1// SPDX-License-Identifier: GPL-2.0
2/*
3 * rtc and date/time utility functions
4 *
5 * Copyright (C) 2005-06 Tower Technologies
6 * Author: Alessandro Zummo <a.zummo@towertech.it>
7 *
8 * U-Boot rtc_time differs from Linux rtc_time:
9 * - The year field takes the actual value, not year - 1900.
10 * - January is month 1.
11 */
12
13#include <rtc.h>
14#include <linux/math64.h>
15
16static const unsigned char rtc_days_in_month[] = {
17	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
18};
19
20#define LEAPS_THRU_END_OF(y) ((y) / 4 - (y) / 100 + (y) / 400)
21
22/*
23 * The number of days in the month.
24 */
25int rtc_month_days(unsigned int month, unsigned int year)
26{
27	return rtc_days_in_month[month] + (is_leap_year(year) && month == 1);
28}
29
30/*
31 * rtc_to_tm - Converts u64 to rtc_time.
32 * Convert seconds since 01-01-1970 00:00:00 to Gregorian date.
33 *
34 * This function is copied from rtc_time64_to_tm() in the Linux kernel.
35 * But in U-Boot January is month 1 and we do not subtract 1900 from the year.
36 */
37void rtc_to_tm(u64 time, struct rtc_time *tm)
38{
39	unsigned int month, year, secs;
40	int days;
41
42	days = div_u64_rem(time, 86400, &secs);
43
44	/* day of the week, 1970-01-01 was a Thursday */
45	tm->tm_wday = (days + 4) % 7;
46
47	year = 1970 + days / 365;
48	days -= (year - 1970) * 365
49		+ LEAPS_THRU_END_OF(year - 1)
50		- LEAPS_THRU_END_OF(1970 - 1);
51	while (days < 0) {
52		year -= 1;
53		days += 365 + is_leap_year(year);
54	}
55	tm->tm_year = year; /* Not year - 1900 */
56	tm->tm_yday = days + 1;
57
58	for (month = 0; month < 11; month++) {
59		int newdays;
60
61		newdays = days - rtc_month_days(month, year);
62		if (newdays < 0)
63			break;
64		days = newdays;
65	}
66	tm->tm_mon = month + 1; /* January = 1 */
67	tm->tm_mday = days + 1;
68
69	tm->tm_hour = secs / 3600;
70	secs -= tm->tm_hour * 3600;
71	tm->tm_min = secs / 60;
72	tm->tm_sec = secs - tm->tm_min * 60;
73
74	/* Zero unused fields */
75	tm->tm_isdst = 0;
76}
77