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 * linked list with the registered clocksources
115 * protects manipulations to curr_clocksource and the clocksource_list
117 * Name of the user-specified clocksource.
119 static struct clocksource *curr_clocksource;
120 static LIST_HEAD(clocksource_list);
121 static DEFINE_MUTEX(clocksource_mutex);
122 static char override_name[32];
124 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
125 static LIST_HEAD(watchdog_list);
126 static struct clocksource *watchdog;
127 static struct timer_list watchdog_timer;
128 static struct work_struct watchdog_work;
129 static DEFINE_SPINLOCK(watchdog_lock);
130 static cycle_t watchdog_last;
131 static int watchdog_running;
133 static void clocksource_watchdog_work(struct work_struct *work);
134 static void __clocksource_change_rating(struct clocksource *cs, int rating);
137 * Interval: 0.5sec Threshold: 0.0625s
139 #define WATCHDOG_INTERVAL (HZ >> 1)
140 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
142 static void clocksource_unstable(struct clocksource *cs, int64_t delta)
144 printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
146 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
147 cs->flags |= CLOCK_SOURCE_UNSTABLE;
148 schedule_work(&watchdog_work);
151 static void clocksource_watchdog(unsigned long data)
153 struct clocksource *cs;
154 cycle_t csnow, wdnow;
155 int64_t wd_nsec, cs_nsec;
158 spin_lock(&watchdog_lock);
159 if (!watchdog_running)
162 wdnow = watchdog->read(watchdog);
163 wd_nsec = clocksource_cyc2ns((wdnow - watchdog_last) & watchdog->mask,
164 watchdog->mult, watchdog->shift);
165 watchdog_last = wdnow;
167 list_for_each_entry(cs, &watchdog_list, wd_list) {
169 /* Clocksource already marked unstable? */
170 if (cs->flags & CLOCK_SOURCE_UNSTABLE)
173 csnow = cs->read(cs);
175 /* Clocksource initialized ? */
176 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
177 cs->flags |= CLOCK_SOURCE_WATCHDOG;
182 /* Check the deviation from the watchdog clocksource. */
183 cs_nsec = clocksource_cyc2ns((csnow - cs->wd_last) &
184 cs->mask, cs->mult, cs->shift);
186 if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
187 clocksource_unstable(cs, cs_nsec - wd_nsec);
191 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
192 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
193 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
194 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
196 * We just marked the clocksource as highres-capable,
197 * notify the rest of the system as well so that we
198 * transition into high-res mode:
205 * Cycle through CPUs to check if the CPUs stay synchronized
208 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
209 if (next_cpu >= nr_cpu_ids)
210 next_cpu = cpumask_first(cpu_online_mask);
211 watchdog_timer.expires += WATCHDOG_INTERVAL;
212 add_timer_on(&watchdog_timer, next_cpu);
214 spin_unlock(&watchdog_lock);
217 static inline void clocksource_start_watchdog(void)
219 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
221 INIT_WORK(&watchdog_work, clocksource_watchdog_work);
222 init_timer(&watchdog_timer);
223 watchdog_timer.function = clocksource_watchdog;
224 watchdog_last = watchdog->read(watchdog);
225 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
226 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
227 watchdog_running = 1;
230 static inline void clocksource_stop_watchdog(void)
232 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
234 del_timer(&watchdog_timer);
235 watchdog_running = 0;
238 static inline void clocksource_reset_watchdog(void)
240 struct clocksource *cs;
242 list_for_each_entry(cs, &watchdog_list, wd_list)
243 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
246 static void clocksource_resume_watchdog(void)
250 spin_lock_irqsave(&watchdog_lock, flags);
251 clocksource_reset_watchdog();
252 spin_unlock_irqrestore(&watchdog_lock, flags);
255 static void clocksource_enqueue_watchdog(struct clocksource *cs)
259 spin_lock_irqsave(&watchdog_lock, flags);
260 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
261 /* cs is a clocksource to be watched. */
262 list_add(&cs->wd_list, &watchdog_list);
263 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
265 /* cs is a watchdog. */
266 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
267 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
268 /* Pick the best watchdog. */
269 if (!watchdog || cs->rating > watchdog->rating) {
271 /* Reset watchdog cycles */
272 clocksource_reset_watchdog();
275 /* Check if the watchdog timer needs to be started. */
276 clocksource_start_watchdog();
277 spin_unlock_irqrestore(&watchdog_lock, flags);
280 static void clocksource_dequeue_watchdog(struct clocksource *cs)
282 struct clocksource *tmp;
