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