blob: b9ec4a16db1f6b6fd113c5661a28aa0e9153eeaa [file] [log] [blame]
* RTC subsystem, initialize system time on startup
* Copyright (C) 2005 Tower Technologies
* Author: Alessandro Zummo <>
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/rtc.h>
/* IMPORTANT: the RTC only stores whole seconds. It is arbitrary
* whether it stores the most close value or the value with partial
* seconds truncated. However, it is important that we use it to store
* the truncated value. This is because otherwise it is necessary,
* in an rtc sync function, to read both xtime.tv_sec and
* xtime.tv_nsec. On some processors (i.e. ARM), an atomic read
* of >32bits is not possible. So storing the most close value would
* slow down the sync API. So here we have the truncated value and
* the best guess is to add 0.5s.
static int __init rtc_hctosys(void)
int err = -ENODEV;
struct rtc_time tm;
struct timespec64 tv64 = {
.tv_nsec = NSEC_PER_SEC >> 1,
struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
if (rtc == NULL) {
pr_info("unable to open rtc device (%s)\n",
goto err_open;
err = rtc_read_time(rtc, &tm);
if (err) {
"hctosys: unable to read the hardware clock\n");
goto err_read;
tv64.tv_sec = rtc_tm_to_time64(&tm);
#if BITS_PER_LONG == 32
if (tv64.tv_sec > INT_MAX) {
err = -ERANGE;
goto err_read;
err = do_settimeofday64(&tv64);
"setting system clock to "
"%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n",
tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec,
(long long) tv64.tv_sec);
rtc_hctosys_ret = err;
return err;