LXR linux/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
  25static 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
  69late_initcall(rtc_hctosys);
  70