Loading...
1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * This file contains the functions which manage clocksource drivers.
4 *
5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
6 */
7
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9
10#include <linux/device.h>
11#include <linux/clocksource.h>
12#include <linux/init.h>
13#include <linux/module.h>
14#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
15#include <linux/tick.h>
16#include <linux/kthread.h>
17#include <linux/prandom.h>
18#include <linux/cpu.h>
19
20#include "tick-internal.h"
21#include "timekeeping_internal.h"
22
23/**
24 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
25 * @mult: pointer to mult variable
26 * @shift: pointer to shift variable
27 * @from: frequency to convert from
28 * @to: frequency to convert to
29 * @maxsec: guaranteed runtime conversion range in seconds
30 *
31 * The function evaluates the shift/mult pair for the scaled math
32 * operations of clocksources and clockevents.
33 *
34 * @to and @from are frequency values in HZ. For clock sources @to is
35 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
36 * event @to is the counter frequency and @from is NSEC_PER_SEC.
37 *
38 * The @maxsec conversion range argument controls the time frame in
39 * seconds which must be covered by the runtime conversion with the
40 * calculated mult and shift factors. This guarantees that no 64bit
41 * overflow happens when the input value of the conversion is
42 * multiplied with the calculated mult factor. Larger ranges may
43 * reduce the conversion accuracy by choosing smaller mult and shift
44 * factors.
45 */
46void
47clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
48{
49 u64 tmp;
50 u32 sft, sftacc= 32;
51
52 /*
53 * Calculate the shift factor which is limiting the conversion
54 * range:
55 */
56 tmp = ((u64)maxsec * from) >> 32;
57 while (tmp) {
58 tmp >>=1;
59 sftacc--;
60 }
61
62 /*
63 * Find the conversion shift/mult pair which has the best
64 * accuracy and fits the maxsec conversion range:
65 */
66 for (sft = 32; sft > 0; sft--) {
67 tmp = (u64) to << sft;
68 tmp += from / 2;
69 do_div(tmp, from);
70 if ((tmp >> sftacc) == 0)
71 break;
72 }
73 *mult = tmp;
74 *shift = sft;
75}
76EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
77
78/*[Clocksource internal variables]---------
79 * curr_clocksource:
80 * currently selected clocksource.
81 * suspend_clocksource:
82 * used to calculate the suspend time.
83 * clocksource_list:
84 * linked list with the registered clocksources
85 * clocksource_mutex:
86 * protects manipulations to curr_clocksource and the clocksource_list
87 * override_name:
88 * Name of the user-specified clocksource.
89 */
90static struct clocksource *curr_clocksource;
91static struct clocksource *suspend_clocksource;
92static LIST_HEAD(clocksource_list);
93static DEFINE_MUTEX(clocksource_mutex);
94static char override_name[CS_NAME_LEN];
95static int finished_booting;
96static u64 suspend_start;
97
98/*
99 * Interval: 0.5sec.
100 */
101#define WATCHDOG_INTERVAL (HZ >> 1)
102#define WATCHDOG_INTERVAL_MAX_NS ((2 * WATCHDOG_INTERVAL) * (NSEC_PER_SEC / HZ))
103
104/*
105 * Threshold: 0.0312s, when doubled: 0.0625s.
106 * Also a default for cs->uncertainty_margin when registering clocks.
107 */
108#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)
109
110/*
111 * Maximum permissible delay between two readouts of the watchdog
112 * clocksource surrounding a read of the clocksource being validated.
113 * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as
114 * a lower bound for cs->uncertainty_margin values when registering clocks.
115 *
116 * The default of 500 parts per million is based on NTP's limits.
117 * If a clocksource is good enough for NTP, it is good enough for us!
118 */
119#ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
120#define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
121#else
122#define MAX_SKEW_USEC (125 * WATCHDOG_INTERVAL / HZ)
123#endif
124
125#define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
126
127#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
128static void clocksource_watchdog_work(struct work_struct *work);
129static void clocksource_select(void);
130
131static LIST_HEAD(watchdog_list);
132static struct clocksource *watchdog;
133static struct timer_list watchdog_timer;
134static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
135static DEFINE_SPINLOCK(watchdog_lock);
136static int watchdog_running;
137static atomic_t watchdog_reset_pending;
138static int64_t watchdog_max_interval;
139
140static inline void clocksource_watchdog_lock(unsigned long *flags)
141{
142 spin_lock_irqsave(&watchdog_lock, *flags);
143}
144
145static inline void clocksource_watchdog_unlock(unsigned long *flags)
146{
147 spin_unlock_irqrestore(&watchdog_lock, *flags);
148}
149
150static int clocksource_watchdog_kthread(void *data);
151static void __clocksource_change_rating(struct clocksource *cs, int rating);
152
153static void clocksource_watchdog_work(struct work_struct *work)
154{
155 /*
156 * We cannot directly run clocksource_watchdog_kthread() here, because
157 * clocksource_select() calls timekeeping_notify() which uses
158 * stop_machine(). One cannot use stop_machine() from a workqueue() due
159 * lock inversions wrt CPU hotplug.
160 *
161 * Also, we only ever run this work once or twice during the lifetime
162 * of the kernel, so there is no point in creating a more permanent
163 * kthread for this.
164 *
165 * If kthread_run fails the next watchdog scan over the
166 * watchdog_list will find the unstable clock again.
167 */
168 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
169}
170
171static void __clocksource_unstable(struct clocksource *cs)
172{
173 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
174 cs->flags |= CLOCK_SOURCE_UNSTABLE;
175
176 /*
177 * If the clocksource is registered clocksource_watchdog_kthread() will
178 * re-rate and re-select.
179 */
180 if (list_empty(&cs->list)) {
181 cs->rating = 0;
182 return;
183 }
184
185 if (cs->mark_unstable)
186 cs->mark_unstable(cs);
187
188 /* kick clocksource_watchdog_kthread() */
189 if (finished_booting)
190 schedule_work(&watchdog_work);
191}
192
193/**
194 * clocksource_mark_unstable - mark clocksource unstable via watchdog
195 * @cs: clocksource to be marked unstable
196 *
197 * This function is called by the x86 TSC code to mark clocksources as unstable;
198 * it defers demotion and re-selection to a kthread.
199 */
200void clocksource_mark_unstable(struct clocksource *cs)
201{
202 unsigned long flags;
203
204 spin_lock_irqsave(&watchdog_lock, flags);
205 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
206 if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
207 list_add(&cs->wd_list, &watchdog_list);
208 __clocksource_unstable(cs);
209 }
210 spin_unlock_irqrestore(&watchdog_lock, flags);
211}
212
213ulong max_cswd_read_retries = 2;
214module_param(max_cswd_read_retries, ulong, 0644);
215EXPORT_SYMBOL_GPL(max_cswd_read_retries);
216static int verify_n_cpus = 8;
217module_param(verify_n_cpus, int, 0644);
218
219enum wd_read_status {
220 WD_READ_SUCCESS,
221 WD_READ_UNSTABLE,
222 WD_READ_SKIP
223};
224
225static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
226{
227 unsigned int nretries;
228 u64 wd_end, wd_end2, wd_delta;
229 int64_t wd_delay, wd_seq_delay;
230
231 for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) {
232 local_irq_disable();
233 *wdnow = watchdog->read(watchdog);
234 *csnow = cs->read(cs);
235 wd_end = watchdog->read(watchdog);
236 wd_end2 = watchdog->read(watchdog);
237 local_irq_enable();
238
239 wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
240 wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult,
241 watchdog->shift);
242 if (wd_delay <= WATCHDOG_MAX_SKEW) {
243 if (nretries > 1 || nretries >= max_cswd_read_retries) {
244 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
245 smp_processor_id(), watchdog->name, nretries);
246 }
247 return WD_READ_SUCCESS;
248 }
249
250 /*
251 * Now compute delay in consecutive watchdog read to see if
252 * there is too much external interferences that cause
253 * significant delay in reading both clocksource and watchdog.
254 *
255 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2,
256 * report system busy, reinit the watchdog and skip the current
257 * watchdog test.
