lib: Add real-time-clock functions

Add functions to convert between seconds and a struct rtc_time. Also
add a function that can display the time on the console.

BUG=chrome-os-partner:52220
BRANCH=none
TEST=(partial) with future commits and after setting RTC on the EC:
boot on gru into linux shell, check firmware log:

localhost ~ # grep Date: /sys/firmware/log
Date: 2016-06-20 (Monday)  Time: 18:01:44

Then reboot ~10 seconds and check again:

localhost ~ # grep Date: /sys/firmware/log
Date: 2016-06-20 (Monday)  Time: 18:01:54

Change-Id: Id148ccb7a18a05865b903307358666ff6c7b4a3d
Signed-off-by: Martin Roth <martinroth@chromium.org>
Original-Commit-Id: 3b02dbcd7d9023ce0acabebcf904e70007428d27
Original-Change-Id: I344c385e2e4cb995d3a374025c205f01c38b660d
Original-Signed-off-by: Simon Glass <sjg@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/351782
Original-Commit-Ready: Vadim Bendebury <vbendeb@chromium.org>
Original-Tested-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://review.coreboot.org/15301
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/rtc.h

@@ -27,7 +27,13 @@ struct rtc_time
 	int wday;
 };
 
+/* Implemented by the RTC driver (there can be only one) */
 int rtc_set(const struct rtc_time *time);
 int rtc_get(struct rtc_time *time);
 
+/* Common functions */
+int rtc_to_tm(int tim, struct rtc_time *tm);
+unsigned long rtc_mktime(const struct rtc_time *tm);
+void rtc_display(const struct rtc_time *tm);
+
 #endif /* _RTC_H_ */

src/lib/Makefile.inc

@@ -79,6 +79,7 @@ ramstage-$(CONFIG_PRIMITIVE_MEMTEST) += primitive_memtest.c
 romstage-$(CONFIG_CACHE_AS_RAM) += ramtest.c
 romstage-$(CONFIG_GENERIC_GPIO_LIB) += gpio.c
 romstage-y += stack.c
+ramstage-y += rtc.c
 
 ifeq ($(CONFIG_EARLY_CBMEM_INIT),y)
 romstage-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c

src/lib/rtc.c

@@ -0,0 +1,154 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * (C) Copyright 2001 Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * From U-Boot 2016.05
+ */
+
+#include <console/console.h>
+#include <rtc.h>
+
+#define FEBRUARY		2
+#define STARTOFTIME		1970
+#define SECDAY			86400L
+#define SECYR			(SECDAY * 365)
+#define LEAP_YEAR(year)		((year) % 4 == 0)
+#define DAYS_IN_YEAR(a)		(LEAP_YEAR(a) ? 366 : 365)
+#define DAYS_IN_MONTH(a)	(month_days[(a) - 1])
+
+static const int month_offset[] = {
+	0,  31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
+};
+
+static const char * const weekdays[] = {
+	"Sun",  "Mon",  "Tues",  "Wednes",  "Thurs",  "Fri",  "Satur",
+};
+
+static int leaps_to_year(int year)
+{
+	return year / 4 - year / 100 + year / 400;
+}
+
+/* This only works for the Gregorian calendar after Jan 1 1971. */
+static int rtc_calc_weekday(struct rtc_time *tm)
+{
+	int leaps_to_date;
+	int day;
+
+	if (tm->year < 1971)
+		return -1;
+
+	day = 4; /* Jan 1 1970 was a Thursday. */
+
+	/* Number of leap corrections to apply up to end of last year */
+	leaps_to_date = leaps_to_year(tm->year - 1) - leaps_to_year(1970);
+
+	/*
+	 * This year is a leap year if it is divisible by 4 except when it is
+	 * divisible by 100 unless it is divisible by 400
+	 *
+	 * e.g. 1904 was a leap year,  1900 was not,  1996 is, and 2000 is.
+	 */
+	if ((tm->year % 4) &&
+	    ((tm->year % 100 != 0) || (tm->year % 400 == 0)) &&
+	    (tm->mon > 2)) {
+		/* We are past Feb. 29 in a leap year */
+		day++;
+	}
+
+	day += (tm->year - 1970) * 365 + leaps_to_date +
+		month_offset[tm->mon-1] + tm->mday;
+	tm->wday = day % 7;
+
+	return 0;
+}
+
+int rtc_to_tm(int tim, struct rtc_time *tm)
+{
+	int month_days[12] = {
+		31,  28,  31,  30,  31,  30,  31,  31,  30,  31,  30,  31
+	};
+	register int i;
+	register long hms, day;
+
+	day = tim / SECDAY;
+	hms = tim % SECDAY;
+
+	/* Hours, minutes, seconds are easy */
+	tm->hour = hms / 3600;
+	tm->min = (hms % 3600) / 60;
+	tm->sec = (hms % 3600) % 60;
+
+	/* Number of years in days */
+	for (i = STARTOFTIME; day >= DAYS_IN_YEAR(i); i++)
+		day -= DAYS_IN_YEAR(i);
+	tm->year = i;
+
+	/* Number of months in days left */
+	if (LEAP_YEAR(tm->year))
+		DAYS_IN_MONTH(FEBRUARY) = 29;
+	for (i = 1; day >= DAYS_IN_MONTH(i); i++)
+		day -= DAYS_IN_MONTH(i);
+	DAYS_IN_MONTH(FEBRUARY) = 28;
+	tm->mon = i;
+
+	/* Days are what is left over (+1) from all that */
+	tm->mday = day + 1;
+
+	/* Determine the day of week */
+	return rtc_calc_weekday(tm);
+}
+
+/*
+ * Converts Gregorian date to seconds since 1970-01-01 00:00:00.
+ * Assumes input in normal date format,  i.e. 1980-12-31 23:59:59
+ * => year=1980,  mon=12,  day=31,  hour=23,  min=59,  sec=59.
+ *
+ * [For the Julian calendar (which was used in Russia before 1917,
+ * Britain & colonies before 1752,  anywhere else before 1582,
+ * and is still in use by some communities) leave out the
+ * -year / 100 + year / 400 terms,  and add 10.]
+ *
+ * This algorithm was first published by Gauss (I think).
+ *
+ * WARNING: this function will overflow on 2106-02-07 06:28:16 on
+ * machines where long is 32-bit! (However, as time_t is signed, we
+ * will already get problems at other places on 2038-01-19 03:14:08)
+ */
+unsigned long rtc_mktime(const struct rtc_time *tm)
+{
+	int mon = tm->mon;
+	int year = tm->year;
+	int days,  hours;
+
+	mon -= 2;
+	if (0 >= (int)mon) {	/* 1..12 -> 11, 12, 1..10 */
+		mon += 12;	/* Puts Feb last since it has leap day */
+		year -= 1;
+	}
+
+	days = (unsigned long)(year / 4 - year / 100 + year / 400 +
+			367 * mon / 12 + tm->mday) +
+			year * 365 - 719499;
+	hours = days * 24 + tm->hour;
+	return (hours * 60 + tm->min) * 60 + tm->sec;
+}
+
+void rtc_display(const struct rtc_time *tm)
+{
+	printk(BIOS_INFO,  "Date: %4d-%02d-%02d (%sday)  Time: %2d:%02d:%02d\n",
+	       tm->year,  tm->mon,  tm->mday,
+	       (tm->wday < 0 || tm->wday > 6) ? "unknown " : weekdays[tm->wday],
+	       tm->hour,  tm->min,  tm->sec);
+}