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/*
* linux/kernel/time/timekeeping.c
*
* Kernel timekeeping code and accessor functions
*
* This code was moved from linux/kernel/timer.c.
* Please see that file for copyright and history logs.
*
*/

#include <linux/timekeeper_internal.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/syscore_ops.h>
#include <linux/clocksource.h>
#include <linux/jiffies.h>
#include <linux/time.h>
#include <linux/tick.h>
#include <linux/stop_machine.h>


static struct timekeeper timekeeper;

/*
* This read-write spinlock protects us from races in SMP while
* playing with xtime.
*/
__cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);

/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;

static inline void tk_normalize_xtime(struct timekeeper *tk)
{
while (tk->xtime_nsec >= ((u64)NSEC_PER_SEC << tk->shift)) {
tk->xtime_nsec -= (u64)NSEC_PER_SEC << tk->shift;
tk->xtime_sec++;
}
}

static void tk_set_xtime(struct timekeeper *tk, const struct timespec *ts)
{
tk->xtime_sec = ts->tv_sec;
tk->xtime_nsec = (u64)ts->tv_nsec << tk->shift;
}

static void tk_xtime_add(struct timekeeper *tk, const struct timespec *ts)
{
tk->xtime_sec += ts->tv_sec;
tk->xtime_nsec += (u64)ts->tv_nsec << tk->shift;
tk_normalize_xtime(tk);
}

static void tk_set_wall_to_mono(struct timekeeper *tk, struct timespec wtm)
{
struct timespec tmp;

/*
* Verify consistency of: offset_real = -wall_to_monotonic
* before modifying anything
*/
set_normalized_timespec(&tmp, -tk->wall_to_monotonic.tv_sec,
-tk->wall_to_monotonic.tv_nsec);
WARN_ON_ONCE(tk->offs_real.tv64 != timespec_to_ktime(tmp).tv64);
tk->wall_to_monotonic = wtm;
set_normalized_timespec(&tmp, -wtm.tv_sec, -wtm.tv_nsec);
tk->offs_real = timespec_to_ktime(tmp);
}

static void tk_set_sleep_time(struct timekeeper *tk, struct timespec t)
{
/* Verify consistency before modifying */
WARN_ON_ONCE(tk->offs_boot.tv64 != timespec_to_ktime(tk->total_sleep_time).tv64);

tk->total_sleep_time = t;
tk->offs_boot = timespec_to_ktime(t);
}

/**
* timekeeper_setup_internals - Set up internals to use clocksource clock.
*
* @clock: Pointer to clocksource.
*
* Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
* pair and interval request.
*
* Unless you're the timekeeping code, you should not be using this!
*/
static void tk_setup_internals(struct timekeeper *tk, struct clocksource *clock)
{
cycle_t interval;
u64 tmp, ntpinterval;
struct clocksource *old_clock;

old_clock = tk->clock;
tk->clock = clock;
clock->cycle_last = clock->read(clock);

/* Do the ns -> cycle conversion first, using original mult */
tmp = NTP_INTERVAL_LENGTH;
tmp <<= clock->shift;
ntpinterval = tmp;
tmp += clock->mult/2;
do_div(tmp, clock->mult);
if (tmp == 0)
tmp = 1;

interval = (cycle_t) tmp;
tk->cycle_interval = interval;

/* Go back from cycles -> shifted ns */
tk->xtime_interval = (u64) interval * clock->mult;
tk->xtime_remainder = ntpinterval - tk->xtime_interval;
tk->raw_interval =
((u64) interval * clock->mult) >> clock->shift;

/* if changing clocks, convert xtime_nsec shift units */
if (old_clock) {
int shift_change = clock->shift - old_clock->shift;
if (shift_change < 0)
tk->xtime_nsec >>= -shift_change;
else
tk->xtime_nsec <<= shift_change;
}
tk->shift = clock->shift;

tk->ntp_error = 0;
tk->ntp_error_shift = NTP_SCALE_SHIFT - clock->shift;

/*
* The timekeeper keeps its own mult values for the currently
* active clocksource. These value will be adjusted via NTP
* to counteract clock drifting.
*/
tk->mult = clock->mult;
}

/* Timekeeper helper functions. */
static inline s64 timekeeping_get_ns(struct timekeeper *tk)
{
cycle_t cycle_now, cycle_delta;
struct clocksource *clock;
s64 nsec;

/* read clocksource: */
clock = tk->clock;
cycle_now = clock->read(clock);

/* calculate the delta since the last update_wall_time: */
cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

nsec = cycle_delta * tk->mult + tk->xtime_nsec;
nsec >>= tk->shift;

/* If arch requires, add in gettimeoffset() */
return nsec + arch_gettimeoffset();
}

static inline s64 timekeeping_get_ns_raw(struct timekeeper *tk)
{
cycle_t cycle_now, cycle_delta;
struct clocksource *clock;
s64 nsec;

/* read clocksource: */
clock = tk->clock;
cycle_now = clock->read(clock);

/* calculate the delta since the last update_wall_time: */
cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

/* convert delta to nanoseconds. */
nsec = clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);

