pmtmr")) {
1470 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1471 return boot_override_clocksource("acpi_pm");
1472 }
1473 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1474 return boot_override_clocksource(str);
1475}
1476
1477__setup("clock=", boot_override_clock);
1/*
2 * linux/kernel/time/clocksource.c
3 *
4 * This file contains the functions which manage clocksource drivers.
5 *
6 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
17 *
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
21 *
22 * TODO WishList:
23 * o Allow clocksource drivers to be unregistered
24 */
25
26#include <linux/device.h>
27#include <linux/clocksource.h>
28#include <linux/init.h>
29#include <linux/module.h>
30#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
31#include <linux/tick.h>
32#include <linux/kthread.h>
33
34void timecounter_init(struct timecounter *tc,
35 const struct cyclecounter *cc,
36 u64 start_tstamp)
37{
38 tc->cc = cc;
39 tc->cycle_last = cc->read(cc);
40 tc->nsec = start_tstamp;
41}
42EXPORT_SYMBOL_GPL(timecounter_init);
43
44/**
45 * timecounter_read_delta - get nanoseconds since last call of this function
46 * @tc: Pointer to time counter
47 *
48 * When the underlying cycle counter runs over, this will be handled
49 * correctly as long as it does not run over more than once between
50 * calls.
51 *
52 * The first call to this function for a new time counter initializes
53 * the time tracking and returns an undefined result.
54 */
55static u64 timecounter_read_delta(struct timecounter *tc)
56{
57 cycle_t cycle_now, cycle_delta;
58 u64 ns_offset;
59
60 /* read cycle counter: */
61 cycle_now = tc->cc->read(tc->cc);
62
63 /* calculate the delta since the last timecounter_read_delta(): */
64 cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
65
66 /* convert to nanoseconds: */
67 ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta);
68
69 /* update time stamp of timecounter_read_delta() call: */
70 tc->cycle_last = cycle_now;
71
72 return ns_offset;
73}
74
75u64 timecounter_read(struct timecounter *tc)
76{
77 u64 nsec;
78
79 /* increment time by nanoseconds since last call */
80 nsec = timecounter_read_delta(tc);
81 nsec += tc->nsec;
82 tc->nsec = nsec;
83
84 return nsec;
85}
86EXPORT_SYMBOL_GPL(timecounter_read);
87
88u64 timecounter_cyc2time(struct timecounter *tc,
89 cycle_t cycle_tstamp)
90{
91 u64 cycle_delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
92 u64 nsec;
93
94 /*
95 * Instead of always treating cycle_tstamp as more recent
96 * than tc->cycle_last, detect when it is too far in the
97 * future and treat it as old time stamp instead.
98 */
99 if (cycle_delta > tc->cc->mask / 2) {
100 cycle_delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
101 nsec = tc->nsec - cyclecounter_cyc2ns(tc->cc, cycle_delta);
102 } else {
103 nsec = cyclecounter_cyc2ns(tc->cc, cycle_delta) + tc->nsec;
104 }
105
106 return nsec;
107}
108EXPORT_SYMBOL_GPL(timecounter_cyc2time);
109
110/**
111 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
112 * @mult: pointer to mult variable
113 * @shift: pointer to shift variable
114 * @from: frequency to convert from
115 * @to: frequency to convert to
116 * @maxsec: guaranteed runtime conversion range in seconds
117 *
118 * The function evaluates the shift/mult pair for the scaled math
119 * operations of clocksources and clockevents.
120 *
121 * @to and @from are frequency values in HZ. For clock sources @to is
122 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
123 * event @to is the counter frequency and @from is NSEC_PER_SEC.
124 *
125 * The @maxsec conversion range argument controls the time frame in
126 * seconds which must be covered by the runtime conversion with the
127 * calculated mult and shift factors. This guarantees that no 64bit
128 * overflow happens when the input value of the conversion is
129 * multiplied with the calculated mult factor. Larger ranges may
130 * reduce the conversion accuracy by chosing smaller mult and shift
131 * factors.
