linux-kernel - [PATCH 1/4] rtc: isl1208: Fix unintended clear of SR bits

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Date:   Tue, 23 Jan 2018 13:17:58 +0100
From:   Michael Grzeschik <m.grzeschik@...gutronix.de>
To:     a.zummo@...ertech.it, alexandre.belloni@...e-electrons.com
Cc:     linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux@...ck-us.net, jdelvare@...e.com,
        kernel@...gutronix.de, Denis.Osterland@...hl.com
Subject: [PATCH 1/4] rtc: isl1208: Fix unintended clear of SR bits

From: Denis Osterland <Denis.Osterland@...hl.com>

After successful
sr = isl1208_i2c_set_regs(client, 0, regs, ISL1208_RTC_SECTION_LEN);
sr will be 0.
As a result
sr = i2c_smbus_write_byte_data(client, ISL1208_REG_SR,
			sr & ~ISL1208_REG_SR_WRTC);
is equal to
sr = i2c_smbus_write_byte_data(client, ISL1208_REG_SR, 0);
which clears all flags in SR.

Add an additional read of SR, to have value of SR in sr again.

Signed-off-by: Denis Osterland <Denis.Osterland@...hl.com>
Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>
---
 drivers/rtc/rtc-isl1208.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/rtc/rtc-isl1208.c b/drivers/rtc/rtc-isl1208.c
index 8dd299c6a1f33..c8b4953482296 100644
--- a/drivers/rtc/rtc-isl1208.c
+++ b/drivers/rtc/rtc-isl1208.c
@@ -459,6 +459,11 @@ isl1208_i2c_set_time(struct i2c_client *client, struct rtc_time const *tm)
 	}
 
 	/* clear WRTC again */
+	sr = isl1208_i2c_get_sr(client);
+	if (sr < 0) {
+		dev_err(&client->dev, "%s: reading SR failed\n", __func__);
+		return sr;
+	}
 	sr = i2c_smbus_write_byte_data(client, ISL1208_REG_SR,
 				       sr & ~ISL1208_REG_SR_WRTC);
 	if (sr < 0) {
-- 
2.11.0