rtc: cmos: ignore bogus century byte

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 <[email protected]>
Cc: Alessandro Zummo <[email protected]>
Cc: Sylvain Chouleur <[email protected]>
Cc: Patrick McDermott <[email protected]>
Cc: [email protected]
Signed-off-by: Eric Wong <[email protected]>
Signed-off-by: Alexandre Belloni <[email protected]>

diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
index 2f1772a358ca50342d4375de3e69f2fba451ceaf..18a6f15e313d8b33ae6ae2905ea6b364e9ede701 100644 (file)
--- 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;
 
        /*