258 */
259 wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask);
260 wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift);
261 if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
262 goto skip_test;
263 }
264
265 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",
266 smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name);
267 return WD_READ_UNSTABLE;
268
269skip_test:
270 pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
271 smp_processor_id(), watchdog->name, wd_seq_delay);
272 pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
273 cs->name, wd_delay);
274 return WD_READ_SKIP;
275}
276
277static u64 csnow_mid;
278static cpumask_t cpus_ahead;
279static cpumask_t cpus_behind;
280static cpumask_t cpus_chosen;
281
282static void clocksource_verify_choose_cpus(void)
283{
284 int cpu, i, n = verify_n_cpus;
285
286 if (n < 0) {
287 /* Check all of the CPUs. */
288 cpumask_copy(&cpus_chosen, cpu_online_mask);
289 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
290 return;
291 }
292
293 /* If no checking desired, or no other CPU to check, leave. */
294 cpumask_clear(&cpus_chosen);
295 if (n == 0 || num_online_cpus() <= 1)
296 return;
297
298 /* Make sure to select at least one CPU other than the current CPU. */
299 cpu = cpumask_first(cpu_online_mask);
300 if (cpu == smp_processor_id())
301 cpu = cpumask_next(cpu, cpu_online_mask);
302 if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
303 return;
304 cpumask_set_cpu(cpu, &cpus_chosen);
305
306 /* Force a sane value for the boot parameter. */
307 if (n > nr_cpu_ids)
308 n = nr_cpu_ids;
309
310 /*
311 * Randomly select the specified number of CPUs. If the same
312 * CPU is selected multiple times, that CPU is checked only once,
313 * and no replacement CPU is selected. This gracefully handles
314 * situations where verify_n_cpus is greater than the number of
315 * CPUs that are currently online.
316 */
317 for (i = 1; i < n; i++) {
318 cpu = get_random_u32_below(nr_cpu_ids);
319 cpu = cpumask_next(cpu - 1, cpu_online_mask);
320 if (cpu >= nr_cpu_ids)
321 cpu = cpumask_first(cpu_online_mask);
322 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
323 cpumask_set_cpu(cpu, &cpus_chosen);
324 }
325
326 /* Don't verify ourselves. */
327 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
328}
329
330static void clocksource_verify_one_cpu(void *csin)
331{
332 struct clocksource *cs = (struct clocksource *)csin;
333
334 csnow_mid = cs->read(cs);
335}
336
337void clocksource_verify_percpu(struct clocksource *cs)
338{
339 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
340 u64 csnow_begin, csnow_end;
341 int cpu, testcpu;
342 s64 delta;
343
344 if (verify_n_cpus == 0)
345 return;
346 cpumask_clear(&cpus_ahead);
347 cpumask_clear(&cpus_behind);
348 cpus_read_lock();
349 preempt_disable();
350 clocksource_verify_choose_cpus();
351 if (cpumask_empty(&cpus_chosen)) {
352 preempt_enable();
353 cpus_read_unlock();
354 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
355 return;
356 }
357 testcpu = smp_processor_id();
358 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
359 for_each_cpu(cpu, &cpus_chosen) {
360 if (cpu == testcpu)
361 continue;
362 csnow_begin = cs->read(cs);
363 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
364 csnow_end = cs->read(cs);
365 delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
366 if (delta < 0)
367 cpumask_set_cpu(cpu, &cpus_behind);
368 delta = (csnow_end - csnow_mid) & cs->mask;
369 if (delta < 0)
370 cpumask_set_cpu(cpu, &cpus_ahead);
371 delta = clocksource_delta(csnow_end, csnow_begin, cs->mask);
372 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
373 if (cs_nsec > cs_nsec_max)
374 cs_nsec_max = cs_nsec;
375 if (cs_nsec < cs_nsec_min)
376 cs_nsec_min = cs_nsec;
377 }
378 preempt_enable();
379 cpus_read_unlock();
380 if (!cpumask_empty(&cpus_ahead))
381 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
382 cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
383 if (!cpumask_empty(&cpus_behind))
384 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n",
385 cpumask_pr_args(&cpus_behind), testcpu, cs->name);
386 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
387 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n",
388 testcpu, cs_nsec_min, cs_nsec_max, cs->name);
389}
390EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
391
392static inline void clocksource_reset_watchdog(void)
393{
394 struct clocksource *cs;
395
396 list_for_each_entry(cs, &watchdog_list, wd_list)
397 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
398}
399
400
401static void clocksource_watchdog(struct timer_list *unused)
402{
403 u64 csnow, wdnow, cslast, wdlast, delta;
404 int64_t wd_nsec, cs_nsec, interval;
405 int next_cpu, reset_pending;
406 struct clocksource *cs;
407 enum wd_read_status read_ret;
408 unsigned long extra_wait = 0;
409 u32 md;
410
411 spin_lock(&watchdog_lock);
412 if (!watchdog_running)
413 goto out;
414
415 reset_pending = atomic_read(&watchdog_reset_pending);
416
417 list_for_each_entry(cs, &watchdog_list, wd_list) {
418
419 /* Clocksource already marked unstable? */
420 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
421 if (finished_booting)
422 schedule_work(&watchdog_work);
423 continue;
424 }
425
426 read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
427
428 if (read_ret == WD_READ_UNSTABLE) {
429 /* Clock readout unreliable, so give it up. */
430 __clocksource_unstable(cs);
431 continue;
432 }
433
434 /*
435 * When WD_READ_SKIP is returned, it means the system is likely
436 * under very heavy load, where the latency of reading
437 * watchdog/clocksource is very big, and affect the accuracy of
438 * watchdog check. So give system some space and suspend the
439 * watchdog check for 5 minutes.
440 */
441 if (read_ret == WD_READ_SKIP) {
442 /*
443 * As the watchdog timer will be suspended, and
444 * cs->last could keep unchanged for 5 minutes, reset
445 * the counters.
446 */
447 clocksource_reset_watchdog();
448 extra_wait = HZ * 300;
449 break;
450 }
451
452 /* Clocksource initialized ? */
453 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
454 atomic_read(&watchdog_reset_pending)) {
455 cs->flags |= CLOCK_SOURCE_WATCHDOG;
456 cs->wd_last = wdnow;
457 cs->cs_last = csnow;
458 continue;
459 }
460
461 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
462 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
463 watchdog->shift);
464
465 delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
466 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
467 wdlast = cs->wd_last; /* save these in case we print them */
468 cslast = cs->cs_last;
469 cs->cs_last = csnow;
470 cs->wd_last = wdnow;
471
472 if (atomic_read(&watchdog_reset_pending))
473 continue;
474
475 /*
476 * The processing of timer softirqs can get delayed (usually
477 * on account of ksoftirqd not getting to run in a timely
478 * manner), which causes the watchdog interval to stretch.
479 * Skew detection may fail for longer watchdog intervals
480 * on account of fixed margins being used.
481 * Some clocksources, e.g. acpi_pm, cannot tolerate
482 * watchdog intervals longer than a few seconds.
483 */
484 interval = max(cs_nsec, wd_nsec);
485 if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) {
486 if (system_state > SYSTEM_SCHEDULING &&
487 interval > 2 * watchdog_max_interval) {
488 watchdog_max_interval = interval;
489 pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n",
490 cs_nsec, wd_nsec);
491 }
492 watchdog_timer.expires = jiffies;
493 continue;
494 }
495
496 /* Check the deviation from the watchdog clocksource. */
497 md = cs->uncertainty_margin + watchdog->uncertainty_margin;
498 if (abs(cs_nsec - wd_nsec) > md) {
499 s64 cs_wd_msec;
500 s64 wd_msec;
501 u32 wd_rem;
502
503 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
504 smp_processor_id(), cs->name);
505 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
506 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
507 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
508 cs->name, cs_nsec, csnow, cslast, cs->mask);
509 cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem);
510 wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem);
511 pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n",
512 cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec);
513 if (curr_clocksource == cs)
514 pr_warn(" '%s' is current clocksource.\n", cs->name);
515 else if (curr_clocksource)
516 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
517 else
518 pr_warn(" No current clocksource.\n");
519 __clocksource_unstable(cs);
520 continue;
521 }
522
523 if (cs == curr_clocksource && cs->tick_stable)
524 cs->tick_stable(cs);
525
526 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
527 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
528 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
529 /* Mark it valid for high-res. */
530 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
531
532 /*
533 * clocksource_done_booting() will sort it if
534 * finished_booting is not set yet.
535 */
536 if (!finished_booting)
537 continue;
538
539 /*
540 * If this is not the current clocksource let
541 * the watchdog thread reselect it. Due to the
542 * change to high res this clocksource might
543 * be preferred now. If it is the current
544 * clocksource let the tick code know about
545 * that change.
546 */
547 if (cs != curr_clocksource) {
548 cs->flags |= CLOCK_SOURCE_RESELECT;
549 schedule_work(&watchdog_work);
550 } else {
551 tick_clock_notify();
552 }
553 }
554 }
555
556 /*
557 * We only clear the watchdog_reset_pending, when we did a
558 * full cycle through all clocksources.
