time.c

来自「LINUX 2.6.17.4的源码」· C语言 代码 · 共 1,200 行 · 第 1/3 页

	 * is cleared.  Tools like clock/hwclock either copy the RTC
	 * to the system time, in which case there is no point in writing
	 * to the RTC again, or write to the RTC but then they don't call
	 * settimeofday to perform this operation.
	 */
#ifdef CONFIG_PPC_ISERIES
	if (first_settimeofday) {
		iSeries_tb_recal();
		first_settimeofday = 0;
	}
#endif

	/* Make userspace gettimeofday spin until we're done. */
	++vdso_data->tb_update_count;
	smp_mb();

	/*
	 * Subtract off the number of nanoseconds since the
	 * beginning of the last tick.
	 * Note that since we don't increment jiffies_64 anywhere other
	 * than in do_timer (since we don't have a lost tick problem),
	 * wall_jiffies will always be the same as jiffies,
	 * and therefore the (jiffies - wall_jiffies) computation
	 * has been removed.
	 */
	tb_delta = tb_ticks_since(tb_last_stamp);
	tb_delta = mulhdu(tb_delta, do_gtod.varp->tb_to_xs); /* in xsec */
	new_nsec -= SCALE_XSEC(tb_delta, 1000000000);

	wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - new_sec);
	wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - new_nsec);

 	set_normalized_timespec(&xtime, new_sec, new_nsec);
	set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);

	/* In case of a large backwards jump in time with NTP, we want the 
	 * clock to be updated as soon as the PLL is again in lock.
	 */
	last_rtc_update = new_sec - 658;

	ntp_clear();

	new_xsec = xtime.tv_nsec;
	if (new_xsec != 0) {
		new_xsec *= XSEC_PER_SEC;
		do_div(new_xsec, NSEC_PER_SEC);
	}
	new_xsec += (u64)xtime.tv_sec * XSEC_PER_SEC;
	update_gtod(tb_last_jiffy, new_xsec, do_gtod.varp->tb_to_xs);

	vdso_data->tz_minuteswest = sys_tz.tz_minuteswest;
	vdso_data->tz_dsttime = sys_tz.tz_dsttime;

	write_sequnlock_irqrestore(&xtime_lock, flags);
	clock_was_set();
	return 0;
}

EXPORT_SYMBOL(do_settimeofday);

void __init generic_calibrate_decr(void)
{
	struct device_node *cpu;
	unsigned int *fp;
	int node_found;

	/*
	 * The cpu node should have a timebase-frequency property
	 * to tell us the rate at which the decrementer counts.
	 */
	cpu = of_find_node_by_type(NULL, "cpu");

	ppc_tb_freq = DEFAULT_TB_FREQ;		/* hardcoded default */
	node_found = 0;
	if (cpu) {
		fp = (unsigned int *)get_property(cpu, "timebase-frequency",
						  NULL);
		if (fp) {
			node_found = 1;
			ppc_tb_freq = *fp;
		}
	}
	if (!node_found)
		printk(KERN_ERR "WARNING: Estimating decrementer frequency "
				"(not found)\n");

	ppc_proc_freq = DEFAULT_PROC_FREQ;
	node_found = 0;
	if (cpu) {
		fp = (unsigned int *)get_property(cpu, "clock-frequency",
						  NULL);
		if (fp) {
			node_found = 1;
			ppc_proc_freq = *fp;
		}
	}
#ifdef CONFIG_BOOKE
	/* Set the time base to zero */
	mtspr(SPRN_TBWL, 0);
	mtspr(SPRN_TBWU, 0);

	/* Clear any pending timer interrupts */
	mtspr(SPRN_TSR, TSR_ENW | TSR_WIS | TSR_DIS | TSR_FIS);

	/* Enable decrementer interrupt */
	mtspr(SPRN_TCR, TCR_DIE);
#endif
	if (!node_found)
		printk(KERN_ERR "WARNING: Estimating processor frequency "
				"(not found)\n");

	of_node_put(cpu);
}

unsigned long get_boot_time(void)
{
	struct rtc_time tm;

	if (ppc_md.get_boot_time)
		return ppc_md.get_boot_time();
	if (!ppc_md.get_rtc_time)
		return 0;
	ppc_md.get_rtc_time(&tm);
	return mktime(tm.tm_year+1900, tm.tm_mon+1, tm.tm_mday,
		      tm.tm_hour, tm.tm_min, tm.tm_sec);
}