132 */
133void
134clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
135{
136 u64 tmp;
137 u32 sft, sftacc= 32;
138
139 /*
140 * Calculate the shift factor which is limiting the conversion
141 * range:
142 */
143 tmp = ((u64)maxsec * from) >> 32;
144 while (tmp) {
145 tmp >>=1;
146 sftacc--;
147 }
148
149 /*
150 * Find the conversion shift/mult pair which has the best
151 * accuracy and fits the maxsec conversion range:
152 */
153 for (sft = 32; sft > 0; sft--) {
154 tmp = (u64) to << sft;
155 tmp += from / 2;
156 do_div(tmp, from);
157 if ((tmp >> sftacc) == 0)
158 break;
159 }
160 *mult = tmp;
161 *shift = sft;
162}
163
164/*[Clocksource internal variables]---------
165 * curr_clocksource:
166 * currently selected clocksource.
167 * clocksource_list:
168 * linked list with the registered clocksources
169 * clocksource_mutex:
170 * protects manipulations to curr_clocksource and the clocksource_list
171 * override_name:
172 * Name of the user-specified clocksource.
173 */
174static struct clocksource *curr_clocksource;
175static LIST_HEAD(clocksource_list);
176static DEFINE_MUTEX(clocksource_mutex);
177static char override_name[32];
178static int finished_booting;
179
180#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
181static void clocksource_watchdog_work(struct work_struct *work);
182
183static LIST_HEAD(watchdog_list);
184static struct clocksource *watchdog;
185static struct timer_list watchdog_timer;
186static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
187static DEFINE_SPINLOCK(watchdog_lock);
188static int watchdog_running;
189static atomic_t watchdog_reset_pending;
190
191static int clocksource_watchdog_kthread(void *data);
192static void __clocksource_change_rating(struct clocksource *cs, int rating);
193
194/*
195 * Interval: 0.5sec Threshold: 0.0625s
196 */
197#define WATCHDOG_INTERVAL (HZ >> 1)
198#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
199
200static void clocksource_watchdog_work(struct work_struct *work)
201{
202 /*
203 * If kthread_run fails the next watchdog scan over the
204 * watchdog_list will find the unstable clock again.
205 */
206 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
207}
208
209static void __clocksource_unstable(struct clocksource *cs)
210{
211 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
212 cs->flags |= CLOCK_SOURCE_UNSTABLE;
213 if (finished_booting)
214 schedule_work(&watchdog_work);
215}
216
217static void clocksource_unstable(struct clocksource *cs, int64_t delta)
218{
219 printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
220 cs->name, delta);
221 __clocksource_unstable(cs);
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 instead of clocksource_change_rating from
229 * cpu hotplug code to avoid a deadlock between the clocksource mutex
230 * and the cpu hotplug mutex. It defers the update of the clocksource
231 * to the watchdog thread.
232 */
233void clocksource_mark_unstable(struct clocksource *cs)
234{
235 unsigned long flags;
236
237 spin_lock_irqsave(&watchdog_lock, flags);
238 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
239 if (list_empty(&cs->wd_list))
240 list_add(&cs->wd_list, &watchdog_list);
241 __clocksource_unstable(cs);
242 }
243 spin_unlock_irqrestore(&watchdog_lock, flags);
244}
245
246static void clocksource_watchdog(unsigned long data)
247{
248 struct clocksource *cs;
249 cycle_t csnow, wdnow;
250 int64_t wd_nsec, cs_nsec;
251 int next_cpu, reset_pending;
252
253 spin_lock(&watchdog_lock);
254 if (!watchdog_running)
255 goto out;
256
257 reset_pending = atomic_read(&watchdog_reset_pending);
258
259 list_for_each_entry(cs, &watchdog_list, wd_list) {
260
261 /* Clocksource already marked unstable? */
262 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
263 if (finished_booting)
264 schedule_work(&watchdog_work);
265 continue;
266 }
267
268 local_irq_disable();
269 csnow = cs->read(cs);
270 wdnow = watchdog->read(watchdog);
271 local_irq_enable();
272
273 /* Clocksource initialized ? */
274 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
275 atomic_read(&watchdog_reset_pending)) {
276 cs->flags |= CLOCK_SOURCE_WATCHDOG;
277 cs->wd_last = wdnow;
278 cs->cs_last = csnow;
279 continue;
280 }
281
282 wd_nsec = clocksource_cyc2ns((wdnow - cs->wd_last) & watchdog->mask,
283 watchdog->mult, watchdog->shift);
284
285 cs_nsec = clocksource_cyc2ns((csnow - cs->cs_last) &
286 cs->mask, cs->mult, cs->shift);
287 cs->cs_last = csnow;
288 cs->wd_last = wdnow;
289
290 if (atomic_read(&watchdog_reset_pending))
291 continue;
292
293 /* Check the deviation from the watchdog clocksource. */
294 if ((abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD)) {
295 clocksource_unstable(cs, cs_nsec - wd_nsec);
296 continue;
297 }
298
299 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
300 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
301 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
302 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
303 /*
304 * We just marked the clocksource as highres-capable,
305 * notify the rest of the system as well so that we
306 * transition into high-res mode:
307 */
308 tick_clock_notify();
309 }
310 }
311
312 /*
313 * We only clear the watchdog_reset_pending, when we did a
314 * full cycle through all clocksources.