559 */
560 if (reset_pending)
561 atomic_dec(&watchdog_reset_pending);
562
563 /*
564 * Cycle through CPUs to check if the CPUs stay synchronized
565 * to each other.
566 */
567 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
568 if (next_cpu >= nr_cpu_ids)
569 next_cpu = cpumask_first(cpu_online_mask);
570
571 /*
572 * Arm timer if not already pending: could race with concurrent
573 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
574 */
575 if (!timer_pending(&watchdog_timer)) {
576 watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait;
577 add_timer_on(&watchdog_timer, next_cpu);
578 }
579out:
580 spin_unlock(&watchdog_lock);
581}
582
583static inline void clocksource_start_watchdog(void)
584{
585 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
586 return;
587 timer_setup(&watchdog_timer, clocksource_watchdog, 0);
588 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
589 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
590 watchdog_running = 1;
591}
592
593static inline void clocksource_stop_watchdog(void)
594{
595 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
596 return;
597 del_timer(&watchdog_timer);
598 watchdog_running = 0;
599}
600
601static void clocksource_resume_watchdog(void)
602{
603 atomic_inc(&watchdog_reset_pending);
604}
605
606static void clocksource_enqueue_watchdog(struct clocksource *cs)
607{
608 INIT_LIST_HEAD(&cs->wd_list);
609
610 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
611 /* cs is a clocksource to be watched. */
612 list_add(&cs->wd_list, &watchdog_list);
613 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
614 } else {
615 /* cs is a watchdog. */
616 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
617 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
618 }
619}
620
621static void clocksource_select_watchdog(bool fallback)
622{
623 struct clocksource *cs, *old_wd;
624 unsigned long flags;
625
626 spin_lock_irqsave(&watchdog_lock, flags);
627 /* save current watchdog */
628 old_wd = watchdog;
629 if (fallback)
630 watchdog = NULL;
631
632 list_for_each_entry(cs, &clocksource_list, list) {
633 /* cs is a clocksource to be watched. */
634 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
635 continue;
636
637 /* Skip current if we were requested for a fallback. */
638 if (fallback && cs == old_wd)
639 continue;
640
641 /* Pick the best watchdog. */
642 if (!watchdog || cs->rating > watchdog->rating)
643 watchdog = cs;
644 }
645 /* If we failed to find a fallback restore the old one. */
646 if (!watchdog)
647 watchdog = old_wd;
648
649 /* If we changed the watchdog we need to reset cycles. */
650 if (watchdog != old_wd)
651 clocksource_reset_watchdog();
652
653 /* Check if the watchdog timer needs to be started. */
654 clocksource_start_watchdog();
655 spin_unlock_irqrestore(&watchdog_lock, flags);
656}
657
658static void clocksource_dequeue_watchdog(struct clocksource *cs)
659{
660 if (cs != watchdog) {
661 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
662 /* cs is a watched clocksource. */
663 list_del_init(&cs->wd_list);
664 /* Check if the watchdog timer needs to be stopped. */
665 clocksource_stop_watchdog();
666 }
667 }
668}
669
670static int __clocksource_watchdog_kthread(void)
671{
672 struct clocksource *cs, *tmp;
673 unsigned long flags;
674 int select = 0;
675
676 /* Do any required per-CPU skew verification. */
677 if (curr_clocksource &&
678 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
679 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
680 clocksource_verify_percpu(curr_clocksource);
681
682 spin_lock_irqsave(&watchdog_lock, flags);
683 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
684 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
685 list_del_init(&cs->wd_list);
686 __clocksource_change_rating(cs, 0);
687 select = 1;
688 }
689 if (cs->flags & CLOCK_SOURCE_RESELECT) {
690 cs->flags &= ~CLOCK_SOURCE_RESELECT;
691 select = 1;
692 }
693 }
694 /* Check if the watchdog timer needs to be stopped. */
695 clocksource_stop_watchdog();
696 spin_unlock_irqrestore(&watchdog_lock, flags);
697
698 return select;
699}
700
701static int clocksource_watchdog_kthread(void *data)
702{
703 mutex_lock(&clocksource_mutex);
704 if (__clocksource_watchdog_kthread())
705 clocksource_select();
706 mutex_unlock(&clocksource_mutex);
707 return 0;
708}
709
710static bool clocksource_is_watchdog(struct clocksource *cs)
711{
712 return cs == watchdog;
713}
714
715#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
716
717static void clocksource_enqueue_watchdog(struct clocksource *cs)
718{
719 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
720 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
721}
722
723static void clocksource_select_watchdog(bool fallback) { }
724static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
725static inline void clocksource_resume_watchdog(void) { }
726static inline int __clocksource_watchdog_kthread(void) { return 0; }
727static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
728void clocksource_mark_unstable(struct clocksource *cs) { }
729
730static inline void clocksource_watchdog_lock(unsigned long *flags) { }
731static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
732
733#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
734
735static bool clocksource_is_suspend(struct clocksource *cs)
736{
737 return cs == suspend_clocksource;
738}
739
740static void __clocksource_suspend_select(struct clocksource *cs)
741{
742 /*
743 * Skip the clocksource which will be stopped in suspend state.
744 */
745 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
746 return;
747
748 /*
749 * The nonstop clocksource can be selected as the suspend clocksource to
750 * calculate the suspend time, so it should not supply suspend/resume
751 * interfaces to suspend the nonstop clocksource when system suspends.
752 */
753 if (cs->suspend || cs->resume) {
754 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
755 cs->name);
756 }
757
758 /* Pick the best rating. */
759 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
760 suspend_clocksource = cs;
761}
762
763/**
764 * clocksource_suspend_select - Select the best clocksource for suspend timing
765 * @fallback: if select a fallback clocksource
766 */
767static void clocksource_suspend_select(bool fallback)
768{
769 struct clocksource *cs, *old_suspend;
770
771 old_suspend = suspend_clocksource;
772 if (fallback)
773 suspend_clocksource = NULL;
774
775 list_for_each_entry(cs, &clocksource_list, list) {
776 /* Skip current if we were requested for a fallback. */
777 if (fallback && cs == old_suspend)
778 continue;
779
780 __clocksource_suspend_select(cs);
781 }
782}
783
784/**
785 * clocksource_start_suspend_timing - Start measuring the suspend timing
786 * @cs: current clocksource from timekeeping
787 * @start_cycles: current cycles from timekeeping
788 *
789 * This function will save the start cycle values of suspend timer to calculate
790 * the suspend time when resuming system.
791 *
792 * This function is called late in the suspend process from timekeeping_suspend(),
793 * that means processes are frozen, non-boot cpus and interrupts are disabled
794 * now. It is therefore possible to start the suspend timer without taking the
795 * clocksource mutex.
796 */
797void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
798{
799 if (!suspend_clocksource)
800 return;
801
802 /*
803 * If current clocksource is the suspend timer, we should use the
804 * tkr_mono.cycle_last value as suspend_start to avoid same reading
805 * from suspend timer.
806 */
807 if (clocksource_is_suspend(cs)) {
808 suspend_start = start_cycles;
809 return;
810 }
811
812 if (suspend_clocksource->enable &&
813 suspend_clocksource->enable(suspend_clocksource)) {
814 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
815 return;
816 }
817
818 suspend_start = suspend_clocksource->read(suspend_clocksource);
819}
820
821/**
822 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
823 * @cs: current clocksource from timekeeping
824 * @cycle_now: current cycles from timekeeping
825 *
826 * This function will calculate the suspend time from suspend timer.
827 *
828 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
829 *
830 * This function is called early in the resume process from timekeeping_resume(),
831 * that means there is only one cpu, no processes are running and the interrupts
832 * are disabled. It is therefore possible to stop the suspend timer without
833 * taking the clocksource mutex.
834 */
835u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
836{
837 u64 now, delta, nsec = 0;
838
839 if (!suspend_clocksource)
840 return 0;
841
842 /*
843 * If current clocksource is the suspend timer, we should use the
844 * tkr_mono.cycle_last value from timekeeping as current cycle to
845 * avoid same reading from suspend timer.
846 */
847 if (clocksource_is_suspend(cs))
848 now = cycle_now;
849 else
850 now = suspend_clocksource->read(suspend_clocksource);
851
852 if (now > suspend_start) {
853 delta = clocksource_delta(now, suspend_start,
854 suspend_clocksource->mask);
855 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
856 suspend_clocksource->shift);
857 }
858
859 /*
860 * Disable the suspend timer to save power if current clocksource is
861 * not the suspend timer.
