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
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