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 */
120