862 */
863 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
864 suspend_clocksource->disable(suspend_clocksource);
865
866 return nsec;
867}
868
869/**
870 * clocksource_suspend - suspend the clocksource(s)
871 */
872void clocksource_suspend(void)
873{
874 struct clocksource *cs;
875
876 list_for_each_entry_reverse(cs, &clocksource_list, list)
877 if (cs->suspend)
878 cs->suspend(cs);
879}
880
881/**
882 * clocksource_resume - resume the clocksource(s)
883 */
884void clocksource_resume(void)
885{
886 struct clocksource *cs;
887
888 list_for_each_entry(cs, &clocksource_list, list)
889 if (cs->resume)
890 cs->resume(cs);
891
892 clocksource_resume_watchdog();
893}
894
895/**
896 * clocksource_touch_watchdog - Update watchdog
897 *
898 * Update the watchdog after exception contexts such as kgdb so as not
899 * to incorrectly trip the watchdog. This might fail when the kernel
900 * was stopped in code which holds watchdog_lock.
901 */
902void clocksource_touch_watchdog(void)
903{
904 clocksource_resume_watchdog();
905}
906
907/**
908 * clocksource_max_adjustment- Returns max adjustment amount
909 * @cs: Pointer to clocksource
910 *
911 */
912static u32 clocksource_max_adjustment(struct clocksource *cs)
913{
914 u64 ret;
915 /*
916 * We won't try to correct for more than 11% adjustments (110,000 ppm),
917 */
918 ret = (u64)cs->mult * 11;
919 do_div(ret,100);
920 return (u32)ret;
921}
922
923/**
924 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
925 * @mult: cycle to nanosecond multiplier
926 * @shift: cycle to nanosecond divisor (power of two)
927 * @maxadj: maximum adjustment value to mult (~11%)
928 * @mask: bitmask for two's complement subtraction of non 64 bit counters
929 * @max_cyc: maximum cycle value before potential overflow (does not include
930 * any safety margin)
931 *
932 * NOTE: This function includes a safety margin of 50%, in other words, we
933 * return half the number of nanoseconds the hardware counter can technically
934 * cover. This is done so that we can potentially detect problems caused by
935 * delayed timers or bad hardware, which might result in time intervals that
936 * are larger than what the math used can handle without overflows.
937 */
938u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
939{
940 u64 max_nsecs, max_cycles;
941
942 /*
943 * Calculate the maximum number of cycles that we can pass to the
944 * cyc2ns() function without overflowing a 64-bit result.
945 */
946 max_cycles = ULLONG_MAX;
947 do_div(max_cycles, mult+maxadj);
948
949 /*
950 * The actual maximum number of cycles we can defer the clocksource is
951 * determined by the minimum of max_cycles and mask.
952 * Note: Here we subtract the maxadj to make sure we don't sleep for
953 * too long if there's a large negative adjustment.
954 */
955 max_cycles = min(max_cycles, mask);
956 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
957
958 /* return the max_cycles value as well if requested */
959 if (max_cyc)
960 *max_cyc = max_cycles;
961
962 /* Return 50% of the actual maximum, so we can detect bad values */
963 max_nsecs >>= 1;
964
965 return max_nsecs;
966}
967
968/**
969 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
970 * @cs: Pointer to clocksource to be updated
971 *
972 */
973static inline void clocksource_update_max_deferment(struct clocksource *cs)
974{
975 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
976 cs->maxadj, cs->mask,
977 &cs->max_cycles);
978}
979
980static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
981{
982 struct clocksource *cs;
983
984 if (!finished_booting || list_empty(&clocksource_list))
985 return NULL;
986
987 /*
988 * We pick the clocksource with the highest rating. If oneshot
989 * mode is active, we pick the highres valid clocksource with
990 * the best rating.
991 */
992 list_for_each_entry(cs, &clocksource_list, list) {
993 if (skipcur && cs == curr_clocksource)
994 continue;
995 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
996 continue;
997 return cs;
998 }
999 return NULL;
1000}
1001
1002static void __clocksource_select(bool skipcur)
1003{
1004 bool oneshot = tick_oneshot_mode_active();
1005 struct clocksource *best, *cs;
1006
1007 /* Find the best suitable clocksource */
1008 best = clocksource_find_best(oneshot, skipcur);
1009 if (!best)
1010 return;
1011
1012 if (!strlen(override_name))
1013 goto found;
1014
1015 /* Check for the override clocksource. */
1016 list_for_each_entry(cs, &clocksource_list, list) {
1017 if (skipcur && cs == curr_clocksource)
1018 continue;
1019 if (strcmp(cs->name, override_name) != 0)
1020 continue;
1021 /*
1022 * Check to make sure we don't switch to a non-highres
1023 * capable clocksource if the tick code is in oneshot
1024 * mode (highres or nohz)
1025 */
1026 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
1027 /* Override clocksource cannot be used. */
1028 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
1029 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
1030 cs->name);
1031 override_name[0] = 0;
1032 } else {
1033 /*
1034 * The override cannot be currently verified.
1035 * Deferring to let the watchdog check.
1036 */
1037 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
1038 cs->name);
1039 }
1040 } else
1041 /* Override clocksource can be used. */
1042 best = cs;
1043 break;
1044 }
1045
1046found:
1047 if (curr_clocksource != best && !timekeeping_notify(best)) {
1048 pr_info("Switched to clocksource %s\n", best->name);
1049 curr_clocksource = best;
1050 }
1051}
1052
1053/**
1054 * clocksource_select - Select the best clocksource available
1055 *
1056 * Private function. Must hold clocksource_mutex when called.
1057 *
1058 * Select the clocksource with the best rating, or the clocksource,
1059 * which is selected by userspace override.
1060 */
1061static void clocksource_select(void)
1062{
1063 __clocksource_select(false);
1064}
1065
1066static void clocksource_select_fallback(void)
1067{
1068 __clocksource_select(true);
1069}
1070
1071/*
1072 * clocksource_done_booting - Called near the end of core bootup
1073 *
1074 * Hack to avoid lots of clocksource churn at boot time.
1075 * We use fs_initcall because we want this to start before
1076 * device_initcall but after subsys_initcall.
1077 */
1078static int __init clocksource_done_booting(void)
1079{
1080 mutex_lock(&clocksource_mutex);
1081 curr_clocksource = clocksource_default_clock();
1082 finished_booting = 1;
1083 /*
1084 * Run the watchdog first to eliminate unstable clock sources
1085 */
1086 __clocksource_watchdog_kthread();
1087 clocksource_select();
1088 mutex_unlock(&clocksource_mutex);
1089 return 0;
1090}
1091fs_initcall(clocksource_done_booting);
1092
1093/*
1094 * Enqueue the clocksource sorted by rating
1095 */
1096static void clocksource_enqueue(struct clocksource *cs)
1097{
1098 struct list_head *entry = &clocksource_list;
1099 struct clocksource *tmp;
1100
1101 list_for_each_entry(tmp, &clocksource_list, list) {
1102 /* Keep track of the place, where to insert */
1103 if (tmp->rating < cs->rating)
1104 break;
1105 entry = &tmp->list;
1106 }
1107 list_add(&cs->list, entry);
1108}
1109
1110/**
1111 * __clocksource_update_freq_scale - Used update clocksource with new freq
1112 * @cs: clocksource to be registered
1113 * @scale: Scale factor multiplied against freq to get clocksource hz
1114 * @freq: clocksource frequency (cycles per second) divided by scale
1115 *
1116 * This should only be called from the clocksource->enable() method.
1117 *
1118 * This *SHOULD NOT* be called directly! Please use the
1119 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
1120 * functions.
1121 */
1122void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1123{
1124 u64 sec;
1125
1126 /*
1127 * Default clocksources are *special* and self-define their mult/shift.
1128 * But, you're not special, so you should specify a freq value.
1129 */
1130 if (freq) {
1131 /*
1132 * Calc the maximum number of seconds which we can run before
1133 * wrapping around. For clocksources which have a mask > 32-bit
1134 * we need to limit the max sleep time to have a good
1135 * conversion precision. 10 minutes is still a reasonable
1136 * amount. That results in a shift value of 24 for a
1137 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1138 * ~ 0.06ppm granularity for NTP.
1139 */
1140 sec = cs->mask;
1141 do_div(sec, freq);
1142 do_div(sec, scale);
1143 if (!sec)
1144 sec = 1;
1145 else if (sec > 600 && cs->mask > UINT_MAX)
1146 sec = 600;
1147
1148 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1149 NSEC_PER_SEC / scale, sec * scale);
1150 }
1151
1152 /*
1153 * If the uncertainty margin is not specified, calculate it.
