iio: mlx90614: Add emissivity setting

The mapping from the 16-bit EEPROM value to the decimal 0-1 range is
approximate.  A special case ensures 0xFFFF shows as 1.0 instead of
0.999998565.

Writing to EEPROM requires an explicit erase by writing zero.  In
addition, it takes 20ms for the erase/write to complete.  During this
time no EEPROM register should be accessed.  Therefore, two msleep()s
are added to the write function and a mutex protects against concurrent
access.
Signed-off-by: Vianney le Clément de Saint-Marcq <vianney.leclement@essensium.com>
Cc: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/temperature/mlx90614.c

@@ -12,12 +12,13 @@
  *
  * (7-bit I2C slave address 0x5a, 100KHz bus speed only!)
  *
- * TODO: sleep mode, configuration EEPROM
+ * TODO: sleep mode, filter configuration
  */
 
 #include <linux/err.h>
 #include <linux/i2c.h>
 #include <linux/module.h>
+#include <linux/delay.h>
 
 #include <linux/iio/iio.h>
 
@@ -53,8 +54,47 @@
 
 struct mlx90614_data {
 	struct i2c_client *client;
+	struct mutex lock; /* for EEPROM access only */
 };
 
+/*
+ * Erase an address and write word.
+ * The mutex must be locked before calling.
+ */
+static s32 mlx90614_write_word(const struct i2c_client *client, u8 command,
+			       u16 value)
+{
+	/*
+	 * Note: The mlx90614 requires a PEC on writing but does not send us a
+	 * valid PEC on reading.  Hence, we cannot set I2C_CLIENT_PEC in
+	 * i2c_client.flags.  As a workaround, we use i2c_smbus_xfer here.
+	 */
+	union i2c_smbus_data data;
+	s32 ret;
+
+	dev_dbg(&client->dev, "Writing 0x%x to address 0x%x", value, command);
+
+	data.word = 0x0000; /* erase command */
+	ret = i2c_smbus_xfer(client->adapter, client->addr,
+			     client->flags | I2C_CLIENT_PEC,
+			     I2C_SMBUS_WRITE, command,
+			     I2C_SMBUS_WORD_DATA, &data);
+	if (ret < 0)
+		return ret;
+
+	msleep(MLX90614_TIMING_EEPROM);
+
+	data.word = value; /* actual write */
+	ret = i2c_smbus_xfer(client->adapter, client->addr,
+			     client->flags | I2C_CLIENT_PEC,
+			     I2C_SMBUS_WRITE, command,
+			     I2C_SMBUS_WORD_DATA, &data);
+
+	msleep(MLX90614_TIMING_EEPROM);
+
+	return ret;
+}
+
 static int mlx90614_read_raw(struct iio_dev *indio_dev,
 			    struct iio_chan_spec const *channel, int *val,
 			    int *val2, long mask)
@@ -97,6 +137,61 @@ static int mlx90614_read_raw(struct iio_dev *indio_dev,
 	case IIO_CHAN_INFO_SCALE:
 		*val = 20;
 		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_CALIBEMISSIVITY: /* 1/65535 / LSB */
+		mutex_lock(&data->lock);
+		ret = i2c_smbus_read_word_data(data->client,
+					       MLX90614_EMISSIVITY);
+		mutex_unlock(&data->lock);
+
+		if (ret < 0)
+			return ret;
+
+		if (ret == 65535) {
+			*val = 1;
+			*val2 = 0;
+		} else {
+			*val = 0;
+			*val2 = ret * 15259; /* 1/65535 ~ 0.000015259 */
+		}
+		return IIO_VAL_INT_PLUS_NANO;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int mlx90614_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *channel, int val,
+			     int val2, long mask)
+{
+	struct mlx90614_data *data = iio_priv(indio_dev);
+	s32 ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_CALIBEMISSIVITY: /* 1/65535 / LSB */
+		if (val < 0 || val2 < 0 || val > 1 || (val == 1 && val2 != 0))
+			return -EINVAL;
+		val = val * 65535 + val2 / 15259; /* 1/65535 ~ 0.000015259 */
+
+		mutex_lock(&data->lock);
+		ret = mlx90614_write_word(data->client, MLX90614_EMISSIVITY,
+					  val);
+		mutex_unlock(&data->lock);
+
+		if (ret < 0)
+			return ret;
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int mlx90614_write_raw_get_fmt(struct iio_dev *indio_dev,
+				     const struct iio_chan_spec const *channel,
+				     long mask)
+{
+	switch (mask) {
+	case IIO_CHAN_INFO_CALIBEMISSIVITY:
+		return IIO_VAL_INT_PLUS_NANO;
 	default:
 		return -EINVAL;
 	}
@@ -115,7 +210,8 @@ static const struct iio_chan_spec mlx90614_channels[] = {
 		.type = IIO_TEMP,
 		.modified = 1,
 		.channel2 = IIO_MOD_TEMP_OBJECT,
-		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+		    BIT(IIO_CHAN_INFO_CALIBEMISSIVITY),
 		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) |
 		    BIT(IIO_CHAN_INFO_SCALE),
 	},
@@ -125,7 +221,8 @@ static const struct iio_chan_spec mlx90614_channels[] = {
 		.modified = 1,
 		.channel = 1,
 		.channel2 = IIO_MOD_TEMP_OBJECT,
-		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+		    BIT(IIO_CHAN_INFO_CALIBEMISSIVITY),
 		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) |
 		    BIT(IIO_CHAN_INFO_SCALE),
 	},
@@ -133,6 +230,8 @@ static const struct iio_chan_spec mlx90614_channels[] = {
 
 static const struct iio_info mlx90614_info = {
 	.read_raw = mlx90614_read_raw,
+	.write_raw = mlx90614_write_raw,
+	.write_raw_get_fmt = mlx90614_write_raw_get_fmt,
 	.driver_module = THIS_MODULE,
 };
 
@@ -166,6 +265,7 @@ static int mlx90614_probe(struct i2c_client *client,
 	data = iio_priv(indio_dev);
 	i2c_set_clientdata(client, indio_dev);
 	data->client = client;
+	mutex_init(&data->lock);
 
 	indio_dev->dev.parent = &client->dev;
 	indio_dev->name = id->name;