path: root/kernel/time/timekeeping.c

/*
 *  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/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>

/* Structure holding internal timekeeping values. */
struct timekeeper {
	/* Current clocksource used for timekeeping. */
	struct clocksource *clock;
	/* The shift value of the current clocksource. */
	int	shift;

	/* Number of clock cycles in one NTP interval. */
	cycle_t cycle_interval;
	/* Number of clock shifted nano seconds in one NTP interval. */
	u64	xtime_interval;
	/* shifted nano seconds left over when rounding cycle_interval */
	s64	xtime_remainder;
	/* Raw nano seconds accumulated per NTP interval. */
	u32	raw_interval;

	/* Clock shifted nano seconds remainder not stored in xtime.tv_nsec. */
	u64	xtime_nsec;
	/* Difference between accumulated time and NTP time in ntp
	 * shifted nano seconds. */
	s64	ntp_error;
	/* Shift conversion between clock shifted nano seconds and
	 * ntp shifted nano seconds. */
	int	ntp_error_shift;
	/* NTP adjusted clock multiplier */
	u32	mult;
};

static struct timekeeper timekeeper;

/**
 * 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 timekeeper_setup_internals(struct clocksource *clock)
{
	cycle_t interval;
	u64 tmp, ntpinterval;

	timekeeper.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;
	timekeeper.cycle_interval = interval;

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

	timekeeper.xtime_nsec = 0;
	timekeeper.shift = clock->shift;

	timekeeper.ntp_error = 0;
	timekeeper.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.
	 */
	timekeeper.mult = clock->mult;
}

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

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

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

	/* return delta convert to nanoseconds using ntp adjusted mult. */
	return clocksource_cyc2ns(cycle_delta, timekeeper.mult,
				  timekeeper.shift);
}

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

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

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

	/* return delta convert to nanoseconds using ntp adjusted mult. */
	return clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift