drivers/rtc/lib.c

Source file repositories/reference/linux-study-clean/drivers/rtc/lib.c

File Facts

System
Linux kernel
Corpus path
drivers/rtc/lib.c
Extension
.c
Size
5864 bytes
Lines
212
Domain
Driver Families
Bucket
drivers/rtc
Inferred role
Driver Families: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

Repeatable hardware-adapter layer. Deep compatibility for every driver is out of scope; this atlas records patterns, probe lifecycles, bus glue, IRQ/DMA usage, and links back to core abstractions.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0
/*
 * rtc and date/time utility functions
 *
 * Copyright (C) 2005-06 Tower Technologies
 * Author: Alessandro Zummo <a.zummo@towertech.it>
 *
 * based on arch/arm/common/rtctime.c and other bits
 *
 * Author: Cassio Neri <cassio.neri@gmail.com> (rtc_time64_to_tm)
 */

#include <linux/export.h>
#include <linux/rtc.h>

static const unsigned char rtc_days_in_month[] = {
	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};

static const unsigned short rtc_ydays[2][13] = {
	/* Normal years */
	{ 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
	/* Leap years */
	{ 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
};

/*
 * The number of days in the month.
 */
int rtc_month_days(unsigned int month, unsigned int year)
{
	return rtc_days_in_month[month] + (is_leap_year(year) && month == 1);
}
EXPORT_SYMBOL(rtc_month_days);

/*
 * The number of days since January 1. (0 to 365)
 */
int rtc_year_days(unsigned int day, unsigned int month, unsigned int year)
{
	return rtc_ydays[is_leap_year(year)][month] + day - 1;
}
EXPORT_SYMBOL(rtc_year_days);

/**
 * rtc_time64_to_tm - converts time64_t to rtc_time.
 *
 * @time:	The number of seconds since 01-01-1970 00:00:00.
 *		Works for values since at least 1900
 * @tm:		Pointer to the struct rtc_time.
 */
void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
{
	int secs;

	u64 u64tmp;
	u32 u32tmp, udays, century, day_of_century, year_of_century, year,
		day_of_year, month, day;
	bool is_Jan_or_Feb, is_leap_year;

	/*
	 * The time represented by `time` is given in seconds since 1970-01-01
	 * (UTC). As the division done below might misbehave for negative
	 * values, we convert it to seconds since 0000-03-01 and then assume it
	 * will be non-negative.
	 * Below we do 4 * udays + 3 which should fit into a 32 bit unsigned
	 * variable. So the latest date this algorithm works for is 1073741823
	 * days after 0000-03-01 which is in the year 2939805.
	 */
	time += (u64)719468 * 86400;

	udays = div_s64_rem(time, 86400, &secs);

	/*
	 * day of the week, 0000-03-01 was a Wednesday (in the proleptic
	 * Gregorian calendar)
	 */
	tm->tm_wday = (udays + 3) % 7;

	/*
	 * The following algorithm is, basically, Figure 12 of Neri
	 * and Schneider [1]. In a few words: it works on the computational
	 * (fictitious) calendar where the year starts in March, month = 2
	 * (*), and finishes in February, month = 13. This calendar is
	 * mathematically convenient because the day of the year does not
	 * depend on whether the year is leap or not. For instance:
	 *
	 * March 1st		0-th day of the year;
	 * ...
	 * April 1st		31-st day of the year;

Annotation

Implementation Notes