linux/kernel/time/clocksource.c

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/*
* 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
*/
#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>
#include <linux/kthread.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_GPL(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_GPL(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_GPL(timecounter_cyc2time);
/**
* clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
* @mult: pointer to mult variable
* @shift: pointer to shift variable
* @from: frequency to convert from
* @to: frequency to convert to
* @maxsec: guaranteed runtime conversion range in seconds
*
* The function evaluates the shift/mult pair for the scaled math
* operations of clocksources and clockevents.
*
* @to and @from are frequency values in HZ. For clock sources @to is
* NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
* event @to is the counter frequency and @from is NSEC_PER_SEC.
*
* The @maxsec conversion range argument controls the time frame in
* seconds which must be covered by the runtime conversion with the
* calculated mult and shift factors. This guarantees that no 64bit
* overflow happens when the input value of the conversion is
* multiplied with the calculated mult factor. Larger ranges may
* reduce the conversion accuracy by chosing smaller mult and shift
* factors.
*/
void
clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
{
u64 tmp;
u32 sft, sftacc= 32;
/*
* Calculate the shift factor which is limiting the conversion
* range:
*/
tmp = ((u64)maxsec * from) >> 32;
while (tmp) {
tmp >>=1;
sftacc--;
}
/*
* Find the conversion shift/mult pair which has the best
* accuracy and fits the maxsec conversion range:
*/
for (sft = 32; sft > 0; sft--) {
tmp = (u64) to << sft;
tmp += from / 2;
do_div(tmp, from);
if ((tmp >> sftacc) == 0)
break;
}
*mult = tmp;
*shift = sft;
}
/*[Clocksource internal variables]---------
* curr_clocksource:
* currently selected clocksource.
* clocksource_list:
* linked list with the registered clocksources
* clocksource_mutex:
* protects manipulations to curr_clocksource and the clocksource_list
* override_name:
* Name of the user-specified clocksource.
*/
static struct clocksource *curr_clocksource;
static LIST_HEAD(clocksource_list);
static DEFINE_MUTEX(clocksource_mutex);
static char override_name[32];
static int finished_booting;
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
static void clocksource_watchdog_work(struct work_struct *work);
static LIST_HEAD(watchdog_list);
static struct clocksource *watchdog;
static struct timer_list watchdog_timer;
static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
static DEFINE_SPINLOCK(watchdog_lock);
static cycle_t watchdog_last;
static int watchdog_running;
static int clocksource_watchdog_kthread(void *data);
static void __clocksource_change_rating(struct clocksource *cs, int rating);
/*
* Interval: 0.5sec Threshold: 0.0625s
*/
#define WATCHDOG_INTERVAL (HZ >> 1)
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
static void clocksource_watchdog_work(struct work_struct *work)
{
/*
* If kthread_run fails the next watchdog scan over the
* watchdog_list will find the unstable clock again.
*/
kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
}
static void __clocksource_unstable(struct clocksource *cs)
{
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
cs->flags |= CLOCK_SOURCE_UNSTABLE;
if (finished_booting)
schedule_work(&watchdog_work);
}
static void clocksource_unstable(struct clocksource *cs, int64_t delta)
{
printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
cs->name, delta);
__clocksource_unstable(cs);
}
/**
* clocksource_mark_unstable - mark clocksource unstable via watchdog
* @cs: clocksource to be marked unstable
*
* This function is called instead of clocksource_change_rating from
* cpu hotplug code to avoid a deadlock between the clocksource mutex
* and the cpu hotplug mutex. It defers the update of the clocksource
* to the watchdog thread.
