linux/kernel/time/clocksource.c
Patrick Ohly a038a353c3 clocksource: allow usage independent of timekeeping.c
So far struct clocksource acted as the interface between time/timekeeping.c
and hardware. This patch generalizes the concept so that a similar
interface can also be used in other contexts. For that it introduces
new structures and related functions *without* touching the existing
struct clocksource.

The reasons for adding these new structures to clocksource.[ch] are
* the APIs are clearly related
* struct clocksource could be cleaned up to use the new structs
* avoids proliferation of files with similar names (timesource.h?
  timecounter.h?)

As outlined in the discussion with John Stultz, this patch adds
* struct cyclecounter: stateless API to hardware which counts clock cycles
* struct timecounter: stateful utility code built on a cyclecounter which
  provides a nanosecond counter
* only the function to read the nanosecond counter; deltas are used internally
  and not exposed to users of timecounter

The code does no locking of the shared state. It must be called at least
as often as the cycle counter wraps around to detect these wrap arounds.
Both is the responsibility of the timecounter user.

Acked-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2009-02-15 22:43:31 -08:00

632 lines
16 KiB
C

/*
* linux/kernel/time/clocksource.c
*
* This file contains the functions which manage clocksource drivers.
*
* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
* TODO WishList:
* o Allow clocksource drivers to be unregistered
* o get rid of clocksource_jiffies extern
*/
#include <linux/clocksource.h>
#include <linux/sysdev.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
#include <linux/tick.h>
void timecounter_init(struct timecounter *tc,
const struct cyclecounter *cc,
u64 start_tstamp)
{
tc->cc = cc;
tc->cycle_last = cc->read(cc);
tc->nsec = start_tstamp;
}
EXPORT_SYMBOL(timecounter_init);
/**
* timecounter_read_delta - get nanoseconds since last call of this function
* @tc: Pointer to time counter
*
* When the underlying cycle counter runs over, this will be handled
* correctly as long as it does not run over more than once between
* calls.
*
* The first call to this function for a new time counter initializes
* the time tracking and returns an undefined result.
*/
static u64 timecounter_read_delta(struct timecounter *tc)
{
cycle_t cycle_now, cycle_delta;
u64 ns_offset;
/* read cycle counter: */
cycle_now = tc->cc->read(tc->cc);
/* calculate the delta since the last timecounter_read_delta(): */
cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
/* convert to nanoseconds: */
ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta);
/* update time stamp of timecounter_read_delta() call: */
tc->cycle_last = cycle_now;
return ns_offset;
}
u64 timecounter_read(struct timecounter *tc)
{
u64 nsec;
/* increment time by nanoseconds since last call */
nsec = timecounter_read_delta(tc);
nsec += tc->nsec;
tc->nsec = nsec;
return nsec;
}
EXPORT_SYMBOL(timecounter_read);
u64 timecounter_cyc2time(struct timecounter *tc,
cycle_t cycle_tstamp)
{
u64 cycle_delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
u64 nsec;
/*
* Instead of always treating cycle_tstamp as more recent
* than tc->cycle_last, detect when it is too far in the
* future and treat it as old time stamp instead.
*/
if (cycle_delta > tc->cc->mask / 2) {
cycle_delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
nsec = tc->nsec - cyclecounter_cyc2ns(tc->cc, cycle_delta);
} else {
nsec = cyclecounter_cyc2ns(tc->cc, cycle_delta) + tc->nsec;
}
return nsec;
}
EXPORT_SYMBOL(timecounter_cyc2time);
/* XXX - Would like a better way for initializing curr_clocksource */
extern struct clocksource clocksource_jiffies;
/*[Clocksource internal variables]---------
* curr_clocksource:
* currently selected clocksource. Initialized to clocksource_jiffies.
* next_clocksource:
* pending next selected clocksource.
* clocksource_list:
* linked list with the registered clocksources
* clocksource_lock:
* protects manipulations to curr_clocksource and next_clocksource
* and the clocksource_list
* override_name:
* Name of the user-specified clocksource.
