linux/arch/x86/kernel/rtc.c

/*
 * RTC related functions
 */
#include <linux/bcd.h>
#include <linux/mc146818rtc.h>

#include <asm/time.h>

/*
 * In order to set the CMOS clock precisely, set_rtc_mmss has to be
 * called 500 ms after the second nowtime has started, because when
 * nowtime is written into the registers of the CMOS clock, it will
 * jump to the next second precisely 500 ms later. Check the Motorola
 * MC146818A or Dallas DS12887 data sheet for details.
 *
 * BUG: This routine does not handle hour overflow properly; it just
 *      sets the minutes. Usually you'll only notice that after reboot!
 */
int mach_set_rtc_mmss(unsigned long nowtime)
{
	int retval = 0;
	int real_seconds, real_minutes, cmos_minutes;
	unsigned char save_control, save_freq_select;

	save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
	CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);

	save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
	CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);

	cmos_minutes = CMOS_READ(RTC_MINUTES);
	if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
		BCD_TO_BIN(cmos_minutes);

	/*
	 * since we're only adjusting minutes and seconds,
	 * don't interfere with hour overflow. This avoids
	 * messing with unknown time zones but requires your
	 * RTC not to be off by more than 15 minutes
	 */
	real_seconds = nowtime % 60;
	real_minutes = nowtime / 60;
	if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
		real_minutes += 30;		/* correct for half hour time zone */
	real_minutes %= 60;

	if (abs(real_minutes - cmos_minutes) < 30) {
		if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
			BIN_TO_BCD(real_seconds);
			BIN_TO_BCD(real_minutes);
		}
		CMOS_WRITE(real_seconds,RTC_SECONDS);
		CMOS_WRITE(real_minutes,RTC_MINUTES);
	} else {
		printk(KERN_WARNING
		       "set_rtc_mmss: can't update from %d to %d\n",
		       cmos_minutes, real_minutes);
		retval = -1;
	}

	/* The following flags have to be released exactly in this order,
	 * otherwise the DS12887 (popular MC146818A clone with integrated
	 * battery and quartz) will not reset the oscillator and will not
	 * update precisely 500 ms later. You won't find this mentioned in
	 * the Dallas Semiconductor data sheets, but who believes data
	 * sheets anyway ...                           -- Markus Kuhn
	 */
	CMOS_WRITE(save_control, RTC_CONTROL);
	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);

	return retval;
}

unsigned long mach_get_cmos_time(void)
{
	unsigned int year, mon, day, hour, min, sec;

	do {
		sec = CMOS_READ(RTC_SECONDS);
		min = CMOS_READ(RTC_MINUTES);
		hour = CMOS_READ(RTC_HOURS);
		day = CMOS_READ(RTC_DAY_OF_MONTH);
		mon = CMOS_READ(RTC_MONTH);
		year = CMOS_READ(RTC_YEAR);
	} while (sec != CMOS_READ(RTC_SECONDS));

	if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
		BCD_TO_BIN(sec);
		BCD_TO_BIN(min);
		BCD_TO_BIN(hour);
		BCD_TO_BIN(day);
		BCD_TO_BIN(mon);
		BCD_TO_BIN(year);
	}

	year += 1900;
	if (year < 1970)
		year += 100;

	return mktime(year, mon, day, hour, min, sec);
}

DEFINE_SPINLOCK(rtc_lock);
EXPORT_SYMBOL(rtc_lock);

/*
 * This is a special lock that is owned by the CPU and holds the index
 * register we are working with.  It is required for NMI access to the
 * CMOS/RTC registers.  See include/asm-i386/mc146818rtc.h for details.
 */
volatile unsigned long cmos_lock = 0;
EXPORT_SYMBOL(cmos_lock);

/* Routines for accessing the CMOS RAM/RTC. */
unsigned char rtc_cmos_read(unsigned char addr)
{
	unsigned char val;

	lock_cmos_prefix(addr);
	outb_p(addr, RTC_PORT(0));
	val = inb_p(RTC_PORT(1));
	lock_cmos_suffix(addr);
	return val;
}
EXPORT_SYMBOL(rtc_cmos_read);

void rtc_cmos_write(unsigned char val, unsigned char addr)
{
	lock_cmos_prefix(addr);
	outb_p(addr, RTC_PORT(0));
	outb_p(val, RTC_PORT(1));
	lock_cmos_suffix(addr);
}
EXPORT_SYMBOL(rtc_cmos_write);

static int set_rtc_mmss(unsigned long nowtime)
{
	int retval;
	unsigned long flags;

	/* gets recalled with irq locally disabled */
	/* XXX - does irqsave resolve this? -johnstul */
	spin_lock_irqsave(&rtc_lock, flags);
	retval = set_wallclock(nowtime);
	spin_unlock_irqrestore(&rtc_lock, flags);

	return retval;
}

/* not static: needed by APM */
unsigned long read_persistent_clock(void)
{
	unsigned long retval;
	unsigned long flags;

	spin_lock_irqsave(&rtc_lock, flags);
	retval = get_wallclock();
	spin_unlock_irqrestore(&rtc_lock, flags);

	return retval;
}

int update_persistent_clock(struct timespec now)
{
	return set_rtc_mmss(now.tv_sec);
}