1/*
2 * RTC subsystem, initialize system time on startup
3 *
4 * Copyright (C) 2005 Tower Technologies
5 * Author: Alessandro Zummo <a.zummo@towertech.it>
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
10*/
11
12#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
13
14#include <linux/rtc.h>
15
16/* IMPORTANT: the RTC only stores whole seconds. It is arbitrary
17 * whether it stores the most close value or the value with partial
18 * seconds truncated. However, it is important that we use it to store
19 * the truncated value. This is because otherwise it is necessary,
20 * in an rtc sync function, to read both xtime.tv_sec and
21 * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read
22 * of >32bits is not possible. So storing the most close value would
23 * slow down the sync API. So here we have the truncated value and
24 * the best guess is to add 0.5s.
25 */
26
27static int __init rtc_hctosys(void)
28{
29	int err = -ENODEV;
30	struct rtc_time tm;
31	struct timespec64 tv64 = {
32		.tv_nsec = NSEC_PER_SEC >> 1,
33	};
34	struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
35
36	if (rtc == NULL) {
37		pr_info("unable to open rtc device (%s)\n",
38			CONFIG_RTC_HCTOSYS_DEVICE);
39		goto err_open;
40	}
41
42	err = rtc_read_time(rtc, &tm);
43	if (err) {
44		dev_err(rtc->dev.parent,
45			"hctosys: unable to read the hardware clock\n");
46		goto err_read;
47
48	}
49
50	tv64.tv_sec = rtc_tm_to_time64(&tm);
51
52	err = do_settimeofday64(&tv64);
53
54	dev_info(rtc->dev.parent,
55		"setting system clock to "
56		"%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n",
57		tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
58		tm.tm_hour, tm.tm_min, tm.tm_sec,
59		(long long) tv64.tv_sec);
60
61err_read:
62	rtc_class_close(rtc);
63
64err_open:
65	rtc_hctosys_ret = err;
66
67	return err;
68}
69
70late_initcall(rtc_hctosys);
71