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#if BITS_PER_LONG == 32
53	if (tv64.tv_sec > INT_MAX)
54		goto err_read;
55#endif
56
57	err = do_settimeofday64(&tv64);
58
59	dev_info(rtc->dev.parent,
60		"setting system clock to "
61		"%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n",
62		tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
63		tm.tm_hour, tm.tm_min, tm.tm_sec,
64		(long long) tv64.tv_sec);
65
66err_read:
67	rtc_class_close(rtc);
68
69err_open:
70	rtc_hctosys_ret = err;
71
72	return err;
73}
74
75late_initcall(rtc_hctosys);