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 DEFINE_SPINLOCK(watchdog_lock
);
147 static cycle_t watchdog_last
;
148 static unsigned long watchdog_resumed
;
151 * Interval: 0.5sec Threshold: 0.0625s
153 #define WATCHDOG_INTERVAL (HZ >> 1)
154 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
156 static void clocksource_ratewd(struct clocksource
*cs
, int64_t delta
)
158 if (delta
> -WATCHDOG_THRESHOLD
&& delta
< WATCHDOG_THRESHOLD
)
161 printk(KERN_WARNING
"Clocksource %s unstable (delta = %Ld ns)\n",
163 cs
->flags
&= ~(CLOCK_SOURCE_VALID_FOR_HRES
| CLOCK_SOURCE_WATCHDOG
);
164 clocksource_change_rating(cs
, 0);
165 list_del(&cs
->wd_list
);
168 static void clocksource_watchdog(unsigned long data
)
170 struct clocksource
*cs
, *tmp
;
171 cycle_t csnow
, wdnow
;
172 int64_t wd_nsec
, cs_nsec
;
175 spin_lock(&watchdog_lock
);
177 resumed
= test_and_clear_bit(0, &watchdog_resumed
);
179 wdnow
= watchdog
->read(watchdog
);
180 wd_nsec
= cyc2ns(watchdog
, (wdnow
- watchdog_last
) & watchdog
->mask
);
181 watchdog_last
= wdnow
;
183 list_for_each_entry_safe(cs
, tmp
, &watchdog_list
, wd_list
) {
184 csnow
= cs
->read(cs
);
186 if (unlikely(resumed
)) {
192 if (!(cs
->flags
& CLOCK_SOURCE_WATCHDOG
)) {
193 if ((cs
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
) &&
194 (watchdog
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
)) {
195 cs
->flags
|= CLOCK_SOURCE_VALID_FOR_HRES
;
197 * We just marked the clocksource as
198 * highres-capable, notify the rest of the
199 * system as well so that we transition
200 * into high-res mode:
204 cs
->flags
|= CLOCK_SOURCE_WATCHDOG
;
207 cs_nsec
= cyc2ns(cs
, (csnow
- cs
->wd_last
) & cs
->mask
);
209 /* Check the delta. Might remove from the list ! */
210 clocksource_ratewd(cs
, cs_nsec
- wd_nsec
);
214 if (!list_empty(&watchdog_list
)) {
216 * Cycle through CPUs to check if the CPUs stay
217 * synchronized to each other.
219 int next_cpu
= cpumask_next(raw_smp_processor_id(),
222 if (next_cpu
>= nr_cpu_ids
)
223 next_cpu
= cpumask_first(cpu_online_mask
);
224 watchdog_timer
.expires
+= WATCHDOG_INTERVAL
;
225 add_timer_on(&watchdog_timer
, next_cpu
);
227 spin_unlock(&watchdog_lock
);
229 static void clocksource_resume_watchdog(void)
231 set_bit(0, &watchdog_resumed
);
234 static void clocksource_check_watchdog(struct clocksource
*cs
)
236 struct clocksource
*cse
;
239 spin_lock_irqsave(&watchdog_lock
, flags
);
240 if (cs
->flags
& CLOCK_SOURCE_MUST_VERIFY
) {
241 int started
= !list_empty(&watchdog_list
);
243 list_add(&cs
->wd_list
, &watchdog_list
);
244 if (!started
&& watchdog
) {
245 watchdog_last
= watchdog
->read(watchdog
);
246 watchdog_timer
.expires
= jiffies
+ WATCHDOG_INTERVAL
;
247 add_timer_on(&watchdog_timer
,
248 cpumask_first(cpu_online_mask
));
251 if (cs
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
)
252 cs
->flags
|= CLOCK_SOURCE_VALID_FOR_HRES
;
254 if (!watchdog
|| cs
->rating
> watchdog
->rating
) {
256 del_timer(&watchdog_timer
);
258 init_timer(&watchdog_timer
);
259 watchdog_timer
.function
= clocksource_watchdog
;
261 /* Reset watchdog cycles */
262 list_for_each_entry(cse
, &watchdog_list
, wd_list
)
263 cse
->flags
&= ~CLOCK_SOURCE_WATCHDOG
;
264 /* Start if list is not empty */
265 if (!list_empty(&watchdog_list
)) {
266 watchdog_last
= watchdog
->read(watchdog
);
267 watchdog_timer
.expires
=
268 jiffies
+ WATCHDOG_INTERVAL
;
269 add_timer_on(&watchdog_timer
,
270 cpumask_first(cpu_online_mask
));
274 spin_unlock_irqrestore(&watchdog_lock
, flags
);
277 static void clocksource_check_watchdog(struct clocksource
*cs
)
279 if (cs
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
)
280 cs
->flags
|= CLOCK_SOURCE_VALID_FOR_HRES
;
283 static inline void clocksource_resume_watchdog(void) { }
287 * clocksource_resume - resume the clocksource(s)
289 void clocksource_resume(void)
291 struct clocksource
*cs
;
294 spin_lock_irqsave(&clocksource_lock
, flags
);
296 list_for_each_entry(cs
, &clocksource_list
, list
) {
301 clocksource_resume_watchdog();
303 spin_unlock_irqrestore(&clocksource_lock
, flags
);
307 * clocksource_touch_watchdog - Update watchdog
309 * Update the watchdog after exception contexts such as kgdb so as not
310 * to incorrectly trip the watchdog.