1154 * If both scale and freq are non-zero, calculate the clock
1155 * period, but bound below at 2*WATCHDOG_MAX_SKEW. However,
1156 * if either of scale or freq is zero, be very conservative and
1157 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the
1158 * uncertainty margin. Allow stupidly small uncertainty margins
1159 * to be specified by the caller for testing purposes, but warn
1160 * to discourage production use of this capability.
1161 */
1162 if (scale && freq && !cs->uncertainty_margin) {
1163 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
1164 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
1165 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
1166 } else if (!cs->uncertainty_margin) {
1167 cs->uncertainty_margin = WATCHDOG_THRESHOLD;
1168 }
1169 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
1170
1171 /*
1172 * Ensure clocksources that have large 'mult' values don't overflow
1173 * when adjusted.
1174 */
1175 cs->maxadj = clocksource_max_adjustment(cs);
1176 while (freq && ((cs->mult + cs->maxadj < cs->mult)
1177 || (cs->mult - cs->maxadj > cs->mult))) {
1178 cs->mult >>= 1;
1179 cs->shift--;
1180 cs->maxadj = clocksource_max_adjustment(cs);
1181 }
1182
1183 /*
1184 * Only warn for *special* clocksources that self-define
1185 * their mult/shift values and don't specify a freq.
1186 */
1187 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1188 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1189 cs->name);
1190
1191 clocksource_update_max_deferment(cs);
1192
1193 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1194 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1195}
1196EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
1197
1198/**
1199 * __clocksource_register_scale - Used to install new clocksources
1200 * @cs: clocksource to be registered
1201 * @scale: Scale factor multiplied against freq to get clocksource hz
1202 * @freq: clocksource frequency (cycles per second) divided by scale
1203 *
1204 * Returns -EBUSY if registration fails, zero otherwise.
1205 *
1206 * This *SHOULD NOT* be called directly! Please use the
1207 * clocksource_register_hz() or clocksource_register_khz helper functions.
1208 */
1209int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1210{
1211 unsigned long flags;
1212
1213 clocksource_arch_init(cs);
1214
1215 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1216 cs->id = CSID_GENERIC;
1217 if (cs->vdso_clock_mode < 0 ||
1218 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1219 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1220 cs->name, cs->vdso_clock_mode);
1221 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1222 }
1223
1224 /* Initialize mult/shift and max_idle_ns */
1225 __clocksource_update_freq_scale(cs, scale, freq);
1226
1227 /* Add clocksource to the clocksource list */
1228 mutex_lock(&clocksource_mutex);
1229
1230 clocksource_watchdog_lock(&flags);
1231 clocksource_enqueue(cs);
1232 clocksource_enqueue_watchdog(cs);
1233 clocksource_watchdog_unlock(&flags);
1234
1235 clocksource_select();
1236 clocksource_select_watchdog(false);
1237 __clocksource_suspend_select(cs);
1238 mutex_unlock(&clocksource_mutex);
1239 return 0;
1240}
1241EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1242
1243static void __clocksource_change_rating(struct clocksource *cs, int rating)
1244{
1245 list_del(&cs->list);
1246 cs->rating = rating;
1247 clocksource_enqueue(cs);
1248}
1249
1250/**
1251 * clocksource_change_rating - Change the rating of a registered clocksource
1252 * @cs: clocksource to be changed
1253 * @rating: new rating
1254 */
1255void clocksource_change_rating(struct clocksource *cs, int rating)
1256{
1257 unsigned long flags;
1258
1259 mutex_lock(&clocksource_mutex);
1260 clocksource_watchdog_lock(&flags);
1261 __clocksource_change_rating(cs, rating);
1262 clocksource_watchdog_unlock(&flags);
1263
1264 clocksource_select();
1265 clocksource_select_watchdog(false);
1266 clocksource_suspend_select(false);
1267 mutex_unlock(&clocksource_mutex);
1268}
1269EXPORT_SYMBOL(clocksource_change_rating);
1270
1271/*
1272 * Unbind clocksource @cs. Called with clocksource_mutex held
1273 */
1274static int clocksource_unbind(struct clocksource *cs)
1275{
1276 unsigned long flags;
1277
1278 if (clocksource_is_watchdog(cs)) {
1279 /* Select and try to install a replacement watchdog. */
1280 clocksource_select_watchdog(true);
1281 if (clocksource_is_watchdog(cs))
1282 return -EBUSY;
1283 }
1284
1285 if (cs == curr_clocksource) {
1286 /* Select and try to install a replacement clock source */
1287 clocksource_select_fallback();
1288 if (curr_clocksource == cs)
1289 return -EBUSY;
1290 }
1291
1292 if (clocksource_is_suspend(cs)) {
1293 /*
1294 * Select and try to install a replacement suspend clocksource.
1295 * If no replacement suspend clocksource, we will just let the
1296 * clocksource go and have no suspend clocksource.
1297 */
1298 clocksource_suspend_select(true);
1299 }
1300
1301 clocksource_watchdog_lock(&flags);
1302 clocksource_dequeue_watchdog(cs);
1303 list_del_init(&cs->list);
1304 clocksource_watchdog_unlock(&flags);
1305
1306 return 0;
1307}
1308
1309/**
1310 * clocksource_unregister - remove a registered clocksource
1311 * @cs: clocksource to be unregistered
1312 */
1313int clocksource_unregister(struct clocksource *cs)
1314{
1315 int ret = 0;
1316
1317 mutex_lock(&clocksource_mutex);
1318 if (!list_empty(&cs->list))
1319 ret = clocksource_unbind(cs);
1320 mutex_unlock(&clocksource_mutex);
1321 return ret;
1322}
1323EXPORT_SYMBOL(clocksource_unregister);
1324
1325#ifdef CONFIG_SYSFS
1326/**
1327 * current_clocksource_show - sysfs interface for current clocksource
1328 * @dev: unused
1329 * @attr: unused
1330 * @buf: char buffer to be filled with clocksource list
1331 *
1332 * Provides sysfs interface for listing current clocksource.
1333 */
1334static ssize_t current_clocksource_show(struct device *dev,
1335 struct device_attribute *attr,
1336 char *buf)
1337{
1338 ssize_t count = 0;
1339
1340 mutex_lock(&clocksource_mutex);
1341 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
1342 mutex_unlock(&clocksource_mutex);
1343
1344 return count;
1345}
1346
1347ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1348{
1349 size_t ret = cnt;
1350
1351 /* strings from sysfs write are not 0 terminated! */
1352 if (!cnt || cnt >= CS_NAME_LEN)
1353 return -EINVAL;
1354
1355 /* strip of \n: */
1356 if (buf[cnt-1] == '\n')
1357 cnt--;
1358 if (cnt > 0)
1359 memcpy(dst, buf, cnt);
1360 dst[cnt] = 0;
1361 return ret;
1362}
1363
1364/**
1365 * current_clocksource_store - interface for manually overriding clocksource
1366 * @dev: unused
1367 * @attr: unused
1368 * @buf: name of override clocksource
1369 * @count: length of buffer
1370 *
1371 * Takes input from sysfs interface for manually overriding the default
1372 * clocksource selection.
1373 */
1374static ssize_t current_clocksource_store(struct device *dev,
1375 struct device_attribute *attr,
1376 const char *buf, size_t count)
1377{
1378 ssize_t ret;
1379
1380 mutex_lock(&clocksource_mutex);
1381
1382 ret = sysfs_get_uname(buf, override_name, count);
1383 if (ret >= 0)
1384 clocksource_select();
1385
1386 mutex_unlock(&clocksource_mutex);
1387
1388 return ret;
1389}
1390static DEVICE_ATTR_RW(current_clocksource);
1391
1392/**
1393 * unbind_clocksource_store - interface for manually unbinding clocksource
1394 * @dev: unused
1395 * @attr: unused
1396 * @buf: unused
1397 * @count: length of buffer
1398 *
1399 * Takes input from sysfs interface for manually unbinding a clocksource.