/* This function is only called on the boot processor */
void __init time_init(void)
{
	unsigned long flags;
	unsigned long tm = 0;
	struct div_result res;
	u64 scale, x;
	unsigned shift;

        if (ppc_md.time_init != NULL)
                timezone_offset = ppc_md.time_init();

	if (__USE_RTC()) {
		/* 601 processor: dec counts down by 128 every 128ns */
		ppc_tb_freq = 1000000000;
		tb_last_stamp = get_rtcl();
		tb_last_jiffy = tb_last_stamp;
	} else {
		/* Normal PowerPC with timebase register */
		ppc_md.calibrate_decr();
		printk(KERN_INFO "time_init: decrementer frequency = %lu.%.6lu MHz\n",
		       ppc_tb_freq / 1000000, ppc_tb_freq % 1000000);
		printk(KERN_INFO "time_init: processor frequency   = %lu.%.6lu MHz\n",
		       ppc_proc_freq / 1000000, ppc_proc_freq % 1000000);
		tb_last_stamp = tb_last_jiffy = get_tb();
	}

	tb_ticks_per_jiffy = ppc_tb_freq / HZ;
	tb_ticks_per_sec = ppc_tb_freq;
	tb_ticks_per_usec = ppc_tb_freq / 1000000;
	tb_to_us = mulhwu_scale_factor(ppc_tb_freq, 1000000);
	calc_cputime_factors();

	/*
	 * Calculate the length of each tick in ns.  It will not be
	 * exactly 1e9/HZ unless ppc_tb_freq is divisible by HZ.
	 * We compute 1e9 * tb_ticks_per_jiffy / ppc_tb_freq,
	 * rounded up.
	 */
	x = (u64) NSEC_PER_SEC * tb_ticks_per_jiffy + ppc_tb_freq - 1;
	do_div(x, ppc_tb_freq);
	tick_nsec = x;
	last_tick_len = x << TICKLEN_SCALE;

	/*
	 * Compute ticklen_to_xs, which is a factor which gets multiplied
	 * by (last_tick_len << TICKLEN_SHIFT) to get a tb_to_xs value.
	 * It is computed as:
	 * ticklen_to_xs = 2^N / (tb_ticks_per_jiffy * 1e9)
	 * where N = 64 + 20 - TICKLEN_SCALE - TICKLEN_SHIFT
	 * which turns out to be N = 51 - SHIFT_HZ.
	 * This gives the result as a 0.64 fixed-point fraction.
	 * That value is reduced by an offset amounting to 1 xsec per
	 * 2^31 timebase ticks to avoid problems with time going backwards
	 * by 1 xsec when we do timer_recalc_offset due to losing the
	 * fractional xsec.  That offset is equal to ppc_tb_freq/2^51
	 * since there are 2^20 xsec in a second.
	 */
	div128_by_32((1ULL << 51) - ppc_tb_freq, 0,
		     tb_ticks_per_jiffy << SHIFT_HZ, &res);
	div128_by_32(res.result_high, res.result_low, NSEC_PER_SEC, &res);
	ticklen_to_xs = res.result_low;

	/* Compute tb_to_xs from tick_nsec */
	tb_to_xs = mulhdu(last_tick_len << TICKLEN_SHIFT, ticklen_to_xs);

	/*
	 * Compute scale factor for sched_clock.
	 * The calibrate_decr() function has set tb_ticks_per_sec,
	 * which is the timebase frequency.
	 * We compute 1e9 * 2^64 / tb_ticks_per_sec and interpret
	 * the 128-bit result as a 64.64 fixed-point number.
	 * We then shift that number right until it is less than 1.0,
	 * giving us the scale factor and shift count to use in
	 * sched_clock().
	 */
	div128_by_32(1000000000, 0, tb_ticks_per_sec, &res);
	scale = res.result_low;
	for (shift = 0; res.result_high != 0; ++shift) {
		scale = (scale >> 1) | (res.result_high << 63);
		res.result_high >>= 1;
	}
	tb_to_ns_scale = scale;
	tb_to_ns_shift = shift;

#ifdef CONFIG_PPC_ISERIES
	if (!piranha_simulator)
#endif
		tm = get_boot_time();

	write_seqlock_irqsave(&xtime_lock, flags);

	/* If platform provided a timezone (pmac), we correct the time */
        if (timezone_offset) {
		sys_tz.tz_minuteswest = -timezone_offset / 60;
		sys_tz.tz_dsttime = 0;
		tm -= timezone_offset;
        }

	xtime.tv_sec = tm;
	xtime.tv_nsec = 0;
	do_gtod.varp = &do_gtod.vars[0];
	do_gtod.var_idx = 0;
	do_gtod.varp->tb_orig_stamp = tb_last_jiffy;
	__get_cpu_var(last_jiffy) = tb_last_stamp;
	do_gtod.varp->stamp_xsec = (u64) xtime.tv_sec * XSEC_PER_SEC;
	do_gtod.tb_ticks_per_sec = tb_ticks_per_sec;
	do_gtod.varp->tb_to_xs = tb_to_xs;
	do_gtod.tb_to_us = tb_to_us;

	vdso_data->tb_orig_stamp = tb_last_jiffy;
	vdso_data->tb_update_count = 0;
	vdso_data->tb_ticks_per_sec = tb_ticks_per_sec;
	vdso_data->stamp_xsec = (u64) xtime.tv_sec * XSEC_PER_SEC;
	vdso_data->tb_to_xs = tb_to_xs;

	time_freq = 0;

	last_rtc_update = xtime.tv_sec;
	set_normalized_timespec(&wall_to_monotonic,
	                        -xtime.tv_sec, -xtime.tv_nsec);
	write_sequnlock_irqrestore(&xtime_lock, flags);

