linux/drivers/rtc/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 <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
  25int rtc_hctosys_ret = -ENODEV;
  26
  27static 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
  68err_invalid:
  69err_read:
  70        rtc_class_close(rtc);
  71
  72err_open:
  73        rtc_hctosys_ret = err;
  74
  75        return err;
  76}
  77
  78late_initcall(rtc_hctosys);
  79
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