linux-kernel - RE: [PATCH v2 2/2] rtc: bq32k: Fix handling of oscillator failure flag

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Message-ID: <DB4PR06MB2530178BF4DC79773EBC09BD0120@DB4PR06MB253.eurprd06.prod.outlook.com>
Date:	Mon, 15 Aug 2016 07:10:53 +0000
From:	Jan Östlund <jao@....se>
To:	Daniel Romell <danielromell@...il.com>,
	"a.zummo@...ertech.it" <a.zummo@...ertech.it>
CC:	"alexandre.belloni@...e-electrons.com" 
	<alexandre.belloni@...e-electrons.com>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daniel Romell <Daro@....se>, Magnus Olsson <Mago@....se>
Subject: RE: [PATCH v2 2/2] rtc: bq32k: Fix handling of oscillator failure
 flag

Signed-off-by: Jan Östlund <jao@....se>

-----Original Message-----
From: Daniel Romell [mailto:danielromell@...il.com] 
Sent: den 11 augusti 2016 13:32
To: a.zummo@...ertech.it
Cc: alexandre.belloni@...e-electrons.com; rtc-linux@...glegroups.com; linux-kernel@...r.kernel.org; Daniel Romell <Daro@....se>; Jan Östlund <jao@....se>; Magnus Olsson <Mago@....se>
Subject: [PATCH v2 2/2] rtc: bq32k: Fix handling of oscillator failure flag

From: Jan Östlund <jao@....se>

While the oscillator failure flag is set, the RTC registers
should be considered invalid. bq32k_rtc_read_time() now
returns an error instead of an invalid time.

The failure flag is cleared the next time the clock is set.

Signed-off-by: Daniel Romell <daro@....se>
---
 drivers/rtc/rtc-bq32k.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c
index 5a0c137..3977424 100644
--- a/drivers/rtc/rtc-bq32k.c
+++ b/drivers/rtc/rtc-bq32k.c
@@ -93,6 +93,13 @@ static int bq32k_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	if (error)
 		return error;
 
+	/*
+	 * In case of oscillator failure, the register contents should be
+	 * considered invalid. The flag is cleared the next time the RTC is set.
+	 */
+	if (regs.minutes & BQ32K_OF)
+		return -EINVAL;
+
 	tm->tm_sec = bcd2bin(regs.seconds & BQ32K_SECONDS_MASK);
 	tm->tm_min = bcd2bin(regs.minutes & BQ32K_MINUTES_MASK);
 	tm->tm_hour = bcd2bin(regs.cent_hours & BQ32K_HOURS_MASK);
@@ -204,13 +211,10 @@ static int bq32k_probe(struct i2c_client *client,
 
 	/* Check Oscillator Failure flag */
 	error = bq32k_read(dev, &reg, BQ32K_MINUTES, 1);
-	if (!error && (reg & BQ32K_OF)) {
-		dev_warn(dev, "Oscillator Failure. Check RTC battery.\n");
-		reg &= ~BQ32K_OF;
-		error = bq32k_write(dev, &reg, BQ32K_MINUTES, 1);
-	}
 	if (error)
 		return error;
+	if (reg & BQ32K_OF)
+		dev_warn(dev, "Oscillator Failure. Check RTC battery.\n");
 
 	if (client->dev.of_node)
 		trickle_charger_of_init(dev, client->dev.of_node);
-- 
2.7.4