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;
	/* NTP adjusted clock multiplier */
	u32			mult;
	/* The shift value of the current clocksource. */
	u32			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;

	/* Current CLOCK_REALTIME time in seconds */
	u64			xtime_sec;
	/* Clock shifted nano seconds */
	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. */
	u32			ntp_error_shift;

	/*
	 * wall_to_monotonic is what we need to add to xtime (or xtime corrected
	 * for sub jiffie times) to get to monotonic time.  Monotonic is pegged
	 * at zero at system boot time, so wall_to_monotonic will be negative,
	 * however, we will ALWAYS keep the tv_nsec part positive so we can use
	 * the usual normalization.
	 *
	 * wall_to_monotonic is moved after resume from suspend for the
	 * monotonic time not to jump. We need to add total_sleep_time to
	 * wall_to_monotonic to get the real boot based time offset.
	 *
	 * - wall_to_monotonic is no longer the boot time, getboottime must be
	 * used instead.
	 */
	struct timespec		wall_to_monotonic;
	/* Offset clock monotonic -> clock realtime */
	ktime_t			offs_real;
	/* time spent in suspend */
	struct timespec		total_sleep_time;
	/* Offset clock monotonic -> clock boottime */
	ktime_t			offs_boot;
	/* The raw monotonic time for the CLOCK_MONOTONIC_RAW posix clock. */
	struct timespec		raw_time;
	/* Seqlock for all timekeeper values */
	seqlock_t		lock;
};

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