313 void clocksource_touch_watchdog(void)
315 clocksource_resume_watchdog();
318 #ifdef CONFIG_GENERIC_TIME
320 * clocksource_get_next - Returns the selected clocksource
323 struct clocksource
*clocksource_get_next(void)
327 spin_lock_irqsave(&clocksource_lock
, flags
);
328 if (next_clocksource
&& finished_booting
) {
329 curr_clocksource
= next_clocksource
;
330 next_clocksource
= NULL
;
332 spin_unlock_irqrestore(&clocksource_lock
, flags
);
334 return curr_clocksource
;
338 * clocksource_select - Select the best clocksource available
340 * Private function. Must hold clocksource_lock when called.
342 * Select the clocksource with the best rating, or the clocksource,
343 * which is selected by userspace override.
345 static void clocksource_select(void)
347 struct clocksource
*best
, *cs
;
349 if (list_empty(&clocksource_list
))
351 /* First clocksource on the list has the best rating. */
352 best
= list_first_entry(&clocksource_list
, struct clocksource
, list
);
353 /* Check for the override clocksource. */
354 list_for_each_entry(cs
, &clocksource_list
, list
) {
355 if (strcmp(cs
->name
, override_name
) != 0)
358 * Check to make sure we don't switch to a non-highres
359 * capable clocksource if the tick code is in oneshot
360 * mode (highres or nohz)
362 if (!(cs
->flags
& CLOCK_SOURCE_VALID_FOR_HRES
) &&
363 tick_oneshot_mode_active()) {
364 /* Override clocksource cannot be used. */
365 printk(KERN_WARNING
"Override clocksource %s is not "
366 "HRT compatible. Cannot switch while in "
367 "HRT/NOHZ mode\n", cs
->name
);
368 override_name
[0] = 0;
370 /* Override clocksource can be used. */
374 if (curr_clocksource
!= best
)
375 next_clocksource
= best
;
378 #else /* CONFIG_GENERIC_TIME */
380 static void clocksource_select(void) { }
385 * Enqueue the clocksource sorted by rating
387 static void clocksource_enqueue(struct clocksource
*cs
)
389 struct list_head
*entry
= &clocksource_list
;
390 struct clocksource
*tmp
;
392 list_for_each_entry(tmp
, &clocksource_list
, list
)
393 /* Keep track of the place, where to insert */
394 if (tmp
->rating
>= cs
->rating
)
396 list_add(&cs
->list
, entry
);
400 * clocksource_register - Used to install new clocksources
401 * @t: clocksource to be registered
403 * Returns -EBUSY if registration fails, zero otherwise.
405 int clocksource_register(struct clocksource
*cs
)
409 spin_lock_irqsave(&clocksource_lock
, flags
);
410 clocksource_enqueue(cs
);
411 clocksource_select();
412 spin_unlock_irqrestore(&clocksource_lock
, flags
);
413 clocksource_check_watchdog(cs
);
416 EXPORT_SYMBOL(clocksource_register
);
419 * clocksource_change_rating - Change the rating of a registered clocksource
422 void clocksource_change_rating(struct clocksource
*cs
, int rating
)
426 spin_lock_irqsave(&clocksource_lock
, flags
);
429 clocksource_enqueue(cs
);
430 clocksource_select();
431 spin_unlock_irqrestore(&clocksource_lock
, flags
);
435 * clocksource_unregister - remove a registered clocksource
437 void clocksource_unregister(struct clocksource
*cs
)
441 spin_lock_irqsave(&clocksource_lock
, flags
);
443 clocksource_select();
444 spin_unlock_irqrestore(&clocksource_lock
, flags
);
449 * sysfs_show_current_clocksources - sysfs interface for current clocksource
451 * @buf: char buffer to be filled with clocksource list
453 * Provides sysfs interface for listing current clocksource.