315 */
316 if (reset_pending)
317 atomic_dec(&watchdog_reset_pending);
318
319 /*
320 * Cycle through CPUs to check if the CPUs stay synchronized
321 * to each other.
322 */
323 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
324 if (next_cpu >= nr_cpu_ids)
325 next_cpu = cpumask_first(cpu_online_mask);
326 watchdog_timer.expires += WATCHDOG_INTERVAL;
327 add_timer_on(&watchdog_timer, next_cpu);
328out:
329 spin_unlock(&watchdog_lock);
330}
331
332static inline void clocksource_start_watchdog(void)
333{
334 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
335 return;
336 init_timer(&watchdog_timer);
337 watchdog_timer.function = clocksource_watchdog;
338 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
339 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
340 watchdog_running = 1;
341}
342
343static inline void clocksource_stop_watchdog(void)
344{
345 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
346 return;
347 del_timer(&watchdog_timer);
348 watchdog_running = 0;
349}
350
351static inline void clocksource_reset_watchdog(void)
352{
353 struct clocksource *cs;
354
355 list_for_each_entry(cs, &watchdog_list, wd_list)
356 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
357}
358
359static void clocksource_resume_watchdog(void)
360{
361 atomic_inc(&watchdog_reset_pending);
362}
363
364static void clocksource_enqueue_watchdog(struct clocksource *cs)
365{
366 unsigned long flags;
367
368 spin_lock_irqsave(&watchdog_lock, flags);
369 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
370 /* cs is a clocksource to be watched. */
371 list_add(&cs->wd_list, &watchdog_list);
372 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
373 } else {
374 /* cs is a watchdog. */
375 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
376 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
377 /* Pick the best watchdog. */
378 if (!watchdog || cs->rating > watchdog->rating) {
379 watchdog = cs;
380 /* Reset watchdog cycles */
381 clocksource_reset_watchdog();
382 }
383 }
384 /* Check if the watchdog timer needs to be started. */
385 clocksource_start_watchdog();
386 spin_unlock_irqrestore(&watchdog_lock, flags);
387}
388
389static void clocksource_dequeue_watchdog(struct clocksource *cs)
390{
391 struct clocksource *tmp;
392 unsigned long flags;
393
394 spin_lock_irqsave(&watchdog_lock, flags);
395 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
396 /* cs is a watched clocksource. */
397 list_del_init(&cs->wd_list);
398 } else if (cs == watchdog) {
399 /* Reset watchdog cycles */
400 clocksource_reset_watchdog();
401 /* Current watchdog is removed. Find an alternative. */
402 watchdog = NULL;
403 list_for_each_entry(tmp, &clocksource_list, list) {
404 if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
405 continue;
406 if (!watchdog || tmp->rating > watchdog->rating)
407 watchdog = tmp;
408 }
409 }
410 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
411 /* Check if the watchdog timer needs to be stopped. */
412 clocksource_stop_watchdog();
413 spin_unlock_irqrestore(&watchdog_lock, flags);
414}
415
416static int clocksource_watchdog_kthread(void *data)
417{
418 struct clocksource *cs, *tmp;
419 unsigned long flags;
420 LIST_HEAD(unstable);
421
422 mutex_lock(&clocksource_mutex);
423 spin_lock_irqsave(&watchdog_lock, flags);
424 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
425 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
426 list_del_init(&cs->wd_list);
427 list_add(&cs->wd_list, &unstable);
428 }
429 /* Check if the watchdog timer needs to be stopped. */
430 clocksource_stop_watchdog();
431 spin_unlock_irqrestore(&watchdog_lock, flags);
432
433 /* Needs to be done outside of watchdog lock */
