2 * linux/kernel/time/clocksource.c
4 * This file contains the functions which manage clocksource drivers.
6 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
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.
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.
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.
23 * o Allow clocksource drivers to be unregistered
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>
33 void timecounter_init(struct timecounter *tc,
34 const struct cyclecounter *cc,
38 tc->cycle_last = cc->read(cc);
39 tc->nsec = start_tstamp;
41 EXPORT_SYMBOL(timecounter_init);
44 * timecounter_read_delta - get nanoseconds since last call of this function
45 * @tc: Pointer to time counter
47 * When the underlying cycle counter runs over, this will be handled
48 * correctly as long as it does not run over more than once between
51 * The first call to this function for a new time counter initializes
52 * the time tracking and returns an undefined result.
54 static u64 timecounter_read_delta(struct timecounter *tc)
56 cycle_t cycle_now, cycle_delta;
59 /* read cycle counter: */
60 cycle_now = tc->cc->read(tc->cc);
62 /* calculate the delta since the last timecounter_read_delta(): */
63 cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
65 /* convert to nanoseconds: */
66 ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta);
68 /* update time stamp of timecounter_read_delta() call: */
69 tc->cycle_last = cycle_now;
74 u64 timecounter_read(struct timecounter *tc)
78 /* increment time by nanoseconds since last call */
79 nsec = timecounter_read_delta(tc);
85 EXPORT_SYMBOL(timecounter_read);
87 u64 timecounter_cyc2time(struct timecounter *tc,
90 u64 cycle_delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
94 * Instead of always treating cycle_tstamp as more recent
95 * than tc->cycle_last, detect when it is too far in the
96 * future and treat it as old time stamp instead.
98 if (cycle_delta > tc->cc->mask / 2) {
99 cycle_delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
100 nsec = tc->nsec - cyclecounter_cyc2ns(tc->cc, cycle_delta);
102 nsec = cyclecounter_cyc2ns(tc->cc, cycle_delta) + tc->nsec;
107 EXPORT_SYMBOL(timecounter_cyc2time);
109 /*[Clocksource internal variables]---------
111 * currently selected clocksource.
113 * pending next selected clocksource.
115 * linked list with the registered clocksources
117 * protects manipulations to curr_clocksource and next_clocksource
118 * and the clocksource_list
120 * Name of the user-specified clocksource.
122 static struct clocksource *curr_clocksource;
123 static struct clocksource *next_clocksource;
124 static LIST_HEAD(clocksource_list);
125 static DEFINE_SPINLOCK(clocksource_lock);
126 static char override_name[32];
127 static int finished_booting;
129 /* clocksource_done_booting - Called near the end of core bootup
131 * Hack to avoid lots of clocksource churn at boot time.
132 * We use fs_initcall because we want this to start before
133 * device_initcall but after subsys_initcall.
