1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * RTC subsystem, initialize system time on startup
4 *
5 * Copyright (C) 2005 Tower Technologies
6 * Author: Alessandro Zummo <a.zummo@towertech.it>
7 */
8
9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10
11 #include <linux/rtc.h>
12
13 /* IMPORTANT: the RTC only stores whole seconds. It is arbitrary
14 * whether it stores the most close value or the value with partial
15 * seconds truncated. However, it is important that we use it to store
16 * the truncated value. This is because otherwise it is necessary,
17 * in an rtc sync function, to read both xtime.tv_sec and
18 * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read
19 * of >32bits is not possible. So storing the most close value would
20 * slow down the sync API. So here we have the truncated value and
21 * the best guess is to add 0.5s.
22 */
23
24 static int __init rtc_hctosys(void)
25 {
26 int err = -ENODEV;
27 struct rtc_time tm;
28 struct timespec64 tv64 = {
29 .tv_nsec = NSEC_PER_SEC >> 1,
30 };
31 struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
32
33 if (!rtc) {
34 pr_info("unable to open rtc device (%s)\n",
35 CONFIG_RTC_HCTOSYS_DEVICE);
36 goto err_open;
37 }
38
39 err = rtc_read_time(rtc, &tm);
40 if (err) {
41 dev_err(rtc->dev.parent,
42 "hctosys: unable to read the hardware clock\n");
43 goto err_read;
44 }
45
46 tv64.tv_sec = rtc_tm_to_time64(&tm);
47
48 #if BITS_PER_LONG == 32
49 if (tv64.tv_sec > INT_MAX) {
50 err = -ERANGE;
51 goto err_read;
52 }
53 #endif
54
55 err = do_settimeofday64(&tv64);
56
57 dev_info(rtc->dev.parent, "setting system clock to %ptR UTC (%lld)\n",
58 &tm, (long long)tv64.tv_sec);
59
60 err_read:
61 rtc_class_close(rtc);
62
63 err_open:
64 rtc_hctosys_ret = err;
65
66 return err;
67 }
68
69 late_initcall(rtc_hctosys);