434 list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
435 list_del_init(&cs->wd_list);
436 __clocksource_change_rating(cs, 0);
437 }
438 mutex_unlock(&clocksource_mutex);
439 return 0;
440}
441
442#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
443
444static void clocksource_enqueue_watchdog(struct clocksource *cs)
445{
446 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
447 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
448}
449
450static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
451static inline void clocksource_resume_watchdog(void) { }
452static inline int clocksource_watchdog_kthread(void *data) { return 0; }
453
454#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
455
456/**
457 * clocksource_suspend - suspend the clocksource(s)
458 */
459void clocksource_suspend(void)
460{
461 struct clocksource *cs;
462
463 list_for_each_entry_reverse(cs, &clocksource_list, list)
464 if (cs->suspend)
465 cs->suspend(cs);
466}
467
468/**
469 * clocksource_resume - resume the clocksource(s)
470 */
471void clocksource_resume(void)
472{
473 struct clocksource *cs;
474
475 list_for_each_entry(cs, &clocksource_list, list)
476 if (cs->resume)
477 cs->resume(cs);
478
479 clocksource_resume_watchdog();
480}
481
482/**
483 * clocksource_touch_watchdog - Update watchdog
484 *
485 * Update the watchdog after exception contexts such as kgdb so as not
486 * to incorrectly trip the watchdog. This might fail when the kernel
487 * was stopped in code which holds watchdog_lock.
488 */
489void clocksource_touch_watchdog(void)
490{
491 clocksource_resume_watchdog();
492}
493
494/**
495 * clocksource_max_adjustment- Returns max adjustment amount
496 * @cs: Pointer to clocksource
497 *
498 */
499static u32 clocksource_max_adjustment(struct clocksource *cs)
500{
501 u64 ret;
502 /*
503 * We won't try to correct for more than 11% adjustments (110,000 ppm),
504 */
505 ret = (u64)cs->mult * 11;
506 do_div(ret,100);
507 return (u32)ret;
508}
509
510/**
511 * clocksource_max_deferment - Returns max time the clocksource can be deferred
512 * @cs: Pointer to clocksource
513 *
514 */
515static u64 clocksource_max_deferment(struct clocksource *cs)
516{
517 u64 max_nsecs, max_cycles;
518
519 /*
520 * Calculate the maximum number of cycles that we can pass to the
521 * cyc2ns function without overflowing a 64-bit signed result. The
522 * maximum number of cycles is equal to ULLONG_MAX/(cs->mult+cs->maxadj)
523 * which is equivalent to the below.
524 * max_cycles < (2^63)/(cs->mult + cs->maxadj)
525 * max_cycles < 2^(log2((2^63)/(cs->mult + cs->maxadj)))
526 * max_cycles < 2^(log2(2^63) - log2(cs->mult + cs->maxadj))
527 * max_cycles < 2^(63 - log2(cs->mult + cs->maxadj))
528 * max_cycles < 1 << (63 - log2(cs->mult + cs->maxadj))
529 * Please note that we add 1 to the result of the log2 to account for
530 * any rounding errors, ensure the above inequality is satisfied and
531 * no overflow will occur.
532 */
533 max_cycles = 1ULL << (63 - (ilog2(cs->mult + cs->maxadj) + 1));
534
535 /*
536 * The actual maximum number of cycles we can defer the clocksource is
537 * determined by the minimum of max_cycles and cs->mask.
538 * Note: Here we subtract the maxadj to make sure we don't sleep for
539 * too long if there's a large negative adjustment.
540 */
541 max_cycles = min_t(u64, max_cycles, (u64) cs->mask);
542 max_nsecs = clocksource_cyc2ns(max_cycles, cs->mult - cs->maxadj,
543 cs->shift);
544
545 /*
546 * To ensure that the clocksource does not wrap whilst we are idle,
547 * limit the time the clocksource can be deferred by 12.5%. Please
548 * note a margin of 12.5% is used because this can be computed with
549 * a shift, versus say 10% which would require division.
