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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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
27
28#include <linux/device.h>
29#include <linux/clocksource.h>
30#include <linux/init.h>
31#include <linux/module.h>
32#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
33#include <linux/tick.h>
34#include <linux/kthread.h>
35
36#include "tick-internal.h"
37#include "timekeeping_internal.h"
38
39/**
40 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
41 * @mult: pointer to mult variable
42 * @shift: pointer to shift variable
43 * @from: frequency to convert from
44 * @to: frequency to convert to
45 * @maxsec: guaranteed runtime conversion range in seconds
46 *
47 * The function evaluates the shift/mult pair for the scaled math
48 * operations of clocksources and clockevents.
49 *
50 * @to and @from are frequency values in HZ. For clock sources @to is
51 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
52 * event @to is the counter frequency and @from is NSEC_PER_SEC.
53 *
54 * The @maxsec conversion range argument controls the time frame in
55 * seconds which must be covered by the runtime conversion with the
56 * calculated mult and shift factors. This guarantees that no 64bit
57 * overflow happens when the input value of the conversion is
58 * multiplied with the calculated mult factor. Larger ranges may
59 * reduce the conversion accuracy by chosing smaller mult and shift
60 * factors.
61 */
62void
63clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
64{
65 u64 tmp;
66 u32 sft, sftacc= 32;
67
68 /*
69 * Calculate the shift factor which is limiting the conversion
70 * range:
71 */
72 tmp = ((u64)maxsec * from) >> 32;
73 while (tmp) {
74 tmp >>=1;
75 sftacc--;
76 }
77
78 /*
79 * Find the conversion shift/mult pair which has the best
80 * accuracy and fits the maxsec conversion range:
81 */
82 for (sft = 32; sft > 0; sft--) {
83 tmp = (u64) to << sft;
84 tmp += from / 2;
85 do_div(tmp, from);
86 if ((tmp >> sftacc) == 0)
87 break;
88 }
89 *mult = tmp;
90 *shift = sft;
91}
92EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
93
94/*[Clocksource internal variables]---------
95 * curr_clocksource:
96 * currently selected clocksource.
97 * clocksource_list:
98 * linked list with the registered clocksources
99 * clocksource_mutex:
100 * protects manipulations to curr_clocksource and the clocksource_list
101 * override_name:
102 * Name of the user-specified clocksource.
103 */
104static struct clocksource *curr_clocksource;
105static LIST_HEAD(clocksource_list);
106static DEFINE_MUTEX(clocksource_mutex);
107static char override_name[CS_NAME_LEN];
108static int finished_booting;
109
110#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
111static void clocksource_watchdog_work(struct work_struct *work);
112static void clocksource_select(void);
113
114static LIST_HEAD(watchdog_list);
115static struct clocksource *watchdog;
116static struct timer_list watchdog_timer;
117static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
118static DEFINE_SPINLOCK(watchdog_lock);
119static int watchdog_running;
120static atomic_t watchdog_reset_pending;
121
122static int clocksource_watchdog_kthread(void *data);
123static void __clocksource_change_rating(struct clocksource *cs, int rating);
124
125/*
126 * Interval: 0.5sec Threshold: 0.0625s
127 */
128#define WATCHDOG_INTERVAL (HZ >> 1)
129#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
130
131static void clocksource_watchdog_work(struct work_struct *work)
132{
133 /*
134 * If kthread_run fails the next watchdog scan over the
135 * watchdog_list will find the unstable clock again.
136 */
137 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
138}
139
140static void __clocksource_unstable(struct clocksource *cs)
141{
142 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
143 cs->flags |= CLOCK_SOURCE_UNSTABLE;
144 if (finished_booting)
145 schedule_work(&watchdog_work);
146}
147
148/**
149 * clocksource_mark_unstable - mark clocksource unstable via watchdog
150 * @cs: clocksource to be marked unstable
151 *
152 * This function is called instead of clocksource_change_rating from
153 * cpu hotplug code to avoid a deadlock between the clocksource mutex
154 * and the cpu hotplug mutex. It defers the update of the clocksource
155 * to the watchdog thread.
156 */
157void clocksource_mark_unstable(struct clocksource *cs)
158{
159 unsigned long flags;
160
161 spin_lock_irqsave(&watchdog_lock, flags);
162 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
163 if (list_empty(&cs->wd_list))
164 list_add(&cs->wd_list, &watchdog_list);
165 __clocksource_unstable(cs);
166 }
167 spin_unlock_irqrestore(&watchdog_lock, flags);
168}
169
170static void clocksource_watchdog(unsigned long data)
171{
172 struct clocksource *cs;
173 u64 csnow, wdnow, cslast, wdlast, delta;
174 int64_t wd_nsec, cs_nsec;
175 int next_cpu, reset_pending;
176
177 spin_lock(&watchdog_lock);
178 if (!watchdog_running)
179 goto out;
180
181 reset_pending = atomic_read(&watchdog_reset_pending);
182
183 list_for_each_entry(cs, &watchdog_list, wd_list) {
184
185 /* Clocksource already marked unstable? */
186 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
187 if (finished_booting)
188 schedule_work(&watchdog_work);
189 continue;
190 }
191
192 local_irq_disable();
193 csnow = cs->read(cs);
194 wdnow = watchdog->read(watchdog);
195 local_irq_enable();
196
197 /* Clocksource initialized ? */
198 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
199 atomic_read(&watchdog_reset_pending)) {
200 cs->flags |= CLOCK_SOURCE_WATCHDOG;
201 cs->wd_last = wdnow;
202 cs->cs_last = csnow;
203 continue;
204 }
205
206 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
207 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
208 watchdog->shift);
209
210 delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
211 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
212 wdlast = cs->wd_last; /* save these in case we print them */
213 cslast = cs->cs_last;
214 cs->cs_last = csnow;
215 cs->wd_last = wdnow;
216
217 if (atomic_read(&watchdog_reset_pending))
218 continue;
219
220 /* Check the deviation from the watchdog clocksource. */
221 if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
222 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
223 smp_processor_id(), cs->name);
224 pr_warn(" '%s' wd_now: %llx wd_last: %llx mask: %llx\n",
225 watchdog->name, wdnow, wdlast, watchdog->mask);
226 pr_warn(" '%s' cs_now: %llx cs_last: %llx mask: %llx\n",
227 cs->name, csnow, cslast, cs->mask);
228 __clocksource_unstable(cs);
229 continue;
230 }
231
232 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
233 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
234 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
235 /* Mark it valid for high-res. */
236 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
237
238 /*
239 * clocksource_done_booting() will sort it if
240 * finished_booting is not set yet.
241 */
242 if (!finished_booting)
243 continue;
244
245 /*
246 * If this is not the current clocksource let
247 * the watchdog thread reselect it. Due to the
248 * change to high res this clocksource might
249 * be preferred now. If it is the current
250 * clocksource let the tick code know about
251 * that change.
252 */
253 if (cs != curr_clocksource) {
254 cs->flags |= CLOCK_SOURCE_RESELECT;
255 schedule_work(&watchdog_work);
256 } else {
257 tick_clock_notify();
258 }
259 }
260 }
261
262 /*
263 * We only clear the watchdog_reset_pending, when we did a
264 * full cycle through all clocksources.
265 */
266 if (reset_pending)
267 atomic_dec(&watchdog_reset_pending);
268
269 /*
270 * Cycle through CPUs to check if the CPUs stay synchronized
271 * to each other.