1400 */
1401static ssize_t unbind_clocksource_store(struct device *dev,
1402 struct device_attribute *attr,
1403 const char *buf, size_t count)
1404{
1405 struct clocksource *cs;
1406 char name[CS_NAME_LEN];
1407 ssize_t ret;
1408
1409 ret = sysfs_get_uname(buf, name, count);
1410 if (ret < 0)
1411 return ret;
1412
1413 ret = -ENODEV;
1414 mutex_lock(&clocksource_mutex);
1415 list_for_each_entry(cs, &clocksource_list, list) {
1416 if (strcmp(cs->name, name))
1417 continue;
1418 ret = clocksource_unbind(cs);
1419 break;
1420 }
1421 mutex_unlock(&clocksource_mutex);
1422
1423 return ret ? ret : count;
1424}
1425static DEVICE_ATTR_WO(unbind_clocksource);
1426
1427/**
1428 * available_clocksource_show - sysfs interface for listing clocksource
1429 * @dev: unused
1430 * @attr: unused
1431 * @buf: char buffer to be filled with clocksource list
1432 *
1433 * Provides sysfs interface for listing registered clocksources
1434 */
1435static ssize_t available_clocksource_show(struct device *dev,
1436 struct device_attribute *attr,
1437 char *buf)
1438{
1439 struct clocksource *src;
1440 ssize_t count = 0;
1441
1442 mutex_lock(&clocksource_mutex);
1443 list_for_each_entry(src, &clocksource_list, list) {
1444 /*
1445 * Don't show non-HRES clocksource if the tick code is
1446 * in one shot mode (highres=on or nohz=on)
1447 */
1448 if (!tick_oneshot_mode_active() ||
1449 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1450 count += snprintf(buf + count,
1451 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1452 "%s ", src->name);
1453 }
1454 mutex_unlock(&clocksource_mutex);
1455
1456 count += snprintf(buf + count,
1457 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1458
1459 return count;
1460}
1461static DEVICE_ATTR_RO(available_clocksource);
1462
1463static struct attribute *clocksource_attrs[] = {
1464 &dev_attr_current_clocksource.attr,
1465 &dev_attr_unbind_clocksource.attr,
1466 &dev_attr_available_clocksource.attr,
1467 NULL
1468};
1469ATTRIBUTE_GROUPS(clocksource);
1470
1471static struct bus_type clocksource_subsys = {
1472 .name = "clocksource",
1473 .dev_name = "clocksource",
1474};
1475
1476static struct device device_clocksource = {
1477 .id = 0,
1478 .bus = &clocksource_subsys,
1479 .groups = clocksource_groups,
1480};
1481
1482static int __init init_clocksource_sysfs(void)
1483{
1484 int error = subsys_system_register(&clocksource_subsys, NULL);
1485
1486 if (!error)
1487 error = device_register(&device_clocksource);
1488
1489 return error;
1490}
1491
1492device_initcall(init_clocksource_sysfs);
1493#endif /* CONFIG_SYSFS */
1494
1495/**
1496 * boot_override_clocksource - boot clock override
1497 * @str: override name
1498 *
1499 * Takes a clocksource= boot argument and uses it
1500 * as the clocksource override name.
1501 */
1502static int __init boot_override_clocksource(char* str)
1503{
1504 mutex_lock(&clocksource_mutex);
1505 if (str)
1506 strscpy(override_name, str, sizeof(override_name));
1507 mutex_unlock(&clocksource_mutex);
1508 return 1;
1509}
1510
1511__setup("clocksource=", boot_override_clocksource);
1512
1513/**
1514 * boot_override_clock - Compatibility layer for deprecated boot option
1515 * @str: override name
1516 *
1517 * DEPRECATED! Takes a clock= boot argument and uses it
1518 * as the clocksource override name
1519 */
1520static int __init boot_override_clock(char* str)
1521{
1522 if (!strcmp(str, "pmtmr")) {
1523 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1524 return boot_override_clocksource("acpi_pm");
1525 }
1526 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1527 return boot_override_clocksource(str);
1528}
1529
1530__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/clocksource.h>
27#include <linux/sysdev.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;
189
190static int clocksource_watchdog_kthread(void *data);
191static void __clocksource_change_rating(struct clocksource *cs, int rating);
192
193/*
194 * Interval: 0.5sec Threshold: 0.0625s
195 */
196#define WATCHDOG_INTERVAL (HZ >> 1)
197#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
198
199static void clocksource_watchdog_work(struct work_struct *work)
200{
201 /*
202 * If kthread_run fails the next watchdog scan over the
203 * watchdog_list will find the unstable clock again.
204 */
205 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
206}
207
208static void __clocksource_unstable(struct clocksource *cs)
209{
210 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
211 cs->flags |= CLOCK_SOURCE_UNSTABLE;
212 if (finished_booting)
213 schedule_work(&watchdog_work);
214}
215
216static void clocksource_unstable(struct clocksource *cs, int64_t delta)
217{
218 printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
219 cs->name, delta);
220 __clocksource_unstable(cs);
221}
222
223/**
224 * clocksource_mark_unstable - mark clocksource unstable via watchdog
225 * @cs: clocksource to be marked unstable
226 *
227 * This function is called instead of clocksource_change_rating from
228 * cpu hotplug code to avoid a deadlock between the clocksource mutex
229 * and the cpu hotplug mutex. It defers the update of the clocksource
230 * to the watchdog thread.
231 */
232void clocksource_mark_unstable(struct clocksource *cs)
233{
234 unsigned long flags;
235
236 spin_lock_irqsave(&watchdog_lock, flags);
237 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
238 if (list_empty(&cs->wd_list))
239 list_add(&cs->wd_list, &watchdog_list);
240 __clocksource_unstable(cs);
241 }
242 spin_unlock_irqrestore(&watchdog_lock, flags);
243}
244
245static void clocksource_watchdog(unsigned long data)
246{
247 struct clocksource *cs;
248 cycle_t csnow, wdnow;
249 int64_t wd_nsec, cs_nsec;
250 int next_cpu;
251
252 spin_lock(&watchdog_lock);
253 if (!watchdog_running)
254 goto out;
255
256 list_for_each_entry(cs, &watchdog_list, wd_list) {
257
258 /* Clocksource already marked unstable? */
259 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
260 if (finished_booting)
261 schedule_work(&watchdog_work);
262 continue;
263 }
264
265 local_irq_disable();
266 csnow = cs->read(cs);
267 wdnow = watchdog->read(watchdog);
268 local_irq_enable();
269
270 /* Clocksource initialized ? */
271 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
272 cs->flags |= CLOCK_SOURCE_WATCHDOG;
273 cs->wd_last = wdnow;
274 cs->cs_last = csnow;
275 continue;
276 }
277
278 wd_nsec = clocksource_cyc2ns((wdnow - cs->wd_last) & watchdog->mask,
279 watchdog->mult, watchdog->shift);
280
281 cs_nsec = clocksource_cyc2ns((csnow - cs->cs_last) &
282 cs->mask, cs->mult, cs->shift);
283 cs->cs_last = csnow;
284 cs->wd_last = wdnow;
285
286 /* Check the deviation from the watchdog clocksource. */
287 if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
288 clocksource_unstable(cs, cs_nsec - wd_nsec);
289 continue;
290 }
291
292 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
293 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
294 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
295 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
296 /*
297 * We just marked the clocksource as highres-capable,
298 * notify the rest of the system as well so that we
299 * transition into high-res mode:
300 */
301 tick_clock_notify();
302 }
303 }
304
305 /*
306 * Cycle through CPUs to check if the CPUs stay synchronized
307 * to each other.
308 */
309 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
310 if (next_cpu >= nr_cpu_ids)
311 next_cpu = cpumask_first(cpu_online_mask);
312 watchdog_timer.expires += WATCHDOG_INTERVAL;
313 add_timer_on(&watchdog_timer, next_cpu);
314out:
315 spin_unlock(&watchdog_lock);
316}
317
318static inline void clocksource_start_watchdog(void)
319{
320 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
321 return;
322 init_timer(&watchdog_timer);
323 watchdog_timer.function = clocksource_watchdog;
324 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
325 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
326 watchdog_running = 1;
327}
328
329static inline void clocksource_stop_watchdog(void)
330{
331 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
332 return;
333 del_timer(&watchdog_timer);
334 watchdog_running = 0;
335}
336
337static inline void clocksource_reset_watchdog(void)
338{
339 struct clocksource *cs;
340
341 list_for_each_entry(cs, &watchdog_list, wd_list)
342 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
343}
344
345static void clocksource_resume_watchdog(void)
346{
347 unsigned long flags;
348
349 /*
350 * We use trylock here to avoid a potential dead lock when
351 * kgdb calls this code after the kernel has been stopped with
352 * watchdog_lock held. When watchdog_lock is held we just
353 * return and accept, that the watchdog might trigger and mark
354 * the monitored clock source (usually TSC) unstable.
355 *
356 * This does not affect the other caller clocksource_resume()
357 * because at this point the kernel is UP, interrupts are
358 * disabled and nothing can hold watchdog_lock.