*/
void clocksource_mark_unstable(struct clocksource *cs)
{
unsigned long flags;
spin_lock_irqsave(&watchdog_lock, flags);
if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
if (list_empty(&cs->wd_list))
list_add(&cs->wd_list, &watchdog_list);
__clocksource_unstable(cs);
}
spin_unlock_irqrestore(&watchdog_lock, flags);
}
static void clocksource_watchdog(unsigned long data)
{
struct clocksource *cs;
cycle_t csnow, wdnow;
int64_t wd_nsec, cs_nsec;
int next_cpu;
spin_lock(&watchdog_lock);
if (!watchdog_running)
goto out;
wdnow = watchdog->read(watchdog);
wd_nsec = clocksource_cyc2ns((wdnow - watchdog_last) & watchdog->mask,
watchdog->mult, watchdog->shift);
watchdog_last = wdnow;
list_for_each_entry(cs, &watchdog_list, wd_list) {
/* Clocksource already marked unstable? */
if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
if (finished_booting)
schedule_work(&watchdog_work);
continue;
}
csnow = cs->read(cs);
/* Clocksource initialized ? */
if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
cs->flags |= CLOCK_SOURCE_WATCHDOG;
cs->wd_last = csnow;
continue;
}
/* Check the deviation from the watchdog clocksource. */
cs_nsec = clocksource_cyc2ns((csnow - cs->wd_last) &
cs->mask, cs->mult, cs->shift);
cs->wd_last = csnow;
if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
clocksource_unstable(cs, cs_nsec - wd_nsec);
continue;
}
if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
(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();
}
}
/*
* Cycle through CPUs to check if the CPUs stay synchronized
* to each other.
*/
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);
out:
spin_unlock(&watchdog_lock);
}
static inline void clocksource_start_watchdog(void)
{
if (watchdog_running || !watchdog || list_empty(&watchdog_list))
return;
init_timer(&watchdog_timer);
watchdog_timer.function = clocksource_watchdog;
watchdog_last = watchdog->read(watchdog);
watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
watchdog_running = 1;
}
static inline void clocksource_stop_watchdog(void)
{
if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
return;
del_timer(&watchdog_timer);
watchdog_running = 0;
}
static inline void clocksource_reset_watchdog(void)
{
struct clocksource *cs;
list_for_each_entry(cs, &watchdog_list, wd_list)
cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
}
static void clocksource_resume_watchdog(void)
{
unsigned long flags;
clocksource: Prevent potential kgdb dead lock commit 0f8e8ef7 (clocksource: Simplify clocksource watchdog resume logic) introduced a potential kgdb dead lock. When the kernel is stopped by kgdb inside code which holds watchdog_lock then kgdb dead locks in clocksource_resume_watchdog(). clocksource_resume_watchdog() is called from kbdg via clocksource_touch_watchdog() to avoid that the clock source watchdog marks TSC unstable after the kernel has been stopped. Solve this by replacing spin_lock with a spin_trylock and just return in case the lock is held. Not resetting the watchdog might result in TSC becoming marked unstable, but that's an acceptable penalty for using kgdb. The timekeeping is anyway easily screwed up by kgdb when the system uses either jiffies or a clock source which wraps in short intervals (e.g. pm_timer wraps about every 4.6s), so we really do not have to worry about that occasional TSC marked unstable side effect. The second caller of clocksource_resume_watchdog() is clocksource_resume(). The trylock is safe here as well because the system is UP at this point, interrupts are disabled and nothing else can hold watchdog_lock(). Reported-by: Jason Wessel <jason.wessel@windriver.com> LKML-Reference: <1264480000-6997-4-git-send-email-jason.wessel@windriver.com> Cc: kgdb-bugreport@lists.sourceforge.net Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: John Stultz <johnstul@us.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2010-01-26 11:51:10 +00:00
/*
* We use trylock here to avoid a potential dead lock when
* kgdb calls this code after the kernel has been stopped with
* watchdog_lock held. When watchdog_lock is held we just
* return and accept, that the watchdog might trigger and mark
* the monitored clock source (usually TSC) unstable.
*
* This does not affect the other caller clocksource_resume()
* because at this point the kernel is UP, interrupts are
* disabled and nothing can hold watchdog_lock.