272 */
273 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
274 if (next_cpu >= nr_cpu_ids)
275 next_cpu = cpumask_first(cpu_online_mask);
276 watchdog_timer.expires += WATCHDOG_INTERVAL;
277 add_timer_on(&watchdog_timer, next_cpu);
278out:
279 spin_unlock(&watchdog_lock);
280}
281
282static inline void clocksource_start_watchdog(void)
283{
284 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
285 return;
286 init_timer(&watchdog_timer);
287 watchdog_timer.function = clocksource_watchdog;
288 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
289 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
290 watchdog_running = 1;
291}
292
293static inline void clocksource_stop_watchdog(void)
294{
295 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
296 return;
297 del_timer(&watchdog_timer);
298 watchdog_running = 0;
299}
300
301static inline void clocksource_reset_watchdog(void)
302{
303 struct clocksource *cs;
304
305 list_for_each_entry(cs, &watchdog_list, wd_list)
306 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
307}
308
309static void clocksource_resume_watchdog(void)
310{
311 atomic_inc(&watchdog_reset_pending);
312}
313
314static void clocksource_enqueue_watchdog(struct clocksource *cs)
315{
316 unsigned long flags;
317
318 spin_lock_irqsave(&watchdog_lock, flags);
319 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
320 /* cs is a clocksource to be watched. */
321 list_add(&cs->wd_list, &watchdog_list);
322 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
323 } else {
324 /* cs is a watchdog. */
325 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
326 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
327 }
328 spin_unlock_irqrestore(&watchdog_lock, flags);
329}
330
331static void clocksource_select_watchdog(bool fallback)
332{
333 struct clocksource *cs, *old_wd;
334 unsigned long flags;
335
336 spin_lock_irqsave(&watchdog_lock, flags);
337 /* save current watchdog */
338 old_wd = watchdog;
339 if (fallback)
340 watchdog = NULL;
341
342 list_for_each_entry(cs, &clocksource_list, list) {
343 /* cs is a clocksource to be watched. */
344 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
345 continue;
346
347 /* Skip current if we were requested for a fallback. */
348 if (fallback && cs == old_wd)
349 continue;
350
351 /* Pick the best watchdog. */
352 if (!watchdog || cs->rating > watchdog->rating)
353 watchdog = cs;
354 }
355 /* If we failed to find a fallback restore the old one. */
356 if (!watchdog)
357 watchdog = old_wd;
358
359 /* If we changed the watchdog we need to reset cycles. */
360 if (watchdog != old_wd)
361 clocksource_reset_watchdog();
362
363 /* Check if the watchdog timer needs to be started. */
364 clocksource_start_watchdog();
365 spin_unlock_irqrestore(&watchdog_lock, flags);
366}
367
368static void clocksource_dequeue_watchdog(struct clocksource *cs)
369{
370 unsigned long flags;
371
372 spin_lock_irqsave(&watchdog_lock, flags);
373 if (cs != watchdog) {
374 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
375 /* cs is a watched clocksource. */
376 list_del_init(&cs->wd_list);
377 /* Check if the watchdog timer needs to be stopped. */
378 clocksource_stop_watchdog();
379 }
380 }
381 spin_unlock_irqrestore(&watchdog_lock, flags);
382}
383
384static int __clocksource_watchdog_kthread(void)
385{
386 struct clocksource *cs, *tmp;
387 unsigned long flags;
388 LIST_HEAD(unstable);
389 int select = 0;
390
391 spin_lock_irqsave(&watchdog_lock, flags);
392 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
393 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
394 list_del_init(&cs->wd_list);
395 list_add(&cs->wd_list, &unstable);
396 select = 1;
397 }
398 if (cs->flags & CLOCK_SOURCE_RESELECT) {
399 cs->flags &= ~CLOCK_SOURCE_RESELECT;
400 select = 1;
401 }
402 }
403 /* Check if the watchdog timer needs to be stopped. */
404 clocksource_stop_watchdog();
405 spin_unlock_irqrestore(&watchdog_lock, flags);
406
407 /* Needs to be done outside of watchdog lock */
408 list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
409 list_del_init(&cs->wd_list);
410 __clocksource_change_rating(cs, 0);
411 }
412 return select;
413}
414
415static int clocksource_watchdog_kthread(void *data)
416{
417 mutex_lock(&clocksource_mutex);
418 if (__clocksource_watchdog_kthread())
419 clocksource_select();
420 mutex_unlock(&clocksource_mutex);
421 return 0;
422}
423
424static bool clocksource_is_watchdog(struct clocksource *cs)
425{
426 return cs == watchdog;
427}
428
429#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
430
431static void clocksource_enqueue_watchdog(struct clocksource *cs)
432{
433 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
434 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
435}
436
437static void clocksource_select_watchdog(bool fallback) { }
438static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
439static inline void clocksource_resume_watchdog(void) { }
440static inline int __clocksource_watchdog_kthread(void) { return 0; }
441static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
442void clocksource_mark_unstable(struct clocksource *cs) { }
443
444#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
445
446/**
447 * clocksource_suspend - suspend the clocksource(s)
448 */
449void clocksource_suspend(void)
450{
451 struct clocksource *cs;
452
453 list_for_each_entry_reverse(cs, &clocksource_list, list)
454 if (cs->suspend)
455 cs->suspend(cs);
456}
457
458/**
459 * clocksource_resume - resume the clocksource(s)
460 */
461void clocksource_resume(void)
462{
463 struct clocksource *cs;
464
465 list_for_each_entry(cs, &clocksource_list, list)
466 if (cs->resume)
467 cs->resume(cs);
468
469 clocksource_resume_watchdog();
470}
471
472/**
473 * clocksource_touch_watchdog - Update watchdog
474 *
475 * Update the watchdog after exception contexts such as kgdb so as not
476 * to incorrectly trip the watchdog. This might fail when the kernel
477 * was stopped in code which holds watchdog_lock.
478 */
479void clocksource_touch_watchdog(void)
480{
481 clocksource_resume_watchdog();
482}
483
484/**
485 * clocksource_max_adjustment- Returns max adjustment amount
486 * @cs: Pointer to clocksource
487 *
488 */
489static u32 clocksource_max_adjustment(struct clocksource *cs)
490{
491 u64 ret;
492 /*
493 * We won't try to correct for more than 11% adjustments (110,000 ppm),
494 */
495 ret = (u64)cs->mult * 11;
496 do_div(ret,100);
497 return (u32)ret;
498}
499
500/**
501 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
502 * @mult: cycle to nanosecond multiplier
503 * @shift: cycle to nanosecond divisor (power of two)
504 * @maxadj: maximum adjustment value to mult (~11%)
505 * @mask: bitmask for two's complement subtraction of non 64 bit counters
506 * @max_cyc: maximum cycle value before potential overflow (does not include
507 * any safety margin)
508 *
509 * NOTE: This function includes a safety margin of 50%, in other words, we
510 * return half the number of nanoseconds the hardware counter can technically
511 * cover. This is done so that we can potentially detect problems caused by
512 * delayed timers or bad hardware, which might result in time intervals that
513 * are larger than what the math used can handle without overflows.
514 */
515u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
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 result.
522 */
523 max_cycles = ULLONG_MAX;
524 do_div(max_cycles, mult+maxadj);
525
526 /*
527 * The actual maximum number of cycles we can defer the clocksource is
528 * determined by the minimum of max_cycles and mask.
529 * Note: Here we subtract the maxadj to make sure we don't sleep for
530 * too long if there's a large negative adjustment.
531 */
532 max_cycles = min(max_cycles, mask);
533 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
534
535 /* return the max_cycles value as well if requested */
536 if (max_cyc)
537 *max_cyc = max_cycles;
538
539 /* Return 50% of the actual maximum, so we can detect bad values */
540 max_nsecs >>= 1;
541
542 return max_nsecs;
543}
544
545/**
546 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
547 * @cs: Pointer to clocksource to be updated
548 *
549 */
550static inline void clocksource_update_max_deferment(struct clocksource *cs)
551{
552 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
553 cs->maxadj, cs->mask,
554 &cs->max_cycles);
555}
556
557#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
558
559static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
560{
561 struct clocksource *cs;
562
563 if (!finished_booting || list_empty(&clocksource_list))
564 return NULL;
565
566 /*
567 * We pick the clocksource with the highest rating. If oneshot
568 * mode is active, we pick the highres valid clocksource with
569 * the best rating.
570 */
571 list_for_each_entry(cs, &clocksource_list, list) {
572 if (skipcur && cs == curr_clocksource)
573 continue;
574 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
575 continue;
576 return cs;
577 }
578 return NULL;
579}
580
581static void __clocksource_select(bool skipcur)
582{
583 bool oneshot = tick_oneshot_mode_active();
584 struct clocksource *best, *cs;
585
586 /* Find the best suitable clocksource */
587 best = clocksource_find_best(oneshot, skipcur);
588 if (!best)
589 return;
590
591 /* Check for the override clocksource. */
592 list_for_each_entry(cs, &clocksource_list, list) {
593 if (skipcur && cs == curr_clocksource)
594 continue;
595 if (strcmp(cs->name, override_name) != 0)
596 continue;
597 /*
598 * Check to make sure we don't switch to a non-highres
599 * capable clocksource if the tick code is in oneshot
600 * mode (highres or nohz)
601 */
602 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
603 /* Override clocksource cannot be used. */
604 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
605 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
606 cs->name);
607 override_name[0] = 0;
608 } else {
609 /*
610 * The override cannot be currently verified.
611 * Deferring to let the watchdog check.
612 */
613 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
614 cs->name);
615 }
616 } else
617 /* Override clocksource can be used. */
618 best = cs;
619 break;
620 }
621
622 if (curr_clocksource != best && !timekeeping_notify(best)) {
623 pr_info("Switched to clocksource %s\n", best->name);
624 curr_clocksource = best;
625 }
626}
627
628/**
629 * clocksource_select - Select the best clocksource available
630 *
631 * Private function. Must hold clocksource_mutex when called.
632 *
633 * Select the clocksource with the best rating, or the clocksource,
634 * which is selected by userspace override.
635 */
636static void clocksource_select(void)
637{
638 __clocksource_select(false);
639}
640
641static void clocksource_select_fallback(void)
642{
643 __clocksource_select(true);
644}
645
646#else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
647static inline void clocksource_select(void) { }
648static inline void clocksource_select_fallback(void) { }
649
650#endif
651
652/*
653 * clocksource_done_booting - Called near the end of core bootup
654 *
655 * Hack to avoid lots of clocksource churn at boot time.
656 * We use fs_initcall because we want this to start before
657 * device_initcall but after subsys_initcall.
