openwrtv4/target/linux/brcm2708/patches-4.4/0354-rtc-ds1307-ensure-that-any-pending-alarm-is-cleared-.patch

From 82be650e97522260a9694ae56dc3475f40c4240e Mon Sep 17 00:00:00 2001
From: Nicolas Boullis <nboullis@debian.org>
Date: Sun, 10 Apr 2016 13:23:05 +0200
Subject: [PATCH 354/423] rtc: ds1307: ensure that any pending alarm is cleared
 before a new alarm is enabled
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If a previously-set alarm was disabled and then triggered, it may still
be pending when a new alarm is configured.

Then, if the alarm is enabled before the pending alarm is cleared, then
an interrupt is immediately raised.

Unfortunately, when the alarm is cleared and enabled during the same I²C
block write, the chip (at least the DS1339 I have) considers that the
alarm is enabled before it is cleared, and raises an interrupt.

This patch ensures that the pending alarm is cleared before the alarm is
enabled.

Signed-off-by: Nicolas Boullis <nboullis@debian.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
---
 drivers/rtc/rtc-ds1307.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -540,12 +540,8 @@ static int ds1337_set_alarm(struct devic
 	buf[5] = 0;
 	buf[6] = 0;
 
-	/* optionally enable ALARM1 */
+	/* disable alarms */
 	buf[7] = control & ~(DS1337_BIT_A1IE | DS1337_BIT_A2IE);
-	if (t->enabled) {
-		dev_dbg(dev, "alarm IRQ armed\n");
-		buf[7] |= DS1337_BIT_A1IE;	/* only ALARM1 is used */
-	}
 	buf[8] = status & ~(DS1337_BIT_A1I | DS1337_BIT_A2I);
 
 	ret = ds1307->write_block_data(client,
@@ -555,6 +551,13 @@ static int ds1337_set_alarm(struct devic
 		return ret;
 	}
 
+	/* optionally enable ALARM1 */
+	if (t->enabled) {
+		dev_dbg(dev, "alarm IRQ armed\n");
+		buf[7] |= DS1337_BIT_A1IE;	/* only ALARM1 is used */
+		i2c_smbus_write_byte_data(client, DS1337_REG_CONTROL, buf[7]);
+	}
+
 	return 0;
 }