*/
if (!spin_trylock_irqsave(&watchdog_lock, flags))
return;
clocksource_reset_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
}
static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
unsigned long flags;
spin_lock_irqsave(&watchdog_lock, flags);
if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
/* cs is a clocksource to be watched. */
list_add(&cs->wd_list, &watchdog_list);
cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
} else {
/* cs is a watchdog. */
if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
/* Pick the best watchdog. */
if (!watchdog || cs->rating > watchdog->rating) {
watchdog = cs;
/* Reset watchdog cycles */
clocksource_reset_watchdog();
}
}
/* Check if the watchdog timer needs to be started. */
clocksource_start_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
}
static void clocksource_dequeue_watchdog(struct clocksource *cs)
{
struct clocksource *tmp;
unsigned long flags;
spin_lock_irqsave(&watchdog_lock, flags);
if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
/* cs is a watched clocksource. */
list_del_init(&cs->wd_list);
} else if (cs == watchdog) {
/* Reset watchdog cycles */
clocksource_reset_watchdog();
/* Current watchdog is removed. Find an alternative. */
watchdog = NULL;
list_for_each_entry(tmp, &clocksource_list, list) {
if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
continue;
if (!watchdog || tmp->rating > watchdog->rating)
watchdog = tmp;
}
}
cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
/* Check if the watchdog timer needs to be stopped. */
clocksource_stop_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
}
static int clocksource_watchdog_kthread(void *data)
{
struct clocksource *cs, *tmp;
unsigned long flags;
LIST_HEAD(unstable);
mutex_lock(&clocksource_mutex);
spin_lock_irqsave(&watchdog_lock, flags);
list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
list_del_init(&cs->wd_list);
list_add(&cs->wd_list, &unstable);
}
/* Check if the watchdog timer needs to be stopped. */
clocksource_stop_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
/* Needs to be done outside of watchdog lock */
list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
list_del_init(&cs->wd_list);
__clocksource_change_rating(cs, 0);
}
mutex_unlock(&clocksource_mutex);
return 0;
}
#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
}
static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
static inline void clocksource_resume_watchdog(void) { }
static inline int clocksource_watchdog_kthread(void *data) { return 0; }
#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
/**
* clocksource_suspend - suspend the clocksource(s)
*/
void clocksource_suspend(void)
{
struct clocksource *cs;
list_for_each_entry_reverse(cs, &clocksource_list, list)
if (cs->suspend)
cs->suspend(cs);
}
/**
* clocksource_resume - resume the clocksource(s)
*/
void clocksource_resume(void)
{
struct clocksource *cs;
list_for_each_entry(cs, &clocksource_list, list)
if (cs->resume)
cs->resume(cs);
clocksource_resume_watchdog();
}
/**
* clocksource_touch_watchdog - Update watchdog
*
* Update the watchdog after exception contexts such as kgdb so as not
clocksource: Prevent potential kgdb dead lock commit 0f8e8ef7 (clocksource: Simplify clocksource watchdog resume logic) introduced a potential kgdb dead lock. When the kernel is stopped by kgdb inside code which holds watchdog_lock then kgdb dead locks in clocksource_resume_watchdog(). clocksource_resume_watchdog() is called from kbdg via clocksource_touch_watchdog() to avoid that the clock source watchdog marks TSC unstable after the kernel has been stopped. Solve this by replacing spin_lock with a spin_trylock and just return in case the lock is held. Not resetting the watchdog might result in TSC becoming marked unstable, but that's an acceptable penalty for using kgdb. The timekeeping is anyway easily screwed up by kgdb when the system uses either jiffies or a clock source which wraps in short intervals (e.g. pm_timer wraps about every 4.6s), so we really do not have to worry about that occasional TSC marked unstable side effect. The second caller of clocksource_resume_watchdog() is clocksource_resume(). The trylock is safe here as well because the system is UP at this point, interrupts are disabled and nothing else can hold watchdog_lock(). Reported-by: Jason Wessel <jason.wessel@windriver.com> LKML-Reference: <1264480000-6997-4-git-send-email-jason.wessel@windriver.com> Cc: kgdb-bugreport@lists.sourceforge.net Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: John Stultz <johnstul@us.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2010-01-26 11:51:10 +00:00
* to incorrectly trip the watchdog. This might fail when the kernel
* was stopped in code which holds watchdog_lock.
*/
void clocksource_touch_watchdog(void)
{
clocksource_resume_watchdog();
}
/**
* clocksource_max_deferment - Returns max time the clocksource can be deferred
* @cs: Pointer to clocksource
*
*/
static u64 clocksource_max_deferment(struct clocksource *cs)
{
u64 max_nsecs, max_cycles;
/*
* Calculate the maximum number of cycles that we can pass to the
* cyc2ns function without overflowing a 64-bit signed result. The
* maximum number of cycles is equal to ULLONG_MAX/cs->mult which
* is equivalent to the below.