550 */
551 return max_nsecs - (max_nsecs >> 3);
552}
553
554#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
555
556/**
557 * clocksource_select - Select the best clocksource available
558 *
559 * Private function. Must hold clocksource_mutex when called.
560 *
561 * Select the clocksource with the best rating, or the clocksource,
562 * which is selected by userspace override.
563 */
564static void clocksource_select(void)
565{
566 struct clocksource *best, *cs;
567
568 if (!finished_booting || list_empty(&clocksource_list))
569 return;
570 /* First clocksource on the list has the best rating. */
571 best = list_first_entry(&clocksource_list, struct clocksource, list);
572 /* Check for the override clocksource. */
573 list_for_each_entry(cs, &clocksource_list, list) {
574 if (strcmp(cs->name, override_name) != 0)
575 continue;
576 /*
577 * Check to make sure we don't switch to a non-highres
578 * capable clocksource if the tick code is in oneshot
579 * mode (highres or nohz)
580 */
581 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
582 tick_oneshot_mode_active()) {
583 /* Override clocksource cannot be used. */
584 printk(KERN_WARNING "Override clocksource %s is not "
585 "HRT compatible. Cannot switch while in "
586 "HRT/NOHZ mode\n", cs->name);
587 override_name[0] = 0;
588 } else
589 /* Override clocksource can be used. */
590 best = cs;
591 break;
592 }
593 if (curr_clocksource != best) {
594 printk(KERN_INFO "Switching to clocksource %s\n", best->name);
595 curr_clocksource = best;
596 timekeeping_notify(curr_clocksource);
597 }
598}
599
600#else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
601
602static inline void clocksource_select(void) { }
603
604#endif
605
606/*
607 * clocksource_done_booting - Called near the end of core bootup
608 *
609 * Hack to avoid lots of clocksource churn at boot time.
610 * We use fs_initcall because we want this to start before
611 * device_initcall but after subsys_initcall.
612 */
613static int __init clocksource_done_booting(void)
614{
615 mutex_lock(&clocksource_mutex);
616 curr_clocksource = clocksource_default_clock();
617 mutex_unlock(&clocksource_mutex);
618
619 finished_booting = 1;
620
621 /*
622 * Run the watchdog first to eliminate unstable clock sources
623 */
624 clocksource_watchdog_kthread(NULL);
625
626 mutex_lock(&clocksource_mutex);
627 clocksource_select();
628 mutex_unlock(&clocksource_mutex);
629 return 0;
630}
631fs_initcall(clocksource_done_booting);
632
633/*
634 * Enqueue the clocksource sorted by rating
635 */
636static void clocksource_enqueue(struct clocksource *cs)
637{
638 struct list_head *entry = &clocksource_list;
639 struct clocksource *tmp;
640
641 list_for_each_entry(tmp, &clocksource_list, list)
642 /* Keep track of the place, where to insert */
643 if (tmp->rating >= cs->rating)
644 entry = &tmp->list;
645 list_add(&cs->list, entry);
646}
647
648/**
649 * __clocksource_updatefreq_scale - Used update clocksource with new freq
650 * @cs: clocksource to be registered
651 * @scale: Scale factor multiplied against freq to get clocksource hz
652 * @freq: clocksource frequency (cycles per second) divided by scale
653 *
654 * This should only be called from the clocksource->enable() method.
655 *
656 * This *SHOULD NOT* be called directly! Please use the
657 * clocksource_updatefreq_hz() or clocksource_updatefreq_khz helper functions.
658 */
659void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
660{
661 u64 sec;
662 /*
663 * Calc the maximum number of seconds which we can run before
664 * wrapping around. For clocksources which have a mask > 32bit
665 * we need to limit the max sleep time to have a good
666 * conversion precision. 10 minutes is still a reasonable
667 * amount. That results in a shift value of 24 for a
668 * clocksource with mask >= 40bit and f >= 4GHz. That maps to
669 * ~ 0.06ppm granularity for NTP. We apply the same 12.5%
670 * margin as we do in clocksource_max_deferment()
671 */
672 sec = (cs->mask - (cs->mask >> 3));
673 do_div(sec, freq);
674 do_div(sec, scale);
675 if (!sec)
676 sec = 1;
677 else if (sec > 600 && cs->mask > UINT_MAX)
678 sec = 600;
679
680 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
681 NSEC_PER_SEC / scale, sec * scale);
682
683 /*
684 * for clocksources that have large mults, to avoid overflow.
