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clocksource.c
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// SPDX-License-Identifier: GPL-2.0+
/*
* This file contains the functions which manage clocksource drivers.
*
* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/device.h>
#include <linux/clocksource.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>
#include <linux/prandom.h>
#include <linux/cpu.h>
#include "tick-internal.h"
#include "timekeeping_internal.h"
static noinline u64 cycles_to_nsec_safe(struct clocksource *cs, u64 start, u64 end)
{
u64 delta = clocksource_delta(end, start, cs->mask);
if (likely(delta < cs->max_cycles))
return clocksource_cyc2ns(delta, cs->mult, cs->shift);
return mul_u64_u32_shr(delta, cs->mult, cs->shift);
}
/**
* 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 choosing 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;
}
EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
/*[Clocksource internal variables]---------
* curr_clocksource:
* currently selected clocksource.
* suspend_clocksource:
* used to calculate the suspend time.
* 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 struct clocksource *suspend_clocksource;
static LIST_HEAD(clocksource_list);
static DEFINE_MUTEX(clocksource_mutex);
static char override_name[CS_NAME_LEN];
static int finished_booting;
static u64 suspend_start;
/*
* Interval: 0.5sec.
*/
#define WATCHDOG_INTERVAL (HZ >> 1)
#define WATCHDOG_INTERVAL_MAX_NS ((2 * WATCHDOG_INTERVAL) * (NSEC_PER_SEC / HZ))
/*
* Threshold: 0.0312s, when doubled: 0.0625s.
* Also a default for cs->uncertainty_margin when registering clocks.
*/
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)
/*
* Maximum permissible delay between two readouts of the watchdog
* clocksource surrounding a read of the clocksource being validated.
* This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as
* a lower bound for cs->uncertainty_margin values when registering clocks.
*
* The default of 500 parts per million is based on NTP's limits.
* If a clocksource is good enough for NTP, it is good enough for us!
*/
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
#define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
#else
#define MAX_SKEW_USEC (125 * WATCHDOG_INTERVAL / HZ)
#endif
#define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
static void clocksource_watchdog_work(struct work_struct *work);
static void clocksource_select(void);
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 int watchdog_running;
static atomic_t watchdog_reset_pending;
static int64_t watchdog_max_interval;
static inline void clocksource_watchdog_lock(unsigned long *flags)
{
spin_lock_irqsave(&watchdog_lock, *flags);
}
static inline void clocksource_watchdog_unlock(unsigned long *flags)
{
spin_unlock_irqrestore(&watchdog_lock, *flags);
}
static int clocksource_watchdog_kthread(void *data);
static void __clocksource_change_rating(struct clocksource *cs, int rating);
static void clocksource_watchdog_work(struct work_struct *work)
{
/*
* We cannot directly run clocksource_watchdog_kthread() here, because
* clocksource_select() calls timekeeping_notify() which uses
* stop_machine(). One cannot use stop_machine() from a workqueue() due
* lock inversions wrt CPU hotplug.
*
* Also, we only ever run this work once or twice during the lifetime
* of the kernel, so there is no point in creating a more permanent
* kthread for this.
*
* 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 the clocksource is registered clocksource_watchdog_kthread() will
* re-rate and re-select.
*/
if (list_empty(&cs->list)) {
cs->rating = 0;
return;
}
if (cs->mark_unstable)
cs->mark_unstable(cs);
/* kick clocksource_watchdog_kthread() */
if (finished_booting)
schedule_work(&watchdog_work);
}
/**
* clocksource_mark_unstable - mark clocksource unstable via watchdog
* @cs: clocksource to be marked unstable
*
* This function is called by the x86 TSC code to mark clocksources as unstable;
* it defers demotion and re-selection to a kthread.
