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
24 * o get rid of clocksource_jiffies extern
27 #include <linux/clocksource.h>
28 #include <linux/sysdev.h>
29 #include <linux/init.h>
30 #include <linux/module.h>
31 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
32 #include <linux/tick.h>
34 void timecounter_init(struct timecounter *tc,
35 const struct cyclecounter *cc,
39 tc->cycle_last = cc->read(cc);
40 tc->nsec = start_tstamp;
42 EXPORT_SYMBOL(timecounter_init);
45 * timecounter_read_delta - get nanoseconds since last call of this function
46 * @tc: Pointer to time counter
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
52 * The first call to this function for a new time counter initializes
53 * the time tracking and returns an undefined result.
55 static u64 timecounter_read_delta(struct timecounter *tc)
57 cycle_t cycle_now, cycle_delta;
60 /* read cycle counter: */
61 cycle_now = tc->cc->read(tc->cc);
63 /* calculate the delta since the last timecounter_read_delta(): */
64 cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
66 /* convert to nanoseconds: */
67 ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta);
69 /* update time stamp of timecounter_read_delta() call: */
70 tc->cycle_last = cycle_now;
75 u64 timecounter_read(struct timecounter *tc)
79 /* increment time by nanoseconds since last call */
80 nsec = timecounter_read_delta(tc);
86 EXPORT_SYMBOL(timecounter_read);
88 u64 timecounter_cyc2time(struct timecounter *tc,
91 u64 cycle_delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
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.
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);
103 nsec = cyclecounter_cyc2ns(tc->cc, cycle_delta) + tc->nsec;
108 EXPORT_SYMBOL(timecounter_cyc2time);
110 /* XXX - Would like a better way for initializing curr_clocksource */
111 extern struct clocksource clocksource_jiffies;
113 /*[Clocksource internal variables]---------
115 * currently selected clocksource. Initialized to clocksource_jiffies.
117 * pending next selected clocksource.
119 * linked list with the registered clocksources
121 * protects manipulations to curr_clocksource and next_clocksource
122 * and the clocksource_list
124 * Name of the user-specified clocksource.
126 static struct clocksource *curr_clocksource = &clocksource_jiffies;
127 static struct clocksource *next_clocksource;
128 static struct clocksource *clocksource_override;
129 static LIST_HEAD(clocksource_list);
130 static DEFINE_SPINLOCK(clocksource_lock);
131 static char override_name[32];
132 static int finished_booting;
134 /* clocksource_done_booting - Called near the end of core bootup
136 * Hack to avoid lots of clocksource churn at boot time.
137 * We use fs_initcall because we want this to start before
138 * device_initcall but after subsys_initcall.
140 static int __init clocksource_done_booting(void)
142 finished_booting = 1;
145 fs_initcall(clocksource_done_booting);
147 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
148 static LIST_HEAD(watchdog_list);
149 static struct clocksource *watchdog;
150 static struct timer_list watchdog_timer;
151 static DEFINE_SPINLOCK(watchdog_lock);
152 static cycle_t watchdog_last;
153 static unsigned long watchdog_resumed;
156 * Interval: 0.5sec Threshold: 0.0625s
158 #define WATCHDOG_INTERVAL (HZ >> 1)
159 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
161 static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
163 if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
166 printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
168 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
169 clocksource_change_rating(cs, 0);
170 list_del(&cs->wd_list);
173 static void clocksource_watchdog(unsigned long data)
175 struct clocksource *cs, *tmp;
176 cycle_t csnow, wdnow;
177 int64_t wd_nsec, cs_nsec;
180 spin_lock(&watchdog_lock);
182 resumed = test_and_clear_bit(0, &watchdog_resumed);
184 wdnow = watchdog->read(watchdog);
185 wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
186 watchdog_last = wdnow;
188 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
189 csnow = cs->read(cs);
191 if (unlikely(resumed)) {
197 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
198 if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
199 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
200 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
202 * We just marked the clocksource as
203 * highres-capable, notify the rest of the
204 * system as well so that we transition
205 * into high-res mode:
209 cs->flags |= CLOCK_SOURCE_WATCHDOG;
212 cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
214 /* Check the delta. Might remove from the list ! */
215 clocksource_ratewd(cs, cs_nsec - wd_nsec);
219 if (!list_empty(&watchdog_list)) {
221 * Cycle through CPUs to check if the CPUs stay
222 * synchronized to each other.
