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  */
31 static 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 
89 static 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 */
120