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 /* XXX - Would like a better way for initializing curr_clocksource */
35 extern struct clocksource clocksource_jiffies;
37 /*[Clocksource internal variables]---------
39 * currently selected clocksource. Initialized to clocksource_jiffies.
41 * pending next selected clocksource.
43 * linked list with the registered clocksources
45 * protects manipulations to curr_clocksource and next_clocksource
46 * and the clocksource_list
48 * Name of the user-specified clocksource.
50 static struct clocksource *curr_clocksource = &clocksource_jiffies;
51 static struct clocksource *next_clocksource;
52 static struct clocksource *clocksource_override;
53 static LIST_HEAD(clocksource_list);
54 static DEFINE_SPINLOCK(clocksource_lock);
55 static char override_name[32];
56 static int finished_booting;
58 /* clocksource_done_booting - Called near the end of core bootup
60 * Hack to avoid lots of clocksource churn at boot time.
61 * We use fs_initcall because we want this to start before
62 * device_initcall but after subsys_initcall.
64 static int __init clocksource_done_booting(void)
69 fs_initcall(clocksource_done_booting);
71 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
72 static LIST_HEAD(watchdog_list);
73 static struct clocksource *watchdog;
74 static struct timer_list watchdog_timer;
75 static DEFINE_SPINLOCK(watchdog_lock);
76 static cycle_t watchdog_last;
77 static unsigned long watchdog_resumed;
80 * Interval: 0.5sec Threshold: 0.0625s
82 #define WATCHDOG_INTERVAL (HZ >> 1)
83 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
85 static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
87 if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
90 printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
92 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
93 clocksource_change_rating(cs, 0);
94 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
95 list_del(&cs->wd_list);
98 static void clocksource_watchdog(unsigned long data)
100 struct clocksource *cs, *tmp;
101 cycle_t csnow, wdnow;
102 int64_t wd_nsec, cs_nsec;
105 spin_lock(&watchdog_lock);
107 resumed = test_and_clear_bit(0, &watchdog_resumed);
109 wdnow = watchdog->read();
110 wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
111 watchdog_last = wdnow;
113 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
116 if (unlikely(resumed)) {
122 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
123 if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
124 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
125 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
127 * We just marked the clocksource as
128 * highres-capable, notify the rest of the
129 * system as well so that we transition
130 * into high-res mode:
134 cs->flags |= CLOCK_SOURCE_WATCHDOG;
137 cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
139 /* Check the delta. Might remove from the list ! */
140 clocksource_ratewd(cs, cs_nsec - wd_nsec);
144 if (!list_empty(&watchdog_list)) {
145 /* Cycle through CPUs to check if the CPUs stay synchronized to
147 int next_cpu = next_cpu(raw_smp_processor_id(), cpu_online_map);
148 if (next_cpu >= NR_CPUS)
149 next_cpu = first_cpu(cpu_online_map);
150 watchdog_timer.expires += WATCHDOG_INTERVAL;
151 add_timer_on(&watchdog_timer, next_cpu);
153 spin_unlock(&watchdog_lock);
155 static void clocksource_resume_watchdog(void)
157 set_bit(0, &watchdog_resumed);
160 static void clocksource_check_watchdog(struct clocksource *cs)
162 struct clocksource *cse;
165 spin_lock_irqsave(&watchdog_lock, flags);
166 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
167 int started = !list_empty(&watchdog_list);
169 list_add(&cs->wd_list, &watchdog_list);
170 if (!started && watchdog) {
171 watchdog_last = watchdog->read();
172 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
173 add_timer_on(&watchdog_timer, first_cpu(cpu_online_map));
176 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
177 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
179 if (!watchdog || cs->rating > watchdog->rating) {
181 del_timer(&watchdog_timer);
183 init_timer_deferrable(&watchdog_timer);
184 watchdog_timer.function = clocksource_watchdog;
186 /* Reset watchdog cycles */
187 list_for_each_entry(cse, &watchdog_list, wd_list)
188 cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
189 /* Start if list is not empty */
190 if (!list_empty(&watchdog_list)) {
191 watchdog_last = watchdog->read();
192 watchdog_timer.expires =
193 jiffies + WATCHDOG_INTERVAL;
194 add_timer_on(&watchdog_timer,
195 first_cpu(cpu_online_map));
199 spin_unlock_irqrestore(&watchdog_lock, flags);
202 static void clocksource_check_watchdog(struct clocksource *cs)
204 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
205 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
208 static inline void clocksource_resume_watchdog(void) { }
212 * clocksource_resume - resume the clocksource(s)
214 void clocksource_resume(void)
216 struct clocksource *cs;
219 spin_lock_irqsave(&clocksource_lock, flags);
221 list_for_each_entry(cs, &clocksource_list, list) {
226 clocksource_resume_watchdog();
228 spin_unlock_irqrestore(&clocksource_lock, flags);
232 * clocksource_get_next - Returns the selected clocksource
235 struct clocksource *clocksource_get_next(void)
239 spin_lock_irqsave(&clocksource_lock, flags);
240 if (next_clocksource && finished_booting) {
241 curr_clocksource = next_clocksource;
242 next_clocksource = NULL;
244 spin_unlock_irqrestore(&clocksource_lock, flags);
246 return curr_clocksource;
250 * select_clocksource - Selects the best registered clocksource.
252 * Private function. Must hold clocksource_lock when called.
254 * Select the clocksource with the best rating, or the clocksource,
255 * which is selected by userspace override.
257 static struct clocksource *select_clocksource(void)
259 struct clocksource *next;
261 if (list_empty(&clocksource_list))
264 if (clocksource_override)
265 next = clocksource_override;
267 next = list_entry(clocksource_list.next, struct clocksource,
270 if (next == curr_clocksource)
277 * Enqueue the clocksource sorted by rating
279 static int clocksource_enqueue(struct clocksource *c)
281 struct list_head *tmp, *entry = &clocksource_list;
283 list_for_each(tmp, &clocksource_list) {
284 struct clocksource *cs;
286 cs = list_entry(tmp, struct clocksource, list);
289 /* Keep track of the place, where to insert */
290 if (cs->rating >= c->rating)
293 list_add(&c->list, entry);
295 if (strlen(c->name) == strlen(override_name) &&
296 !strcmp(c->name, override_name))
297 clocksource_override = c;
303 * clocksource_register - Used to install new clocksources
304 * @t: clocksource to be registered
306 * Returns -EBUSY if registration fails, zero otherwise.
308 int clocksource_register(struct clocksource *c)
313 spin_lock_irqsave(&clocksource_lock, flags);
314 ret = clocksource_enqueue(c);
316 next_clocksource = select_clocksource();
317 spin_unlock_irqrestore(&clocksource_lock, flags);
319 clocksource_check_watchdog(c);
322 EXPORT_SYMBOL(clocksource_register);
325 * clocksource_change_rating - Change the rating of a registered clocksource
328 void clocksource_change_rating(struct clocksource *cs, int rating)
332 spin_lock_irqsave(&clocksource_lock, flags);
335 clocksource_enqueue(cs);
336 next_clocksource = select_clocksource();
337 spin_unlock_irqrestore(&clocksource_lock, flags);
341 * clocksource_unregister - remove a registered clocksource
343 void clocksource_unregister(struct clocksource *cs)
347 spin_lock_irqsave(&clocksource_lock, flags);
349 if (clocksource_override == cs)
350 clocksource_override = NULL;
351 next_clocksource = select_clocksource();
352 spin_unlock_irqrestore(&clocksource_lock, flags);
357 * sysfs_show_current_clocksources - sysfs interface for current clocksource
359 * @buf: char buffer to be filled with clocksource list
361 * Provides sysfs interface for listing current clocksource.
364 sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
368 spin_lock_irq(&clocksource_lock);
369 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
370 spin_unlock_irq(&clocksource_lock);
376 * sysfs_override_clocksource - interface for manually overriding clocksource
378 * @buf: name of override clocksource
379 * @count: length of buffer
381 * Takes input from sysfs interface for manually overriding the default
382 * clocksource selction.
384 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
385 const char *buf, size_t count)
387 struct clocksource *ovr = NULL;
391 /* strings from sysfs write are not 0 terminated! */
392 if (count >= sizeof(override_name))
396 if (buf[count-1] == '\n')
399 spin_lock_irq(&clocksource_lock);
402 memcpy(override_name, buf, count);
403 override_name[count] = 0;
405 len = strlen(override_name);
407 struct clocksource *cs;
409 ovr = clocksource_override;
410 /* try to select it: */
411 list_for_each_entry(cs, &clocksource_list, list) {
412 if (strlen(cs->name) == len &&
413 !strcmp(cs->name, override_name))
418 /* Reselect, when the override name has changed */
419 if (ovr != clocksource_override) {
420 clocksource_override = ovr;
421 next_clocksource = select_clocksource();
424 spin_unlock_irq(&clocksource_lock);
430 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
432 * @buf: char buffer to be filled with clocksource list
434 * Provides sysfs interface for listing registered clocksources
437 sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
439 struct clocksource *src;
442 spin_lock_irq(&clocksource_lock);
443 list_for_each_entry(src, &clocksource_list, list) {
444 count += snprintf(buf + count,
445 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
448 spin_unlock_irq(&clocksource_lock);
450 count += snprintf(buf + count,
451 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
459 static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
460 sysfs_override_clocksource);
462 static SYSDEV_ATTR(available_clocksource, 0600,
463 sysfs_show_available_clocksources, NULL);
465 static struct sysdev_class clocksource_sysclass = {
466 .name = "clocksource",
469 static struct sys_device device_clocksource = {
471 .cls = &clocksource_sysclass,
474 static int __init init_clocksource_sysfs(void)
476 int error = sysdev_class_register(&clocksource_sysclass);
479 error = sysdev_register(&device_clocksource);
481 error = sysdev_create_file(
483 &attr_current_clocksource);
485 error = sysdev_create_file(
487 &attr_available_clocksource);
491 device_initcall(init_clocksource_sysfs);
492 #endif /* CONFIG_SYSFS */
495 * boot_override_clocksource - boot clock override
496 * @str: override name
498 * Takes a clocksource= boot argument and uses it
499 * as the clocksource override name.
501 static int __init boot_override_clocksource(char* str)
504 spin_lock_irqsave(&clocksource_lock, flags);
506 strlcpy(override_name, str, sizeof(override_name));
507 spin_unlock_irqrestore(&clocksource_lock, flags);
511 __setup("clocksource=", boot_override_clocksource);
514 * boot_override_clock - Compatibility layer for deprecated boot option
515 * @str: override name
517 * DEPRECATED! Takes a clock= boot argument and uses it
518 * as the clocksource override name
520 static int __init boot_override_clock(char* str)
522 if (!strcmp(str, "pmtmr")) {
523 printk("Warning: clock=pmtmr is deprecated. "
524 "Use clocksource=acpi_pm.\n");
525 return boot_override_clocksource("acpi_pm");
527 printk("Warning! clock= boot option is deprecated. "
528 "Use clocksource=xyz\n");
529 return boot_override_clocksource(str);
532 __setup("clock=", boot_override_clock);