* max_cycles < (2^63)/cs->mult
* max_cycles < 2^(log2((2^63)/cs->mult))
* max_cycles < 2^(log2(2^63) - log2(cs->mult))
* max_cycles < 2^(63 - log2(cs->mult))
* max_cycles < 1 << (63 - log2(cs->mult))
* Please note that we add 1 to the result of the log2 to account for
* any rounding errors, ensure the above inequality is satisfied and
* no overflow will occur.
*/
max_cycles = 1ULL << (63 - (ilog2(cs->mult) + 1));
/*
* The actual maximum number of cycles we can defer the clocksource is
* determined by the minimum of max_cycles and cs->mask.
*/
max_cycles = min_t(u64, max_cycles, (u64) cs->mask);
max_nsecs = clocksource_cyc2ns(max_cycles, cs->mult, cs->shift);
/*
* To ensure that the clocksource does not wrap whilst we are idle,
* limit the time the clocksource can be deferred by 12.5%. Please
* note a margin of 12.5% is used because this can be computed with
* a shift, versus say 10% which would require division.
*/
return max_nsecs - (max_nsecs >> 5);
}
#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
/**
* clocksource_select - Select the best clocksource available
*
* Private function. Must hold clocksource_mutex when called.
*
* Select the clocksource with the best rating, or the clocksource,
* which is selected by userspace override.
*/
static void clocksource_select(void)
{
struct clocksource *best, *cs;
if (!finished_booting || list_empty(&clocksource_list))
return;
/* First clocksource on the list has the best rating. */
best = list_first_entry(&clocksource_list, struct clocksource, list);
/* Check for the override clocksource. */
list_for_each_entry(cs, &clocksource_list, list) {
if (strcmp(cs->name, override_name) != 0)
continue;
/*
* Check to make sure we don't switch to a non-highres
* capable clocksource if the tick code is in oneshot
* mode (highres or nohz)
*/
if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
tick_oneshot_mode_active()) {
/* Override clocksource cannot be used. */
printk(KERN_WARNING "Override clocksource %s is not "
"HRT compatible. Cannot switch while in "
"HRT/NOHZ mode\n", cs->name);
override_name[0] = 0;
} else
/* Override clocksource can be used. */
best = cs;
break;
}
if (curr_clocksource != best) {
printk(KERN_INFO "Switching to clocksource %s\n", best->name);
curr_clocksource = best;
timekeeping_notify(curr_clocksource);
}
}
#else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
static inline void clocksource_select(void) { }
#endif
/*
* 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)
{
mutex_lock(&clocksource_mutex);
curr_clocksource = clocksource_default_clock();
mutex_unlock(&clocksource_mutex);
finished_booting = 1;
/*
* Run the watchdog first to eliminate unstable clock sources
*/
clocksource_watchdog_kthread(NULL);
mutex_lock(&clocksource_mutex);
clocksource_select();
mutex_unlock(&clocksource_mutex);
return 0;
}
fs_initcall(clocksource_done_booting);
/*
* Enqueue the clocksource sorted by rating
*/
static void clocksource_enqueue(struct clocksource *cs)
{
struct list_head *entry = &clocksource_list;
struct clocksource *tmp;
list_for_each_entry(tmp, &clocksource_list, list)
/* Keep track of the place, where to insert */
if (tmp->rating >= cs->rating)
entry = &tmp->list;
list_add(&cs->list, entry);
}
/**
* __clocksource_updatefreq_scale - Used update clocksource with new freq
* @t: clocksource to be registered
* @scale: Scale factor multiplied against freq to get clocksource hz
* @freq: clocksource frequency (cycles per second) divided by scale
*
* This should only be called from the clocksource->enable() method.
*
* This *SHOULD NOT* be called directly! Please use the
* clocksource_updatefreq_hz() or clocksource_updatefreq_khz helper functions.
*/
void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
{
u64 sec;
/*
* Calc the maximum number of seconds which we can run before
* wrapping around. For clocksources which have a mask > 32bit
* we need to limit the max sleep time to have a good
* conversion precision. 10 minutes is still a reasonable
* amount. That results in a shift value of 24 for a
* clocksource with mask >= 40bit and f >= 4GHz. That maps to
* ~ 0.06ppm granularity for NTP. We apply the same 12.5%
* margin as we do in clocksource_max_deferment()
*/
sec = (cs->mask - (cs->mask >> 5));
do_div(sec, freq);
do_div(sec, scale);
if (!sec)
sec = 1;
else if (sec > 600 && cs->mask > UINT_MAX)
sec = 600;
clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
NSEC_PER_SEC / scale, sec * scale);
cs->max_idle_ns = clocksource_max_deferment(cs);
}
EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);
/**
* __clocksource_register_scale - Used to install new clocksources
* @t: clocksource to be registered
* @scale: Scale factor multiplied against freq to get clocksource hz
* @freq: clocksource frequency (cycles per second) divided by scale
*
* Returns -EBUSY if registration fails, zero otherwise.
*
* This *SHOULD NOT* be called directly! Please use the
* clocksource_register_hz() or clocksource_register_khz helper functions.
*/
int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
{
/* Initialize mult/shift and max_idle_ns */
__clocksource_updatefreq_scale(cs, scale, freq);
/* Add clocksource to the clcoksource list */
mutex_lock(&clocksource_mutex);
clocksource_enqueue(cs);
clocksource_enqueue_watchdog(cs);
clocksource_select();
mutex_unlock(&clocksource_mutex);
return 0;
}
EXPORT_SYMBOL_GPL(__clocksource_register_scale);
/**
* clocksource_register - Used to install new clocksources
* @t: clocksource to be registered
*
* Returns -EBUSY if registration fails, zero otherwise.
*/
int clocksource_register(struct clocksource *cs)
{
/* calculate max idle time permitted for this clocksource */
cs->max_idle_ns = clocksource_max_deferment(cs);
mutex_lock(&clocksource_mutex);
clocksource_enqueue(cs);
clocksource_enqueue_watchdog(cs);
clocksource_select();
mutex_unlock(&clocksource_mutex);
return 0;
}
EXPORT_SYMBOL(clocksource_register);
static void __clocksource_change_rating(struct clocksource *cs, int rating)
{
list_del(&cs->list);
cs->rating = rating;
clocksource_enqueue(cs);
clocksource_select();
}
/**
* clocksource_change_rating - Change the rating of a registered clocksource
*/
void clocksource_change_rating(struct clocksource *cs, int rating)
{
mutex_lock(&clocksource_mutex);
__clocksource_change_rating(cs, rating);
mutex_unlock(&clocksource_mutex);
}
EXPORT_SYMBOL(clocksource_change_rating);
/**
* clocksource_unregister - remove a registered clocksource
*/
void clocksource_unregister(struct clocksource *cs)
{
mutex_lock(&clocksource_mutex);
clocksource_dequeue_watchdog(cs);
list_del(&cs->list);
clocksource_select();
mutex_unlock(&clocksource_mutex);
}
EXPORT_SYMBOL(clocksource_unregister);
#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;
mutex_lock(&clocksource_mutex);
count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
mutex_unlock(&clocksource_mutex);
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 selection.
*/
static ssize_t sysfs_override_clocksource(struct sys_device *dev,
struct sysdev_attribute *attr,
const char *buf, size_t count)
{
size_t ret = count;
/* strings from sysfs write are not 0 terminated! */
if (count >= sizeof(override_name))
return -EINVAL;
/* strip of \n: */
if (buf[count-1] == '\n')
count--;
mutex_lock(&clocksource_mutex);
if (count > 0)
memcpy(override_name, buf, count);
override_name[count] = 0;
clocksource_select();
mutex_unlock(&clocksource_mutex);
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;
mutex_lock(&clocksource_mutex);
list_for_each_entry(src, &clocksource_list, list) {
/*
* Don't show non-HRES clocksource if the tick code is
* in one shot mode (highres=on or nohz=on)
*/
if (!tick_oneshot_mode_active() ||
(src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
count += snprintf(buf + count,
max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
"%s ", src->name);
}
mutex_unlock(&clocksource_mutex);
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)
{
mutex_lock(&clocksource_mutex);
if (str)
strlcpy(override_name, str, sizeof(override_name));
mutex_unlock(&clocksource_mutex);
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);