/* If arch requires, add in gettimeoffset() */
return nsec + arch_gettimeoffset();
}

/* must hold write on timekeeper.lock */
static void timekeeping_update(struct timekeeper *tk, bool clearntp)
{
if (clearntp) {
tk->ntp_error = 0;
ntp_clear();
}
update_vsyscall(tk);
}

/**
* timekeeping_forward_now - update clock to the current time
*
* Forward the current clock to update its state since the last call to
* update_wall_time(). This is useful before significant clock changes,
* as it avoids having to deal with this time offset explicitly.
*/
static void timekeeping_forward_now(struct timekeeper *tk)
{
cycle_t cycle_now, cycle_delta;
struct clocksource *clock;
s64 nsec;

clock = tk->clock;
cycle_now = clock->read(clock);
cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
clock->cycle_last = cycle_now;

tk->xtime_nsec += cycle_delta * tk->mult;

/* If arch requires, add in gettimeoffset() */
tk->xtime_nsec += (u64)arch_gettimeoffset() << tk->shift;

tk_normalize_xtime(tk);

nsec = clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);
timespec_add_ns(&tk->raw_time, nsec);
}

/**
* getnstimeofday - Returns the time of day in a timespec
* @ts: pointer to the timespec to be set
*
* Returns the time of day in a timespec.
*/
void getnstimeofday(struct timespec *ts)
{
struct timekeeper *tk = &timekeeper;
unsigned long seq;
s64 nsecs = 0;

WARN_ON(timekeeping_suspended);

do {
seq = read_seqbegin(&tk->lock);

ts->tv_sec = tk->xtime_sec;
nsecs = timekeeping_get_ns(tk);

} while (read_seqretry(&tk->lock, seq));

ts->tv_nsec = 0;
timespec_add_ns(ts, nsecs);
}
EXPORT_SYMBOL(getnstimeofday);

ktime_t ktime_get(void)
{
struct timekeeper *tk = &timekeeper;
unsigned int seq;
s64 secs, nsecs;

WARN_ON(timekeeping_suspended);

do {
seq = read_seqbegin(&tk->lock);
secs = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
nsecs = timekeeping_get_ns(tk) + tk->wall_to_monotonic.tv_nsec;

} while (read_seqretry(&tk->lock, seq));
/*
* Use ktime_set/ktime_add_ns to create a proper ktime on
* 32-bit architectures without CONFIG_KTIME_SCALAR.
*/
return ktime_add_ns(ktime_set(secs, 0), nsecs);
}
EXPORT_SYMBOL_GPL(ktime_get);

/**
* ktime_get_ts - get the monotonic clock in timespec format
* @ts: pointer to timespec variable
*
* The function calculates the monotonic clock from the realtime
* clock and the wall_to_monotonic offset and stores the result
* in normalized timespec format in the variable pointed to by @ts.
*/
void ktime_get_ts(struct timespec *ts)
{
struct timekeeper *tk = &timekeeper;
struct timespec tomono;
s64 nsec;
unsigned int seq;

WARN_ON(timekeeping_suspended);

do {
seq = read_seqbegin(&tk->lock);
ts->tv_sec = tk->xtime_sec;
nsec = timekeeping_get_ns(tk);
tomono = tk->wall_to_monotonic;

} while (read_seqretry(&tk->lock, seq));

ts->tv_sec += tomono.tv_sec;
ts->tv_nsec = 0;
timespec_add_ns(ts, nsec + tomono.tv_nsec);
}
EXPORT_SYMBOL_GPL(ktime_get_ts);

#ifdef CONFIG_NTP_PPS

/**
* getnstime_raw_and_real - get day and raw monotonic time in timespec format
* @ts_raw: pointer to the timespec to be set to raw monotonic time
* @ts_real: pointer to the timespec to be set to the time of day
*
* This function reads both the time of day and raw monotonic time at the
* same time atomically and stores the resulting timestamps in timespec
* format.
*/
void getnstime_raw_and_real(struct timespec *ts_raw, struct timespec *ts_real)
{
struct timekeeper *tk = &timekeeper;
unsigned long seq;
s64 nsecs_raw, nsecs_real;

WARN_ON_ONCE(timekeeping_suspended);

do {
seq = read_seqbegin(&tk->lock);

*ts_raw = tk->raw_time;
ts_real->tv_sec = tk->xtime_sec;
ts_real->tv_nsec = 0;

nsecs_raw = timekeeping_get_ns_raw(tk);
nsecs_real = timekeeping_get_ns(tk);

} while (read_seqretry(&tk->lock, seq));

timespec_add_ns(ts_raw, nsecs_raw);
timespec_add_ns(ts_real, nsecs_real);
}
EXPORT_SYMBOL(getnstime_raw_and_real);

#endif /* CONFIG_NTP_PPS */

/**
* do_gettimeofday - Returns the time of day in a timeval
* @tv: pointer to the timeval to be set
*
* NOTE: Users should be converted to using getnstimeofday()
*/
void do_gettimeofday(struct timeval *tv)
{
struct timespec now;

getnstimeofday(&now);
tv->tv_sec = now.tv_sec;
tv->tv_usec = now.tv_nsec/1000;
}
EXPORT_SYMBOL(do_gettimeofday);