658 */
659static int __init clocksource_done_booting(void)
660{
661 mutex_lock(&clocksource_mutex);
662 curr_clocksource = clocksource_default_clock();
663 finished_booting = 1;
664 /*
665 * Run the watchdog first to eliminate unstable clock sources
666 */
667 __clocksource_watchdog_kthread();
668 clocksource_select();
669 mutex_unlock(&clocksource_mutex);
670 return 0;
671}
672fs_initcall(clocksource_done_booting);
673
674/*
675 * Enqueue the clocksource sorted by rating
676 */
677static void clocksource_enqueue(struct clocksource *cs)
678{
679 struct list_head *entry = &clocksource_list;
680 struct clocksource *tmp;
681
682 list_for_each_entry(tmp, &clocksource_list, list) {
683 /* Keep track of the place, where to insert */
684 if (tmp->rating < cs->rating)
685 break;
686 entry = &tmp->list;
687 }
688 list_add(&cs->list, entry);
689}
690
691/**
692 * __clocksource_update_freq_scale - Used update clocksource with new freq
693 * @cs: clocksource to be registered
694 * @scale: Scale factor multiplied against freq to get clocksource hz
695 * @freq: clocksource frequency (cycles per second) divided by scale
696 *
697 * This should only be called from the clocksource->enable() method.
698 *
699 * This *SHOULD NOT* be called directly! Please use the
700 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
701 * functions.
702 */
703void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
704{
705 u64 sec;
706
707 /*
708 * Default clocksources are *special* and self-define their mult/shift.
709 * But, you're not special, so you should specify a freq value.
710 */
711 if (freq) {
712 /*
713 * Calc the maximum number of seconds which we can run before
714 * wrapping around. For clocksources which have a mask > 32-bit
715 * we need to limit the max sleep time to have a good
716 * conversion precision. 10 minutes is still a reasonable
717 * amount. That results in a shift value of 24 for a
718 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
719 * ~ 0.06ppm granularity for NTP.
720 */
721 sec = cs->mask;
722 do_div(sec, freq);
723 do_div(sec, scale);
724 if (!sec)
725 sec = 1;
726 else if (sec > 600 && cs->mask > UINT_MAX)
727 sec = 600;
728
729 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
730 NSEC_PER_SEC / scale, sec * scale);
731 }
732 /*
733 * Ensure clocksources that have large 'mult' values don't overflow
734 * when adjusted.
735 */
736 cs->maxadj = clocksource_max_adjustment(cs);
737 while (freq && ((cs->mult + cs->maxadj < cs->mult)
738 || (cs->mult - cs->maxadj > cs->mult))) {
739 cs->mult >>= 1;
740 cs->shift--;
741 cs->maxadj = clocksource_max_adjustment(cs);
742 }
743
744 /*
745 * Only warn for *special* clocksources that self-define
746 * their mult/shift values and don't specify a freq.
747 */
748 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
749 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
750 cs->name);
751
752 clocksource_update_max_deferment(cs);
753
754 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
755 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
756}
757EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
758
759/**
760 * __clocksource_register_scale - Used to install new clocksources
761 * @cs: clocksource to be registered
762 * @scale: Scale factor multiplied against freq to get clocksource hz
763 * @freq: clocksource frequency (cycles per second) divided by scale
764 *
765 * Returns -EBUSY if registration fails, zero otherwise.
766 *
767 * This *SHOULD NOT* be called directly! Please use the
768 * clocksource_register_hz() or clocksource_register_khz helper functions.
769 */
770int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
771{
772
773 /* Initialize mult/shift and max_idle_ns */
774 __clocksource_update_freq_scale(cs, scale, freq);
775
776 /* Add clocksource to the clocksource list */
777 mutex_lock(&clocksource_mutex);
778 clocksource_enqueue(cs);
779 clocksource_enqueue_watchdog(cs);
780 clocksource_select();
781 clocksource_select_watchdog(false);
782 mutex_unlock(&clocksource_mutex);
783 return 0;
784}
785EXPORT_SYMBOL_GPL(__clocksource_register_scale);
786
787static void __clocksource_change_rating(struct clocksource *cs, int rating)
788{
789 list_del(&cs->list);
790 cs->rating = rating;
791 clocksource_enqueue(cs);
792}
793
794/**
795 * clocksource_change_rating - Change the rating of a registered clocksource
796 * @cs: clocksource to be changed
797 * @rating: new rating
798 */
799void clocksource_change_rating(struct clocksource *cs, int rating)
800{
801 mutex_lock(&clocksource_mutex);
802 __clocksource_change_rating(cs, rating);
803 clocksource_select();
804 clocksource_select_watchdog(false);
805 mutex_unlock(&clocksource_mutex);
806}
807EXPORT_SYMBOL(clocksource_change_rating);
808
809/*
810 * Unbind clocksource @cs. Called with clocksource_mutex held
811 */
812static int clocksource_unbind(struct clocksource *cs)
813{
814 if (clocksource_is_watchdog(cs)) {
815 /* Select and try to install a replacement watchdog. */
816 clocksource_select_watchdog(true);
817 if (clocksource_is_watchdog(cs))
818 return -EBUSY;
819 }
820
821 if (cs == curr_clocksource) {
822 /* Select and try to install a replacement clock source */
823 clocksource_select_fallback();
824 if (curr_clocksource == cs)
825 return -EBUSY;
826 }
827 clocksource_dequeue_watchdog(cs);
828 list_del_init(&cs->list);
829 return 0;
830}
831
832/**
833 * clocksource_unregister - remove a registered clocksource
834 * @cs: clocksource to be unregistered
835 */
836int clocksource_unregister(struct clocksource *cs)
837{
838 int ret = 0;
839
840 mutex_lock(&clocksource_mutex);
841 if (!list_empty(&cs->list))
842 ret = clocksource_unbind(cs);
843 mutex_unlock(&clocksource_mutex);
844 return ret;
845}
846EXPORT_SYMBOL(clocksource_unregister);
847
848#ifdef CONFIG_SYSFS
849/**
850 * sysfs_show_current_clocksources - sysfs interface for current clocksource
851 * @dev: unused
852 * @attr: unused
853 * @buf: char buffer to be filled with clocksource list
854 *
855 * Provides sysfs interface for listing current clocksource.
856 */
857static ssize_t
858sysfs_show_current_clocksources(struct device *dev,
859 struct device_attribute *attr, char *buf)
860{
861 ssize_t count = 0;
862
863 mutex_lock(&clocksource_mutex);
864 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
865 mutex_unlock(&clocksource_mutex);
866
867 return count;
868}
869
870ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
871{
872 size_t ret = cnt;
873
874 /* strings from sysfs write are not 0 terminated! */
875 if (!cnt || cnt >= CS_NAME_LEN)
876 return -EINVAL;
877
878 /* strip of \n: */
879 if (buf[cnt-1] == '\n')
880 cnt--;
881 if (cnt > 0)
882 memcpy(dst, buf, cnt);
883 dst[cnt] = 0;
884 return ret;
885}
886
887/**
888 * sysfs_override_clocksource - interface for manually overriding clocksource
889 * @dev: unused
890 * @attr: unused
891 * @buf: name of override clocksource
892 * @count: length of buffer
893 *
894 * Takes input from sysfs interface for manually overriding the default
895 * clocksource selection.
896 */
897static ssize_t sysfs_override_clocksource(struct device *dev,
898 struct device_attribute *attr,
899 const char *buf, size_t count)
900{
901 ssize_t ret;
902
903 mutex_lock(&clocksource_mutex);
904
905 ret = sysfs_get_uname(buf, override_name, count);
906 if (ret >= 0)
907 clocksource_select();
908
909 mutex_unlock(&clocksource_mutex);
910
911 return ret;
912}
913
914/**
915 * sysfs_unbind_current_clocksource - interface for manually unbinding clocksource
916 * @dev: unused
917 * @attr: unused
918 * @buf: unused
919 * @count: length of buffer
920 *
921 * Takes input from sysfs interface for manually unbinding a clocksource.