359 */
360 if (!spin_trylock_irqsave(&watchdog_lock, flags))
361 return;
362 clocksource_reset_watchdog();
363 spin_unlock_irqrestore(&watchdog_lock, flags);
364}
365
366static void clocksource_enqueue_watchdog(struct clocksource *cs)
367{
368 unsigned long flags;
369
370 spin_lock_irqsave(&watchdog_lock, flags);
371 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
372 /* cs is a clocksource to be watched. */
373 list_add(&cs->wd_list, &watchdog_list);
374 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
375 } else {
376 /* cs is a watchdog. */
377 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
378 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
379 /* Pick the best watchdog. */
380 if (!watchdog || cs->rating > watchdog->rating) {
381 watchdog = cs;
382 /* Reset watchdog cycles */
383 clocksource_reset_watchdog();
384 }
385 }
386 /* Check if the watchdog timer needs to be started. */
387 clocksource_start_watchdog();
388 spin_unlock_irqrestore(&watchdog_lock, flags);
389}
390
391static void clocksource_dequeue_watchdog(struct clocksource *cs)
392{
393 struct clocksource *tmp;
394 unsigned long flags;
395
396 spin_lock_irqsave(&watchdog_lock, flags);
397 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
398 /* cs is a watched clocksource. */
399 list_del_init(&cs->wd_list);
400 } else if (cs == watchdog) {
401 /* Reset watchdog cycles */
402 clocksource_reset_watchdog();
403 /* Current watchdog is removed. Find an alternative. */
404 watchdog = NULL;
405 list_for_each_entry(tmp, &clocksource_list, list) {
406 if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
407 continue;
408 if (!watchdog || tmp->rating > watchdog->rating)
409 watchdog = tmp;
410 }
411 }
412 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
413 /* Check if the watchdog timer needs to be stopped. */
414 clocksource_stop_watchdog();
415 spin_unlock_irqrestore(&watchdog_lock, flags);
416}
417
418static int clocksource_watchdog_kthread(void *data)
419{
420 struct clocksource *cs, *tmp;
421 unsigned long flags;
422 LIST_HEAD(unstable);
423
424 mutex_lock(&clocksource_mutex);
425 spin_lock_irqsave(&watchdog_lock, flags);
426 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
427 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
428 list_del_init(&cs->wd_list);
429 list_add(&cs->wd_list, &unstable);
430 }
431 /* Check if the watchdog timer needs to be stopped. */
432 clocksource_stop_watchdog();
433 spin_unlock_irqrestore(&watchdog_lock, flags);
434
435 /* Needs to be done outside of watchdog lock */
436 list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
437 list_del_init(&cs->wd_list);
438 __clocksource_change_rating(cs, 0);
439 }
440 mutex_unlock(&clocksource_mutex);
441 return 0;
442}
443
444#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
445
446static void clocksource_enqueue_watchdog(struct clocksource *cs)
447{
448 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
449 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
450}
451
452static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
453static inline void clocksource_resume_watchdog(void) { }
454static inline int clocksource_watchdog_kthread(void *data) { return 0; }
455
456#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
457
458/**
459 * clocksource_suspend - suspend the clocksource(s)
460 */
461void clocksource_suspend(void)
462{
463 struct clocksource *cs;
464
465 list_for_each_entry_reverse(cs, &clocksource_list, list)
466 if (cs->suspend)
467 cs->suspend(cs);
468}
469
470/**
471 * clocksource_resume - resume the clocksource(s)
472 */
473void clocksource_resume(void)
474{
475 struct clocksource *cs;
476
477 list_for_each_entry(cs, &clocksource_list, list)
478 if (cs->resume)
479 cs->resume(cs);
480
481 clocksource_resume_watchdog();
482}
483
484/**
485 * clocksource_touch_watchdog - Update watchdog
486 *
487 * Update the watchdog after exception contexts such as kgdb so as not
488 * to incorrectly trip the watchdog. This might fail when the kernel
489 * was stopped in code which holds watchdog_lock.
490 */
491void clocksource_touch_watchdog(void)
492{
493 clocksource_resume_watchdog();
494}
495
496/**
497 * clocksource_max_deferment - Returns max time the clocksource can be deferred
498 * @cs: Pointer to clocksource
499 *
500 */
501static u64 clocksource_max_deferment(struct clocksource *cs)
502{
503 u64 max_nsecs, max_cycles;
504
505 /*
506 * Calculate the maximum number of cycles that we can pass to the
507 * cyc2ns function without overflowing a 64-bit signed result. The
508 * maximum number of cycles is equal to ULLONG_MAX/cs->mult which
509 * is equivalent to the below.
510 * max_cycles < (2^63)/cs->mult
511 * max_cycles < 2^(log2((2^63)/cs->mult))
512 * max_cycles < 2^(log2(2^63) - log2(cs->mult))
513 * max_cycles < 2^(63 - log2(cs->mult))
514 * max_cycles < 1 << (63 - log2(cs->mult))
515 * Please note that we add 1 to the result of the log2 to account for
516 * any rounding errors, ensure the above inequality is satisfied and
517 * no overflow will occur.
518 */
519 max_cycles = 1ULL << (63 - (ilog2(cs->mult) + 1));
520
521 /*
522 * The actual maximum number of cycles we can defer the clocksource is
523 * determined by the minimum of max_cycles and cs->mask.
524 */
525 max_cycles = min_t(u64, max_cycles, (u64) cs->mask);
526 max_nsecs = clocksource_cyc2ns(max_cycles, cs->mult, cs->shift);
527
528 /*
529 * To ensure that the clocksource does not wrap whilst we are idle,
530 * limit the time the clocksource can be deferred by 12.5%. Please
531 * note a margin of 12.5% is used because this can be computed with
532 * a shift, versus say 10% which would require division.
533 */
534 return max_nsecs - (max_nsecs >> 5);
535}
536
537#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
538
539/**
540 * clocksource_select - Select the best clocksource available
541 *
542 * Private function. Must hold clocksource_mutex when called.
543 *
544 * Select the clocksource with the best rating, or the clocksource,
545 * which is selected by userspace override.
546 */
547static void clocksource_select(void)
548{
549 struct clocksource *best, *cs;
550
551 if (!finished_booting || list_empty(&clocksource_list))
552 return;
553 /* First clocksource on the list has the best rating. */
554 best = list_first_entry(&clocksource_list, struct clocksource, list);
555 /* Check for the override clocksource. */
556 list_for_each_entry(cs, &clocksource_list, list) {
557 if (strcmp(cs->name, override_name) != 0)
558 continue;
559 /*
560 * Check to make sure we don't switch to a non-highres
561 * capable clocksource if the tick code is in oneshot
562 * mode (highres or nohz)
563 */
564 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
565 tick_oneshot_mode_active()) {
566 /* Override clocksource cannot be used. */
567 printk(KERN_WARNING "Override clocksource %s is not "
568 "HRT compatible. Cannot switch while in "
569 "HRT/NOHZ mode\n", cs->name);
570 override_name[0] = 0;
571 } else
572 /* Override clocksource can be used. */
573 best = cs;
574 break;
575 }
576 if (curr_clocksource != best) {
577 printk(KERN_INFO "Switching to clocksource %s\n", best->name);
578 curr_clocksource = best;
579 timekeeping_notify(curr_clocksource);
580 }
581}
582
583#else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
584
585static inline void clocksource_select(void) { }
586
587#endif
588
589/*
590 * clocksource_done_booting - Called near the end of core bootup
591 *
592 * Hack to avoid lots of clocksource churn at boot time.
593 * We use fs_initcall because we want this to start before
594 * device_initcall but after subsys_initcall.
595 */
596static int __init clocksource_done_booting(void)
597{
598 mutex_lock(&clocksource_mutex);
599 curr_clocksource = clocksource_default_clock();
600 mutex_unlock(&clocksource_mutex);
601
602 finished_booting = 1;
603
604 /*
605 * Run the watchdog first to eliminate unstable clock sources
606 */
607 clocksource_watchdog_kthread(NULL);
608
609 mutex_lock(&clocksource_mutex);
610 clocksource_select();
611 mutex_unlock(&clocksource_mutex);
612 return 0;
613}
614fs_initcall(clocksource_done_booting);
615
616/*
617 * Enqueue the clocksource sorted by rating
618 */
619static void clocksource_enqueue(struct clocksource *cs)
620{
621 struct list_head *entry = &clocksource_list;
622 struct clocksource *tmp;
623
624 list_for_each_entry(tmp, &clocksource_list, list)
625 /* Keep track of the place, where to insert */
626 if (tmp->rating >= cs->rating)
627 entry = &tmp->list;
628 list_add(&cs->list, entry);
629}
630
631/**
632 * __clocksource_updatefreq_scale - Used update clocksource with new freq
633 * @t: clocksource to be registered
634 * @scale: Scale factor multiplied against freq to get clocksource hz
635 * @freq: clocksource frequency (cycles per second) divided by scale
636 *
637 * This should only be called from the clocksource->enable() method.