*/
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->list) && list_empty(&cs->wd_list))
list_add(&cs->wd_list, &watchdog_list);
__clocksource_unstable(cs);
}
spin_unlock_irqrestore(&watchdog_lock, flags);
}
static int verify_n_cpus = 8;
module_param(verify_n_cpus, int, 0644);
enum wd_read_status {
WD_READ_SUCCESS,
WD_READ_UNSTABLE,
WD_READ_SKIP
};
static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
{
unsigned int nretries, max_retries;
int64_t wd_delay, wd_seq_delay;
u64 wd_end, wd_end2;
max_retries = clocksource_get_max_watchdog_retry();
for (nretries = 0; nretries <= max_retries; nretries++) {
local_irq_disable();
*wdnow = watchdog->read(watchdog);
*csnow = cs->read(cs);
wd_end = watchdog->read(watchdog);
wd_end2 = watchdog->read(watchdog);
local_irq_enable();
wd_delay = cycles_to_nsec_safe(watchdog, *wdnow, wd_end);
if (wd_delay <= WATCHDOG_MAX_SKEW) {
if (nretries > 1 || nretries >= max_retries) {
pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
smp_processor_id(), watchdog->name, nretries);
}
return WD_READ_SUCCESS;
}
/*
* Now compute delay in consecutive watchdog read to see if
* there is too much external interferences that cause
* significant delay in reading both clocksource and watchdog.
*
* If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2,
* report system busy, reinit the watchdog and skip the current
* watchdog test.
*/
wd_seq_delay = cycles_to_nsec_safe(watchdog, wd_end, wd_end2);
if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
goto skip_test;
}
pr_warn("timekeeping watchdog on CPU%d: wd-%s-wd excessive read-back delay of %lldns vs. limit of %ldns, wd-wd read-back delay only %lldns, attempt %d, marking %s unstable\n",
smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name);
return WD_READ_UNSTABLE;
skip_test:
pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
smp_processor_id(), watchdog->name, wd_seq_delay);
pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
cs->name, wd_delay);
return WD_READ_SKIP;
}
static u64 csnow_mid;
static cpumask_t cpus_ahead;
static cpumask_t cpus_behind;
static cpumask_t cpus_chosen;
static void clocksource_verify_choose_cpus(void)
{
int cpu, i, n = verify_n_cpus;
if (n < 0) {
/* Check all of the CPUs. */
cpumask_copy(&cpus_chosen, cpu_online_mask);
cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
return;
}
/* If no checking desired, or no other CPU to check, leave. */
cpumask_clear(&cpus_chosen);
if (n == 0 || num_online_cpus() <= 1)
return;
/* Make sure to select at least one CPU other than the current CPU. */
cpu = cpumask_first(cpu_online_mask);
if (cpu == smp_processor_id())
cpu = cpumask_next(cpu, cpu_online_mask);
if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
return;
cpumask_set_cpu(cpu, &cpus_chosen);
/* Force a sane value for the boot parameter. */
if (n > nr_cpu_ids)
n = nr_cpu_ids;
/*
* Randomly select the specified number of CPUs. If the same
* CPU is selected multiple times, that CPU is checked only once,
* and no replacement CPU is selected. This gracefully handles
* situations where verify_n_cpus is greater than the number of
* CPUs that are currently online.
*/
for (i = 1; i < n; i++) {
cpu = get_random_u32_below(nr_cpu_ids);
cpu = cpumask_next(cpu - 1, cpu_online_mask);
if (cpu >= nr_cpu_ids)
cpu = cpumask_first(cpu_online_mask);
if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
cpumask_set_cpu(cpu, &cpus_chosen);
}
/* Don't verify ourselves. */
cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
}
static void clocksource_verify_one_cpu(void *csin)
{
struct clocksource *cs = (struct clocksource *)csin;
csnow_mid = cs->read(cs);
}
void clocksource_verify_percpu(struct clocksource *cs)
{
int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
u64 csnow_begin, csnow_end;
int cpu, testcpu;
s64 delta;
if (verify_n_cpus == 0)
return;
cpumask_clear(&cpus_ahead);
cpumask_clear(&cpus_behind);
cpus_read_lock();
preempt_disable();
clocksource_verify_choose_cpus();
if (cpumask_empty(&cpus_chosen)) {
preempt_enable();
cpus_read_unlock();
pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
return;
}
testcpu = smp_processor_id();
pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
for_each_cpu(cpu, &cpus_chosen) {
if (cpu == testcpu)
continue;
csnow_begin = cs->read(cs);
smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
csnow_end = cs->read(cs);
delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
if (delta < 0)
cpumask_set_cpu(cpu, &cpus_behind);
delta = (csnow_end - csnow_mid) & cs->mask;
if (delta < 0)
cpumask_set_cpu(cpu, &cpus_ahead);
cs_nsec = cycles_to_nsec_safe(cs, csnow_begin, csnow_end);
if (cs_nsec > cs_nsec_max)
cs_nsec_max = cs_nsec;
if (cs_nsec < cs_nsec_min)
cs_nsec_min = cs_nsec;
}
preempt_enable();
cpus_read_unlock();
if (!cpumask_empty(&cpus_ahead))
pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
if (!cpumask_empty(&cpus_behind))
pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n",
cpumask_pr_args(&cpus_behind), testcpu, cs->name);
if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n",
testcpu, cs_nsec_min, cs_nsec_max, cs->name);
}
EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
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_watchdog(struct timer_list *unused)
{
int64_t wd_nsec, cs_nsec, interval;
u64 csnow, wdnow, cslast, wdlast;
int next_cpu, reset_pending;
struct clocksource *cs;
enum wd_read_status read_ret;
unsigned long extra_wait = 0;
u32 md;
spin_lock(&watchdog_lock);
if (!watchdog_running)
goto out;
reset_pending = atomic_read(&watchdog_reset_pending);
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;
}
read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
if (read_ret == WD_READ_UNSTABLE) {
/* Clock readout unreliable, so give it up. */
__clocksource_unstable(cs);
continue;
}
/*
* When WD_READ_SKIP is returned, it means the system is likely
* under very heavy load, where the latency of reading
* watchdog/clocksource is very big, and affect the accuracy of
* watchdog check. So give system some space and suspend the
* watchdog check for 5 minutes.
