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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/*
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);