922 */
923static ssize_t sysfs_unbind_clocksource(struct device *dev,
924 struct device_attribute *attr,
925 const char *buf, size_t count)
926{
927 struct clocksource *cs;
928 char name[CS_NAME_LEN];
929 ssize_t ret;
930
931 ret = sysfs_get_uname(buf, name, count);
932 if (ret < 0)
933 return ret;
934
935 ret = -ENODEV;
936 mutex_lock(&clocksource_mutex);
937 list_for_each_entry(cs, &clocksource_list, list) {
938 if (strcmp(cs->name, name))
939 continue;
940 ret = clocksource_unbind(cs);
941 break;
942 }
943 mutex_unlock(&clocksource_mutex);
944
945 return ret ? ret : count;
946}
947
948/**
949 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
950 * @dev: unused
951 * @attr: unused
952 * @buf: char buffer to be filled with clocksource list
953 *
954 * Provides sysfs interface for listing registered clocksources
955 */
956static ssize_t
957sysfs_show_available_clocksources(struct device *dev,
958 struct device_attribute *attr,
959 char *buf)
960{
961 struct clocksource *src;
962 ssize_t count = 0;
963
964 mutex_lock(&clocksource_mutex);
965 list_for_each_entry(src, &clocksource_list, list) {
966 /*
967 * Don't show non-HRES clocksource if the tick code is
968 * in one shot mode (highres=on or nohz=on)
969 */
970 if (!tick_oneshot_mode_active() ||
971 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
972 count += snprintf(buf + count,
973 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
974 "%s ", src->name);
975 }
976 mutex_unlock(&clocksource_mutex);
977
978 count += snprintf(buf + count,
979 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
980
981 return count;
982}
983
984/*
985 * Sysfs setup bits:
986 */
987static DEVICE_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
988 sysfs_override_clocksource);
989
990static DEVICE_ATTR(unbind_clocksource, 0200, NULL, sysfs_unbind_clocksource);
991
992static DEVICE_ATTR(available_clocksource, 0444,
993 sysfs_show_available_clocksources, NULL);
994
995static struct bus_type clocksource_subsys = {
996 .name = "clocksource",
997 .dev_name = "clocksource",
998};
999
1000static struct device device_clocksource = {
1001 .id = 0,
1002 .bus = &clocksource_subsys,
1003};
1004
1005static int __init init_clocksource_sysfs(void)
1006{
1007 int error = subsys_system_register(&clocksource_subsys, NULL);
1008
1009 if (!error)
1010 error = device_register(&device_clocksource);
1011 if (!error)
1012 error = device_create_file(
1013 &device_clocksource,
1014 &dev_attr_current_clocksource);
1015 if (!error)
1016 error = device_create_file(&device_clocksource,
1017 &dev_attr_unbind_clocksource);
1018 if (!error)
1019 error = device_create_file(
1020 &device_clocksource,
1021 &dev_attr_available_clocksource);
1022 return error;
1023}
1024
1025device_initcall(init_clocksource_sysfs);
1026#endif /* CONFIG_SYSFS */
1027
1028/**
1029 * boot_override_clocksource - boot clock override
1030 * @str: override name
1031 *
1032 * Takes a clocksource= boot argument and uses it
1033 * as the clocksource override name.
1034 */
1035static int __init boot_override_clocksource(char* str)
1036{
1037 mutex_lock(&clocksource_mutex);
1038 if (str)
1039 strlcpy(override_name, str, sizeof(override_name));
1040 mutex_unlock(&clocksource_mutex);
1041 return 1;
1042}
1043
1044__setup("clocksource=", boot_override_clocksource);
1045
1046/**
1047 * boot_override_clock - Compatibility layer for deprecated boot option
1048 * @str: override name
1049 *
1050 * DEPRECATED! Takes a clock= boot argument and uses it
1051 * as the clocksource override name
1052 */
1053static int __init boot_override_clock(char* str)
1054{
1055 if (!strcmp(str, "pmtmr")) {
1056 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1057 return boot_override_clocksource("acpi_pm");
1058 }
1059 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1060 return boot_override_clocksource(str);
1061}
1062
1063__setup("clock=", boot_override_clock);
1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * This file contains the functions which manage clocksource drivers.
4 *
5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
6 */
7
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9
10#include <linux/device.h>
11#include <linux/clocksource.h>
12#include <linux/init.h>
13#include <linux/module.h>
14#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
15#include <linux/tick.h>
16#include <linux/kthread.h>
17#include <linux/prandom.h>
18#include <linux/cpu.h>
19
20#include "tick-internal.h"
21#include "timekeeping_internal.h"
22
23/**
24 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
25 * @mult: pointer to mult variable
26 * @shift: pointer to shift variable
27 * @from: frequency to convert from
28 * @to: frequency to convert to
29 * @maxsec: guaranteed runtime conversion range in seconds
30 *
31 * The function evaluates the shift/mult pair for the scaled math
32 * operations of clocksources and clockevents.
33 *
34 * @to and @from are frequency values in HZ. For clock sources @to is
35 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
36 * event @to is the counter frequency and @from is NSEC_PER_SEC.
37 *
38 * The @maxsec conversion range argument controls the time frame in
39 * seconds which must be covered by the runtime conversion with the
40 * calculated mult and shift factors. This guarantees that no 64bit
41 * overflow happens when the input value of the conversion is
42 * multiplied with the calculated mult factor. Larger ranges may
43 * reduce the conversion accuracy by choosing smaller mult and shift
44 * factors.
45 */
46void
47clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
48{
49 u64 tmp;
50 u32 sft, sftacc= 32;
51
52 /*
53 * Calculate the shift factor which is limiting the conversion
54 * range:
55 */
56 tmp = ((u64)maxsec * from) >> 32;
57 while (tmp) {
58 tmp >>=1;
59 sftacc--;
60 }
61
62 /*
63 * Find the conversion shift/mult pair which has the best
64 * accuracy and fits the maxsec conversion range:
65 */
66 for (sft = 32; sft > 0; sft--) {
67 tmp = (u64) to << sft;
68 tmp += from / 2;
69 do_div(tmp, from);
70 if ((tmp >> sftacc) == 0)
71 break;
72 }
73 *mult = tmp;
74 *shift = sft;
75}
76EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
77
78/*[Clocksource internal variables]---------
79 * curr_clocksource:
80 * currently selected clocksource.
81 * suspend_clocksource:
82 * used to calculate the suspend time.
83 * clocksource_list:
84 * linked list with the registered clocksources
85 * clocksource_mutex:
86 * protects manipulations to curr_clocksource and the clocksource_list
87 * override_name:
88 * Name of the user-specified clocksource.
89 */
90static struct clocksource *curr_clocksource;
91static struct clocksource *suspend_clocksource;
92static LIST_HEAD(clocksource_list);
93static DEFINE_MUTEX(clocksource_mutex);
94static char override_name[CS_NAME_LEN];
95static int finished_booting;
96static u64 suspend_start;
97
98/*
99 * 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#define WATCHDOG_MAX_SKEW (50 * NSEC_PER_USEC)
111
112#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
113static void clocksource_watchdog_work(struct work_struct *work);
114static void clocksource_select(void);
115
116static LIST_HEAD(watchdog_list);
117static struct clocksource *watchdog;
118static struct timer_list watchdog_timer;
119static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
120static DEFINE_SPINLOCK(watchdog_lock);
121static int watchdog_running;
122static atomic_t watchdog_reset_pending;
123
124static inline void clocksource_watchdog_lock(unsigned long *flags)
125{
126 spin_lock_irqsave(&watchdog_lock, *flags);
127}
128
129static inline void clocksource_watchdog_unlock(unsigned long *flags)
130{
131 spin_unlock_irqrestore(&watchdog_lock, *flags);
132}
133
134static int clocksource_watchdog_kthread(void *data);
135static void __clocksource_change_rating(struct clocksource *cs, int rating);
136
137/*
138 * Interval: 0.5sec.
139 */
140#define WATCHDOG_INTERVAL (HZ >> 1)
141
142static void clocksource_watchdog_work(struct work_struct *work)
143{
144 /*
145 * We cannot directly run clocksource_watchdog_kthread() here, because
146 * clocksource_select() calls timekeeping_notify() which uses
147 * stop_machine(). One cannot use stop_machine() from a workqueue() due
148 * lock inversions wrt CPU hotplug.
149 *
150 * Also, we only ever run this work once or twice during the lifetime
151 * of the kernel, so there is no point in creating a more permanent
152 * kthread for this.
153 *
154 * If kthread_run fails the next watchdog scan over the
155 * watchdog_list will find the unstable clock again.
156 */
157 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
158}
159
160static void __clocksource_unstable(struct clocksource *cs)
161{
162 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
163 cs->flags |= CLOCK_SOURCE_UNSTABLE;
164
165 /*
166 * If the clocksource is registered clocksource_watchdog_kthread() will
167 * re-rate and re-select.
168 */
169 if (list_empty(&cs->list)) {
170 cs->rating = 0;
171 return;
172 }
173
174 if (cs->mark_unstable)
175 cs->mark_unstable(cs);
176
177 /* kick clocksource_watchdog_kthread() */
178 if (finished_booting)
179 schedule_work(&watchdog_work);
180}
181
182/**
183 * clocksource_mark_unstable - mark clocksource unstable via watchdog
184 * @cs: clocksource to be marked unstable
185 *
186 * This function is called by the x86 TSC code to mark clocksources as unstable;
187 * it defers demotion and re-selection to a kthread.
