linux-kernel - [PATCH v2 2/3] RTC/PCF85063: fix time/date reading

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Date:	Tue,  9 Feb 2016 11:57:26 +0100
From:	Juergen Borleis <jbe@...gutronix.de>
To:	rtc-linux@...glegroups.com
Cc:	Alessandro Zummo <a.zummo@...ertech.it>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: [PATCH v2 2/3] RTC/PCF85063: fix time/date reading

Check if the RTC signals an invalid time/date (due to a battery power loss
for example). In this case ignore the time/date until it is really set again.

Signed-off-by: Juergen Borleis <jbe@...gutronix.de>
---
 drivers/rtc/rtc-pcf85063.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/rtc/rtc-pcf85063.c b/drivers/rtc/rtc-pcf85063.c
index 7f9caee..e0343e6 100644
--- a/drivers/rtc/rtc-pcf85063.c
+++ b/drivers/rtc/rtc-pcf85063.c
@@ -22,6 +22,7 @@
 #define PCF85063_REG_CTRL2		0x01
 
 #define PCF85063_REG_SC			0x04 /* datetime */
+#define PCF85063_REG_SC_OS		0x80
 #define PCF85063_REG_MN			0x05
 #define PCF85063_REG_HR			0x06
 #define PCF85063_REG_DM			0x07
@@ -62,6 +63,12 @@ static int pcf85063_get_datetime(struct i2c_client *client, struct rtc_time *tm)
 		return -EIO;
 	}
 
+	/* if the clock has lost its power it makes no sense to use its time */
+	if (regs[0] & PCF85063_REG_SC_OS) {
+		dev_warn(&client->dev, "Power loss detected, invalid time\n");
+		return -EINVAL;
+	}
+
 	tm->tm_sec = bcd2bin(regs[0] & 0x7F);
 	tm->tm_min = bcd2bin(regs[1] & 0x7F);
 	tm->tm_hour = bcd2bin(regs[2] & 0x3F); /* rtc hr 0-23 */
-- 
2.7.0.rc3