hctosys.c

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/*
 * RTC subsystem, initialize system time on startup
 *
 * Copyright (C) 2005 Tower Technologies
 * Author: Alessandro Zummo <a.zummo@towertech.it>
 *
 * 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.
*/

#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 timespec tv = {
        .tv_nsec = NSEC_PER_SEC >> 1,
    };
    struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);

    if (rtc == NULL) {
        pr_err("%s: unable to open rtc device (%s)\n",
            __FILE__, CONFIG_RTC_HCTOSYS_DEVICE);
        goto err_open;
    }

    err = rtc_read_time(rtc, &tm);
    if (err) {
        dev_err(rtc->dev.parent,
            "hctosys: unable to read the hardware clock\n");
        goto err_read;

    }

    err = rtc_valid_tm(&tm);
    if (err) {
        dev_err(rtc->dev.parent,
            "hctosys: invalid date/time\n");
        goto err_invalid;
    }

    rtc_tm_to_time(&tm, &tv.tv_sec);

    err = do_settimeofday(&tv);

    dev_info(rtc->dev.parent,
        "setting system clock to "
        "%d-%02d-%02d %02d:%02d:%02d UTC (%u)\n",
        tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
        tm.tm_hour, tm.tm_min, tm.tm_sec,
        (unsigned int) tv.tv_sec);

err_invalid:
err_read:
    rtc_class_close(rtc);

err_open:
    rtc_hctosys_ret = err;

    return err;
}

late_initcall(rtc_hctosys);