*/
static struct clocksource *curr_clocksource = &clocksource_jiffies;
static struct clocksource *next_clocksource;
static struct clocksource *clocksource_override;
static LIST_HEAD(clocksource_list);
static DEFINE_SPINLOCK(clocksource_lock);
static char override_name[32];
static int finished_booting;
/* clocksource_done_booting - Called near the end of core bootup
*
* Hack to avoid lots of clocksource churn at boot time.
* We use fs_initcall because we want this to start before
* device_initcall but after subsys_initcall.
*/
static int __init clocksource_done_booting(void)
{
finished_booting = 1;
return 0;
}
fs_initcall(clocksource_done_booting);
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
static LIST_HEAD(watchdog_list);
static struct clocksource *watchdog;
static struct timer_list watchdog_timer;
static DEFINE_SPINLOCK(watchdog_lock);
static cycle_t watchdog_last;
static unsigned long watchdog_resumed;
/*
* Interval: 0.5sec Threshold: 0.0625s
*/
#define WATCHDOG_INTERVAL (HZ >> 1)
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
{
if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
return;
printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
cs->name, delta);
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
clocksource_change_rating(cs, 0);
list_del(&cs->wd_list);
}
static void clocksource_watchdog(unsigned long data)
{
struct clocksource *cs, *tmp;
cycle_t csnow, wdnow;
int64_t wd_nsec, cs_nsec;
int resumed;
spin_lock(&watchdog_lock);
resumed = test_and_clear_bit(0, &watchdog_resumed);
wdnow = watchdog->read();
wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
watchdog_last = wdnow;
list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
csnow = cs->read();
if (unlikely(resumed)) {
cs->wd_last = csnow;
continue;
}
/* Initialized ? */
if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
(watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
/*
* We just marked the clocksource as
* highres-capable, notify the rest of the
* system as well so that we transition
* into high-res mode:
*/
tick_clock_notify();
}
cs->flags |= CLOCK_SOURCE_WATCHDOG;
cs->wd_last = csnow;
} else {
cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
cs->wd_last = csnow;
/* Check the delta. Might remove from the list ! */
clocksource_ratewd(cs, cs_nsec - wd_nsec);
}
}
if (!list_empty(&watchdog_list)) {
/*
* Cycle through CPUs to check if the CPUs stay
* synchronized to each other.
*/
int next_cpu = cpumask_next(raw_smp_processor_id(),
cpu_online_mask);
if (next_cpu >= nr_cpu_ids)
next_cpu = cpumask_first(cpu_online_mask);
watchdog_timer.expires += WATCHDOG_INTERVAL;
add_timer_on(&watchdog_timer, next_cpu);
}
spin_unlock(&watchdog_lock);
}
static void clocksource_resume_watchdog(void)
{
set_bit(0, &watchdog_resumed);
}
static void clocksource_check_watchdog(struct clocksource *cs)
{
struct clocksource *cse;
unsigned long flags;
spin_lock_irqsave(&watchdog_lock, flags);
if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
int started = !list_empty(&watchdog_list);
list_add(&cs->wd_list, &watchdog_list);
if (!started && watchdog) {
watchdog_last = watchdog->read();
watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
add_timer_on(&watchdog_timer,
cpumask_first(cpu_online_mask));
}
} else {
if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
if (!watchdog || cs->rating > watchdog->rating) {
if (watchdog)
del_timer(&watchdog_timer);
watchdog = cs;
init_timer(&watchdog_timer);
watchdog_timer.function = clocksource_watchdog;
/* Reset watchdog cycles */
list_for_each_entry(cse, &watchdog_list, wd_list)
cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
/* Start if list is not empty */
if (!list_empty(&watchdog_list)) {
watchdog_last = watchdog->read();
watchdog_timer.expires =
jiffies + WATCHDOG_INTERVAL;
add_timer_on(&watchdog_timer,
cpumask_first(cpu_online_mask));
}
}
}
spin_unlock_irqrestore(&watchdog_lock, flags);
}
#else
static void clocksource_check_watchdog(struct clocksource *cs)
{
if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
}
static inline void clocksource_resume_watchdog(void) { }
#endif
/**
* clocksource_resume - resume the clocksource(s)
*/
void clocksource_resume(void)
{
struct clocksource *cs;
unsigned long flags;
spin_lock_irqsave(&clocksource_lock, flags);
list_for_each_entry(cs, &clocksource_list, list) {
if (cs->resume)
cs->resume();
}
clocksource_resume_watchdog();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
/**
* clocksource_touch_watchdog - Update watchdog
*
* Update the watchdog after exception contexts such as kgdb so as not
* to incorrectly trip the watchdog.