*/
if (read_ret == WD_READ_SKIP) {
/*
* As the watchdog timer will be suspended, and
* cs->last could keep unchanged for 5 minutes, reset
* the counters.
*/
clocksource_reset_watchdog();
extra_wait = HZ * 300;
break;
}
/* Clocksource initialized ? */
if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
atomic_read(&watchdog_reset_pending)) {
cs->flags |= CLOCK_SOURCE_WATCHDOG;
cs->wd_last = wdnow;
cs->cs_last = csnow;
continue;
}
wd_nsec = cycles_to_nsec_safe(watchdog, cs->wd_last, wdnow);
cs_nsec = cycles_to_nsec_safe(cs, cs->cs_last, csnow);
wdlast = cs->wd_last; /* save these in case we print them */
cslast = cs->cs_last;
cs->cs_last = csnow;
cs->wd_last = wdnow;
if (atomic_read(&watchdog_reset_pending))
continue;
/*
* The processing of timer softirqs can get delayed (usually
* on account of ksoftirqd not getting to run in a timely
* manner), which causes the watchdog interval to stretch.
* Skew detection may fail for longer watchdog intervals
* on account of fixed margins being used.
* Some clocksources, e.g. acpi_pm, cannot tolerate
* watchdog intervals longer than a few seconds.
*/
interval = max(cs_nsec, wd_nsec);
if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) {
if (system_state > SYSTEM_SCHEDULING &&
interval > 2 * watchdog_max_interval) {
watchdog_max_interval = interval;
pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n",
cs_nsec, wd_nsec);
}
watchdog_timer.expires = jiffies;
continue;
}
/* Check the deviation from the watchdog clocksource. */
md = cs->uncertainty_margin + watchdog->uncertainty_margin;
if (abs(cs_nsec - wd_nsec) > md) {
s64 cs_wd_msec;
s64 wd_msec;
u32 wd_rem;
pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
smp_processor_id(), cs->name);
pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
cs->name, cs_nsec, csnow, cslast, cs->mask);
cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem);
wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem);
pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n",
cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec);
if (curr_clocksource == cs)
pr_warn(" '%s' is current clocksource.\n", cs->name);
else if (curr_clocksource)
pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
else
pr_warn(" No current clocksource.\n");
__clocksource_unstable(cs);
continue;
}
if (cs == curr_clocksource && cs->tick_stable)
cs->tick_stable(cs);
if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
(cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
(watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
/* Mark it valid for high-res. */
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
/*
* clocksource_done_booting() will sort it if
* finished_booting is not set yet.
*/
if (!finished_booting)
continue;
/*
* If this is not the current clocksource let
* the watchdog thread reselect it. Due to the
* change to high res this clocksource might
* be preferred now. If it is the current
* clocksource let the tick code know about
* that change.
*/
if (cs != curr_clocksource) {
cs->flags |= CLOCK_SOURCE_RESELECT;
schedule_work(&watchdog_work);
} else {
tick_clock_notify();
}
}
}
/*
* We only clear the watchdog_reset_pending, when we did a
* full cycle through all clocksources.