285 spin_lock_irqsave(&watchdog_lock, flags);
286 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
287 /* cs is a watched clocksource. */
288 list_del_init(&cs->wd_list);
289 } else if (cs == watchdog) {
290 /* Reset watchdog cycles */
291 clocksource_reset_watchdog();
292 /* Current watchdog is removed. Find an alternative. */
294 list_for_each_entry(tmp, &clocksource_list, list) {
295 if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
297 if (!watchdog || tmp->rating > watchdog->rating)
301 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
302 /* Check if the watchdog timer needs to be stopped. */
303 clocksource_stop_watchdog();
304 spin_unlock_irqrestore(&watchdog_lock, flags);
307 static void clocksource_watchdog_work(struct work_struct *work)
309 struct clocksource *cs, *tmp;
313 mutex_lock(&clocksource_mutex);
314 spin_lock_irqsave(&watchdog_lock, flags);
315 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
316 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
317 list_del_init(&cs->wd_list);
318 list_add(&cs->wd_list, &unstable);
320 /* Check if the watchdog timer needs to be stopped. */
321 clocksource_stop_watchdog();
322 spin_unlock_irqrestore(&watchdog_lock, flags);
324 /* Needs to be done outside of watchdog lock */
325 list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
326 list_del_init(&cs->wd_list);
327 __clocksource_change_rating(cs, 0);
329 mutex_unlock(&clocksource_mutex);
332 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
334 static void clocksource_enqueue_watchdog(struct clocksource *cs)
336 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
337 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
340 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
341 static inline void clocksource_resume_watchdog(void) { }
343 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
346 * clocksource_resume - resume the clocksource(s)
348 void clocksource_resume(void)
350 struct clocksource *cs;
352 mutex_lock(&clocksource_mutex);
354 list_for_each_entry(cs, &clocksource_list, list)
358 clocksource_resume_watchdog();
360 mutex_unlock(&clocksource_mutex);
364 * clocksource_touch_watchdog - Update watchdog
366 * Update the watchdog after exception contexts such as kgdb so as not
367 * to incorrectly trip the watchdog.
370 void clocksource_touch_watchdog(void)
372 clocksource_resume_watchdog();
375 #ifdef CONFIG_GENERIC_TIME
377 static int finished_booting;
380 * clocksource_select - Select the best clocksource available
382 * Private function. Must hold clocksource_mutex when called.
384 * Select the clocksource with the best rating, or the clocksource,
385 * which is selected by userspace override.
387 static void clocksource_select(void)
389 struct clocksource *best, *cs;
391 if (!finished_booting || list_empty(&clocksource_list))
393 /* First clocksource on the list has the best rating. */
394 best = list_first_entry(&clocksource_list, struct clocksource, list);
395 /* Check for the override clocksource. */
396 list_for_each_entry(cs, &clocksource_list, list) {
397 if (strcmp(cs->name, override_name) != 0)
400 * Check to make sure we don't switch to a non-highres
401 * capable clocksource if the tick code is in oneshot
402 * mode (highres or nohz)
404 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
405 tick_oneshot_mode_active()) {
406 /* Override clocksource cannot be used. */
407 printk(KERN_WARNING "Override clocksource %s is not "
408 "HRT compatible. Cannot switch while in "
409 "HRT/NOHZ mode\n", cs->name);
410 override_name[0] = 0;
412 /* Override clocksource can be used. */
416 if (curr_clocksource != best) {
417 printk(KERN_INFO "Switching to clocksource %s\n", best->name);
418 curr_clocksource = best;
419 timekeeping_notify(curr_clocksource);
424 * clocksource_done_booting - Called near the end of core bootup
426 * Hack to avoid lots of clocksource churn at boot time.
427 * We use fs_initcall because we want this to start before
428 * device_initcall but after subsys_initcall.
430 static int __init clocksource_done_booting(void)
432 finished_booting = 1;
433 clocksource_select();
436 fs_initcall(clocksource_done_booting);
438 #else /* CONFIG_GENERIC_TIME */
440 static inline void clocksource_select(void) { }
445 * Enqueue the clocksource sorted by rating
447 static void clocksource_enqueue(struct clocksource *cs)
449 struct list_head *entry = &clocksource_list;
450 struct clocksource *tmp;
452 list_for_each_entry(tmp, &clocksource_list, list)
453 /* Keep track of the place, where to insert */
454 if (tmp->rating >= cs->rating)
456 list_add(&cs->list, entry);
460 * clocksource_register - Used to install new clocksources
461 * @t: clocksource to be registered
463 * Returns -EBUSY if registration fails, zero otherwise.