*
*/
void clocksource_touch_watchdog(void)
{
clocksource_resume_watchdog();
}
/**
* clocksource_get_next - Returns the selected clocksource
*
*/
struct clocksource *clocksource_get_next(void)
{
unsigned long flags;
spin_lock_irqsave(&clocksource_lock, flags);
if (next_clocksource && finished_booting) {
curr_clocksource = next_clocksource;
next_clocksource = NULL;
}
spin_unlock_irqrestore(&clocksource_lock, flags);
return curr_clocksource;
}
/**
* select_clocksource - Selects the best registered clocksource.
*
* Private function. Must hold clocksource_lock when called.
*
* Select the clocksource with the best rating, or the clocksource,
* which is selected by userspace override.
*/
static struct clocksource *select_clocksource(void)
{
struct clocksource *next;
if (list_empty(&clocksource_list))
return NULL;
if (clocksource_override)
next = clocksource_override;
else
next = list_entry(clocksource_list.next, struct clocksource,
list);
if (next == curr_clocksource)
return NULL;
return next;
}
/*
* Enqueue the clocksource sorted by rating
*/
static int clocksource_enqueue(struct clocksource *c)
{
struct list_head *tmp, *entry = &clocksource_list;
list_for_each(tmp, &clocksource_list) {
struct clocksource *cs;
cs = list_entry(tmp, struct clocksource, list);
if (cs == c)
return -EBUSY;
/* Keep track of the place, where to insert */
if (cs->rating >= c->rating)
entry = tmp;
}
list_add(&c->list, entry);
if (strlen(c->name) == strlen(override_name) &&
!strcmp(c->name, override_name))
clocksource_override = c;
return 0;
}
/**
* clocksource_register - Used to install new clocksources
* @t: clocksource to be registered
*
* Returns -EBUSY if registration fails, zero otherwise.
*/
int clocksource_register(struct clocksource *c)
{
unsigned long flags;
int ret;
/* save mult_orig on registration */
c->mult_orig = c->mult;
spin_lock_irqsave(&clocksource_lock, flags);
ret = clocksource_enqueue(c);
if (!ret)
next_clocksource = select_clocksource();
spin_unlock_irqrestore(&clocksource_lock, flags);
if (!ret)
clocksource_check_watchdog(c);
return ret;
}
EXPORT_SYMBOL(clocksource_register);
/**
* clocksource_change_rating - Change the rating of a registered clocksource
*
*/
void clocksource_change_rating(struct clocksource *cs, int rating)
{
unsigned long flags;
spin_lock_irqsave(&clocksource_lock, flags);
list_del(&cs->list);
cs->rating = rating;
clocksource_enqueue(cs);
next_clocksource = select_clocksource();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
/**
* clocksource_unregister - remove a registered clocksource
*/
void clocksource_unregister(struct clocksource *cs)
{
unsigned long flags;
spin_lock_irqsave(&clocksource_lock, flags);
list_del(&cs->list);
if (clocksource_override == cs)
clocksource_override = NULL;
next_clocksource = select_clocksource();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
#ifdef CONFIG_SYSFS
/**
* sysfs_show_current_clocksources - sysfs interface for current clocksource
* @dev: unused
* @buf: char buffer to be filled with clocksource list
*
* Provides sysfs interface for listing current clocksource.
