linux-kernel - [PATCH] iio: humidity: hdc100x: use i2c_master

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Message-ID: <20160804033253.GA31586@d830.WORKGROUP>
Date:	Wed, 3 Aug 2016 20:33:03 -0700
From:	Alison Schofield <amsfield22@...il.com>
To:	jic23@...nel.org
Cc:	mranostay@...il.com, knaack.h@....de, lars@...afoo.de,
	pmeerw@...erw.net, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] iio: humidity: hdc100x: use i2c_master_recv to read sensor
 data

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.

Signed-off-by: Alison Schofield <amsfield22@...il.com>
Cc: Daniel Baluta <daniel.baluta@...il.com>
---
 drivers/iio/humidity/hdc100x.c | 27 +++++++--------------------
 1 file changed, 7 insertions(+), 20 deletions(-)

diff --git a/drivers/iio/humidity/hdc100x.c b/drivers/iio/humidity/hdc100x.c
index a03832a..643a42d 100644
--- a/drivers/iio/humidity/hdc100x.c
+++ b/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;
+	u8 buf[2];
 
 	/* 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 the 2 byte measurement */
+	ret = i2c_master_recv(data->client, buf, 2);
 	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 (int)(buf[0] << 8 | buf[1]);
 }
 
 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));
-- 
2.1.4