time.c

linux-2.4.29操作系统的源码

/*
 * Copyright 2001 MontaVista Software Inc.
 * Author: Jun Sun, [e-mail] or [e-mail]
 * Copyright (c) 2003, 2004  Maciej W. Rozycki
 *
 * Common time service routines for MIPS machines. See
 * Documentation/mips/time.README.
 *
 * 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.
 */
#include <linux/config.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/param.h>
#include <linux/time.h>
#include <linux/timex.h>
#include <linux/smp.h>
#include <linux/kernel_stat.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/module.h>

#include <asm/bootinfo.h>
#include <asm/compiler.h>
#include <asm/cpu.h>
#include <asm/time.h>
#include <asm/hardirq.h>
#include <asm/div64.h>

/*
 * The integer part of the number of usecs per jiffy is taken from tick,
 * but the fractional part is not recorded, so we calculate it using the
 * initial value of HZ.  This aids systems where tick isn't really an
 * integer (e.g. for HZ = 128).
 */
#define USECS_PER_JIFFY		tick
#define USECS_PER_JIFFY_FRAC	((unsigned long)(u32)((1000000ULL << 32) / HZ))

/*
 * forward reference
 */
extern rwlock_t xtime_lock;
extern volatile unsigned long wall_jiffies;

spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED;

/*
 * whether we emulate local_timer_interrupts for SMP machines.
 */
int emulate_local_timer_interrupt;


/*
 * By default we provide the null RTC ops
 */
static unsigned long null_rtc_get_time(void)
{
	return mktime(2000, 1, 1, 0, 0, 0);
}

static int null_rtc_set_time(unsigned long sec)
{
	return 0;
}

unsigned long (*rtc_get_time)(void) = null_rtc_get_time;
int (*rtc_set_time)(unsigned long) = null_rtc_set_time;
int (*rtc_set_mmss)(unsigned long);


/* usecs per counter cycle, shifted to left by 32 bits */
static unsigned int sll32_usecs_per_cycle;

/* how many counter cycles in a jiffy */
static unsigned long cycles_per_jiffy;

/* Cycle counter value at the previous timer interrupt.. */
static unsigned int timerhi, timerlo;

/* expirelo is the count value for next CPU timer interrupt */
static unsigned int expirelo;


/*
 * Null timer ack for systems not needing one (e.g. i8254).
 */
static void null_timer_ack(void) { /* nothing */ }

/*
 * Null high precision timer functions for systems lacking one.
 */
static unsigned int null_hpt_read(void)
{
	return 0;
}

static void null_hpt_init(unsigned int count) { /* nothing */ }


/*
 * Timer ack for an R4k-compatible timer of a known frequency.
 */
static void c0_timer_ack(void)
{
	unsigned int count;

	/* Ack this timer interrupt and set the next one.  */
	expirelo += cycles_per_jiffy;
	write_c0_compare(expirelo);

	/* Check to see if we have missed any timer interrupts.  */
	count = read_c0_count();
	if ((count - expirelo) < 0x7fffffff) {
		/* missed_timer_count++; */
		expirelo = count + cycles_per_jiffy;
		write_c0_compare(expirelo);
	}
}

/*
 * High precision timer functions for a R4k-compatible timer.
 */
static unsigned int c0_hpt_read(void)
{
	return read_c0_count();
}

/* For use solely as a high precision timer.  */
static void c0_hpt_init(unsigned int count)
{
	write_c0_count(read_c0_count() - count);
}

/* For use both as a high precision timer and an interrupt source.  */
static void c0_hpt_timer_init(unsigned int count)
{
	count = read_c0_count() - count;
	expirelo = (count / cycles_per_jiffy + 1) * cycles_per_jiffy;
	write_c0_count(expirelo - cycles_per_jiffy);
	write_c0_compare(expirelo);
	write_c0_count(count);
}

int (*mips_timer_state)(void);
void (*mips_timer_ack)(void);
unsigned int (*mips_hpt_read)(void);
void (*mips_hpt_init)(unsigned int);


/*
 * timeofday services, for syscalls.
 */
void do_gettimeofday(struct timeval *tv)
{
	unsigned long flags, lost;

	read_lock_irqsave(&xtime_lock, flags);

	*tv = xtime;
	tv->tv_usec += do_gettimeoffset();
	/*
	 * xtime is atomically updated in timer_bh.  jiffies - wall_jiffies
	 * is nonzero if the timer bottom half hasn't executed yet.
	 */
	lost = jiffies - wall_jiffies;
	if (lost)
		tv->tv_usec += lost * USECS_PER_JIFFY;

	read_unlock_irqrestore(&xtime_lock, flags);

	while (tv->tv_usec >= 1000000) {
		tv->tv_usec -= 1000000;
		tv->tv_sec++;
	}
}

void do_settimeofday(struct timeval *tv)
{
	write_lock_irq(&xtime_lock);

