FAILED: patch "[PATCH] rtc: rv8803: workaround i2c HW issue" failed to apply to 4.4-stable tree

FAILED: patch "[PATCH] rtc: rv8803: workaround i2c HW issue" failed to apply to 4.4-stable tree

[gregkh]

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 85062c9b990b1dc8bbb8971ee7d3044a999cf25f Mon Sep 17 00:00:00 2001
From: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Date: Mon, 21 Mar 2016 15:58:38 +0100
Subject: [PATCH] rtc: rv8803: workaround i2c HW issue
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The rv8803 has a 60µs window where it will not answer on the i2c bus.
It also means there will be no ack for the communication. Make sure
communication is tried multiple times when this happens (the i2c subsystem
mandates -ENXIO is that case but the number of retries is host specific).
The critical parts are the probe function and the alarm callback so make
sure we handle the failure there.

Cc: stable@vger.kernel.org # v4.4
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

diff --git a/drivers/rtc/rtc-rv8803.c b/drivers/rtc/rtc-rv8803.c
index 8d9f35ceb808..f623038e586e 100644
--- a/drivers/rtc/rtc-rv8803.c
+++ b/drivers/rtc/rtc-rv8803.c
@@ -61,11 +61,14 @@ static irqreturn_t rv8803_handle_irq(int irq, void *dev_id)
 	struct i2c_client *client = dev_id;
 	struct rv8803_data *rv8803 = i2c_get_clientdata(client);
 	unsigned long events = 0;
-	int flags;
+	int flags, try = 0;
 
 	mutex_lock(&rv8803->flags_lock);
 
-	flags = i2c_smbus_read_byte_data(client, RV8803_FLAG);
+	do {
+		flags = i2c_smbus_read_byte_data(client, RV8803_FLAG);
+		try++;
+	} while ((flags == -ENXIO) && (try < 3));
 	if (flags <= 0) {
 		mutex_unlock(&rv8803->flags_lock);
 		return IRQ_NONE;
@@ -424,7 +427,7 @@ static int rv8803_probe(struct i2c_client *client,
 {
 	struct i2c_adapter *adapter = to_i2c_adapter(client->dev.parent);
 	struct rv8803_data *rv8803;
-	int err, flags;
+	int err, flags, try = 0;
 
 	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
 				     I2C_FUNC_SMBUS_I2C_BLOCK)) {
@@ -441,7 +444,16 @@ static int rv8803_probe(struct i2c_client *client,
 	rv8803->client = client;
 	i2c_set_clientdata(client, rv8803);
 
-	flags = i2c_smbus_read_byte_data(client, RV8803_FLAG);
+	/*
+	 * There is a 60µs window where the RTC may not reply on the i2c bus in
+	 * that case, the transfer is not ACKed. In that case, ensure there are
+	 * multiple attempts.
+	 */
+	do {
+		flags = i2c_smbus_read_byte_data(client, RV8803_FLAG);
+		try++;
+	} while ((flags == -ENXIO) && (try < 3));
+
 	if (flags < 0)
 		return flags;
 
@@ -476,8 +488,12 @@ static int rv8803_probe(struct i2c_client *client,
 		return PTR_ERR(rv8803->rtc);
 	}
 
-	err = i2c_smbus_write_byte_data(rv8803->client, RV8803_EXT,
-					RV8803_EXT_WADA);
+	try = 0;
+	do {
+		err = i2c_smbus_write_byte_data(rv8803->client, RV8803_EXT,
+						RV8803_EXT_WADA);
+		try++;
+	} while ((err == -ENXIO) && (try < 3));
 	if (err)
 		return err;