RTC: Add a routine to check if the CMOS date is valid

If the CMOS is cleared or someone writes some random date/time
on purpose, the CMOS date register has a invalid date. This will
hurts some OS, like Windows 7, which hangs at MS logo forever.
When we detect that, we need to write a reasonable date in CMOS.

Alexandru Gagniuc:
Hmm, it would be interesting to use the date the coreboot image
was built and set that as the default date. At least until time
travel is invented.

Change-Id: Ic1c7a2d60e711265686441c77bdf7891a7efb42e
Signed-off-by: Zheng Bao <zheng.bao@amd.com>
Signed-off-by: zbao <fishbaozi@gmail.com>
Reviewed-on: http://review.coreboot.org/1389
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/drivers/pc80/mc146818rtc.c

@@ -77,6 +77,20 @@
 # define RTC_VRT 0x80		/* valid RAM and time */
 /**********************************************************************/
 
+static void rtc_update_cmos_date(u8 has_century)
+{
+	/* Now setup a default date of Sat 1 January 2000 */
+	/* TODO: Set the time as building time? Is it reasonable? */
+	cmos_write(0, RTC_CLK_SECOND);
+	cmos_write(0, RTC_CLK_MINUTE);
+	cmos_write(1, RTC_CLK_HOUR);
+	cmos_write(7, RTC_CLK_DAYOFWEEK);
+	cmos_write(1, RTC_CLK_DAYOFMONTH);
+	cmos_write(1, RTC_CLK_MINUTE);
+	cmos_write(0, RTC_CLK_YEAR);
+	if (has_century) cmos_write(0x20, RTC_CLK_ALTCENTURY);
+}
+
 #if CONFIG_USE_OPTION_TABLE
 static int rtc_checksum_valid(int range_start, int range_end, int cks_loc)
 {
@@ -147,14 +161,7 @@ void rtc_init(int invalid)
 		}
 
 		if (cmos_invalid) {
-			/* Now setup a default date of Sat 1 January 2000 */
+			rtc_update_cmos_date(RTC_HAS_NO_ALTCENTURY);
-			cmos_write(0, 0x00); /* seconds */
-			cmos_write(0, 0x02); /* minutes */
-			cmos_write(1, 0x04); /* hours */
-			cmos_write(7, 0x06); /* day of week */
-			cmos_write(1, 0x07); /* day of month */
-			cmos_write(1, 0x08); /* month */
-			cmos_write(0, 0x09); /* year */
 		}
 #endif
 	}
@@ -338,3 +345,23 @@ int set_option(const char *name, void *value)
 	return 0;
 }
 #endif /* CONFIG_USE_OPTION_TABLE */
+
+/*
+ * If the CMOS is cleared, the rtc_reg has the invalid date. That
+ * hurts some OSes. Even if we don't set USE_OPTION_TABLE, we need
+ * to make sure the date is valid.
+ */
+void rtc_check_update_cmos_date(u8 has_century)
+{
+	u8 year, century;
+
+	/* Note: We need to check if the hardware supports RTC_CLK_ALTCENTURY. */
+	century	= has_century ? cmos_read(RTC_CLK_ALTCENTURY) : 0;
+	year	= cmos_read(RTC_CLK_YEAR);
+
+	/* TODO: If century is 0xFF, 100% that the cmos is cleared.
+	 * Other than that, so far rtc_year is the only entry to check if the date is valid. */
+	if (century > 0x99 || year > 0x99) {	/* Invalid date */
+		rtc_update_cmos_date(has_century);
+	}
+}

src/include/pc80/mc146818rtc.h

@@ -87,6 +87,10 @@
 #define RTC_CLK_DAYOFMONTH	7
 #define RTC_CLK_MONTH		8
 #define RTC_CLK_YEAR		9
+#define RTC_CLK_ALTCENTURY	0x32
+
+#define RTC_HAS_ALTCENTURY	1
+#define RTC_HAS_NO_ALTCENTURY	0
 
 /* On PCs, the checksum is built only over bytes 16..45 */
 #define PC_CKS_RANGE_START	16
@@ -136,6 +140,7 @@ static inline void cmos_write32(u8 offset, u32 value)
 
 #if !defined(__ROMCC__)
 void rtc_init(int invalid);
+void rtc_check_update_cmos_date(u8 has_century);
 #if CONFIG_USE_OPTION_TABLE
 int set_option(const char *name, void *val);
 int get_option(void *dest, const char *name);