/**
* do_settimeofday - Sets the time of day
* @tv: pointer to the timespec variable containing the new time
*
* Sets the time of day to the new time and update NTP and notify hrtimers
*/
int do_settimeofday(const struct timespec *tv)
{
struct timekeeper *tk = &timekeeper;
struct timespec ts_delta, xt;
unsigned long flags;

if (!timespec_valid_strict(tv))
return -EINVAL;

write_seqlock_irqsave(&tk->lock, flags);

timekeeping_forward_now(tk);

xt = tk_xtime(tk);
ts_delta.tv_sec = tv->tv_sec - xt.tv_sec;
ts_delta.tv_nsec = tv->tv_nsec - xt.tv_nsec;

tk_set_wall_to_mono(tk, timespec_sub(tk->wall_to_monotonic, ts_delta));

tk_set_xtime(tk, tv);

timekeeping_update(tk, true);

write_sequnlock_irqrestore(&tk->lock, flags);

/* signal hrtimers about time change */
clock_was_set();

return 0;
}
EXPORT_SYMBOL(do_settimeofday);

/**
* timekeeping_inject_offset - Adds or subtracts from the current time.
* @tv: pointer to the timespec variable containing the offset
*
* Adds or subtracts an offset value from the current time.
*/
int timekeeping_inject_offset(struct timespec *ts)
{
struct timekeeper *tk = &timekeeper;
unsigned long flags;
struct timespec tmp;
int ret = 0;

if ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC)
return -EINVAL;

write_seqlock_irqsave(&tk->lock, flags);

timekeeping_forward_now(tk);

/* Make sure the proposed value is valid */
tmp = timespec_add(tk_xtime(tk), *ts);
if (!timespec_valid_strict(&tmp)) {
ret = -EINVAL;
goto error;
}

tk_xtime_add(tk, ts);
tk_set_wall_to_mono(tk, timespec_sub(tk->wall_to_monotonic, *ts));

error: /* even if we error out, we forwarded the time, so call update */
timekeeping_update(tk, true);

write_sequnlock_irqrestore(&tk->lock, flags);

/* signal hrtimers about time change */
clock_was_set();

return ret;
}
EXPORT_SYMBOL(timekeeping_inject_offset);

/**
* change_clocksource - Swaps clocksources if a new one is available
*
* Accumulates current time interval and initializes new clocksource
*/
static int change_clocksource(void *data)
{
struct timekeeper *tk = &timekeeper;
struct clocksource *new, *old;
unsigned long flags;

new = (struct clocksource *) data;

write_seqlock_irqsave(&tk->lock, flags);

timekeeping_forward_now(tk);
if (!new->enable || new->enable(new) == 0) {
old = tk->clock;
tk_setup_internals(tk, new);
if (old->disable)
old->disable(old);
}
timekeeping_update(tk, true);

write_sequnlock_irqrestore(&tk->lock, flags);

return 0;
}

/**
* timekeeping_notify - Install a new clock source
* @clock: pointer to the clock source
*
* This function is called from clocksource.c after a new, better clock
* source has been registered. The caller holds the clocksource_mutex.
*/
void timekeeping_notify(struct clocksource *clock)
{
struct timekeeper *tk = &timekeeper;

if (tk->clock == clock)
return;
stop_machine(change_clocksource, clock, NULL);
tick_clock_notify();
}

/**
* ktime_get_real - get the real (wall-) time in ktime_t format
*
* returns the time in ktime_t format
*/
ktime_t ktime_get_real(void)
{
struct timespec now;

getnstimeofday(&now);

return timespec_to_ktime(now);
}
EXPORT_SYMBOL_GPL(ktime_get_real);

/**
* getrawmonotonic - Returns the raw monotonic time in a timespec
* @ts: pointer to the timespec to be set
*
* Returns the raw monotonic time (completely un-modified by ntp)
*/
void getrawmonotonic(struct timespec *ts)
{
struct timekeeper *tk = &timekeeper;
unsigned long seq;
s64 nsecs;

do {
seq = read_seqbegin(&tk->lock);
nsecs = timekeeping_get_ns_raw(tk);
*ts = tk->raw_time;

} while (read_seqretry(&tk->lock, seq));

timespec_add_ns(ts, nsecs);
}
EXPORT_SYMBOL(getrawmonotonic);

/**
* timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
*/
int timekeeping_valid_for_hres(void)
{
struct timekeeper *tk = &timekeeper;
unsigned long seq;
int ret;

do {
seq = read_seqbegin(&tk->lock);

ret = tk->clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

} while (read_seqretry(&tk->lock, seq));

return ret;
}

/**
* timekeeping_max_deferment - Returns max time the clocksource can be deferred
*/
u64 timekeeping_max_deferment(void)
{
struct timekeeper *tk = &timekeeper;
unsigned long seq;
u64 ret;

do {
seq = read_seqbegin(&tk->lock);

ret = tk->clock->max_idle_ns;

