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 int rtc_hctosys_ret = -ENODEV;
  26
  27 static int __init rtc_hctosys(void)
  28 {
  29         int err = -ENODEV;
  30         struct rtc_time tm;
  31         struct timespec tv = {
  32                 .tv_nsec = NSEC_PER_SEC >> 1,
  33         };
  34         struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
  35
  36         if (rtc == NULL) {
  37                 pr_err("%s: unable to open rtc device (%s)\n",
  38                         __FILE__, CONFIG_RTC_HCTOSYS_DEVICE);
  39                 goto err_open;
  40         }
  41
  42         err = rtc_read_time(rtc, &tm);
  43         if (err) {
  44                 dev_err(rtc->dev.parent,
  45                         "hctosys: unable to read the hardware clock\n");
  46                 goto err_read;
  47
  48         }
  49
  50         err = rtc_valid_tm(&tm);
  51         if (err) {
  52                 dev_err(rtc->dev.parent,
  53                         "hctosys: invalid date/time\n");
  54                 goto err_invalid;
  55         }
  56
  57         rtc_tm_to_time(&tm, &tv.tv_sec);
  58
  59         do_settimeofday(&tv);
  60
  61         dev_info(rtc->dev.parent,
  62                 "setting system clock to "
  63                 "%d-%02d-%02d %02d:%02d:%02d UTC (%u)\n",
  64                 tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
  65                 tm.tm_hour, tm.tm_min, tm.tm_sec,
  66                 (unsigned int) tv.tv_sec);
  67
  68 err_invalid:
  69 err_read:
  70         rtc_class_close(rtc);
  71
  72 err_open:
  73         rtc_hctosys_ret = err;
  74
  75         return err;
  76 }
  77
  78 late_initcall(rtc_hctosys);