include/asm/mc146818-time.h

0001 /*
0002  * This file is subject to the terms and conditions of the GNU General Public
0003  * License.  See the file "COPYING" in the main directory of this archive
0004  * for more details.
0005  *
0006  * Machine dependent access functions for RTC registers.
0007  */
0008 #ifndef __ASM_MC146818_TIME_H
0009 #define __ASM_MC146818_TIME_H
0010
0011 #include <linux/bcd.h>
0012 #include <linux/mc146818rtc.h>
0013 #include <linux/time.h>
0014
0015 /*
0016  * For check timing call set_rtc_mmss() 500ms; used in timer interrupt.
0017  */
0018 #define USEC_AFTER  500000
0019 #define USEC_BEFORE 500000
0020
0021 /*
0022  * In order to set the CMOS clock precisely, set_rtc_mmss has to be
0023  * called 500 ms after the second nowtime has started, because when
0024  * nowtime is written into the registers of the CMOS clock, it will
0025  * jump to the next second precisely 500 ms later. Check the Motorola
0026  * MC146818A or Dallas DS12887 data sheet for details.
0027  *
0028  * BUG: This routine does not handle hour overflow properly; it just
0029  *  sets the minutes. Usually you'll only notice that after reboot!
0030  */
0031 static inline int mc146818_set_rtc_mmss(unsigned long nowtime)
0032 {
0033     int real_seconds, real_minutes, cmos_minutes;
0034     unsigned char save_control, save_freq_select;
0035     int retval = 0;
0036     unsigned long flags;
0037
0038     spin_lock_irqsave(&rtc_lock, flags);
0039     save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
0040     CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
0041
0042     save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
0043     CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
0044
0045     cmos_minutes = CMOS_READ(RTC_MINUTES);
0046     if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
0047         cmos_minutes = bcd2bin(cmos_minutes);
0048
0049     /*
0050      * since we're only adjusting minutes and seconds,
0051      * don't interfere with hour overflow. This avoids
0052      * messing with unknown time zones but requires your
0053      * RTC not to be off by more than 15 minutes
0054      */
0055     real_seconds = nowtime % 60;
0056     real_minutes = nowtime / 60;
0057     if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
0058         real_minutes += 30;     /* correct for half hour time zone */
0059     real_minutes %= 60;
0060
0061     if (abs(real_minutes - cmos_minutes) < 30) {
0062         if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
0063             real_seconds = bin2bcd(real_seconds);
0064             real_minutes = bin2bcd(real_minutes);
0065         }
0066         CMOS_WRITE(real_seconds, RTC_SECONDS);
0067         CMOS_WRITE(real_minutes, RTC_MINUTES);
0068     } else {
0069         printk_once(KERN_NOTICE
0070                "set_rtc_mmss: can't update from %d to %d\n",
0071                cmos_minutes, real_minutes);
0072         retval = -1;
0073     }
0074
0075     /* The following flags have to be released exactly in this order,
0076      * otherwise the DS12887 (popular MC146818A clone with integrated
0077      * battery and quartz) will not reset the oscillator and will not
0078      * update precisely 500 ms later. You won't find this mentioned in
0079      * the Dallas Semiconductor data sheets, but who believes data
0080      * sheets anyway ...                   -- Markus Kuhn
0081      */
0082     CMOS_WRITE(save_control, RTC_CONTROL);
0083     CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
0084     spin_unlock_irqrestore(&rtc_lock, flags);
0085
0086     return retval;
0087 }
0088
0089 static inline time64_t mc146818_get_cmos_time(void)
0090 {
0091     unsigned int year, mon, day, hour, min, sec;
0092     unsigned long flags;
0093
0094     spin_lock_irqsave(&rtc_lock, flags);
0095
0096     do {
0097         sec = CMOS_READ(RTC_SECONDS);
0098         min = CMOS_READ(RTC_MINUTES);
0099         hour = CMOS_READ(RTC_HOURS);
0100         day = CMOS_READ(RTC_DAY_OF_MONTH);
0101         mon = CMOS_READ(RTC_MONTH);
0102         year = CMOS_READ(RTC_YEAR);
0103     } while (sec != CMOS_READ(RTC_SECONDS));
0104
0105     if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
0106         sec = bcd2bin(sec);
0107         min = bcd2bin(min);
0108         hour = bcd2bin(hour);
0109         day = bcd2bin(day);
0110         mon = bcd2bin(mon);
0111         year = bcd2bin(year);
0112     }
0113     spin_unlock_irqrestore(&rtc_lock, flags);
0114     year = mc146818_decode_year(year);
0115
0116     return mktime64(year, mon, day, hour, min, sec);
0117 }
0118
0119 #endif /* __ASM_MC146818_TIME_H */