	/*
	 * This is revolting.  We need to set "xtime" correctly.  However,
	 * the value in this location is the value at the most recent update
	 * of wall time.  Discover what correction gettimeofday() would have
	 * made, and then undo it!
	 */
	tv->tv_usec -= do_gettimeoffset();
	tv->tv_usec -= (jiffies - wall_jiffies) * USECS_PER_JIFFY;

	while (tv->tv_usec < 0) {
		tv->tv_usec += 1000000;
		tv->tv_sec--;
	}

	xtime = *tv;
	time_adjust = 0;			/* stop active adjtime() */
	time_status |= STA_UNSYNC;
	time_maxerror = NTP_PHASE_LIMIT;
	time_esterror = NTP_PHASE_LIMIT;

	write_unlock_irq(&xtime_lock);
}


/*
 * Gettimeoffset routines.  These routines returns the time duration
 * since last timer interrupt in usecs.
 *
 * If the exact CPU counter frequency is known, use fixed_rate_gettimeoffset.
 * Otherwise use calibrate_gettimeoffset()
 *
 * If the CPU does not have the counter register, you can either supply
 * your own gettimeoffset() routine, or use null_gettimeoffset(), which
 * gives the same resolution as HZ.
 */

static unsigned long null_gettimeoffset(void)
{
	return 0;
}


/* The function pointer to one of the gettimeoffset funcs.  */
unsigned long (*do_gettimeoffset)(void) = null_gettimeoffset;


static unsigned long fixed_rate_gettimeoffset(void)
{
	u32 count;
	unsigned long res;

	/* Get last timer tick in absolute kernel time */
	count = mips_hpt_read();

	/* .. relative to previous jiffy (32 bits is enough) */
	count -= timerlo;

	__asm__("multu	%1,%2"
		: "=h" (res)
		: "r" (count), "r" (sll32_usecs_per_cycle)
		: "lo", GCC_REG_ACCUM);

	/*
	 * Due to possible jiffies inconsistencies, we need to check
	 * the result so that we'll get a timer that is monotonic.
	 */
	if (res >= USECS_PER_JIFFY)
		res = USECS_PER_JIFFY - 1;

	return res;
}


/*
 * Cached "1/(clocks per usec) * 2^32" value.
 * It has to be recalculated once each jiffy.
 */
static unsigned long cached_quotient;

/* Last jiffy when calibrate_divXX_gettimeoffset() was called. */
static unsigned long last_jiffies;

/*
 * This is moved from dec/time.c:do_ioasic_gettimeoffset() by Maciej.
 */
static unsigned long calibrate_div32_gettimeoffset(void)
{
	u32 count;
	unsigned long res, tmp;
	unsigned long quotient;

	tmp = jiffies;

	quotient = cached_quotient;

	if (last_jiffies != tmp) {
		last_jiffies = tmp;
		if (last_jiffies != 0) {
			unsigned long r0;
			do_div64_32(r0, timerhi, timerlo, tmp);
			do_div64_32(quotient, USECS_PER_JIFFY,
				    USECS_PER_JIFFY_FRAC, r0);
			cached_quotient = quotient;
		}
	}

	/* Get last timer tick in absolute kernel time */
	count = mips_hpt_read();

	/* .. relative to previous jiffy (32 bits is enough) */
	count -= timerlo;

	__asm__("multu  %1,%2"
		: "=h" (res)
		: "r" (count), "r" (quotient)
		: "lo", GCC_REG_ACCUM);

	/*
	 * Due to possible jiffies inconsistencies, we need to check
	 * the result so that we'll get a timer that is monotonic.
	 */
	if (res >= USECS_PER_JIFFY)
		res = USECS_PER_JIFFY - 1;

	return res;
}

static unsigned long calibrate_div64_gettimeoffset(void)
{
	u32 count;
	unsigned long res, tmp;
	unsigned long quotient;

	tmp = jiffies;

	quotient = cached_quotient;

	if (last_jiffies != tmp) {
		last_jiffies = tmp;
		if (last_jiffies) {
			unsigned long r0;
			__asm__(".set	push\n\t"
				".set	mips3\n\t"
				"lwu	%0,%3\n\t"
				"dsll32	%1,%2,0\n\t"
				"or	%1,%1,%0\n\t"
				"ddivu	$0,%1,%4\n\t"
				"mflo	%1\n\t"
				"dsll32	%0,%5,0\n\t"
				"or	%0,%0,%6\n\t"
				"ddivu	$0,%0,%1\n\t"
				"mflo	%0\n\t"
				".set	pop"
				: "=&r" (quotient), "=&r" (r0)
				: "r" (timerhi), "m" (timerlo),
				  "r" (tmp), "r" (USECS_PER_JIFFY),
				  "r" (USECS_PER_JIFFY_FRAC)
				: "hi", "lo", GCC_REG_ACCUM);
			cached_quotient = quotient;
		}
	}

	/* Get last timer tick in absolute kernel time */
	count = mips_hpt_read();

	/* .. relative to previous jiffy (32 bits is enough) */
	count -= timerlo;

	__asm__("multu	%1,%2"
		: "=h" (res)
		: "r" (count), "r" (quotient)
		: "lo", GCC_REG_ACCUM);

	/*
	 * Due to possible jiffies inconsistencies, we need to check
	 * the result so that we'll get a timer that is monotonic.
	 */
	if (res >= USECS_PER_JIFFY)
		res = USECS_PER_JIFFY - 1;

	return res;
}


/* last time when xtime and rtc are sync'ed up */
static long last_rtc_update;

/*
 * local_timer_interrupt() does profiling and process accounting
 * on a per-CPU basis.
 *
 * In UP mode, it is invoked from the (global) timer_interrupt.
 *
 * In SMP mode, it might invoked by per-CPU timer interrupt, or
 * a broadcasted inter-processor interrupt which itself is triggered
 * by the global timer interrupt.
 */