1/*
  2 * This file is subject to the terms and conditions of the GNU General Public
  3 * License.  See the file "COPYING" in the main directory of this archive
  4 * for more details.
  5 *
  6 * Machine dependent access functions for RTC registers.
  7 */
  8#ifndef __ASM_MC146818_TIME_H
  9#define __ASM_MC146818_TIME_H
 10
 11#include <linux/bcd.h>
 12#include <linux/mc146818rtc.h>
 13#include <linux/time.h>
 14
 15/*
 16 * For check timing call set_rtc_mmss() 500ms; used in timer interrupt.
 17 */
 18#define USEC_AFTER	500000
 19#define USEC_BEFORE	500000
 20
 21/*
 22 * In order to set the CMOS clock precisely, set_rtc_mmss has to be
 23 * called 500 ms after the second nowtime has started, because when
 24 * nowtime is written into the registers of the CMOS clock, it will
 25 * jump to the next second precisely 500 ms later. Check the Motorola
 26 * MC146818A or Dallas DS12887 data sheet for details.
 27 *
 28 * BUG: This routine does not handle hour overflow properly; it just
 29 *	sets the minutes. Usually you'll only notice that after reboot!
 30 */
 31static inline int mc146818_set_rtc_mmss(unsigned long nowtime)
 32{
 33	int real_seconds, real_minutes, cmos_minutes;
 34	unsigned char save_control, save_freq_select;
 35	int retval = 0;
 36	unsigned long flags;
 37
 38	spin_lock_irqsave(&rtc_lock, flags);
 39	save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
 40	CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
 41
 42	save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
 43	CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
 44
 45	cmos_minutes = CMOS_READ(RTC_MINUTES);
 46	if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
 47		cmos_minutes = bcd2bin(cmos_minutes);
 48
 49	/*
 50	 * since we're only adjusting minutes and seconds,
 51	 * don't interfere with hour overflow. This avoids
 52	 * messing with unknown time zones but requires your
 53	 * RTC not to be off by more than 15 minutes
 54	 */
 55	real_seconds = nowtime % 60;
 56	real_minutes = nowtime / 60;
 57	if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
 58		real_minutes += 30;		/* correct for half hour time zone */
 59	real_minutes %= 60;
 60
 61	if (abs(real_minutes - cmos_minutes) < 30) {
 62		if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
 63			real_seconds = bin2bcd(real_seconds);
 64			real_minutes = bin2bcd(real_minutes);
 65		}
 66		CMOS_WRITE(real_seconds, RTC_SECONDS);
 67		CMOS_WRITE(real_minutes, RTC_MINUTES);
 68	} else {
 69		printk_once(KERN_NOTICE
 70		       "set_rtc_mmss: can't update from %d to %d\n",
 71		       cmos_minutes, real_minutes);
 72		retval = -1;
 73	}
 74
 75	/* The following flags have to be released exactly in this order,
 76	 * otherwise the DS12887 (popular MC146818A clone with integrated
 77	 * battery and quartz) will not reset the oscillator and will not
 78	 * update precisely 500 ms later. You won't find this mentioned in
 79	 * the Dallas Semiconductor data sheets, but who believes data
 80	 * sheets anyway ...			       -- Markus Kuhn
 81	 */
 82	CMOS_WRITE(save_control, RTC_CONTROL);
 83	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
 84	spin_unlock_irqrestore(&rtc_lock, flags);
 85
 86	return retval;
 87}
 88
 89static inline time64_t mc146818_get_cmos_time(void)
 90{
 91	unsigned int year, mon, day, hour, min, sec;
 92	unsigned long flags;
 93
 94	spin_lock_irqsave(&rtc_lock, flags);
 95
 96	do {
 97		sec = CMOS_READ(RTC_SECONDS);
 98		min = CMOS_READ(RTC_MINUTES);
 99		hour = CMOS_READ(RTC_HOURS);
100		day = CMOS_READ(RTC_DAY_OF_MONTH);
101		mon = CMOS_READ(RTC_MONTH);
102		year = CMOS_READ(RTC_YEAR);
103	} while (sec != CMOS_READ(RTC_SECONDS));
104
105	if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
106		sec = bcd2bin(sec);
107		min = bcd2bin(min);
108		hour = bcd2bin(hour);
109		day = bcd2bin(day);
110		mon = bcd2bin(mon);
111		year = bcd2bin(year);
112	}
113	spin_unlock_irqrestore(&rtc_lock, flags);
114	year = mc146818_decode_year(year);
115
116	return mktime64(year, mon, day, hour, min, sec);
117}
118
119#endif /* __ASM_MC146818_TIME_H */