drivers/rtc/hctosys.c

   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
  25 static int __init rtc_hctosys(void)
  26 {
  27         int err;
  28         struct rtc_time tm;
  29         struct class_device *class_dev = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
  30
  31         if (class_dev == 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(class_dev, &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(class_dev->dev,
  50                                 "setting the system clock to "
  51                                 "%d-%02d-%02d %02d:%02d:%02d (%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(class_dev->dev,
  58                                 "hctosys: invalid date/time\n");
  59         }
  60         else
  61                 dev_err(class_dev->dev,
  62                         "hctosys: unable to read the hardware clock\n");
  63
  64         rtc_class_close(class_dev);
  65
  66         return 0;
  67 }
  68
  69 late_initcall(rtc_hctosys);