188 */
189void clocksource_mark_unstable(struct clocksource *cs)
190{
191 unsigned long flags;
192
193 spin_lock_irqsave(&watchdog_lock, flags);
194 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
195 if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
196 list_add(&cs->wd_list, &watchdog_list);
197 __clocksource_unstable(cs);
198 }
199 spin_unlock_irqrestore(&watchdog_lock, flags);
200}
201
202ulong max_cswd_read_retries = 3;
203module_param(max_cswd_read_retries, ulong, 0644);
204EXPORT_SYMBOL_GPL(max_cswd_read_retries);
205static int verify_n_cpus = 8;
206module_param(verify_n_cpus, int, 0644);
207
208static bool cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
209{
210 unsigned int nretries;
211 u64 wd_end, wd_delta;
212 int64_t wd_delay;
213
214 for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) {
215 local_irq_disable();
216 *wdnow = watchdog->read(watchdog);
217 *csnow = cs->read(cs);
218 wd_end = watchdog->read(watchdog);
219 local_irq_enable();
220
221 wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
222 wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult,
223 watchdog->shift);
224 if (wd_delay <= WATCHDOG_MAX_SKEW) {
225 if (nretries > 1 || nretries >= max_cswd_read_retries) {
226 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
227 smp_processor_id(), watchdog->name, nretries);
228 }
229 return true;
230 }
231 }
232
233 pr_warn("timekeeping watchdog on CPU%d: %s read-back delay of %lldns, attempt %d, marking unstable\n",
234 smp_processor_id(), watchdog->name, wd_delay, nretries);
235 return false;
236}
237
238static u64 csnow_mid;
239static cpumask_t cpus_ahead;
240static cpumask_t cpus_behind;
241static cpumask_t cpus_chosen;
242
243static void clocksource_verify_choose_cpus(void)
244{
245 int cpu, i, n = verify_n_cpus;
246
247 if (n < 0) {
248 /* Check all of the CPUs. */
249 cpumask_copy(&cpus_chosen, cpu_online_mask);
250 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
251 return;
252 }
253
254 /* If no checking desired, or no other CPU to check, leave. */
255 cpumask_clear(&cpus_chosen);
256 if (n == 0 || num_online_cpus() <= 1)
257 return;
258
259 /* Make sure to select at least one CPU other than the current CPU. */
260 cpu = cpumask_next(-1, cpu_online_mask);
261 if (cpu == smp_processor_id())
262 cpu = cpumask_next(cpu, cpu_online_mask);
263 if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
264 return;
265 cpumask_set_cpu(cpu, &cpus_chosen);
266
267 /* Force a sane value for the boot parameter. */
268 if (n > nr_cpu_ids)
269 n = nr_cpu_ids;
270
271 /*
272 * Randomly select the specified number of CPUs. If the same
273 * CPU is selected multiple times, that CPU is checked only once,
274 * and no replacement CPU is selected. This gracefully handles
275 * situations where verify_n_cpus is greater than the number of
276 * CPUs that are currently online.
277 */
278 for (i = 1; i < n; i++) {
279 cpu = prandom_u32() % nr_cpu_ids;
280 cpu = cpumask_next(cpu - 1, cpu_online_mask);
281 if (cpu >= nr_cpu_ids)
282 cpu = cpumask_next(-1, cpu_online_mask);
283 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
284 cpumask_set_cpu(cpu, &cpus_chosen);
285 }
286
287 /* Don't verify ourselves. */
288 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
289}
290
291static void clocksource_verify_one_cpu(void *csin)
292{
293 struct clocksource *cs = (struct clocksource *)csin;
294
295 csnow_mid = cs->read(cs);
296}
297
298void clocksource_verify_percpu(struct clocksource *cs)
299{
300 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
301 u64 csnow_begin, csnow_end;
302 int cpu, testcpu;
303 s64 delta;
304
305 if (verify_n_cpus == 0)
306 return;
307 cpumask_clear(&cpus_ahead);
308 cpumask_clear(&cpus_behind);
309 get_online_cpus();
310 preempt_disable();
311 clocksource_verify_choose_cpus();
312 if (cpumask_weight(&cpus_chosen) == 0) {
313 preempt_enable();
314 put_online_cpus();
315 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
316 return;
317 }
318 testcpu = smp_processor_id();
319 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
320 for_each_cpu(cpu, &cpus_chosen) {
321 if (cpu == testcpu)
322 continue;
323 csnow_begin = cs->read(cs);
324 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
325 csnow_end = cs->read(cs);
326 delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
327 if (delta < 0)
328 cpumask_set_cpu(cpu, &cpus_behind);
329 delta = (csnow_end - csnow_mid) & cs->mask;
330 if (delta < 0)
331 cpumask_set_cpu(cpu, &cpus_ahead);
332 delta = clocksource_delta(csnow_end, csnow_begin, cs->mask);
333 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
334 if (cs_nsec > cs_nsec_max)
335 cs_nsec_max = cs_nsec;
336 if (cs_nsec < cs_nsec_min)
337 cs_nsec_min = cs_nsec;
338 }
339 preempt_enable();
340 put_online_cpus();
341 if (!cpumask_empty(&cpus_ahead))
342 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
343 cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
344 if (!cpumask_empty(&cpus_behind))
345 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n",
346 cpumask_pr_args(&cpus_behind), testcpu, cs->name);
347 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
348 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n",
349 testcpu, cs_nsec_min, cs_nsec_max, cs->name);
350}
351EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
352
353static void clocksource_watchdog(struct timer_list *unused)
354{
355 u64 csnow, wdnow, cslast, wdlast, delta;
356 int next_cpu, reset_pending;
357 int64_t wd_nsec, cs_nsec;
358 struct clocksource *cs;
359 u32 md;
360
361 spin_lock(&watchdog_lock);
362 if (!watchdog_running)
363 goto out;
364
365 reset_pending = atomic_read(&watchdog_reset_pending);
366
367 list_for_each_entry(cs, &watchdog_list, wd_list) {
368
369 /* Clocksource already marked unstable? */
370 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
371 if (finished_booting)
372 schedule_work(&watchdog_work);
373 continue;
374 }
375
376 if (!cs_watchdog_read(cs, &csnow, &wdnow)) {
377 /* Clock readout unreliable, so give it up. */
378 __clocksource_unstable(cs);
379 continue;
380 }
381
382 /* Clocksource initialized ? */
383 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
384 atomic_read(&watchdog_reset_pending)) {
385 cs->flags |= CLOCK_SOURCE_WATCHDOG;
386 cs->wd_last = wdnow;
387 cs->cs_last = csnow;
388 continue;
389 }
390
391 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
392 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
393 watchdog->shift);
394
395 delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
396 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
397 wdlast = cs->wd_last; /* save these in case we print them */
398 cslast = cs->cs_last;
399 cs->cs_last = csnow;
400 cs->wd_last = wdnow;
401
402 if (atomic_read(&watchdog_reset_pending))
403 continue;
404
405 /* Check the deviation from the watchdog clocksource. */
406 md = cs->uncertainty_margin + watchdog->uncertainty_margin;
407 if (abs(cs_nsec - wd_nsec) > md) {
408 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
409 smp_processor_id(), cs->name);
410 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
411 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
412 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
413 cs->name, cs_nsec, csnow, cslast, cs->mask);
414 if (curr_clocksource == cs)
415 pr_warn(" '%s' is current clocksource.\n", cs->name);
416 else if (curr_clocksource)
417 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
418 else
419 pr_warn(" No current clocksource.\n");
420 __clocksource_unstable(cs);
421 continue;
422 }
423
424 if (cs == curr_clocksource && cs->tick_stable)
425 cs->tick_stable(cs);
426
427 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
428 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
429 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
430 /* Mark it valid for high-res. */
431 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
432
433 /*
434 * clocksource_done_booting() will sort it if
435 * finished_booting is not set yet.
436 */
437 if (!finished_booting)
438 continue;
439
440 /*
441 * If this is not the current clocksource let
442 * the watchdog thread reselect it. Due to the
443 * change to high res this clocksource might
444 * be preferred now. If it is the current
445 * clocksource let the tick code know about
446 * that change.
447 */
448 if (cs != curr_clocksource) {
449 cs->flags |= CLOCK_SOURCE_RESELECT;
450 schedule_work(&watchdog_work);
451 } else {
452 tick_clock_notify();
453 }
454 }
455 }
456
457 /*
458 * We only clear the watchdog_reset_pending, when we did a
459 * full cycle through all clocksources.
460 */
461 if (reset_pending)
462 atomic_dec(&watchdog_reset_pending);
463
464 /*
465 * Cycle through CPUs to check if the CPUs stay synchronized
466 * to each other.
