iio: humidity: hdc100x: fix sensor data reads of temp and humidity

Replace the i2c_smbus_read_byte commmands used to retrieve the sensor
data with an i2c_master_recv command.

The smbus read byte method fails because the device does not expect a
stop condition after sending the first byte. When we issue the second
read, we are getting the first byte again. Net effect is that of the 14
bits used for the measurement, the 8 most significant bits are correct,
the lower 6 are not.

None of the smbus read protocols follow the pattern this device requires
(S Addr Rd [A] Data [A] Data NA P), hence the switch to an i2c receive
transaction.

Applicable from original introduction of this driver, but will require
backporting due to churn in the code.
Signed-off-by: Alison Schofield <amsfield22@gmail.com>
Cc: Daniel Baluta <daniel.baluta@gmail.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/humidity/hdc100x.c

@@ -142,7 +142,7 @@ static int hdc100x_get_measurement(struct hdc100x_data *data,
 	struct i2c_client *client = data->client;
 	int delay = data->adc_int_us[chan->address];
 	int ret;
-	int val;
+	__be16 val;
 
 	/* start measurement */
 	ret = i2c_smbus_write_byte(client, chan->address);
@@ -154,26 +154,13 @@ static int hdc100x_get_measurement(struct hdc100x_data *data,
 	/* wait for integration time to pass */
 	usleep_range(delay, delay + 1000);
 
-	/*
-	 * i2c_smbus_read_word_data cannot() be used here due to the command
-	 * value not being understood and causes NAKs preventing any reading
-	 * from being accessed.
-	 */
-	ret = i2c_smbus_read_byte(client);
+	/* read measurement */
+	ret = i2c_master_recv(data->client, (char *)&val, sizeof(val));
 	if (ret < 0) {
-		dev_err(&client->dev, "cannot read high byte measurement");
+		dev_err(&client->dev, "cannot read sensor data\n");
 		return ret;
 	}
-	val = ret << 8;
-
-	ret = i2c_smbus_read_byte(client);
-	if (ret < 0) {
-		dev_err(&client->dev, "cannot read low byte measurement");
-		return ret;
-	}
-	val |= ret;
-
-	return val;
+	return be16_to_cpu(val);
 }
 
 static int hdc100x_get_heater_status(struct hdc100x_data *data)
@@ -272,8 +259,8 @@ static int hdc100x_probe(struct i2c_client *client,
 	struct iio_dev *indio_dev;
 	struct hdc100x_data *data;
 
-	if (!i2c_check_functionality(client->adapter,
-				I2C_FUNC_SMBUS_WORD_DATA | I2C_FUNC_SMBUS_BYTE))
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_WORD_DATA |
+				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_I2C))
 		return -EOPNOTSUPP;
 
 	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));