} while (read_seqretry(&tk->lock, seq));

return ret;
}

/**
* read_persistent_clock - Return time from the persistent clock.
*
* Weak dummy function for arches that do not yet support it.
* Reads the time from the battery backed persistent clock.
* Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
*
* XXX - Do be sure to remove it once all arches implement it.
*/
void __attribute__((weak)) read_persistent_clock(struct timespec *ts)
{
ts->tv_sec = 0;
ts->tv_nsec = 0;
}

/**
* read_boot_clock - Return time of the system start.
*
* Weak dummy function for arches that do not yet support it.
* Function to read the exact time the system has been started.
* Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
*
* XXX - Do be sure to remove it once all arches implement it.
*/
void __attribute__((weak)) read_boot_clock(struct timespec *ts)
{
ts->tv_sec = 0;
ts->tv_nsec = 0;
}

/*
* timekeeping_init - Initializes the clocksource and common timekeeping values
*/
void __init timekeeping_init(void)
{
struct timekeeper *tk = &timekeeper;
struct clocksource *clock;
unsigned long flags;
struct timespec now, boot, tmp;

read_persistent_clock(&now);
if (!timespec_valid_strict(&now)) {
pr_warn("WARNING: Persistent clock returned invalid value!\n"
" Check your CMOS/BIOS settings.\n");
now.tv_sec = 0;
now.tv_nsec = 0;
}

read_boot_clock(&boot);
if (!timespec_valid_strict(&boot)) {
pr_warn("WARNING: Boot clock returned invalid value!\n"
" Check your CMOS/BIOS settings.\n");
boot.tv_sec = 0;
boot.tv_nsec = 0;
}

seqlock_init(&tk->lock);

ntp_init();

write_seqlock_irqsave(&tk->lock, flags);
clock = clocksource_default_clock();
if (clock->enable)
clock->enable(clock);
tk_setup_internals(tk, clock);

tk_set_xtime(tk, &now);
tk->raw_time.tv_sec = 0;
tk->raw_time.tv_nsec = 0;
if (boot.tv_sec == 0 && boot.tv_nsec == 0)
boot = tk_xtime(tk);

set_normalized_timespec(&tmp, -boot.tv_sec, -boot.tv_nsec);
tk_set_wall_to_mono(tk, tmp);

tmp.tv_sec = 0;
tmp.tv_nsec = 0;
tk_set_sleep_time(tk, tmp);

write_sequnlock_irqrestore(&tk->lock, flags);
}

/* time in seconds when suspend began */
static struct timespec timekeeping_suspend_time;

/**
* __timekeeping_inject_sleeptime - Internal function to add sleep interval
* @delta: pointer to a timespec delta value
*
* Takes a timespec offset measuring a suspend interval and properly
* adds the sleep offset to the timekeeping variables.
*/
static void __timekeeping_inject_sleeptime(struct timekeeper *tk,
struct timespec *delta)
{
if (!timespec_valid_strict(delta)) {
printk(KERN_WARNING "__timekeeping_inject_sleeptime: Invalid "
"sleep delta value!\n");
return;
}
tk_xtime_add(tk, delta);
tk_set_wall_to_mono(tk, timespec_sub(tk->wall_to_monotonic, *delta));
tk_set_sleep_time(tk, timespec_add(tk->total_sleep_time, *delta));
}

/**
* timekeeping_inject_sleeptime - Adds suspend interval to timeekeeping values
* @delta: pointer to a timespec delta value
*
* This hook is for architectures that cannot support read_persistent_clock
* because their RTC/persistent clock is only accessible when irqs are enabled.
*
* This function should only be called by rtc_resume(), and allows
* a suspend offset to be injected into the timekeeping values.
*/
void timekeeping_inject_sleeptime(struct timespec *delta)
{
struct timekeeper *tk = &timekeeper;
unsigned long flags;
struct timespec ts;

/* Make sure we don't set the clock twice */
read_persistent_clock(&ts);
if (!(ts.tv_sec == 0 && ts.tv_nsec == 0))
return;

write_seqlock_irqsave(&tk->lock, flags);

timekeeping_forward_now(tk);

__timekeeping_inject_sleeptime(tk, delta);

timekeeping_update(tk, true);

write_sequnlock_irqrestore(&tk->lock, flags);

/* signal hrtimers about time change */
clock_was_set();
}

/**
* timekeeping_resume - Resumes the generic timekeeping subsystem.
*
* This is for the generic clocksource timekeeping.
* xtime/wall_to_monotonic/jiffies/etc are
* still managed by arch specific suspend/resume code.
*/
static void timekeeping_resume(void)
{
struct timekeeper *tk = &timekeeper;
unsigned long flags;
struct timespec ts;

read_persistent_clock(&ts);

clockevents_resume();
clocksource_resume();

write_seqlock_irqsave(&tk->lock, flags);

if (timespec_compare(&ts, &timekeeping_suspend_time) > 0) {
ts = timespec_sub(ts, timekeeping_suspend_time);
__timekeeping_inject_sleeptime(tk, &ts);
}
/* re-base the last cycle value */
tk->clock->cycle_last = tk->clock->read(tk->clock);
tk->ntp_error = 0;
timekeeping_suspended = 0;
timekeeping_update(tk, false);
write_sequnlock_irqrestore(&tk->lock, flags);

touch_softlockup_watchdog();

clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);