467 */
468 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
469 if (next_cpu >= nr_cpu_ids)
470 next_cpu = cpumask_first(cpu_online_mask);
471
472 /*
473 * Arm timer if not already pending: could race with concurrent
474 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
475 */
476 if (!timer_pending(&watchdog_timer)) {
477 watchdog_timer.expires += WATCHDOG_INTERVAL;
478 add_timer_on(&watchdog_timer, next_cpu);
479 }
480out:
481 spin_unlock(&watchdog_lock);
482}
483
484static inline void clocksource_start_watchdog(void)
485{
486 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
487 return;
488 timer_setup(&watchdog_timer, clocksource_watchdog, 0);
489 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
490 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
491 watchdog_running = 1;
492}
493
494static inline void clocksource_stop_watchdog(void)
495{
496 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
497 return;
498 del_timer(&watchdog_timer);
499 watchdog_running = 0;
500}
501
502static inline void clocksource_reset_watchdog(void)
503{
504 struct clocksource *cs;
505
506 list_for_each_entry(cs, &watchdog_list, wd_list)
507 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
508}
509
510static void clocksource_resume_watchdog(void)
511{
512 atomic_inc(&watchdog_reset_pending);
513}
514
515static void clocksource_enqueue_watchdog(struct clocksource *cs)
516{
517 INIT_LIST_HEAD(&cs->wd_list);
518
519 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
520 /* cs is a clocksource to be watched. */
521 list_add(&cs->wd_list, &watchdog_list);
522 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
523 } else {
524 /* cs is a watchdog. */
525 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
526 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
527 }
528}
529
530static void clocksource_select_watchdog(bool fallback)
531{
532 struct clocksource *cs, *old_wd;
533 unsigned long flags;
534
535 spin_lock_irqsave(&watchdog_lock, flags);
536 /* save current watchdog */
537 old_wd = watchdog;
538 if (fallback)
539 watchdog = NULL;
540
541 list_for_each_entry(cs, &clocksource_list, list) {
542 /* cs is a clocksource to be watched. */
543 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
544 continue;
545
546 /* Skip current if we were requested for a fallback. */
547 if (fallback && cs == old_wd)
548 continue;
549
550 /* Pick the best watchdog. */
551 if (!watchdog || cs->rating > watchdog->rating)
552 watchdog = cs;
553 }
554 /* If we failed to find a fallback restore the old one. */
555 if (!watchdog)
556 watchdog = old_wd;
557
558 /* If we changed the watchdog we need to reset cycles. */
559 if (watchdog != old_wd)
560 clocksource_reset_watchdog();
561
562 /* Check if the watchdog timer needs to be started. */
563 clocksource_start_watchdog();
564 spin_unlock_irqrestore(&watchdog_lock, flags);
565}
566
567static void clocksource_dequeue_watchdog(struct clocksource *cs)
568{
569 if (cs != watchdog) {
570 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
571 /* cs is a watched clocksource. */
572 list_del_init(&cs->wd_list);
573 /* Check if the watchdog timer needs to be stopped. */
574 clocksource_stop_watchdog();
575 }
576 }
577}
578
579static int __clocksource_watchdog_kthread(void)
580{
581 struct clocksource *cs, *tmp;
582 unsigned long flags;
583 int select = 0;
584
585 /* Do any required per-CPU skew verification. */
586 if (curr_clocksource &&
587 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
588 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
589 clocksource_verify_percpu(curr_clocksource);
590
591 spin_lock_irqsave(&watchdog_lock, flags);
592 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
593 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
594 list_del_init(&cs->wd_list);
595 __clocksource_change_rating(cs, 0);
596 select = 1;
597 }
598 if (cs->flags & CLOCK_SOURCE_RESELECT) {
599 cs->flags &= ~CLOCK_SOURCE_RESELECT;
600 select = 1;
601 }
602 }
603 /* Check if the watchdog timer needs to be stopped. */
604 clocksource_stop_watchdog();
605 spin_unlock_irqrestore(&watchdog_lock, flags);
606
607 return select;
608}
609
610static int clocksource_watchdog_kthread(void *data)
611{
612 mutex_lock(&clocksource_mutex);
613 if (__clocksource_watchdog_kthread())
614 clocksource_select();
615 mutex_unlock(&clocksource_mutex);
616 return 0;
617}
618
619static bool clocksource_is_watchdog(struct clocksource *cs)
620{
621 return cs == watchdog;
622}
623
624#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
625
626static void clocksource_enqueue_watchdog(struct clocksource *cs)
627{
628 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
629 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
630}
631
632static void clocksource_select_watchdog(bool fallback) { }
633static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
634static inline void clocksource_resume_watchdog(void) { }
635static inline int __clocksource_watchdog_kthread(void) { return 0; }
636static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
637void clocksource_mark_unstable(struct clocksource *cs) { }
638
639static inline void clocksource_watchdog_lock(unsigned long *flags) { }
640static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
641
642#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
643
644static bool clocksource_is_suspend(struct clocksource *cs)
645{
646 return cs == suspend_clocksource;
647}
648
649static void __clocksource_suspend_select(struct clocksource *cs)
650{
651 /*
652 * Skip the clocksource which will be stopped in suspend state.
653 */
654 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
655 return;
656
657 /*
658 * The nonstop clocksource can be selected as the suspend clocksource to
659 * calculate the suspend time, so it should not supply suspend/resume
660 * interfaces to suspend the nonstop clocksource when system suspends.
661 */
662 if (cs->suspend || cs->resume) {
663 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
664 cs->name);
665 }
666
667 /* Pick the best rating. */
668 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
669 suspend_clocksource = cs;
670}
671
672/**
673 * clocksource_suspend_select - Select the best clocksource for suspend timing
674 * @fallback: if select a fallback clocksource
675 */
676static void clocksource_suspend_select(bool fallback)
677{
678 struct clocksource *cs, *old_suspend;
679
680 old_suspend = suspend_clocksource;
681 if (fallback)
682 suspend_clocksource = NULL;
683
684 list_for_each_entry(cs, &clocksource_list, list) {
685 /* Skip current if we were requested for a fallback. */
686 if (fallback && cs == old_suspend)
687 continue;
688
689 __clocksource_suspend_select(cs);
690 }
691}
692
693/**
694 * clocksource_start_suspend_timing - Start measuring the suspend timing
695 * @cs: current clocksource from timekeeping
696 * @start_cycles: current cycles from timekeeping
697 *
698 * This function will save the start cycle values of suspend timer to calculate
699 * the suspend time when resuming system.
700 *
701 * This function is called late in the suspend process from timekeeping_suspend(),
702 * that means processes are frozen, non-boot cpus and interrupts are disabled
703 * now. It is therefore possible to start the suspend timer without taking the
704 * clocksource mutex.
705 */
706void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
707{
708 if (!suspend_clocksource)
709 return;
710
711 /*
712 * If current clocksource is the suspend timer, we should use the
713 * tkr_mono.cycle_last value as suspend_start to avoid same reading
714 * from suspend timer.
715 */
716 if (clocksource_is_suspend(cs)) {
717 suspend_start = start_cycles;
718 return;
719 }
720
721 if (suspend_clocksource->enable &&
722 suspend_clocksource->enable(suspend_clocksource)) {
723 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
724 return;
725 }
726
727 suspend_start = suspend_clocksource->read(suspend_clocksource);
728}
729
730/**
731 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
732 * @cs: current clocksource from timekeeping
733 * @cycle_now: current cycles from timekeeping
734 *
735 * This function will calculate the suspend time from suspend timer.
736 *
737 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
738 *
739 * This function is called early in the resume process from timekeeping_resume(),
740 * that means there is only one cpu, no processes are running and the interrupts
741 * are disabled. It is therefore possible to stop the suspend timer without
742 * taking the clocksource mutex.
743 */
744u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
745{
746 u64 now, delta, nsec = 0;
747
748 if (!suspend_clocksource)
749 return 0;
750
751 /*
752 * If current clocksource is the suspend timer, we should use the
753 * tkr_mono.cycle_last value from timekeeping as current cycle to
754 * avoid same reading from suspend timer.
755 */
756 if (clocksource_is_suspend(cs))
757 now = cycle_now;
758 else
759 now = suspend_clocksource->read(suspend_clocksource);
760
761 if (now > suspend_start) {
762 delta = clocksource_delta(now, suspend_start,
763 suspend_clocksource->mask);
764 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
765 suspend_clocksource->shift);
766 }
767
768 /*
769 * Disable the suspend timer to save power if current clocksource is
770 * not the suspend timer.
771 */
772 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
773 suspend_clocksource->disable(suspend_clocksource);
774
775 return nsec;
776}
777
778/**
779 * clocksource_suspend - suspend the clocksource(s)
780 */
781void clocksource_suspend(void)
782{
783 struct clocksource *cs;
784
785 list_for_each_entry_reverse(cs, &clocksource_list, list)
786 if (cs->suspend)
787 cs->suspend(cs);
788}
789
790/**
791 * clocksource_resume - resume the clocksource(s)
792 */
793void clocksource_resume(void)
794{
795 struct clocksource *cs;
796
797 list_for_each_entry(cs, &clocksource_list, list)
798 if (cs->resume)
799 cs->resume(cs);
800
801 clocksource_resume_watchdog();
802}
803
804/**
805 * clocksource_touch_watchdog - Update watchdog
806 *
807 * Update the watchdog after exception contexts such as kgdb so as not
808 * to incorrectly trip the watchdog. This might fail when the kernel
809 * was stopped in code which holds watchdog_lock.
810 */
811void clocksource_touch_watchdog(void)
812{
813 clocksource_resume_watchdog();
814}
815
816/**
817 * clocksource_max_adjustment- Returns max adjustment amount
818 * @cs: Pointer to clocksource
819 *
820 */
821static u32 clocksource_max_adjustment(struct clocksource *cs)
822{
823 u64 ret;
824 /*
825 * We won't try to correct for more than 11% adjustments (110,000 ppm),
826 */
827 ret = (u64)cs->mult * 11;
828 do_div(ret,100);
829 return (u32)ret;
830}
831
832/**
833 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
834 * @mult: cycle to nanosecond multiplier
835 * @shift: cycle to nanosecond divisor (power of two)
836 * @maxadj: maximum adjustment value to mult (~11%)
837 * @mask: bitmask for two's complement subtraction of non 64 bit counters
838 * @max_cyc: maximum cycle value before potential overflow (does not include
839 * any safety margin)
840 *
841 * NOTE: This function includes a safety margin of 50%, in other words, we
842 * return half the number of nanoseconds the hardware counter can technically
843 * cover. This is done so that we can potentially detect problems caused by
844 * delayed timers or bad hardware, which might result in time intervals that
845 * are larger than what the math used can handle without overflows.