*/
if (reset_pending)
atomic_dec(&watchdog_reset_pending);
/*
* 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);
/*
* Arm timer if not already pending: could race with concurrent
* pair clocksource_stop_watchdog() clocksource_start_watchdog().
*/
if (!timer_pending(&watchdog_timer)) {
watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait;
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;
timer_setup(&watchdog_timer, clocksource_watchdog, 0);
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 void clocksource_resume_watchdog(void)
{
atomic_inc(&watchdog_reset_pending);
}
static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
INIT_LIST_HEAD(&cs->wd_list);
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;
}
}
static void clocksource_select_watchdog(bool fallback)
{
struct clocksource *cs, *old_wd;
unsigned long flags;
spin_lock_irqsave(&watchdog_lock, flags);
/* save current watchdog */
old_wd = watchdog;
if (fallback)
watchdog = NULL;
list_for_each_entry(cs, &clocksource_list, list) {
/* cs is a clocksource to be watched. */
if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
continue;
/* Skip current if we were requested for a fallback. */
if (fallback && cs == old_wd)
continue;
/* Pick the best watchdog. */
if (!watchdog || cs->rating > watchdog->rating)
watchdog = cs;
}
/* If we failed to find a fallback restore the old one. */
if (!watchdog)
watchdog = old_wd;
/* If we changed the watchdog we need to reset cycles. */
if (watchdog != old_wd)
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)
{
if (cs != watchdog) {
if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
/* cs is a watched clocksource. */
list_del_init(&cs->wd_list);
/* Check if the watchdog timer needs to be stopped. */
clocksource_stop_watchdog();
}
}
}
static int __clocksource_watchdog_kthread(void)
{
struct clocksource *cs, *tmp;
unsigned long flags;
int select = 0;
/* Do any required per-CPU skew verification. */
if (curr_clocksource &&
curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
clocksource_verify_percpu(curr_clocksource);
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);
__clocksource_change_rating(cs, 0);
select = 1;
}
if (cs->flags & CLOCK_SOURCE_RESELECT) {
cs->flags &= ~CLOCK_SOURCE_RESELECT;
select = 1;
}
}
/* Check if the watchdog timer needs to be stopped. */
clocksource_stop_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
return select;
}
static int clocksource_watchdog_kthread(void *data)
{
mutex_lock(&clocksource_mutex);
if (__clocksource_watchdog_kthread())
clocksource_select();
mutex_unlock(&clocksource_mutex);
return 0;
}
static bool clocksource_is_watchdog(struct clocksource *cs)
{
return cs == watchdog;
}
#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 void clocksource_select_watchdog(bool fallback) { }
static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
static inline void clocksource_resume_watchdog(void) { }
static inline int __clocksource_watchdog_kthread(void) { return 0; }
static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
void clocksource_mark_unstable(struct clocksource *cs) { }
static inline void clocksource_watchdog_lock(unsigned long *flags) { }
static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
static bool clocksource_is_suspend(struct clocksource *cs)
{
return cs == suspend_clocksource;
}
static void __clocksource_suspend_select(struct clocksource *cs)
{
/*
* Skip the clocksource which will be stopped in suspend state.
*/
if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
return;
/*
* The nonstop clocksource can be selected as the suspend clocksource to
* calculate the suspend time, so it should not supply suspend/resume
* interfaces to suspend the nonstop clocksource when system suspends.
*/
if (cs->suspend || cs->resume) {
pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
cs->name);
}
/* Pick the best rating. */
if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
suspend_clocksource = cs;
}
/**
* clocksource_suspend_select - Select the best clocksource for suspend timing
* @fallback: if select a fallback clocksource
*/
static void clocksource_suspend_select(bool fallback)
{
struct clocksource *cs, *old_suspend;
old_suspend = suspend_clocksource;
if (fallback)
suspend_clocksource = NULL;
list_for_each_entry(cs, &clocksource_list, list) {
/* Skip current if we were requested for a fallback. */
if (fallback && cs == old_suspend)
continue;
__clocksource_suspend_select(cs);
}
}
/**
* clocksource_start_suspend_timing - Start measuring the suspend timing
* @cs: current clocksource from timekeeping
* @start_cycles: current cycles from timekeeping
*
* This function will save the start cycle values of suspend timer to calculate
* the suspend time when resuming system.