	/* Not exact, but the timer interrupt takes care of this */
	set_dec(tb_ticks_per_jiffy);
}


#define FEBRUARY	2
#define	STARTOFTIME	1970
#define SECDAY		86400L
#define SECYR		(SECDAY * 365)
#define	leapyear(year)		((year) % 4 == 0 && \
				 ((year) % 100 != 0 || (year) % 400 == 0))
#define	days_in_year(a) 	(leapyear(a) ? 366 : 365)
#define	days_in_month(a) 	(month_days[(a) - 1])

static int month_days[12] = {
	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};

/*
 * This only works for the Gregorian calendar - i.e. after 1752 (in the UK)
 */
void GregorianDay(struct rtc_time * tm)
{
	int leapsToDate;
	int lastYear;
	int day;
	int MonthOffset[] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };

	lastYear = tm->tm_year - 1;

	/*
	 * Number of leap corrections to apply up to end of last year
	 */
	leapsToDate = lastYear / 4 - lastYear / 100 + lastYear / 400;

	/*
	 * This year is a leap year if it is divisible by 4 except when it is
	 * divisible by 100 unless it is divisible by 400
	 *
	 * e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 was
	 */
	day = tm->tm_mon > 2 && leapyear(tm->tm_year);

	day += lastYear*365 + leapsToDate + MonthOffset[tm->tm_mon-1] +
		   tm->tm_mday;

	tm->tm_wday = day % 7;
}

void to_tm(int tim, struct rtc_time * tm)
{
	register int    i;
	register long   hms, day;

	day = tim / SECDAY;
	hms = tim % SECDAY;

	/* Hours, minutes, seconds are easy */
	tm->tm_hour = hms / 3600;
	tm->tm_min = (hms % 3600) / 60;
	tm->tm_sec = (hms % 3600) % 60;

	/* Number of years in days */
	for (i = STARTOFTIME; day >= days_in_year(i); i++)
		day -= days_in_year(i);
	tm->tm_year = i;

	/* Number of months in days left */
	if (leapyear(tm->tm_year))
		days_in_month(FEBRUARY) = 29;
	for (i = 1; day >= days_in_month(i); i++)
		day -= days_in_month(i);
	days_in_month(FEBRUARY) = 28;
	tm->tm_mon = i;

	/* Days are what is left over (+1) from all that. */
	tm->tm_mday = day + 1;

	/*
	 * Determine the day of week
	 */
	GregorianDay(tm);
}

/* Auxiliary function to compute scaling factors */
/* Actually the choice of a timebase running at 1/4 the of the bus
 * frequency giving resolution of a few tens of nanoseconds is quite nice.
 * It makes this computation very precise (27-28 bits typically) which
 * is optimistic considering the stability of most processor clock
 * oscillators and the precision with which the timebase frequency
 * is measured but does not harm.
 */
unsigned mulhwu_scale_factor(unsigned inscale, unsigned outscale)
{
        unsigned mlt=0, tmp, err;
        /* No concern for performance, it's done once: use a stupid
         * but safe and compact method to find the multiplier.
         */
  
        for (tmp = 1U<<31; tmp != 0; tmp >>= 1) {
                if (mulhwu(inscale, mlt|tmp) < outscale)
			mlt |= tmp;
        }
  
        /* We might still be off by 1 for the best approximation.
         * A side effect of this is that if outscale is too large
         * the returned value will be zero.
         * Many corner cases have been checked and seem to work,
         * some might have been forgotten in the test however.
         */
  
        err = inscale * (mlt+1);
        if (err <= inscale/2)
		mlt++;
        return mlt;
}

/*
 * Divide a 128-bit dividend by a 32-bit divisor, leaving a 128 bit
 * result.
 */
void div128_by_32(u64 dividend_high, u64 dividend_low,
		  unsigned divisor, struct div_result *dr)
{
	unsigned long a, b, c, d;
	unsigned long w, x, y, z;
	u64 ra, rb, rc;

	a = dividend_high >> 32;
	b = dividend_high & 0xffffffff;
	c = dividend_low >> 32;
	d = dividend_low & 0xffffffff;

	w = a / divisor;
	ra = ((u64)(a - (w * divisor)) << 32) + b;

	rb = ((u64) do_div(ra, divisor) << 32) + c;
	x = ra;

	rc = ((u64) do_div(rb, divisor) << 32) + d;
	y = rb;

	do_div(rc, divisor);
	z = rc;

	dr->result_high = ((u64)w << 32) + x;
	dr->result_low  = ((u64)y << 32) + z;

}