[PATCH] rtc: cmos: Evaluate century appropriate

["Mateusz Jończyk" <mat.jonczyk@o2.pl>]

From: Riwen Lu <luriwen@kylinos.cn>

commit ff164ae39b82ee483b24579c8e22a13a8ce5bd04 upstream.

There's limiting the year to 2069. When setting the rtc year to 2070,
reading it returns 1970. Evaluate century starting from 19 to count the
correct year.

$ sudo date -s 20700106
Mon 06 Jan 2070 12:00:00 AM CST
$ sudo hwclock -w
$ sudo hwclock -r
1970-01-06 12:00:49.604968+08:00

Fixes: 2a4daadd4d3e5071 ("rtc: cmos: ignore bogus century byte")

Signed-off-by: Riwen Lu <luriwen@kylinos.cn>
Acked-by: Eric Wong <e@80x24.org>
Reviewed-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220106084609.1223688-1-luriwen@kylinos.cn
Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl> # preparation for stable
---
 drivers/rtc/rtc-mc146818-lib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Hello,

I have prepared this patch for inclusion into stable. Run-tested on top
of 5.16.7 and 4.9.299, works as intended.

Greetings,
Mateusz

diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
index dcfaf09946ee..2065842f775d 100644
--- a/drivers/rtc/rtc-mc146818-lib.c
+++ b/drivers/rtc/rtc-mc146818-lib.c
@@ -104,7 +104,7 @@ unsigned int mc146818_get_time(struct rtc_time *time)
 	time->tm_year += real_year - 72;
 #endif
 
-	if (century > 20)
+	if (century > 19)
 		time->tm_year += (century - 19) * 100;
 
 	/*
-- 
2.25.1