224 int next_cpu = cpumask_next(raw_smp_processor_id(),
227 if (next_cpu >= nr_cpu_ids)
228 next_cpu = cpumask_first(cpu_online_mask);
229 watchdog_timer.expires += WATCHDOG_INTERVAL;
230 add_timer_on(&watchdog_timer, next_cpu);
232 spin_unlock(&watchdog_lock);
234 static void clocksource_resume_watchdog(void)
236 set_bit(0, &watchdog_resumed);
239 static void clocksource_check_watchdog(struct clocksource *cs)
241 struct clocksource *cse;
244 spin_lock_irqsave(&watchdog_lock, flags);
245 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
246 int started = !list_empty(&watchdog_list);
248 list_add(&cs->wd_list, &watchdog_list);
249 if (!started && watchdog) {
250 watchdog_last = watchdog->read(watchdog);
251 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
252 add_timer_on(&watchdog_timer,
253 cpumask_first(cpu_online_mask));
256 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
257 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
259 if (!watchdog || cs->rating > watchdog->rating) {
261 del_timer(&watchdog_timer);
263 init_timer(&watchdog_timer);
264 watchdog_timer.function = clocksource_watchdog;
266 /* Reset watchdog cycles */
267 list_for_each_entry(cse, &watchdog_list, wd_list)
268 cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
269 /* Start if list is not empty */
270 if (!list_empty(&watchdog_list)) {
271 watchdog_last = watchdog->read(watchdog);
272 watchdog_timer.expires =
273 jiffies + WATCHDOG_INTERVAL;
274 add_timer_on(&watchdog_timer,
275 cpumask_first(cpu_online_mask));
279 spin_unlock_irqrestore(&watchdog_lock, flags);
282 static void clocksource_check_watchdog(struct clocksource *cs)
284 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
285 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
288 static inline void clocksource_resume_watchdog(void) { }
292 * clocksource_resume - resume the clocksource(s)
294 void clocksource_resume(void)
296 struct clocksource *cs;
299 spin_lock_irqsave(&clocksource_lock, flags);
301 list_for_each_entry(cs, &clocksource_list, list) {
306 clocksource_resume_watchdog();
308 spin_unlock_irqrestore(&clocksource_lock, flags);
312 * clocksource_touch_watchdog - Update watchdog
314 * Update the watchdog after exception contexts such as kgdb so as not
315 * to incorrectly trip the watchdog.
318 void clocksource_touch_watchdog(void)
320 clocksource_resume_watchdog();
324 * clocksource_get_next - Returns the selected clocksource
327 struct clocksource *clocksource_get_next(void)
331 spin_lock_irqsave(&clocksource_lock, flags);
332 if (next_clocksource && finished_booting) {
333 curr_clocksource = next_clocksource;
334 next_clocksource = NULL;
336 spin_unlock_irqrestore(&clocksource_lock, flags);
338 return curr_clocksource;
342 * select_clocksource - Selects the best registered clocksource.
344 * Private function. Must hold clocksource_lock when called.
346 * Select the clocksource with the best rating, or the clocksource,
347 * which is selected by userspace override.
349 static struct clocksource *select_clocksource(void)
351 struct clocksource *next;
353 if (list_empty(&clocksource_list))
356 if (clocksource_override)
357 next = clocksource_override;
359 next = list_entry(clocksource_list.next, struct clocksource,
362 if (next == curr_clocksource)
369 * Enqueue the clocksource sorted by rating
371 static int clocksource_enqueue(struct clocksource *c)
373 struct list_head *tmp, *entry = &clocksource_list;
375 list_for_each(tmp, &clocksource_list) {
376 struct clocksource *cs;
378 cs = list_entry(tmp, struct clocksource, list);
381 /* Keep track of the place, where to insert */
382 if (cs->rating >= c->rating)
385 list_add(&c->list, entry);
387 if (strlen(c->name) == strlen(override_name) &&
388 !strcmp(c->name, override_name))
389 clocksource_override = c;
395 * clocksource_register - Used to install new clocksources
396 * @t: clocksource to be registered
398 * Returns -EBUSY if registration fails, zero otherwise.