/* Resume hrtimers */
hrtimers_resume();
}

static int timekeeping_suspend(void)
{
struct timekeeper *tk = &timekeeper;
unsigned long flags;
struct timespec delta, delta_delta;
static struct timespec old_delta;

read_persistent_clock(&timekeeping_suspend_time);

write_seqlock_irqsave(&tk->lock, flags);
timekeeping_forward_now(tk);
timekeeping_suspended = 1;

/*
* To avoid drift caused by repeated suspend/resumes,
* which each can add ~1 second drift error,
* try to compensate so the difference in system time
* and persistent_clock time stays close to constant.
*/
delta = timespec_sub(tk_xtime(tk), timekeeping_suspend_time);
delta_delta = timespec_sub(delta, old_delta);
if (abs(delta_delta.tv_sec) >= 2) {
/*
* if delta_delta is too large, assume time correction
* has occured and set old_delta to the current delta.
*/
old_delta = delta;
} else {
/* Otherwise try to adjust old_system to compensate */
timekeeping_suspend_time =
timespec_add(timekeeping_suspend_time, delta_delta);
}
write_sequnlock_irqrestore(&tk->lock, flags);

clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
clocksource_suspend();
clockevents_suspend();

return 0;
}

/* sysfs resume/suspend bits for timekeeping */
static struct syscore_ops timekeeping_syscore_ops = {
.resume = timekeeping_resume,
.suspend = timekeeping_suspend,
};

static int __init timekeeping_init_ops(void)
{
register_syscore_ops(&timekeeping_syscore_ops);
return 0;
}

device_initcall(timekeeping_init_ops);

/*
* If the error is already larger, we look ahead even further
* to compensate for late or lost adjustments.
*/
static __always_inline int timekeeping_bigadjust(struct timekeeper *tk,
s64 error, s64 *interval,
s64 *offset)
{
s64 tick_error, i;
u32 look_ahead, adj;
s32 error2, mult;

/*
* Use the current error value to determine how much to look ahead.
* The larger the error the slower we adjust for it to avoid problems
* with losing too many ticks, otherwise we would overadjust and
* produce an even larger error. The smaller the adjustment the
* faster we try to adjust for it, as lost ticks can do less harm
* here. This is tuned so that an error of about 1 msec is adjusted
* within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
*/
error2 = tk->ntp_error >> (NTP_SCALE_SHIFT + 22 - 2 * SHIFT_HZ);
error2 = abs(error2);
for (look_ahead = 0; error2 > 0; look_ahead++)
error2 >>= 2;

/*
* Now calculate the error in (1 << look_ahead) ticks, but first
* remove the single look ahead already included in the error.
*/
tick_error = ntp_tick_length() >> (tk->ntp_error_shift + 1);
tick_error -= tk->xtime_interval >> 1;
error = ((error - tick_error) >> look_ahead) + tick_error;

/* Finally calculate the adjustment shift value. */
i = *interval;
mult = 1;
if (error < 0) {
error = -error;
*interval = -*interval;
*offset = -*offset;
mult = -1;
}
for (adj = 0; error > i; adj++)
error >>= 1;

*interval <<= adj;
*offset <<= adj;
return mult << adj;
}

/*
* Adjust the multiplier to reduce the error value,
* this is optimized for the most common adjustments of -1,0,1,
* for other values we can do a bit more work.
*/
static void timekeeping_adjust(struct timekeeper *tk, s64 offset)
{
s64 error, interval = tk->cycle_interval;
int adj;

/*
* The point of this is to check if the error is greater than half
* an interval.
*
* First we shift it down from NTP_SHIFT to clocksource->shifted nsecs.
*
* Note we subtract one in the shift, so that error is really error*2.
* This "saves" dividing(shifting) interval twice, but keeps the
* (error > interval) comparison as still measuring if error is
* larger than half an interval.
*
* Note: It does not "save" on aggravation when reading the code.
*/
error = tk->ntp_error >> (tk->ntp_error_shift - 1);
if (error > interval) {
/*
* We now divide error by 4(via shift), which checks if
* the error is greater than twice the interval.
* If it is greater, we need a bigadjust, if its smaller,
* we can adjust by 1.
*/
error >>= 2;
/*
* XXX - In update_wall_time, we round up to the next
* nanosecond, and store the amount rounded up into
* the error. This causes the likely below to be unlikely.
*
* The proper fix is to avoid rounding up by using
* the high precision tk->xtime_nsec instead of
* xtime.tv_nsec everywhere. Fixing this will take some
* time.
*/
if (likely(error <= interval))
adj = 1;
else
adj = timekeeping_bigadjust(tk, error, &interval, &offset);
} else {
if (error < -interval) {
/* See comment above, this is just switched for the negative */
error >>= 2;
if (likely(error >= -interval)) {
adj = -1;
interval = -interval;
offset = -offset;
} else {
adj = timekeeping_bigadjust(tk, error, &interval, &offset);
}
} else {
goto out_adjust;
}
}

