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
rtc_hctosys(void)27 static 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 err = -ERANGE;
55 goto err_read;
56 }
57 #endif
58
59 err = do_settimeofday64(&tv64);
60
61 dev_info(rtc->dev.parent,
62 "setting system clock to "
63 "%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n",
64 tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
65 tm.tm_hour, tm.tm_min, tm.tm_sec,
66 (long long) tv64.tv_sec);
67
68 err_read:
69 rtc_class_close(rtc);
70
71 err_open:
72 rtc_hctosys_ret = err;
73
74 return err;
75 }
76
77 late_initcall(rtc_hctosys);
78