135 static int __init clocksource_done_booting(void)
137 finished_booting = 1;
140 fs_initcall(clocksource_done_booting);
142 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
143 static LIST_HEAD(watchdog_list);
144 static struct clocksource *watchdog;
145 static struct timer_list watchdog_timer;
146 static struct work_struct watchdog_work;
147 static DEFINE_SPINLOCK(watchdog_lock);
148 static cycle_t watchdog_last;
149 static int watchdog_running;
151 static void clocksource_watchdog_work(struct work_struct *work);
154 * Interval: 0.5sec Threshold: 0.0625s
156 #define WATCHDOG_INTERVAL (HZ >> 1)
157 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
159 static void clocksource_unstable(struct clocksource *cs, int64_t delta)
161 printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
163 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
164 cs->flags |= CLOCK_SOURCE_UNSTABLE;
165 schedule_work(&watchdog_work);
168 static void clocksource_watchdog(unsigned long data)
170 struct clocksource *cs;
171 cycle_t csnow, wdnow;
172 int64_t wd_nsec, cs_nsec;
175 spin_lock(&watchdog_lock);
176 if (!watchdog_running)
179 wdnow = watchdog->read(watchdog);
180 wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
181 watchdog_last = wdnow;
183 list_for_each_entry(cs, &watchdog_list, wd_list) {
185 /* Clocksource already marked unstable? */
186 if (cs->flags & CLOCK_SOURCE_UNSTABLE)
189 csnow = cs->read(cs);
191 /* Clocksource initialized ? */
192 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
193 cs->flags |= CLOCK_SOURCE_WATCHDOG;
198 /* Check the deviation from the watchdog clocksource. */
199 cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
201 if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
202 clocksource_unstable(cs, cs_nsec - wd_nsec);
206 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
207 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
208 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
209 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
211 * We just marked the clocksource as highres-capable,
212 * notify the rest of the system as well so that we
213 * transition into high-res mode:
220 * Cycle through CPUs to check if the CPUs stay synchronized
223 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
224 if (next_cpu >= nr_cpu_ids)
225 next_cpu = cpumask_first(cpu_online_mask);
226 watchdog_timer.expires += WATCHDOG_INTERVAL;
227 add_timer_on(&watchdog_timer, next_cpu);
229 spin_unlock(&watchdog_lock);
232 static inline void clocksource_start_watchdog(void)
234 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
236 INIT_WORK(&watchdog_work, clocksource_watchdog_work);
237 init_timer(&watchdog_timer);
238 watchdog_timer.function = clocksource_watchdog;
239 watchdog_last = watchdog->read(watchdog);
240 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
241 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
242 watchdog_running = 1;
245 static inline void clocksource_stop_watchdog(void)
247 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
249 del_timer(&watchdog_timer);
250 watchdog_running = 0;
253 static inline void clocksource_reset_watchdog(void)
255 struct clocksource *cs;
257 list_for_each_entry(cs, &watchdog_list, wd_list)
258 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
261 static void clocksource_resume_watchdog(void)
265 spin_lock_irqsave(&watchdog_lock, flags);
266 clocksource_reset_watchdog();
267 spin_unlock_irqrestore(&watchdog_lock, flags);
270 static void clocksource_enqueue_watchdog(struct clocksource *cs)
274 spin_lock_irqsave(&watchdog_lock, flags);
275 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
276 /* cs is a clocksource to be watched. */
277 list_add(&cs->wd_list, &watchdog_list);
278 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
280 /* cs is a watchdog. */
281 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
282 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
283 /* Pick the best watchdog. */
284 if (!watchdog || cs->rating > watchdog->rating) {
286 /* Reset watchdog cycles */
287 clocksource_reset_watchdog();
290 /* Check if the watchdog timer needs to be started. */
291 clocksource_start_watchdog();
292 spin_unlock_irqrestore(&watchdog_lock, flags);
295 static void clocksource_dequeue_watchdog(struct clocksource *cs)
297 struct clocksource *tmp;
300 spin_lock_irqsave(&watchdog_lock, flags);
301 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
302 /* cs is a watched clocksource. */
303 list_del_init(&cs->wd_list);
304 } else if (cs == watchdog) {
305 /* Reset watchdog cycles */
306 clocksource_reset_watchdog();
307 /* Current watchdog is removed. Find an alternative. */
309 list_for_each_entry(tmp, &clocksource_list, list) {
310 if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
312 if (!watchdog || tmp->rating > watchdog->rating)
316 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
317 /* Check if the watchdog timer needs to be stopped. */
318 clocksource_stop_watchdog();
319 spin_unlock_irqrestore(&watchdog_lock, flags);
322 static void clocksource_watchdog_work(struct work_struct *work)
324 struct clocksource *cs, *tmp;
327 spin_lock_irqsave(&watchdog_lock, flags);
328 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
329 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
330 list_del_init(&cs->wd_list);
331 clocksource_change_rating(cs, 0);
333 /* Check if the watchdog timer needs to be stopped. */
334 clocksource_stop_watchdog();
335 spin_unlock(&watchdog_lock);
338 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
340 static void clocksource_enqueue_watchdog(struct clocksource *cs)
342 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
343 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
346 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
347 static inline void clocksource_resume_watchdog(void) { }
349 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
352 * clocksource_resume - resume the clocksource(s)
354 void clocksource_resume(void)
356 struct clocksource *cs;
359 spin_lock_irqsave(&clocksource_lock, flags);
361 list_for_each_entry(cs, &clocksource_list, list) {
366 clocksource_resume_watchdog();
368 spin_unlock_irqrestore(&clocksource_lock, flags);
372 * clocksource_touch_watchdog - Update watchdog
374 * Update the watchdog after exception contexts such as kgdb so as not
375 * to incorrectly trip the watchdog.
