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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  13
  14#include <linux/rtc.h>
  15
  16/* IMPORTANT: the RTC only stores whole seconds. It is arbitrary
  17 * whether it stores the most close value or the value with partial
  18 * seconds truncated. However, it is important that we use it to store
  19 * the truncated value. This is because otherwise it is necessary,
  20 * in an rtc sync function, to read both xtime.tv_sec and
  21 * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read
  22 * of >32bits is not possible. So storing the most close value would
  23 * slow down the sync API. So here we have the truncated value and
  24 * the best guess is to add 0.5s.
  25 */
  26
  27static int __init rtc_hctosys(void)
  28{
  29        int err = -ENODEV;
  30        struct rtc_time tm;
  31        struct timespec64 tv64 = {
  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_info("unable to open rtc device (%s)\n",
  38                        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        tv64.tv_sec = rtc_tm_to_time64(&tm);
  51
  52        err = do_settimeofday64(&tv64);
  53
  54        dev_info(rtc->dev.parent,
  55                "setting system clock to "
  56                "%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n",
  57                tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
  58                tm.tm_hour, tm.tm_min, tm.tm_sec,
  59                (long long) tv64.tv_sec);
  60
  61err_read:
  62        rtc_class_close(rtc);
  63
  64err_open:
  65        rtc_hctosys_ret = err;
  66
  67        return err;
  68}
  69
  70late_initcall(rtc_hctosys);
  71