685 * Since mult may be adjusted by ntp, add an safety extra margin
686 *
687 */
688 cs->maxadj = clocksource_max_adjustment(cs);
689 while ((cs->mult + cs->maxadj < cs->mult)
690 || (cs->mult - cs->maxadj > cs->mult)) {
691 cs->mult >>= 1;
692 cs->shift--;
693 cs->maxadj = clocksource_max_adjustment(cs);
694 }
695
696 cs->max_idle_ns = clocksource_max_deferment(cs);
697}
698EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);
699
700/**
701 * __clocksource_register_scale - Used to install new clocksources
702 * @cs: clocksource to be registered
703 * @scale: Scale factor multiplied against freq to get clocksource hz
704 * @freq: clocksource frequency (cycles per second) divided by scale
705 *
706 * Returns -EBUSY if registration fails, zero otherwise.
707 *
708 * This *SHOULD NOT* be called directly! Please use the
709 * clocksource_register_hz() or clocksource_register_khz helper functions.
710 */
711int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
712{
713
714 /* Initialize mult/shift and max_idle_ns */
715 __clocksource_updatefreq_scale(cs, scale, freq);
716
717 /* Add clocksource to the clcoksource list */
718 mutex_lock(&clocksource_mutex);
719 clocksource_enqueue(cs);
720 clocksource_enqueue_watchdog(cs);
721 clocksource_select();
722 mutex_unlock(&clocksource_mutex);
723 return 0;
724}
725EXPORT_SYMBOL_GPL(__clocksource_register_scale);
726
727
728/**
729 * clocksource_register - Used to install new clocksources
730 * @cs: clocksource to be registered
731 *
732 * Returns -EBUSY if registration fails, zero otherwise.
733 */
734int clocksource_register(struct clocksource *cs)
735{
736 /* calculate max adjustment for given mult/shift */
737 cs->maxadj = clocksource_max_adjustment(cs);
738 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
739 "Clocksource %s might overflow on 11%% adjustment\n",
740 cs->name);
741
742 /* calculate max idle time permitted for this clocksource */
743 cs->max_idle_ns = clocksource_max_deferment(cs);
744
745 mutex_lock(&clocksource_mutex);
746 clocksource_enqueue(cs);
747 clocksource_enqueue_watchdog(cs);
748 clocksource_select();
749 mutex_unlock(&clocksource_mutex);
750 return 0;
751}
752EXPORT_SYMBOL(clocksource_register);
753
754static void __clocksource_change_rating(struct clocksource *cs, int rating)
755{
756 list_del(&cs->list);
757 cs->rating = rating;
758 clocksource_enqueue(cs);
759 clocksource_select();
760}
761
762/**
763 * clocksource_change_rating - Change the rating of a registered clocksource
764 * @cs: clocksource to be changed
765 * @rating: new rating
766 */
767void clocksource_change_rating(struct clocksource *cs, int rating)
768{
769 mutex_lock(&clocksource_mutex);
770 __clocksource_change_rating(cs, rating);
771 mutex_unlock(&clocksource_mutex);
772}
773EXPORT_SYMBOL(clocksource_change_rating);
774
775/**
776 * clocksource_unregister - remove a registered clocksource
777 * @cs: clocksource to be unregistered
778 */
779void clocksource_unregister(struct clocksource *cs)
780{
781 mutex_lock(&clocksource_mutex);
782 clocksource_dequeue_watchdog(cs);
783 list_del(&cs->list);
784 clocksource_select();
785 mutex_unlock(&clocksource_mutex);
786}
787EXPORT_SYMBOL(clocksource_unregister);
788
789#ifdef CONFIG_SYSFS
790/**
791 * sysfs_show_current_clocksources - sysfs interface for current clocksource
792 * @dev: unused
793 * @attr: unused
794 * @buf: char buffer to be filled with clocksource list
795 *
796 * Provides sysfs interface for listing current clocksource.
