[PATCH 4.9 047/271] rtc: cmos: ignore bogus century byte

[Greg Kroah-Hartman]

From: Eric Wong <e@xxxxxxxxx>

[ Upstream commit 2a4daadd4d3e507138f8937926e6a4df49c6bfdc ]

Older versions of Libreboot and Coreboot had an invalid value
(`3' in my case) in the century byte affecting the GM45 in
the Thinkpad X200.  Not everybody's updated their firmwares,
and Linux <= 4.2 was able to read the RTC without problems,
so workaround this by ignoring invalid values.

Fixes: 3c217e51d8a272b9 ("rtc: cmos: century support")

Cc: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
Cc: Alessandro Zummo <a.zummo@xxxxxxxxxxxx>
Cc: Sylvain Chouleur <sylvain.chouleur@xxxxxxxxx>
Cc: Patrick McDermott <patrick.mcdermott@xxxxxxxxxxxxx>
Cc: linux-rtc@xxxxxxxxxxxxxxx
Signed-off-by: Eric Wong <e@xxxxxxxxx>
Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/rtc/rtc-mc146818-lib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
index 2f1772a358ca5..18a6f15e313d8 100644
--- a/drivers/rtc/rtc-mc146818-lib.c
+++ b/drivers/rtc/rtc-mc146818-lib.c
@@ -82,7 +82,7 @@ unsigned int mc146818_get_time(struct rtc_time *time)
 	time->tm_year += real_year - 72;
 #endif
 
-	if (century)
+	if (century > 20)
 		time->tm_year += (century - 19) * 100;
 
 	/*
-- 
2.20.1