378 void clocksource_touch_watchdog(void)
380 clocksource_resume_watchdog();
383 #ifdef CONFIG_GENERIC_TIME
385 * clocksource_get_next - Returns the selected clocksource
388 struct clocksource *clocksource_get_next(void)
392 spin_lock_irqsave(&clocksource_lock, flags);
393 if (next_clocksource && finished_booting) {
394 curr_clocksource = next_clocksource;
395 next_clocksource = NULL;
397 spin_unlock_irqrestore(&clocksource_lock, flags);
399 return curr_clocksource;
403 * clocksource_select - Select the best clocksource available
405 * Private function. Must hold clocksource_lock when called.
407 * Select the clocksource with the best rating, or the clocksource,
408 * which is selected by userspace override.
410 static void clocksource_select(void)
412 struct clocksource *best, *cs;
414 if (list_empty(&clocksource_list))
416 /* First clocksource on the list has the best rating. */
417 best = list_first_entry(&clocksource_list, struct clocksource, list);
418 /* Check for the override clocksource. */
419 list_for_each_entry(cs, &clocksource_list, list) {
420 if (strcmp(cs->name, override_name) != 0)
423 * Check to make sure we don't switch to a non-highres
424 * capable clocksource if the tick code is in oneshot
425 * mode (highres or nohz)
427 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
428 tick_oneshot_mode_active()) {
429 /* Override clocksource cannot be used. */
430 printk(KERN_WARNING "Override clocksource %s is not "
431 "HRT compatible. Cannot switch while in "
432 "HRT/NOHZ mode\n", cs->name);
433 override_name[0] = 0;
435 /* Override clocksource can be used. */
439 if (curr_clocksource != best)
440 next_clocksource = best;
443 #else /* CONFIG_GENERIC_TIME */
445 static void clocksource_select(void) { }
450 * Enqueue the clocksource sorted by rating
452 static void clocksource_enqueue(struct clocksource *cs)
454 struct list_head *entry = &clocksource_list;
455 struct clocksource *tmp;
457 list_for_each_entry(tmp, &clocksource_list, list)
458 /* Keep track of the place, where to insert */
459 if (tmp->rating >= cs->rating)
461 list_add(&cs->list, entry);
465 * clocksource_register - Used to install new clocksources
466 * @t: clocksource to be registered
468 * Returns -EBUSY if registration fails, zero otherwise.
470 int clocksource_register(struct clocksource *cs)
474 spin_lock_irqsave(&clocksource_lock, flags);
475 clocksource_enqueue(cs);
476 clocksource_select();
477 spin_unlock_irqrestore(&clocksource_lock, flags);
478 clocksource_enqueue_watchdog(cs);
481 EXPORT_SYMBOL(clocksource_register);
484 * clocksource_change_rating - Change the rating of a registered clocksource
486 void clocksource_change_rating(struct clocksource *cs, int rating)
490 spin_lock_irqsave(&clocksource_lock, flags);
493 clocksource_enqueue(cs);
494 clocksource_select();
495 spin_unlock_irqrestore(&clocksource_lock, flags);
497 EXPORT_SYMBOL(clocksource_change_rating);
500 * clocksource_unregister - remove a registered clocksource
502 void clocksource_unregister(struct clocksource *cs)
506 clocksource_dequeue_watchdog(cs);
507 spin_lock_irqsave(&clocksource_lock, flags);
509 clocksource_select();
510 spin_unlock_irqrestore(&clocksource_lock, flags);
512 EXPORT_SYMBOL(clocksource_unregister);
516 * sysfs_show_current_clocksources - sysfs interface for current clocksource
518 * @buf: char buffer to be filled with clocksource list
520 * Provides sysfs interface for listing current clocksource.
