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[PATCH 4.4 121/266] rtc: sh: Fix invalid alarm warning for non-enabled alarm

[ Upstream commit 15d82d22498784966df8e4696174a16b02cc1052 ]

When no alarm has been programmed on RSK-RZA1, an error message is
printed during boot:

    rtc rtc0: invalid alarm value: 2019-03-14T255:255:255

sh_rtc_read_alarm_value() returns 0xff when querying a hardware alarm
field that is not enabled.  __rtc_read_alarm() validates the received
alarm values, and fills in missing fields when needed.
While 0xff is handled fine for the year, month, and day fields, and
corrected as considered being out-of-range, this is not the case for the
hour, minute, and second fields, where -1 is expected for missing

Fix this by returning -1 instead, as this value is handled fine for all

Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
 drivers/rtc/rtc-sh.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-sh.c b/drivers/rtc/rtc-sh.c
index 2b81dd4baf17..104c854d6a8a 100644
--- a/drivers/rtc/rtc-sh.c
+++ b/drivers/rtc/rtc-sh.c
@@ -455,7 +455,7 @@ static int sh_rtc_set_time(struct device *dev, struct rtc_time *tm)
 static inline int sh_rtc_read_alarm_value(struct sh_rtc *rtc, int reg_off)
 	unsigned int byte;
-	int value = 0xff;	/* return 0xff for ignored values */
+	int value = -1;			/* return -1 for ignored values */
 	byte = readb(rtc->regbase + reg_off);
 	if (byte & AR_ENB) {