if (unlikely(tk->clock->maxadj &&
(tk->mult + adj > tk->clock->mult + tk->clock->maxadj))) {
printk_once(KERN_WARNING
"Adjusting %s more than 11%% (%ld vs %ld)\n",
tk->clock->name, (long)tk->mult + adj,
(long)tk->clock->mult + tk->clock->maxadj);
}
/*
* So the following can be confusing.
*
* To keep things simple, lets assume adj == 1 for now.
*
* When adj != 1, remember that the interval and offset values
* have been appropriately scaled so the math is the same.
*
* The basic idea here is that we're increasing the multiplier
* by one, this causes the xtime_interval to be incremented by
* one cycle_interval. This is because:
* xtime_interval = cycle_interval * mult
* So if mult is being incremented by one:
* xtime_interval = cycle_interval * (mult + 1)
* Its the same as:
* xtime_interval = (cycle_interval * mult) + cycle_interval
* Which can be shortened to:
* xtime_interval += cycle_interval
*
* So offset stores the non-accumulated cycles. Thus the current
* time (in shifted nanoseconds) is:
* now = (offset * adj) + xtime_nsec
* Now, even though we're adjusting the clock frequency, we have
* to keep time consistent. In other words, we can't jump back
* in time, and we also want to avoid jumping forward in time.
*
* So given the same offset value, we need the time to be the same
* both before and after the freq adjustment.
* now = (offset * adj_1) + xtime_nsec_1
* now = (offset * adj_2) + xtime_nsec_2
* So:
* (offset * adj_1) + xtime_nsec_1 =
* (offset * adj_2) + xtime_nsec_2
* And we know:
* adj_2 = adj_1 + 1
* So:
* (offset * adj_1) + xtime_nsec_1 =
* (offset * (adj_1+1)) + xtime_nsec_2
* (offset * adj_1) + xtime_nsec_1 =
* (offset * adj_1) + offset + xtime_nsec_2
* Canceling the sides:
* xtime_nsec_1 = offset + xtime_nsec_2
* Which gives us:
* xtime_nsec_2 = xtime_nsec_1 - offset
* Which simplfies to:
* xtime_nsec -= offset
*
* XXX - TODO: Doc ntp_error calculation.
*/
tk->mult += adj;
tk->xtime_interval += interval;
tk->xtime_nsec -= offset;
tk->ntp_error -= (interval - offset) << tk->ntp_error_shift;

out_adjust:
/*
* It may be possible that when we entered this function, xtime_nsec
* was very small. Further, if we're slightly speeding the clocksource
* in the code above, its possible the required corrective factor to
* xtime_nsec could cause it to underflow.
*
* Now, since we already accumulated the second, cannot simply roll
* the accumulated second back, since the NTP subsystem has been
* notified via second_overflow. So instead we push xtime_nsec forward
* by the amount we underflowed, and add that amount into the error.
*
* We'll correct this error next time through this function, when
* xtime_nsec is not as small.
*/
if (unlikely((s64)tk->xtime_nsec < 0)) {
s64 neg = -(s64)tk->xtime_nsec;
tk->xtime_nsec = 0;
tk->ntp_error += neg << tk->ntp_error_shift;
}

}

/**
* accumulate_nsecs_to_secs - Accumulates nsecs into secs
*
* Helper function that accumulates a the nsecs greater then a second
* from the xtime_nsec field to the xtime_secs field.
* It also calls into the NTP code to handle leapsecond processing.
*
*/
static inline void accumulate_nsecs_to_secs(struct timekeeper *tk)
{
u64 nsecps = (u64)NSEC_PER_SEC << tk->shift;

while (tk->xtime_nsec >= nsecps) {
int leap;

tk->xtime_nsec -= nsecps;
tk->xtime_sec++;

/* Figure out if its a leap sec and apply if needed */
leap = second_overflow(tk->xtime_sec);
if (unlikely(leap)) {
struct timespec ts;

tk->xtime_sec += leap;

ts.tv_sec = leap;
ts.tv_nsec = 0;
tk_set_wall_to_mono(tk,
timespec_sub(tk->wall_to_monotonic, ts));

clock_was_set_delayed();
}
}
}

/**
* logarithmic_accumulation - shifted accumulation of cycles
*
* This functions accumulates a shifted interval of cycles into
* into a shifted interval nanoseconds. Allows for O(log) accumulation
* loop.
*
* Returns the unconsumed cycles.
*/
static cycle_t logarithmic_accumulation(struct timekeeper *tk, cycle_t offset,
u32 shift)
{
u64 raw_nsecs;

/* If the offset is smaller then a shifted interval, do nothing */
if (offset < tk->cycle_interval<<shift)
return offset;

/* Accumulate one shifted interval */
offset -= tk->cycle_interval << shift;
tk->clock->cycle_last += tk->cycle_interval << shift;

tk->xtime_nsec += tk->xtime_interval << shift;
accumulate_nsecs_to_secs(tk);