523 sysfs_show_current_clocksources(struct sys_device *dev,
524 struct sysdev_attribute *attr, char *buf)
528 spin_lock_irq(&clocksource_lock);
529 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
530 spin_unlock_irq(&clocksource_lock);
536 * sysfs_override_clocksource - interface for manually overriding clocksource
538 * @buf: name of override clocksource
539 * @count: length of buffer
541 * Takes input from sysfs interface for manually overriding the default
542 * clocksource selction.
544 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
545 struct sysdev_attribute *attr,
546 const char *buf, size_t count)
550 /* strings from sysfs write are not 0 terminated! */
551 if (count >= sizeof(override_name))
555 if (buf[count-1] == '\n')
558 spin_lock_irq(&clocksource_lock);
561 memcpy(override_name, buf, count);
562 override_name[count] = 0;
563 clocksource_select();
565 spin_unlock_irq(&clocksource_lock);
571 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
573 * @buf: char buffer to be filled with clocksource list
575 * Provides sysfs interface for listing registered clocksources
578 sysfs_show_available_clocksources(struct sys_device *dev,
579 struct sysdev_attribute *attr,
582 struct clocksource *src;
585 spin_lock_irq(&clocksource_lock);
586 list_for_each_entry(src, &clocksource_list, list) {
588 * Don't show non-HRES clocksource if the tick code is
589 * in one shot mode (highres=on or nohz=on)
591 if (!tick_oneshot_mode_active() ||
592 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
593 count += snprintf(buf + count,
594 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
597 spin_unlock_irq(&clocksource_lock);
599 count += snprintf(buf + count,
600 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
608 static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
609 sysfs_override_clocksource);
611 static SYSDEV_ATTR(available_clocksource, 0444,
612 sysfs_show_available_clocksources, NULL);
614 static struct sysdev_class clocksource_sysclass = {
615 .name = "clocksource",
618 static struct sys_device device_clocksource = {
620 .cls = &clocksource_sysclass,
623 static int __init init_clocksource_sysfs(void)
625 int error = sysdev_class_register(&clocksource_sysclass);
628 error = sysdev_register(&device_clocksource);
630 error = sysdev_create_file(
632 &attr_current_clocksource);
634 error = sysdev_create_file(
636 &attr_available_clocksource);
640 device_initcall(init_clocksource_sysfs);
641 #endif /* CONFIG_SYSFS */
644 * boot_override_clocksource - boot clock override
645 * @str: override name
647 * Takes a clocksource= boot argument and uses it
648 * as the clocksource override name.
650 static int __init boot_override_clocksource(char* str)
653 spin_lock_irqsave(&clocksource_lock, flags);
655 strlcpy(override_name, str, sizeof(override_name));
656 spin_unlock_irqrestore(&clocksource_lock, flags);
660 __setup("clocksource=", boot_override_clocksource);
663 * boot_override_clock - Compatibility layer for deprecated boot option
664 * @str: override name
666 * DEPRECATED! Takes a clock= boot argument and uses it
667 * as the clocksource override name
669 static int __init boot_override_clock(char* str)
671 if (!strcmp(str, "pmtmr")) {
672 printk("Warning: clock=pmtmr is deprecated. "
673 "Use clocksource=acpi_pm.\n");
674 return boot_override_clocksource("acpi_pm");
676 printk("Warning! clock= boot option is deprecated. "
677 "Use clocksource=xyz\n");
678 return boot_override_clocksource(str);
681 __setup("clock=", boot_override_clock);