465 int clocksource_register(struct clocksource *cs)
467 mutex_lock(&clocksource_mutex);
468 clocksource_enqueue(cs);
469 clocksource_select();
470 clocksource_enqueue_watchdog(cs);
471 mutex_unlock(&clocksource_mutex);
474 EXPORT_SYMBOL(clocksource_register);
476 static void __clocksource_change_rating(struct clocksource *cs, int rating)
480 clocksource_enqueue(cs);
481 clocksource_select();
485 * clocksource_change_rating - Change the rating of a registered clocksource
487 void clocksource_change_rating(struct clocksource *cs, int rating)
489 mutex_lock(&clocksource_mutex);
490 __clocksource_change_rating(cs, rating);
491 mutex_unlock(&clocksource_mutex);
493 EXPORT_SYMBOL(clocksource_change_rating);
496 * clocksource_unregister - remove a registered clocksource
498 void clocksource_unregister(struct clocksource *cs)
500 mutex_lock(&clocksource_mutex);
501 clocksource_dequeue_watchdog(cs);
503 clocksource_select();
504 mutex_unlock(&clocksource_mutex);
506 EXPORT_SYMBOL(clocksource_unregister);
510 * sysfs_show_current_clocksources - sysfs interface for current clocksource
512 * @buf: char buffer to be filled with clocksource list
514 * Provides sysfs interface for listing current clocksource.
517 sysfs_show_current_clocksources(struct sys_device *dev,
518 struct sysdev_attribute *attr, char *buf)
522 mutex_lock(&clocksource_mutex);
523 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
524 mutex_unlock(&clocksource_mutex);
530 * sysfs_override_clocksource - interface for manually overriding clocksource
532 * @buf: name of override clocksource
533 * @count: length of buffer
535 * Takes input from sysfs interface for manually overriding the default
536 * clocksource selction.
538 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
539 struct sysdev_attribute *attr,
540 const char *buf, size_t count)
544 /* strings from sysfs write are not 0 terminated! */
545 if (count >= sizeof(override_name))
549 if (buf[count-1] == '\n')
552 mutex_lock(&clocksource_mutex);
555 memcpy(override_name, buf, count);
556 override_name[count] = 0;
557 clocksource_select();
559 mutex_unlock(&clocksource_mutex);
565 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
567 * @buf: char buffer to be filled with clocksource list
569 * Provides sysfs interface for listing registered clocksources
572 sysfs_show_available_clocksources(struct sys_device *dev,
573 struct sysdev_attribute *attr,
576 struct clocksource *src;
579 mutex_lock(&clocksource_mutex);
580 list_for_each_entry(src, &clocksource_list, list) {
582 * Don't show non-HRES clocksource if the tick code is
583 * in one shot mode (highres=on or nohz=on)
585 if (!tick_oneshot_mode_active() ||
586 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
587 count += snprintf(buf + count,
588 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
591 mutex_unlock(&clocksource_mutex);
593 count += snprintf(buf + count,
594 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
602 static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
603 sysfs_override_clocksource);
605 static SYSDEV_ATTR(available_clocksource, 0444,
606 sysfs_show_available_clocksources, NULL);
608 static struct sysdev_class clocksource_sysclass = {
609 .name = "clocksource",
612 static struct sys_device device_clocksource = {
614 .cls = &clocksource_sysclass,
617 static int __init init_clocksource_sysfs(void)
619 int error = sysdev_class_register(&clocksource_sysclass);
622 error = sysdev_register(&device_clocksource);
624 error = sysdev_create_file(
626 &attr_current_clocksource);
628 error = sysdev_create_file(
630 &attr_available_clocksource);
634 device_initcall(init_clocksource_sysfs);
635 #endif /* CONFIG_SYSFS */
638 * boot_override_clocksource - boot clock override
639 * @str: override name
641 * Takes a clocksource= boot argument and uses it
642 * as the clocksource override name.
644 static int __init boot_override_clocksource(char* str)
646 mutex_lock(&clocksource_mutex);
648 strlcpy(override_name, str, sizeof(override_name));
649 mutex_unlock(&clocksource_mutex);
653 __setup("clocksource=", boot_override_clocksource);
656 * boot_override_clock - Compatibility layer for deprecated boot option
657 * @str: override name
659 * DEPRECATED! Takes a clock= boot argument and uses it
660 * as the clocksource override name
662 static int __init boot_override_clock(char* str)
664 if (!strcmp(str, "pmtmr")) {
665 printk("Warning: clock=pmtmr is deprecated. "
666 "Use clocksource=acpi_pm.\n");
667 return boot_override_clocksource("acpi_pm");
669 printk("Warning! clock= boot option is deprecated. "
670 "Use clocksource=xyz\n");
671 return boot_override_clocksource(str);
674 __setup("clock=", boot_override_clock);