400 int clocksource_register(struct clocksource *c)
405 /* save mult_orig on registration */
406 c->mult_orig = c->mult;
408 spin_lock_irqsave(&clocksource_lock, flags);
409 ret = clocksource_enqueue(c);
411 next_clocksource = select_clocksource();
412 spin_unlock_irqrestore(&clocksource_lock, flags);
414 clocksource_check_watchdog(c);
417 EXPORT_SYMBOL(clocksource_register);
420 * clocksource_change_rating - Change the rating of a registered clocksource
423 void clocksource_change_rating(struct clocksource *cs, int rating)
427 spin_lock_irqsave(&clocksource_lock, flags);
430 clocksource_enqueue(cs);
431 next_clocksource = select_clocksource();
432 spin_unlock_irqrestore(&clocksource_lock, flags);
436 * clocksource_unregister - remove a registered clocksource
438 void clocksource_unregister(struct clocksource *cs)
442 spin_lock_irqsave(&clocksource_lock, flags);
444 if (clocksource_override == cs)
445 clocksource_override = NULL;
446 next_clocksource = select_clocksource();
447 spin_unlock_irqrestore(&clocksource_lock, flags);
452 * sysfs_show_current_clocksources - sysfs interface for current clocksource
454 * @buf: char buffer to be filled with clocksource list
456 * Provides sysfs interface for listing current clocksource.
459 sysfs_show_current_clocksources(struct sys_device *dev,
460 struct sysdev_attribute *attr, char *buf)
464 spin_lock_irq(&clocksource_lock);
465 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
466 spin_unlock_irq(&clocksource_lock);
472 * sysfs_override_clocksource - interface for manually overriding clocksource
474 * @buf: name of override clocksource
475 * @count: length of buffer
477 * Takes input from sysfs interface for manually overriding the default
478 * clocksource selction.
480 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
481 struct sysdev_attribute *attr,
482 const char *buf, size_t count)
484 struct clocksource *ovr = NULL;
488 /* strings from sysfs write are not 0 terminated! */
489 if (count >= sizeof(override_name))
493 if (buf[count-1] == '\n')
496 spin_lock_irq(&clocksource_lock);
499 memcpy(override_name, buf, count);
500 override_name[count] = 0;
502 len = strlen(override_name);
504 struct clocksource *cs;
506 ovr = clocksource_override;
507 /* try to select it: */
508 list_for_each_entry(cs, &clocksource_list, list) {
509 if (strlen(cs->name) == len &&
510 !strcmp(cs->name, override_name))
515 /* Reselect, when the override name has changed */
516 if (ovr != clocksource_override) {
517 clocksource_override = ovr;
518 next_clocksource = select_clocksource();
521 spin_unlock_irq(&clocksource_lock);
527 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
529 * @buf: char buffer to be filled with clocksource list
531 * Provides sysfs interface for listing registered clocksources
534 sysfs_show_available_clocksources(struct sys_device *dev,
535 struct sysdev_attribute *attr,
538 struct clocksource *src;
541 spin_lock_irq(&clocksource_lock);
542 list_for_each_entry(src, &clocksource_list, list) {
543 count += snprintf(buf + count,
544 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
547 spin_unlock_irq(&clocksource_lock);
549 count += snprintf(buf + count,
550 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
558 static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
559 sysfs_override_clocksource);
561 static SYSDEV_ATTR(available_clocksource, 0444,
562 sysfs_show_available_clocksources, NULL);
564 static struct sysdev_class clocksource_sysclass = {
565 .name = "clocksource",
568 static struct sys_device device_clocksource = {
570 .cls = &clocksource_sysclass,
573 static int __init init_clocksource_sysfs(void)
575 int error = sysdev_class_register(&clocksource_sysclass);
578 error = sysdev_register(&device_clocksource);
580 error = sysdev_create_file(
582 &attr_current_clocksource);
584 error = sysdev_create_file(
586 &attr_available_clocksource);
590 device_initcall(init_clocksource_sysfs);
591 #endif /* CONFIG_SYSFS */
594 * boot_override_clocksource - boot clock override
595 * @str: override name
597 * Takes a clocksource= boot argument and uses it
598 * as the clocksource override name.
600 static int __init boot_override_clocksource(char* str)
603 spin_lock_irqsave(&clocksource_lock, flags);
605 strlcpy(override_name, str, sizeof(override_name));
606 spin_unlock_irqrestore(&clocksource_lock, flags);
610 __setup("clocksource=", boot_override_clocksource);
613 * boot_override_clock - Compatibility layer for deprecated boot option
614 * @str: override name
616 * DEPRECATED! Takes a clock= boot argument and uses it
617 * as the clocksource override name
619 static int __init boot_override_clock(char* str)
621 if (!strcmp(str, "pmtmr")) {
622 printk("Warning: clock=pmtmr is deprecated. "
623 "Use clocksource=acpi_pm.\n");
624 return boot_override_clocksource("acpi_pm");
626 printk("Warning! clock= boot option is deprecated. "
627 "Use clocksource=xyz\n");
628 return boot_override_clocksource(str);
631 __setup("clock=", boot_override_clock);