846 */
847u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
848{
849 u64 max_nsecs, max_cycles;
850
851 /*
852 * Calculate the maximum number of cycles that we can pass to the
853 * cyc2ns() function without overflowing a 64-bit result.
854 */
855 max_cycles = ULLONG_MAX;
856 do_div(max_cycles, mult+maxadj);
857
858 /*
859 * The actual maximum number of cycles we can defer the clocksource is
860 * determined by the minimum of max_cycles and mask.
861 * Note: Here we subtract the maxadj to make sure we don't sleep for
862 * too long if there's a large negative adjustment.
863 */
864 max_cycles = min(max_cycles, mask);
865 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
866
867 /* return the max_cycles value as well if requested */
868 if (max_cyc)
869 *max_cyc = max_cycles;
870
871 /* Return 50% of the actual maximum, so we can detect bad values */
872 max_nsecs >>= 1;
873
874 return max_nsecs;
875}
876
877/**
878 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
879 * @cs: Pointer to clocksource to be updated
880 *
881 */
882static inline void clocksource_update_max_deferment(struct clocksource *cs)
883{
884 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
885 cs->maxadj, cs->mask,
886 &cs->max_cycles);
887}
888
889static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
890{
891 struct clocksource *cs;
892
893 if (!finished_booting || list_empty(&clocksource_list))
894 return NULL;
895
896 /*
897 * We pick the clocksource with the highest rating. If oneshot
898 * mode is active, we pick the highres valid clocksource with
899 * the best rating.
900 */
901 list_for_each_entry(cs, &clocksource_list, list) {
902 if (skipcur && cs == curr_clocksource)
903 continue;
904 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
905 continue;
906 return cs;
907 }
908 return NULL;
909}
910
911static void __clocksource_select(bool skipcur)
912{
913 bool oneshot = tick_oneshot_mode_active();
914 struct clocksource *best, *cs;
915
916 /* Find the best suitable clocksource */
917 best = clocksource_find_best(oneshot, skipcur);
918 if (!best)
919 return;
920
921 if (!strlen(override_name))
922 goto found;
923
924 /* Check for the override clocksource. */
925 list_for_each_entry(cs, &clocksource_list, list) {
926 if (skipcur && cs == curr_clocksource)
927 continue;
928 if (strcmp(cs->name, override_name) != 0)
929 continue;
930 /*
931 * Check to make sure we don't switch to a non-highres
932 * capable clocksource if the tick code is in oneshot
933 * mode (highres or nohz)
934 */
935 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
936 /* Override clocksource cannot be used. */
937 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
938 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
939 cs->name);
940 override_name[0] = 0;
941 } else {
942 /*
943 * The override cannot be currently verified.
944 * Deferring to let the watchdog check.
945 */
946 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
947 cs->name);
948 }
949 } else
950 /* Override clocksource can be used. */
951 best = cs;
952 break;
953 }
954
955found:
956 if (curr_clocksource != best && !timekeeping_notify(best)) {
957 pr_info("Switched to clocksource %s\n", best->name);
958 curr_clocksource = best;
959 }
960}
961
962/**
963 * clocksource_select - Select the best clocksource available
964 *
965 * Private function. Must hold clocksource_mutex when called.
966 *
967 * Select the clocksource with the best rating, or the clocksource,
968 * which is selected by userspace override.
969 */
970static void clocksource_select(void)
971{
972 __clocksource_select(false);
973}
974
975static void clocksource_select_fallback(void)
976{
977 __clocksource_select(true);
978}
979
980/*
981 * clocksource_done_booting - Called near the end of core bootup
982 *
983 * Hack to avoid lots of clocksource churn at boot time.
984 * We use fs_initcall because we want this to start before
985 * device_initcall but after subsys_initcall.
986 */
987static int __init clocksource_done_booting(void)
988{
989 mutex_lock(&clocksource_mutex);
990 curr_clocksource = clocksource_default_clock();
991 finished_booting = 1;
992 /*
993 * Run the watchdog first to eliminate unstable clock sources
994 */
995 __clocksource_watchdog_kthread();
996 clocksource_select();
997 mutex_unlock(&clocksource_mutex);
998 return 0;
999}
1000fs_initcall(clocksource_done_booting);
1001
1002/*
1003 * Enqueue the clocksource sorted by rating
1004 */
1005static void clocksource_enqueue(struct clocksource *cs)
1006{
1007 struct list_head *entry = &clocksource_list;
1008 struct clocksource *tmp;
1009
1010 list_for_each_entry(tmp, &clocksource_list, list) {
1011 /* Keep track of the place, where to insert */
1012 if (tmp->rating < cs->rating)
1013 break;
1014 entry = &tmp->list;
1015 }
1016 list_add(&cs->list, entry);
1017}
1018
1019/**
1020 * __clocksource_update_freq_scale - Used update clocksource with new freq
1021 * @cs: clocksource to be registered
1022 * @scale: Scale factor multiplied against freq to get clocksource hz
1023 * @freq: clocksource frequency (cycles per second) divided by scale
1024 *
1025 * This should only be called from the clocksource->enable() method.
1026 *
1027 * This *SHOULD NOT* be called directly! Please use the
1028 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
1029 * functions.
1030 */
1031void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1032{
1033 u64 sec;
1034
1035 /*
1036 * Default clocksources are *special* and self-define their mult/shift.
1037 * But, you're not special, so you should specify a freq value.
1038 */
1039 if (freq) {
1040 /*
1041 * Calc the maximum number of seconds which we can run before
1042 * wrapping around. For clocksources which have a mask > 32-bit
1043 * we need to limit the max sleep time to have a good
1044 * conversion precision. 10 minutes is still a reasonable
1045 * amount. That results in a shift value of 24 for a
1046 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1047 * ~ 0.06ppm granularity for NTP.
1048 */
1049 sec = cs->mask;
1050 do_div(sec, freq);
1051 do_div(sec, scale);
1052 if (!sec)
1053 sec = 1;
1054 else if (sec > 600 && cs->mask > UINT_MAX)
1055 sec = 600;
1056
1057 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1058 NSEC_PER_SEC / scale, sec * scale);
1059 }
1060
1061 /*
1062 * If the uncertainty margin is not specified, calculate it.
1063 * If both scale and freq are non-zero, calculate the clock
1064 * period, but bound below at 2*WATCHDOG_MAX_SKEW. However,
1065 * if either of scale or freq is zero, be very conservative and
1066 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the
1067 * uncertainty margin. Allow stupidly small uncertainty margins
1068 * to be specified by the caller for testing purposes, but warn
1069 * to discourage production use of this capability.
1070 */
1071 if (scale && freq && !cs->uncertainty_margin) {
1072 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
1073 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
1074 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
1075 } else if (!cs->uncertainty_margin) {
1076 cs->uncertainty_margin = WATCHDOG_THRESHOLD;
1077 }
1078 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
1079
1080 /*
1081 * Ensure clocksources that have large 'mult' values don't overflow
1082 * when adjusted.
1083 */
1084 cs->maxadj = clocksource_max_adjustment(cs);
1085 while (freq && ((cs->mult + cs->maxadj < cs->mult)
1086 || (cs->mult - cs->maxadj > cs->mult))) {
1087 cs->mult >>= 1;
1088 cs->shift--;
1089 cs->maxadj = clocksource_max_adjustment(cs);
1090 }
1091
1092 /*
1093 * Only warn for *special* clocksources that self-define
1094 * their mult/shift values and don't specify a freq.
1095 */
1096 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1097 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1098 cs->name);
1099
1100 clocksource_update_max_deferment(cs);
1101
1102 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1103 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1104}
1105EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
1106
1107/**
1108 * __clocksource_register_scale - Used to install new clocksources
1109 * @cs: clocksource to be registered
1110 * @scale: Scale factor multiplied against freq to get clocksource hz
1111 * @freq: clocksource frequency (cycles per second) divided by scale
1112 *
1113 * Returns -EBUSY if registration fails, zero otherwise.
1114 *
1115 * This *SHOULD NOT* be called directly! Please use the
1116 * clocksource_register_hz() or clocksource_register_khz helper functions.
