[ 085/127] drivers/rtc/rtc-rs5c348.c: fix hour decoding in 12-hour mode

From: Greg Kroah-Hartman
Date: Fri Sep 28 2012 - 16:48:11 EST


3.0-stable review patch. If anyone has any objections, please let me know.

------------------

From: Atsushi Nemoto <anemo@xxxxxxxxxxxxx>

commit 7dbfb315b2aaef0a115765946bf3026d074c33a7 upstream.

Correct the offset by subtracting 20 from tm_hour before taking the
modulo 12.

[ "Why 20?" I hear you ask. Or at least I did.

Here's the reason why: RS5C348_BIT_PM is 32, and is - stupidly -
included in the RS5C348_HOURS_MASK define. So it's really subtracting
out that bit to get "hour+12". But then because it does things modulo
12, it needs to add the 12 in again afterwards anyway.

This code is confused. It would be much clearer if RS5C348_HOURS_MASK
just didn't include the RS5C348_BIT_PM bit at all, then it wouldn't
need to do the silly subtract either.

Whatever. It's all just math, the end result is the same. - Linus ]

Reported-by: James Nute <newten82@xxxxxxxxx>
Tested-by: James Nute <newten82@xxxxxxxxx>
Signed-off-by: Atsushi Nemoto <anemo@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
drivers/rtc/rtc-rs5c348.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/rtc/rtc-rs5c348.c
+++ b/drivers/rtc/rtc-rs5c348.c
@@ -121,9 +121,12 @@ rs5c348_rtc_read_time(struct device *dev
tm->tm_min = bcd2bin(rxbuf[RS5C348_REG_MINS] & RS5C348_MINS_MASK);
tm->tm_hour = bcd2bin(rxbuf[RS5C348_REG_HOURS] & RS5C348_HOURS_MASK);
if (!pdata->rtc_24h) {
- tm->tm_hour %= 12;
- if (rxbuf[RS5C348_REG_HOURS] & RS5C348_BIT_PM)
+ if (rxbuf[RS5C348_REG_HOURS] & RS5C348_BIT_PM) {
+ tm->tm_hour -= 20;
+ tm->tm_hour %= 12;
tm->tm_hour += 12;
+ } else
+ tm->tm_hour %= 12;
}
tm->tm_wday = bcd2bin(rxbuf[RS5C348_REG_WDAY] & RS5C348_WDAY_MASK);
tm->tm_mday = bcd2bin(rxbuf[RS5C348_REG_DAY] & RS5C348_DAY_MASK);


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