/* Accumulate raw time */
raw_nsecs = (u64)tk->raw_interval << shift;
raw_nsecs += tk->raw_time.tv_nsec;
if (raw_nsecs >= NSEC_PER_SEC) {
u64 raw_secs = raw_nsecs;
raw_nsecs = do_div(raw_secs, NSEC_PER_SEC);
tk->raw_time.tv_sec += raw_secs;
}
tk->raw_time.tv_nsec = raw_nsecs;

/* Accumulate error between NTP and clock interval */
tk->ntp_error += ntp_tick_length() << shift;
tk->ntp_error -= (tk->xtime_interval + tk->xtime_remainder) <<
(tk->ntp_error_shift + shift);

return offset;
}

#ifdef CONFIG_GENERIC_TIME_VSYSCALL_OLD
static inline void old_vsyscall_fixup(struct timekeeper *tk)
{
s64 remainder;

/*
* Store only full nanoseconds into xtime_nsec after rounding
* it up and add the remainder to the error difference.
* XXX - This is necessary to avoid small 1ns inconsistnecies caused
* by truncating the remainder in vsyscalls. However, it causes
* additional work to be done in timekeeping_adjust(). Once
* the vsyscall implementations are converted to use xtime_nsec
* (shifted nanoseconds), and CONFIG_GENERIC_TIME_VSYSCALL_OLD
* users are removed, this can be killed.
*/
remainder = tk->xtime_nsec & ((1ULL << tk->shift) - 1);
tk->xtime_nsec -= remainder;
tk->xtime_nsec += 1ULL << tk->shift;
tk->ntp_error += remainder << tk->ntp_error_shift;

}
#else
#define old_vsyscall_fixup(tk)
#endif



/**
* update_wall_time - Uses the current clocksource to increment the wall time
*
*/
static void update_wall_time(void)
{
struct clocksource *clock;
struct timekeeper *tk = &timekeeper;
cycle_t offset;
int shift = 0, maxshift;
unsigned long flags;

write_seqlock_irqsave(&tk->lock, flags);

/* Make sure we're fully resumed: */
if (unlikely(timekeeping_suspended))
goto out;

clock = tk->clock;

#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
offset = tk->cycle_interval;
#else
offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
#endif

/* Check if there's really nothing to do */
if (offset < tk->cycle_interval)
goto out;

/*
* With NO_HZ we may have to accumulate many cycle_intervals
* (think "ticks") worth of time at once. To do this efficiently,
* we calculate the largest doubling multiple of cycle_intervals
* that is smaller than the offset. We then accumulate that
* chunk in one go, and then try to consume the next smaller
* doubled multiple.
*/
shift = ilog2(offset) - ilog2(tk->cycle_interval);
shift = max(0, shift);
/* Bound shift to one less than what overflows tick_length */
maxshift = (64 - (ilog2(ntp_tick_length())+1)) - 1;
shift = min(shift, maxshift);
while (offset >= tk->cycle_interval) {
offset = logarithmic_accumulation(tk, offset, shift);
if (offset < tk->cycle_interval<<shift)
shift--;
}

/* correct the clock when NTP error is too big */
timekeeping_adjust(tk, offset);

/*
* XXX This can be killed once everyone converts
* to the new update_vsyscall.
*/
old_vsyscall_fixup(tk);

/*
* Finally, make sure that after the rounding
* xtime_nsec isn't larger than NSEC_PER_SEC
*/
accumulate_nsecs_to_secs(tk);

timekeeping_update(tk, false);

out:
write_sequnlock_irqrestore(&tk->lock, flags);

}

/**
* getboottime - Return the real time of system boot.
* @ts: pointer to the timespec to be set
*
* Returns the wall-time of boot in a timespec.
*
* This is based on the wall_to_monotonic offset and the total suspend
* time. Calls to settimeofday will affect the value returned (which
* basically means that however wrong your real time clock is at boot time,
* you get the right time here).
*/
void getboottime(struct timespec *ts)
{
struct timekeeper *tk = &timekeeper;
struct timespec boottime = {
.tv_sec = tk->wall_to_monotonic.tv_sec +
tk->total_sleep_time.tv_sec,
.tv_nsec = tk->wall_to_monotonic.tv_nsec +
tk->total_sleep_time.tv_nsec
};

set_normalized_timespec(ts, -boottime.tv_sec, -boottime.tv_nsec);
}
EXPORT_SYMBOL_GPL(getboottime);

/**
* get_monotonic_boottime - Returns monotonic time since boot
* @ts: pointer to the timespec to be set
*
* Returns the monotonic time since boot in a timespec.
*
* This is similar to CLOCK_MONTONIC/ktime_get_ts, but also
* includes the time spent in suspend.
*/
void get_monotonic_boottime(struct timespec *ts)
{
struct timekeeper *tk = &timekeeper;
struct timespec tomono, sleep;
s64 nsec;
unsigned int seq;

WARN_ON(timekeeping_suspended);

do {
seq = read_seqbegin(&tk->lock);
ts->tv_sec = tk->xtime_sec;
nsec = timekeeping_get_ns(tk);
tomono = tk->wall_to_monotonic;
sleep = tk->total_sleep_time;

} while (read_seqretry(&tk->lock, seq));

ts->tv_sec += tomono.tv_sec + sleep.tv_sec;
ts->tv_nsec = 0;
timespec_add_ns(ts, nsec + tomono.tv_nsec + sleep.tv_nsec);
}
EXPORT_SYMBOL_GPL(get_monotonic_boottime);

