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
rtc_hctosys(void)25 static int __init rtc_hctosys(void)
26 {
27 int err;
28 struct rtc_time tm;
29 struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
30
31 if (rtc == NULL) {
32 printk("%s: unable to open rtc device (%s)\n",
33 __FILE__, CONFIG_RTC_HCTOSYS_DEVICE);
34 return -ENODEV;
35 }
36
37 err = rtc_read_time(rtc, &tm);
38 if (err == 0) {
39 err = rtc_valid_tm(&tm);
40 if (err == 0) {
41 struct timespec tv;
42
43 tv.tv_nsec = NSEC_PER_SEC >> 1;
44
45 rtc_tm_to_time(&tm, &tv.tv_sec);
46
47 do_settimeofday(&tv);
48
49 dev_info(rtc->dev.parent,
50 "setting system clock to "
51 "%d-%02d-%02d %02d:%02d:%02d UTC (%u)\n",
52 tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
53 tm.tm_hour, tm.tm_min, tm.tm_sec,
54 (unsigned int) tv.tv_sec);
55 }
56 else
57 dev_err(rtc->dev.parent,
58 "hctosys: invalid date/time\n");
59 }
60 else
61 dev_err(rtc->dev.parent,
62 "hctosys: unable to read the hardware clock\n");
63
64 rtc_class_close(rtc);
65
66 return 0;
67 }
68
69 late_initcall(rtc_hctosys);
70