456 sysfs_show_current_clocksources(struct sys_device
*dev
,
457 struct sysdev_attribute
*attr
, char *buf
)
461 spin_lock_irq(&clocksource_lock
);
462 count
= snprintf(buf
, PAGE_SIZE
, "%s\n", curr_clocksource
->name
);
463 spin_unlock_irq(&clocksource_lock
);
469 * sysfs_override_clocksource - interface for manually overriding clocksource
471 * @buf: name of override clocksource
472 * @count: length of buffer
474 * Takes input from sysfs interface for manually overriding the default
475 * clocksource selction.
477 static ssize_t
sysfs_override_clocksource(struct sys_device
*dev
,
478 struct sysdev_attribute
*attr
,
479 const char *buf
, size_t count
)
483 /* strings from sysfs write are not 0 terminated! */
484 if (count
>= sizeof(override_name
))
488 if (buf
[count
-1] == '\n')
491 spin_lock_irq(&clocksource_lock
);
494 memcpy(override_name
, buf
, count
);
495 override_name
[count
] = 0;
496 clocksource_select();
498 spin_unlock_irq(&clocksource_lock
);
504 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
506 * @buf: char buffer to be filled with clocksource list
508 * Provides sysfs interface for listing registered clocksources
511 sysfs_show_available_clocksources(struct sys_device
*dev
,
512 struct sysdev_attribute
*attr
,
515 struct clocksource
*src
;
518 spin_lock_irq(&clocksource_lock
);
519 list_for_each_entry(src
, &clocksource_list
, list
) {
521 * Don't show non-HRES clocksource if the tick code is
522 * in one shot mode (highres=on or nohz=on)
524 if (!tick_oneshot_mode_active() ||
525 (src
->flags
& CLOCK_SOURCE_VALID_FOR_HRES
))
526 count
+= snprintf(buf
+ count
,
527 max((ssize_t
)PAGE_SIZE
- count
, (ssize_t
)0),
530 spin_unlock_irq(&clocksource_lock
);
532 count
+= snprintf(buf
+ count
,
533 max((ssize_t
)PAGE_SIZE
- count
, (ssize_t
)0), "\n");
541 static SYSDEV_ATTR(current_clocksource
, 0644, sysfs_show_current_clocksources
,
542 sysfs_override_clocksource
);
544 static SYSDEV_ATTR(available_clocksource
, 0444,
545 sysfs_show_available_clocksources
, NULL
);
547 static struct sysdev_class clocksource_sysclass
= {
548 .name
= "clocksource",
551 static struct sys_device device_clocksource
= {
553 .cls
= &clocksource_sysclass
,
556 static int __init
init_clocksource_sysfs(void)
558 int error
= sysdev_class_register(&clocksource_sysclass
);
561 error
= sysdev_register(&device_clocksource
);
563 error
= sysdev_create_file(
565 &attr_current_clocksource
);
567 error
= sysdev_create_file(
569 &attr_available_clocksource
);
573 device_initcall(init_clocksource_sysfs
);
574 #endif /* CONFIG_SYSFS */
577 * boot_override_clocksource - boot clock override
578 * @str: override name
580 * Takes a clocksource= boot argument and uses it
581 * as the clocksource override name.
583 static int __init
boot_override_clocksource(char* str
)
586 spin_lock_irqsave(&clocksource_lock
, flags
);
588 strlcpy(override_name
, str
, sizeof(override_name
));
589 spin_unlock_irqrestore(&clocksource_lock
, flags
);
593 __setup("clocksource=", boot_override_clocksource
);
596 * boot_override_clock - Compatibility layer for deprecated boot option
597 * @str: override name
599 * DEPRECATED! Takes a clock= boot argument and uses it
600 * as the clocksource override name
602 static int __init
boot_override_clock(char* str
)
604 if (!strcmp(str
, "pmtmr")) {
605 printk("Warning: clock=pmtmr is deprecated. "
606 "Use clocksource=acpi_pm.\n");
607 return boot_override_clocksource("acpi_pm");
609 printk("Warning! clock= boot option is deprecated. "
610 "Use clocksource=xyz\n");
611 return boot_override_clocksource(str
);
614 __setup("clock=", boot_override_clock
);