[mirror_ubuntu-bionic-kernel.git] / drivers / rtc / hctosys.c

/*
 * 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.
*/

#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",
			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;

	}

	tv64.tv_sec = rtc_tm_to_time64(&tm);

#if BITS_PER_LONG == 32
	if (tv64.tv_sec > INT_MAX) {
		err = -ERANGE;
		goto err_read;
	}
#endif

	err = do_settimeofday64(&tv64);

	dev_info(rtc->dev.parent,
		"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);

err_read:
	rtc_class_close(rtc);

err_open:
	rtc_hctosys_ret = err;

	return err;
}

late_initcall(rtc_hctosys);
Commit	Line	Data
0c86edc0 AZ	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
a737e835 JP	12	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
a737e835 JP	13
0c86edc0 AZ	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
	27	static int __init rtc_hctosys(void)
	28	{
d0ab4a4d	29	int err = -ENODEV;
0c86edc0	30	struct rtc_time tm;
a6d6e1c8	31	struct timespec64 tv64 = {
d0ab4a4d UKK	32	.tv_nsec = NSEC_PER_SEC >> 1,
d0ab4a4d UKK	33	};
ab6a2d70	34	struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
0c86edc0	35
ab6a2d70	36	if (rtc == NULL) {
a737e835 JP	37	pr_info("unable to open rtc device (%s)\n",
a737e835 JP	38	CONFIG_RTC_HCTOSYS_DEVICE);
d0ab4a4d	39	goto err_open;
0c86edc0 AZ	40	}
0c86edc0 AZ	41
ab6a2d70	42	err = rtc_read_time(rtc, &tm);
d0ab4a4d UKK	43	if (err) {
	44	dev_err(rtc->dev.parent,
	45	"hctosys: unable to read the hardware clock\n");
	46	goto err_read;
0c86edc0	47
d0ab4a4d	48	}
0c86edc0	49
a6d6e1c8	50	tv64.tv_sec = rtc_tm_to_time64(&tm);
0c86edc0	51
810aba6a	52	#if BITS_PER_LONG == 32
4e53a21b MR	53	if (tv64.tv_sec > INT_MAX) {
4e53a21b MR	54	err = -ERANGE;
810aba6a	55	goto err_read;
4e53a21b	56	}
810aba6a AB	57	#endif
810aba6a AB	58
a6d6e1c8	59	err = do_settimeofday64(&tv64);
0c86edc0	60
d0ab4a4d UKK	61	dev_info(rtc->dev.parent,
d0ab4a4d UKK	62	"setting system clock to "
a6d6e1c8	63	"%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n",
d0ab4a4d UKK	64	tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
d0ab4a4d UKK	65	tm.tm_hour, tm.tm_min, tm.tm_sec,
a6d6e1c8	66	(long long) tv64.tv_sec);
d0ab4a4d	67
d0ab4a4d	68	err_read:
ab6a2d70	69	rtc_class_close(rtc);
0c86edc0	70
d0ab4a4d UKK	71	err_open:
	72	rtc_hctosys_ret = err;
	73
	74	return err;
0c86edc0 AZ	75	}
	76
	77	late_initcall(rtc_hctosys);