*
* This function is called late in the suspend process from timekeeping_suspend(),
* that means processes are frozen, non-boot cpus and interrupts are disabled
* now. It is therefore possible to start the suspend timer without taking the
* clocksource mutex.
*/
void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
{
if (!suspend_clocksource)
return;
/*
* If current clocksource is the suspend timer, we should use the
* tkr_mono.cycle_last value as suspend_start to avoid same reading
* from suspend timer.
*/
if (clocksource_is_suspend(cs)) {
suspend_start = start_cycles;
return;
}
if (suspend_clocksource->enable &&
suspend_clocksource->enable(suspend_clocksource)) {
pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
return;
}
suspend_start = suspend_clocksource->read(suspend_clocksource);
}
/**
* clocksource_stop_suspend_timing - Stop measuring the suspend timing
* @cs: current clocksource from timekeeping
* @cycle_now: current cycles from timekeeping
*
* This function will calculate the suspend time from suspend timer.
*
* Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
*
* This function is called early in the resume process from timekeeping_resume(),
* that means there is only one cpu, no processes are running and the interrupts
* are disabled. It is therefore possible to stop the suspend timer without
* taking the clocksource mutex.
*/
u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
{
u64 now, nsec = 0;
if (!suspend_clocksource)
return 0;
/*
* If current clocksource is the suspend timer, we should use the
* tkr_mono.cycle_last value from timekeeping as current cycle to
* avoid same reading from suspend timer.
*/
if (clocksource_is_suspend(cs))
now = cycle_now;
else
now = suspend_clocksource->read(suspend_clocksource);
if (now > suspend_start)
nsec = cycles_to_nsec_safe(suspend_clocksource, suspend_start, now);
/*
* Disable the suspend timer to save power if current clocksource is
* not the suspend timer.
*/
if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
suspend_clocksource->disable(suspend_clocksource);
return nsec;
}
/**
* 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
* 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_adjustment- Returns max adjustment amount
* @cs: Pointer to clocksource
*
*/
static u32 clocksource_max_adjustment(struct clocksource *cs)
{
u64 ret;
/*
* We won't try to correct for more than 11% adjustments (110,000 ppm),
*/
ret = (u64)cs->mult * 11;
do_div(ret,100);
return (u32)ret;
}
/**
* clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
* @mult: cycle to nanosecond multiplier
* @shift: cycle to nanosecond divisor (power of two)
* @maxadj: maximum adjustment value to mult (~11%)
* @mask: bitmask for two's complement subtraction of non 64 bit counters
* @max_cyc: maximum cycle value before potential overflow (does not include
* any safety margin)
*
* NOTE: This function includes a safety margin of 50%, in other words, we
* return half the number of nanoseconds the hardware counter can technically
* cover. This is done so that we can potentially detect problems caused by
* delayed timers or bad hardware, which might result in time intervals that
* are larger than what the math used can handle without overflows.
*/
u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
{
u64 max_nsecs, max_cycles;
/*
* Calculate the maximum number of cycles that we can pass to the
* cyc2ns() function without overflowing a 64-bit result.
*/
max_cycles = ULLONG_MAX;
do_div(max_cycles, mult+maxadj);
/*
* The actual maximum number of cycles we can defer the clocksource is
* determined by the minimum of max_cycles and mask.
* Note: Here we subtract the maxadj to make sure we don't sleep for
* too long if there's a large negative adjustment.
*/
max_cycles = min(max_cycles, mask);
max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
/* return the max_cycles value as well if requested */
if (max_cyc)
*max_cyc = max_cycles;
/* Return 50% of the actual maximum, so we can detect bad values */
max_nsecs >>= 1;
return max_nsecs;
}
/**
* clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
* @cs: Pointer to clocksource to be updated
*
*/
static inline void clocksource_update_max_deferment(struct clocksource *cs)
{
cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
cs->maxadj, cs->mask,
&cs->max_cycles);
}
static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
{
struct clocksource *cs;
if (!finished_booting || list_empty(&clocksource_list))
return NULL;
/*
* We pick the clocksource with the highest rating. If oneshot
* mode is active, we pick the highres valid clocksource with
* the best rating.
*/
list_for_each_entry(cs, &clocksource_list, list) {
if (skipcur && cs == curr_clocksource)
continue;
if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
continue;
return cs;
}
return NULL;
}
static void __clocksource_select(bool skipcur)
{
bool oneshot = tick_oneshot_mode_active();