/**
* ktime_get_boottime - Returns monotonic time since boot in a ktime
*
* Returns the monotonic time since boot in a ktime
*
* This is similar to CLOCK_MONTONIC/ktime_get, but also
* includes the time spent in suspend.
*/
ktime_t ktime_get_boottime(void)
{
struct timespec ts;

get_monotonic_boottime(&ts);
return timespec_to_ktime(ts);
}
EXPORT_SYMBOL_GPL(ktime_get_boottime);

/**
* monotonic_to_bootbased - Convert the monotonic time to boot based.
* @ts: pointer to the timespec to be converted
*/
void monotonic_to_bootbased(struct timespec *ts)
{
struct timekeeper *tk = &timekeeper;

*ts = timespec_add(*ts, tk->total_sleep_time);
}
EXPORT_SYMBOL_GPL(monotonic_to_bootbased);

unsigned long get_seconds(void)
{
struct timekeeper *tk = &timekeeper;

return tk->xtime_sec;
}
EXPORT_SYMBOL(get_seconds);

struct timespec __current_kernel_time(void)
{
struct timekeeper *tk = &timekeeper;

return tk_xtime(tk);
}

struct timespec current_kernel_time(void)
{
struct timekeeper *tk = &timekeeper;
struct timespec now;
unsigned long seq;

do {
seq = read_seqbegin(&tk->lock);

now = tk_xtime(tk);
} while (read_seqretry(&tk->lock, seq));

return now;
}
EXPORT_SYMBOL(current_kernel_time);

struct timespec get_monotonic_coarse(void)
{
struct timekeeper *tk = &timekeeper;
struct timespec now, mono;
unsigned long seq;

do {
seq = read_seqbegin(&tk->lock);

now = tk_xtime(tk);
mono = tk->wall_to_monotonic;
} while (read_seqretry(&tk->lock, seq));

set_normalized_timespec(&now, now.tv_sec + mono.tv_sec,
now.tv_nsec + mono.tv_nsec);
return now;
}

/*
* The 64-bit jiffies value is not atomic - you MUST NOT read it
* without sampling the sequence number in xtime_lock.
* jiffies is defined in the linker script...
*/
void do_timer(unsigned long ticks)
{
jiffies_64 += ticks;
update_wall_time();
calc_global_load(ticks);
}

/**
* get_xtime_and_monotonic_and_sleep_offset() - get xtime, wall_to_monotonic,
* and sleep offsets.
* @xtim: pointer to timespec to be set with xtime
* @wtom: pointer to timespec to be set with wall_to_monotonic
* @sleep: pointer to timespec to be set with time in suspend
*/
void get_xtime_and_monotonic_and_sleep_offset(struct timespec *xtim,
struct timespec *wtom, struct timespec *sleep)
{
struct timekeeper *tk = &timekeeper;
unsigned long seq;

do {
seq = read_seqbegin(&tk->lock);
*xtim = tk_xtime(tk);
*wtom = tk->wall_to_monotonic;
*sleep = tk->total_sleep_time;
} while (read_seqretry(&tk->lock, seq));
}

#ifdef CONFIG_HIGH_RES_TIMERS
/**
* ktime_get_update_offsets - hrtimer helper
* @offs_real: pointer to storage for monotonic -> realtime offset
* @offs_boot: pointer to storage for monotonic -> boottime offset
*
* Returns current monotonic time and updates the offsets
* Called from hrtimer_interupt() or retrigger_next_event()
*/
ktime_t ktime_get_update_offsets(ktime_t *offs_real, ktime_t *offs_boot)
{
struct timekeeper *tk = &timekeeper;
ktime_t now;
unsigned int seq;
u64 secs, nsecs;

do {
seq = read_seqbegin(&tk->lock);

secs = tk->xtime_sec;
nsecs = timekeeping_get_ns(tk);

*offs_real = tk->offs_real;
*offs_boot = tk->offs_boot;
} while (read_seqretry(&tk->lock, seq));

now = ktime_add_ns(ktime_set(secs, 0), nsecs);
now = ktime_sub(now, *offs_real);
return now;
}
#endif

/**
* ktime_get_monotonic_offset() - get wall_to_monotonic in ktime_t format
*/
ktime_t ktime_get_monotonic_offset(void)
{
struct timekeeper *tk = &timekeeper;
unsigned long seq;
struct timespec wtom;

do {
seq = read_seqbegin(&tk->lock);
wtom = tk->wall_to_monotonic;
} while (read_seqretry(&tk->lock, seq));

return timespec_to_ktime(wtom);
}
EXPORT_SYMBOL_GPL(ktime_get_monotonic_offset);

/**
* xtime_update() - advances the timekeeping infrastructure
* @ticks: number of ticks, that have elapsed since the last call.
*
* Must be called with interrupts disabled.
*/
void xtime_update(unsigned long ticks)
{
write_seqlock(&xtime_lock);
do_timer(ticks);
write_sequnlock(&xtime_lock);
}
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