638 *
639 * This *SHOULD NOT* be called directly! Please use the
640 * clocksource_updatefreq_hz() or clocksource_updatefreq_khz helper functions.
641 */
642void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
643{
644 u64 sec;
645
646 /*
647 * Calc the maximum number of seconds which we can run before
648 * wrapping around. For clocksources which have a mask > 32bit
649 * we need to limit the max sleep time to have a good
650 * conversion precision. 10 minutes is still a reasonable
651 * amount. That results in a shift value of 24 for a
652 * clocksource with mask >= 40bit and f >= 4GHz. That maps to
653 * ~ 0.06ppm granularity for NTP. We apply the same 12.5%
654 * margin as we do in clocksource_max_deferment()
655 */
656 sec = (cs->mask - (cs->mask >> 5));
657 do_div(sec, freq);
658 do_div(sec, scale);
659 if (!sec)
660 sec = 1;
661 else if (sec > 600 && cs->mask > UINT_MAX)
662 sec = 600;
663
664 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
665 NSEC_PER_SEC / scale, sec * scale);
666 cs->max_idle_ns = clocksource_max_deferment(cs);
667}
668EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);
669
670/**
671 * __clocksource_register_scale - Used to install new clocksources
672 * @t: clocksource to be registered
673 * @scale: Scale factor multiplied against freq to get clocksource hz
674 * @freq: clocksource frequency (cycles per second) divided by scale
675 *
676 * Returns -EBUSY if registration fails, zero otherwise.
677 *
678 * This *SHOULD NOT* be called directly! Please use the
679 * clocksource_register_hz() or clocksource_register_khz helper functions.
680 */
681int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
682{
683
684 /* Initialize mult/shift and max_idle_ns */
685 __clocksource_updatefreq_scale(cs, scale, freq);
686
687 /* Add clocksource to the clcoksource list */
688 mutex_lock(&clocksource_mutex);
689 clocksource_enqueue(cs);
690 clocksource_enqueue_watchdog(cs);
691 clocksource_select();
692 mutex_unlock(&clocksource_mutex);
693 return 0;
694}
695EXPORT_SYMBOL_GPL(__clocksource_register_scale);
696
697
698/**
699 * clocksource_register - Used to install new clocksources
700 * @t: clocksource to be registered
701 *
702 * Returns -EBUSY if registration fails, zero otherwise.
703 */
704int clocksource_register(struct clocksource *cs)
705{
706 /* calculate max idle time permitted for this clocksource */
707 cs->max_idle_ns = clocksource_max_deferment(cs);
708
709 mutex_lock(&clocksource_mutex);
710 clocksource_enqueue(cs);
711 clocksource_enqueue_watchdog(cs);
712 clocksource_select();
713 mutex_unlock(&clocksource_mutex);
714 return 0;
715}
716EXPORT_SYMBOL(clocksource_register);
717
718static void __clocksource_change_rating(struct clocksource *cs, int rating)
719{
720 list_del(&cs->list);
721 cs->rating = rating;
722 clocksource_enqueue(cs);
723 clocksource_select();
724}
725
726/**
727 * clocksource_change_rating - Change the rating of a registered clocksource
728 */
729void clocksource_change_rating(struct clocksource *cs, int rating)
730{
731 mutex_lock(&clocksource_mutex);
732 __clocksource_change_rating(cs, rating);
733 mutex_unlock(&clocksource_mutex);
734}
735EXPORT_SYMBOL(clocksource_change_rating);
736
737/**
738 * clocksource_unregister - remove a registered clocksource
739 */
740void clocksource_unregister(struct clocksource *cs)
741{
742 mutex_lock(&clocksource_mutex);
743 clocksource_dequeue_watchdog(cs);
744 list_del(&cs->list);
745 clocksource_select();
746 mutex_unlock(&clocksource_mutex);
747}
748EXPORT_SYMBOL(clocksource_unregister);
749
750#ifdef CONFIG_SYSFS
751/**
752 * sysfs_show_current_clocksources - sysfs interface for current clocksource
753 * @dev: unused
754 * @buf: char buffer to be filled with clocksource list
755 *
756 * Provides sysfs interface for listing current clocksource.
757 */
758static ssize_t
759sysfs_show_current_clocksources(struct sys_device *dev,
760 struct sysdev_attribute *attr, char *buf)
761{
762 ssize_t count = 0;
763
764 mutex_lock(&clocksource_mutex);
765 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
766 mutex_unlock(&clocksource_mutex);
767
768 return count;
769}
770
771/**
772 * sysfs_override_clocksource - interface for manually overriding clocksource
773 * @dev: unused
774 * @buf: name of override clocksource
775 * @count: length of buffer
776 *
777 * Takes input from sysfs interface for manually overriding the default
778 * clocksource selection.
779 */
780static ssize_t sysfs_override_clocksource(struct sys_device *dev,
781 struct sysdev_attribute *attr,
782 const char *buf, size_t count)
783{
784 size_t ret = count;
785
786 /* strings from sysfs write are not 0 terminated! */
787 if (count >= sizeof(override_name))
788 return -EINVAL;
789
790 /* strip of \n: */
791 if (buf[count-1] == '\n')
792 count--;
793
794 mutex_lock(&clocksource_mutex);
795
796 if (count > 0)
797 memcpy(override_name, buf, count);
798 override_name[count] = 0;
799 clocksource_select();
800
801 mutex_unlock(&clocksource_mutex);
802
803 return ret;
804}
805
806/**
807 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
808 * @dev: unused
809 * @buf: char buffer to be filled with clocksource list
810 *
811 * Provides sysfs interface for listing registered clocksources
812 */
813static ssize_t
814sysfs_show_available_clocksources(struct sys_device *dev,
815 struct sysdev_attribute *attr,
816 char *buf)
817{
818 struct clocksource *src;
819 ssize_t count = 0;
820
821 mutex_lock(&clocksource_mutex);
822 list_for_each_entry(src, &clocksource_list, list) {
823 /*
824 * Don't show non-HRES clocksource if the tick code is
825 * in one shot mode (highres=on or nohz=on)
826 */
827 if (!tick_oneshot_mode_active() ||
828 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
829 count += snprintf(buf + count,
830 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
831 "%s ", src->name);
832 }
833 mutex_unlock(&clocksource_mutex);
834
835 count += snprintf(buf + count,
836 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
837
838 return count;
839}
840
841/*
842 * Sysfs setup bits:
843 */
844static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
845 sysfs_override_clocksource);
846
847static SYSDEV_ATTR(available_clocksource, 0444,
848 sysfs_show_available_clocksources, NULL);
849
850static struct sysdev_class clocksource_sysclass = {
851 .name = "clocksource",
852};
853
854static struct sys_device device_clocksource = {
855 .id = 0,
856 .cls = &clocksource_sysclass,
857};
858
859static int __init init_clocksource_sysfs(void)
860{
861 int error = sysdev_class_register(&clocksource_sysclass);
862
863 if (!error)
864 error = sysdev_register(&device_clocksource);
865 if (!error)
866 error = sysdev_create_file(
867 &device_clocksource,
868 &attr_current_clocksource);
869 if (!error)
870 error = sysdev_create_file(
871 &device_clocksource,
872 &attr_available_clocksource);
873 return error;
874}
875
876device_initcall(init_clocksource_sysfs);
877#endif /* CONFIG_SYSFS */
878
879/**
880 * boot_override_clocksource - boot clock override
881 * @str: override name
882 *
883 * Takes a clocksource= boot argument and uses it
884 * as the clocksource override name.
885 */
886static int __init boot_override_clocksource(char* str)
887{
888 mutex_lock(&clocksource_mutex);
889 if (str)
890 strlcpy(override_name, str, sizeof(override_name));
891 mutex_unlock(&clocksource_mutex);
892 return 1;
893}
894
895__setup("clocksource=", boot_override_clocksource);
896
897/**
898 * boot_override_clock - Compatibility layer for deprecated boot option
899 * @str: override name
900 *
901 * DEPRECATED! Takes a clock= boot argument and uses it
902 * as the clocksource override name
903 */
904static int __init boot_override_clock(char* str)
905{
906 if (!strcmp(str, "pmtmr")) {
907 printk("Warning: clock=pmtmr is deprecated. "
908 "Use clocksource=acpi_pm.\n");
909 return boot_override_clocksource("acpi_pm");
910 }
911 printk("Warning! clock= boot option is deprecated. "
912 "Use clocksource=xyz\n");
913 return boot_override_clocksource(str);
914}
915
916__setup("clock=", boot_override_clock);