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
  25static 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,
  63                tm.tm_hour, tm.tm_min, tm.tm_sec,
  64                (unsigned int) tv.tv_sec);
  65
  66err_invalid:
  67err_read:
  68        rtc_class_close(rtc);
  69
  70err_open:
  71        rtc_hctosys_ret = err;
  72
  73        return err;
  74}
  75
  76late_initcall(rtc_hctosys);
  77
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