*/
static ssize_t
sysfs_show_current_clocksources(struct sys_device *dev,
struct sysdev_attribute *attr, char *buf)
{
ssize_t count = 0;
spin_lock_irq(&clocksource_lock);
count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
spin_unlock_irq(&clocksource_lock);
return count;
}
/**
* sysfs_override_clocksource - interface for manually overriding clocksource
* @dev: unused
* @buf: name of override clocksource
* @count: length of buffer
*
* Takes input from sysfs interface for manually overriding the default
* clocksource selction.
*/
static ssize_t sysfs_override_clocksource(struct sys_device *dev,
struct sysdev_attribute *attr,
const char *buf, size_t count)
{
struct clocksource *ovr = NULL;
size_t ret = count;
int len;
/* strings from sysfs write are not 0 terminated! */
if (count >= sizeof(override_name))
return -EINVAL;
/* strip of \n: */
if (buf[count-1] == '\n')
count--;
spin_lock_irq(&clocksource_lock);
if (count > 0)
memcpy(override_name, buf, count);
override_name[count] = 0;
len = strlen(override_name);
if (len) {
struct clocksource *cs;
ovr = clocksource_override;
/* try to select it: */
list_for_each_entry(cs, &clocksource_list, list) {
if (strlen(cs->name) == len &&
!strcmp(cs->name, override_name))
ovr = cs;
}
}
/* Reselect, when the override name has changed */
if (ovr != clocksource_override) {
clocksource_override = ovr;
next_clocksource = select_clocksource();
}
spin_unlock_irq(&clocksource_lock);
return ret;
}
/**
* sysfs_show_available_clocksources - sysfs interface for listing clocksource
* @dev: unused
* @buf: char buffer to be filled with clocksource list
*
* Provides sysfs interface for listing registered clocksources
*/
static ssize_t
sysfs_show_available_clocksources(struct sys_device *dev,
struct sysdev_attribute *attr,
char *buf)
{
struct clocksource *src;
ssize_t count = 0;
spin_lock_irq(&clocksource_lock);
list_for_each_entry(src, &clocksource_list, list) {
count += snprintf(buf + count,
max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
"%s ", src->name);
}
spin_unlock_irq(&clocksource_lock);
count += snprintf(buf + count,
max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
return count;
}
/*
* Sysfs setup bits:
*/
static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
sysfs_override_clocksource);
static SYSDEV_ATTR(available_clocksource, 0444,
sysfs_show_available_clocksources, NULL);
static struct sysdev_class clocksource_sysclass = {
.name = "clocksource",
};
static struct sys_device device_clocksource = {
.id = 0,
.cls = &clocksource_sysclass,
};
static int __init init_clocksource_sysfs(void)
{
int error = sysdev_class_register(&clocksource_sysclass);
if (!error)
error = sysdev_register(&device_clocksource);
if (!error)
error = sysdev_create_file(
&device_clocksource,
&attr_current_clocksource);
if (!error)
error = sysdev_create_file(
&device_clocksource,
&attr_available_clocksource);
return error;
}
device_initcall(init_clocksource_sysfs);
#endif /* CONFIG_SYSFS */
/**
* boot_override_clocksource - boot clock override
* @str: override name
*
* Takes a clocksource= boot argument and uses it
* as the clocksource override name.
*/
static int __init boot_override_clocksource(char* str)
{
unsigned long flags;
spin_lock_irqsave(&clocksource_lock, flags);
if (str)
strlcpy(override_name, str, sizeof(override_name));
spin_unlock_irqrestore(&clocksource_lock, flags);
return 1;
}
__setup("clocksource=", boot_override_clocksource);
/**
* boot_override_clock - Compatibility layer for deprecated boot option
* @str: override name
*
* DEPRECATED! Takes a clock= boot argument and uses it
* as the clocksource override name
*/
static int __init boot_override_clock(char* str)
{
if (!strcmp(str, "pmtmr")) {
printk("Warning: clock=pmtmr is deprecated. "
"Use clocksource=acpi_pm.\n");
return boot_override_clocksource("acpi_pm");
}
printk("Warning! clock= boot option is deprecated. "
"Use clocksource=xyz\n");
return boot_override_clocksource(str);
}
__setup("clock=", boot_override_clock);