1117 */
1118int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1119{
1120 unsigned long flags;
1121
1122 clocksource_arch_init(cs);
1123
1124 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1125 cs->id = CSID_GENERIC;
1126 if (cs->vdso_clock_mode < 0 ||
1127 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1128 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1129 cs->name, cs->vdso_clock_mode);
1130 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1131 }
1132
1133 /* Initialize mult/shift and max_idle_ns */
1134 __clocksource_update_freq_scale(cs, scale, freq);
1135
1136 /* Add clocksource to the clocksource list */
1137 mutex_lock(&clocksource_mutex);
1138
1139 clocksource_watchdog_lock(&flags);
1140 clocksource_enqueue(cs);
1141 clocksource_enqueue_watchdog(cs);
1142 clocksource_watchdog_unlock(&flags);
1143
1144 clocksource_select();
1145 clocksource_select_watchdog(false);
1146 __clocksource_suspend_select(cs);
1147 mutex_unlock(&clocksource_mutex);
1148 return 0;
1149}
1150EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1151
1152static void __clocksource_change_rating(struct clocksource *cs, int rating)
1153{
1154 list_del(&cs->list);
1155 cs->rating = rating;
1156 clocksource_enqueue(cs);
1157}
1158
1159/**
1160 * clocksource_change_rating - Change the rating of a registered clocksource
1161 * @cs: clocksource to be changed
1162 * @rating: new rating
1163 */
1164void clocksource_change_rating(struct clocksource *cs, int rating)
1165{
1166 unsigned long flags;
1167
1168 mutex_lock(&clocksource_mutex);
1169 clocksource_watchdog_lock(&flags);
1170 __clocksource_change_rating(cs, rating);
1171 clocksource_watchdog_unlock(&flags);
1172
1173 clocksource_select();
1174 clocksource_select_watchdog(false);
1175 clocksource_suspend_select(false);
1176 mutex_unlock(&clocksource_mutex);
1177}
1178EXPORT_SYMBOL(clocksource_change_rating);
1179
1180/*
1181 * Unbind clocksource @cs. Called with clocksource_mutex held
1182 */
1183static int clocksource_unbind(struct clocksource *cs)
1184{
1185 unsigned long flags;
1186
1187 if (clocksource_is_watchdog(cs)) {
1188 /* Select and try to install a replacement watchdog. */
1189 clocksource_select_watchdog(true);
1190 if (clocksource_is_watchdog(cs))
1191 return -EBUSY;
1192 }
1193
1194 if (cs == curr_clocksource) {
1195 /* Select and try to install a replacement clock source */
1196 clocksource_select_fallback();
1197 if (curr_clocksource == cs)
1198 return -EBUSY;
1199 }
1200
1201 if (clocksource_is_suspend(cs)) {
1202 /*
1203 * Select and try to install a replacement suspend clocksource.
1204 * If no replacement suspend clocksource, we will just let the
1205 * clocksource go and have no suspend clocksource.
1206 */
1207 clocksource_suspend_select(true);
1208 }
1209
1210 clocksource_watchdog_lock(&flags);
1211 clocksource_dequeue_watchdog(cs);
1212 list_del_init(&cs->list);
1213 clocksource_watchdog_unlock(&flags);
1214
1215 return 0;
1216}
1217
1218/**
1219 * clocksource_unregister - remove a registered clocksource
1220 * @cs: clocksource to be unregistered
1221 */
1222int clocksource_unregister(struct clocksource *cs)
1223{
1224 int ret = 0;
1225
1226 mutex_lock(&clocksource_mutex);
1227 if (!list_empty(&cs->list))
1228 ret = clocksource_unbind(cs);
1229 mutex_unlock(&clocksource_mutex);
1230 return ret;
1231}
1232EXPORT_SYMBOL(clocksource_unregister);
1233
1234#ifdef CONFIG_SYSFS
1235/**
1236 * current_clocksource_show - sysfs interface for current clocksource
1237 * @dev: unused
1238 * @attr: unused
1239 * @buf: char buffer to be filled with clocksource list
1240 *
1241 * Provides sysfs interface for listing current clocksource.
1242 */
1243static ssize_t current_clocksource_show(struct device *dev,
1244 struct device_attribute *attr,
1245 char *buf)
1246{
1247 ssize_t count = 0;
1248
1249 mutex_lock(&clocksource_mutex);
1250 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
1251 mutex_unlock(&clocksource_mutex);
1252
1253 return count;
1254}
1255
1256ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1257{
1258 size_t ret = cnt;
1259
1260 /* strings from sysfs write are not 0 terminated! */
1261 if (!cnt || cnt >= CS_NAME_LEN)
1262 return -EINVAL;
1263
1264 /* strip of \n: */
1265 if (buf[cnt-1] == '\n')
1266 cnt--;
1267 if (cnt > 0)
1268 memcpy(dst, buf, cnt);
1269 dst[cnt] = 0;
1270 return ret;
1271}
1272
1273/**
1274 * current_clocksource_store - interface for manually overriding clocksource
1275 * @dev: unused
1276 * @attr: unused
1277 * @buf: name of override clocksource
1278 * @count: length of buffer
1279 *
1280 * Takes input from sysfs interface for manually overriding the default
1281 * clocksource selection.
1282 */
1283static ssize_t current_clocksource_store(struct device *dev,
1284 struct device_attribute *attr,
1285 const char *buf, size_t count)
1286{
1287 ssize_t ret;
1288
1289 mutex_lock(&clocksource_mutex);
1290
1291 ret = sysfs_get_uname(buf, override_name, count);
1292 if (ret >= 0)
1293 clocksource_select();
1294
1295 mutex_unlock(&clocksource_mutex);
1296
1297 return ret;
1298}
1299static DEVICE_ATTR_RW(current_clocksource);
1300
1301/**
1302 * unbind_clocksource_store - interface for manually unbinding clocksource
1303 * @dev: unused
1304 * @attr: unused
1305 * @buf: unused
1306 * @count: length of buffer
1307 *
1308 * Takes input from sysfs interface for manually unbinding a clocksource.
1309 */
1310static ssize_t unbind_clocksource_store(struct device *dev,
1311 struct device_attribute *attr,
1312 const char *buf, size_t count)
1313{
1314 struct clocksource *cs;
1315 char name[CS_NAME_LEN];
1316 ssize_t ret;
1317
1318 ret = sysfs_get_uname(buf, name, count);
1319 if (ret < 0)
1320 return ret;
1321
1322 ret = -ENODEV;
1323 mutex_lock(&clocksource_mutex);
1324 list_for_each_entry(cs, &clocksource_list, list) {
1325 if (strcmp(cs->name, name))
1326 continue;
1327 ret = clocksource_unbind(cs);
1328 break;
1329 }
1330 mutex_unlock(&clocksource_mutex);
1331
1332 return ret ? ret : count;
1333}
1334static DEVICE_ATTR_WO(unbind_clocksource);
1335
1336/**
1337 * available_clocksource_show - sysfs interface for listing clocksource
1338 * @dev: unused
1339 * @attr: unused
1340 * @buf: char buffer to be filled with clocksource list
1341 *
1342 * Provides sysfs interface for listing registered clocksources
1343 */
1344static ssize_t available_clocksource_show(struct device *dev,
1345 struct device_attribute *attr,
1346 char *buf)
1347{
1348 struct clocksource *src;
1349 ssize_t count = 0;
1350
1351 mutex_lock(&clocksource_mutex);
1352 list_for_each_entry(src, &clocksource_list, list) {
1353 /*
1354 * Don't show non-HRES clocksource if the tick code is
1355 * in one shot mode (highres=on or nohz=on)
1356 */
1357 if (!tick_oneshot_mode_active() ||
1358 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1359 count += snprintf(buf + count,
1360 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1361 "%s ", src->name);
1362 }
1363 mutex_unlock(&clocksource_mutex);
1364
1365 count += snprintf(buf + count,
1366 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1367
1368 return count;
1369}
1370static DEVICE_ATTR_RO(available_clocksource);
1371
1372static struct attribute *clocksource_attrs[] = {
1373 &dev_attr_current_clocksource.attr,
1374 &dev_attr_unbind_clocksource.attr,
1375 &dev_attr_available_clocksource.attr,
1376 NULL
1377};
1378ATTRIBUTE_GROUPS(clocksource);
1379
1380static struct bus_type clocksource_subsys = {
1381 .name = "clocksource",
1382 .dev_name = "clocksource",
1383};
1384
1385static struct device device_clocksource = {
1386 .id = 0,
1387 .bus = &clocksource_subsys,
1388 .groups = clocksource_groups,
1389};
1390
1391static int __init init_clocksource_sysfs(void)
1392{
1393 int error = subsys_system_register(&clocksource_subsys, NULL);
1394
1395 if (!error)
1396 error = device_register(&device_clocksource);
1397
1398 return error;
1399}
1400
1401device_initcall(init_clocksource_sysfs);
1402#endif /* CONFIG_SYSFS */
1403
1404/**
1405 * boot_override_clocksource - boot clock override
1406 * @str: override name
1407 *
1408 * Takes a clocksource= boot argument and uses it
1409 * as the clocksource override name.
1410 */
1411static int __init boot_override_clocksource(char* str)
1412{
1413 mutex_lock(&clocksource_mutex);
1414 if (str)
1415 strlcpy(override_name, str, sizeof(override_name));
1416 mutex_unlock(&clocksource_mutex);
1417 return 1;
1418}
1419
1420__setup("clocksource=", boot_override_clocksource);
1421
1422/**
1423 * boot_override_clock - Compatibility layer for deprecated boot option
1424 * @str: override name
1425 *
1426 * DEPRECATED! Takes a clock= boot argument and uses it
1427 * as the clocksource override name
1428 */
1429static int __init boot_override_clock(char* str)
1430{
1431 if (!strcmp(str, "pmtmr")) {
1432 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1433 return boot_override_clocksource("acpi_pm");
1434 }
1435 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1436 return boot_override_clocksource(str);
1437}
1438
1439__setup("clock=", boot_override_clock);