797 */
798static ssize_t
799sysfs_show_current_clocksources(struct device *dev,
800 struct device_attribute *attr, char *buf)
801{
802 ssize_t count = 0;
803
804 mutex_lock(&clocksource_mutex);
805 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
806 mutex_unlock(&clocksource_mutex);
807
808 return count;
809}
810
811/**
812 * sysfs_override_clocksource - interface for manually overriding clocksource
813 * @dev: unused
814 * @attr: unused
815 * @buf: name of override clocksource
816 * @count: length of buffer
817 *
818 * Takes input from sysfs interface for manually overriding the default
819 * clocksource selection.
820 */
821static ssize_t sysfs_override_clocksource(struct device *dev,
822 struct device_attribute *attr,
823 const char *buf, size_t count)
824{
825 size_t ret = count;
826
827 /* strings from sysfs write are not 0 terminated! */
828 if (count >= sizeof(override_name))
829 return -EINVAL;
830
831 /* strip of \n: */
832 if (buf[count-1] == '\n')
833 count--;
834
835 mutex_lock(&clocksource_mutex);
836
837 if (count > 0)
838 memcpy(override_name, buf, count);
839 override_name[count] = 0;
840 clocksource_select();
841
842 mutex_unlock(&clocksource_mutex);
843
844 return ret;
845}
846
847/**
848 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
849 * @dev: unused
850 * @attr: unused
851 * @buf: char buffer to be filled with clocksource list
852 *
853 * Provides sysfs interface for listing registered clocksources
854 */
855static ssize_t
856sysfs_show_available_clocksources(struct device *dev,
857 struct device_attribute *attr,
858 char *buf)
859{
860 struct clocksource *src;
861 ssize_t count = 0;
862
863 mutex_lock(&clocksource_mutex);
864 list_for_each_entry(src, &clocksource_list, list) {
865 /*
866 * Don't show non-HRES clocksource if the tick code is
867 * in one shot mode (highres=on or nohz=on)
868 */
869 if (!tick_oneshot_mode_active() ||
870 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
871 count += snprintf(buf + count,
872 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
873 "%s ", src->name);
874 }
875 mutex_unlock(&clocksource_mutex);
876
877 count += snprintf(buf + count,
878 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
879
880 return count;
881}
882
883/*
884 * Sysfs setup bits:
885 */
886static DEVICE_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
887 sysfs_override_clocksource);
888
889static DEVICE_ATTR(available_clocksource, 0444,
890 sysfs_show_available_clocksources, NULL);
891
892static struct bus_type clocksource_subsys = {
893 .name = "clocksource",
894 .dev_name = "clocksource",
895};
896
897static struct device device_clocksource = {
898 .id = 0,
899 .bus = &clocksource_subsys,
900};
901
902static int __init init_clocksource_sysfs(void)
903{
904 int error = subsys_system_register(&clocksource_subsys, NULL);
905
906 if (!error)
907 error = device_register(&device_clocksource);
908 if (!error)
909 error = device_create_file(
910 &device_clocksource,
911 &dev_attr_current_clocksource);
912 if (!error)
913 error = device_create_file(
914 &device_clocksource,
915 &dev_attr_available_clocksource);
916 return error;
917}
918
919device_initcall(init_clocksource_sysfs);
920#endif /* CONFIG_SYSFS */
921
922/**
923 * boot_override_clocksource - boot clock override
924 * @str: override name
925 *
926 * Takes a clocksource= boot argument and uses it
927 * as the clocksource override name.
928 */
929static int __init boot_override_clocksource(char* str)
930{
931 mutex_lock(&clocksource_mutex);
932 if (str)
933 strlcpy(override_name, str, sizeof(override_name));
934 mutex_unlock(&clocksource_mutex);
935 return 1;
936}
937
938__setup("clocksource=", boot_override_clocksource);
939
940/**
941 * boot_override_clock - Compatibility layer for deprecated boot option
942 * @str: override name
943 *
944 * DEPRECATED! Takes a clock= boot argument and uses it
945 * as the clocksource override name
946 */
947static int __init boot_override_clock(char* str)
948{
949 if (!strcmp(str, "pmtmr")) {
950 printk("Warning: clock=pmtmr is deprecated. "
951 "Use clocksource=acpi_pm.\n");
952 return boot_override_clocksource("acpi_pm");
953 }
954 printk("Warning! clock= boot option is deprecated. "
955 "Use clocksource=xyz\n");
956 return boot_override_clocksource(str);
957}
958
959__setup("clock=", boot_override_clock);