[coreboot-gerrit] Change in coreboot[master]: drivers/pc80/rtc: Make use of alt-century byte configurable

[Nico Huber (Code Review)]

Nico Huber has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/56214 )

Change subject: drivers/pc80/rtc: Make use of alt-century byte configurable
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drivers/pc80/rtc: Make use of alt-century byte configurable

This legacy alt-century byte sits amidst CMOS and conflicts many option
tables. It usually has no meaning to the hardware and needs to be main-
tained manually. Let's disable its usage by default if the CMOS option
table is enabled.

Change-Id: Ifba3d77120c2474393ac5e64faac1baeeb58c893
Signed-off-by: Nico Huber 
---
M src/drivers/pc80/rtc/Kconfig
M src/drivers/pc80/rtc/mc146818rtc.c
2 files changed, 16 insertions(+), 7 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/14/56214/1

diff --git a/src/drivers/pc80/rtc/Kconfig b/src/drivers/pc80/rtc/Kconfig
index 350863e..7958682 100644
--- a/src/drivers/pc80/rtc/Kconfig
+++ b/src/drivers/pc80/rtc/Kconfig
@@ -2,3 +2,10 @@
    bool
    default y if ARCH_X86
    depends on PC80_SYSTEM
+
+config USE_PC_CMOS_ALTCENTURY
+	bool "Use legacy-BIOS alt-century byte in CMOS"
+	default y if !USE_OPTION_TABLE
+	depends on DRIVERS_MC146818
+	help
+	  May be useful for legacy OSs that assume its presence.
diff --git a/src/drivers/pc80/rtc/mc146818rtc.c b/src/drivers/pc80/rtc/mc146818rtc.c
index 42671a9..e0c2400 100644
--- a/src/drivers/pc80/rtc/mc146818rtc.c
+++ b/src/drivers/pc80/rtc/mc146818rtc.c
@@ -191,11 +191,11 @@
  */
 void cmos_check_update_date(void)
 {
-	u8 year, century;
+	u8 year, century = 0;

-	/* Assume hardware always supports RTC_CLK_ALTCENTURY. */
    wait_uip();
-	century = cmos_read(RTC_CLK_ALTCENTURY);
+	if (CONFIG(USE_PC_CMOS_ALTCENTURY))
+		century = cmos_read(RTC_CLK_ALTCENTURY);
    year = cmos_read(RTC_CLK_YEAR);

/*
@@ -215,8 +215,8 @@
    cmos_write(bin2bcd(time->mday), RTC_CLK_DAYOFMONTH);
    cmos_write(bin2bcd(time->mon), RTC_CLK_MONTH);
    cmos_write(bin2bcd(time->year % 100), RTC_CLK_YEAR);
-	/* Same assumption as above: We always have RTC_CLK_ALTCENTURY */
-	cmos_write(bin2bcd(time->year / 100), RTC_CLK_ALTCENTURY);
+	if (CONFIG(USE_PC_CMOS_ALTCENTURY))
+		cmos_write(bin2bcd(time->year / 100), RTC_CLK_ALTCENTURY);
    cmos_write(bin2bcd(time->wday + 1), RTC_CLK_DAYOFWEEK);
    return 0;
 }
@@ -230,8 +230,10 @@
    time->mday = bcd2bin(cmos_read(RTC_CLK_DAYOFMONTH));
    time->mon = bcd2bin(cmos_read(RTC_CLK_MONTH));
    time->year = bcd2bin(cmos_read(RTC_CLK_YEAR));
-	/* Same assumption as above: We always have RTC_CLK_ALTCENTURY */
-	time->year += bcd2bin(cmos_read(RTC_CLK_ALTCENTURY)) * 100;
+	if (CONFIG(USE_PC_CMOS_ALTCENTURY))
+		time->year += bcd2bin(cmos_read(RTC_CLK_ALTCENTURY)) * 100;
+	else if (time->year <= 69)
+		time->year += 100;
    time->wday = bcd2bin(cmos_read(RTC_CLK_DAYOFWEEK)) - 1;
    return 0;
 }