tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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#include <linux/rtc.h>
13
14/* IMPORTANT: the RTC only stores whole seconds. It is arbitrary
15 * whether it stores the most close value or the value with partial
16 * seconds truncated. However, it is important that we use it to store
17 * the truncated value. This is because otherwise it is necessary,
18 * in an rtc sync function, to read both xtime.tv_sec and
19 * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read
20 * of >32bits is not possible. So storing the most close value would
21 * slow down the sync API. So here we have the truncated value and
22 * the best guess is to add 0.5s.
23 */
24
25static int __init rtc_hctosys(void)
26{
27 int err = -ENODEV;
28 struct rtc_time tm;
29 struct timespec64 tv64 = {
30 .tv_nsec = NSEC_PER_SEC >> 1,
31 };
32 struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
33
34 if (rtc == NULL) {
35 pr_err("%s: unable to open rtc device (%s)\n",
36 __FILE__, CONFIG_RTC_HCTOSYS_DEVICE);
37 goto err_open;
38 }
39
40 err = rtc_read_time(rtc, &tm);
41 if (err) {
42 dev_err(rtc->dev.parent,
43 "hctosys: unable to read the hardware clock\n");
44 goto err_read;
45
46 }
47
48 tv64.tv_sec = rtc_tm_to_time64(&tm);
49
50 err = do_settimeofday64(&tv64);
51
52 dev_info(rtc->dev.parent,
53 "setting system clock to "
54 "%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n",
55 tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
56 tm.tm_hour, tm.tm_min, tm.tm_sec,
57 (long long) tv64.tv_sec);
58
59err_read:
60 rtc_class_close(rtc);
61
62err_open:
63 rtc_hctosys_ret = err;
64
65 return err;
66}
67
68late_initcall(rtc_hctosys);