Linux Kernel  3.7.1
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hctosys.c
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1 /*
2  * RTC subsystem, initialize system time on startup
3  *
4  * Copyright (C) 2005 Tower Technologies
5  * Author: Alessandro Zummo <[email protected]>
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 
25 static int __init rtc_hctosys(void)
26 {
27  int err = -ENODEV;
28  struct rtc_time tm;
29  struct timespec tv = {
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  err = rtc_valid_tm(&tm);
49  if (err) {
50  dev_err(rtc->dev.parent,
51  "hctosys: invalid date/time\n");
52  goto err_invalid;
53  }
54 
55  rtc_tm_to_time(&tm, &tv.tv_sec);
56 
57  err = do_settimeofday(&tv);
58 
59  dev_info(rtc->dev.parent,
60  "setting system clock to "
61  "%d-%02d-%02d %02d:%02d:%02d UTC (%u)\n",
62  tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
64  (unsigned int) tv.tv_sec);
65 
66 err_invalid:
67 err_read:
68  rtc_class_close(rtc);
69 
70 err_open:
72 
73  return err;
74 }
75 
76 late_initcall(rtc_hctosys);