iio: mlx90614: Define magic numbers

Translates the magic constant numbers to named macros and add some
additional comments about their meaning.

The diff is made towards togreg branch as that branch seems to have the
most recent updates of mlx90614 driver (many are yet to be merged).
Signed-off-by: Crt Mori <cmo@melexis.com>
Acked-by: Peter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/temperature/mlx90614.c

@@ -65,6 +65,13 @@
 
 #define MLX90614_AUTOSLEEP_DELAY 5000 /* default autosleep delay */
 
+/* Magic constants */
+#define MLX90614_CONST_OFFSET_DEC -13657 /* decimal part of the Kelvin offset */
+#define MLX90614_CONST_OFFSET_REM 500000 /* remainder of offset (273.15*50) */
+#define MLX90614_CONST_SCALE 20 /* Scale in milliKelvin (0.02 * 1000) */
+#define MLX90614_CONST_RAW_EMISSIVITY_MAX 65535 /* max value for emissivity */
+#define MLX90614_CONST_EMISSIVITY_RESOLUTION 15259 /* 1/65535 ~ 0.000015259 */
+
 struct mlx90614_data {
 	struct i2c_client *client;
 	struct mutex lock; /* for EEPROM access only */
@@ -204,11 +211,11 @@ static int mlx90614_read_raw(struct iio_dev *indio_dev,
 		*val = ret;
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_OFFSET:
-		*val = 13657;
-		*val2 = 500000;
+		*val = MLX90614_CONST_OFFSET_DEC;
+		*val2 = MLX90614_CONST_OFFSET_REM;
 		return IIO_VAL_INT_PLUS_MICRO;
 	case IIO_CHAN_INFO_SCALE:
-		*val = 20;
+		*val = MLX90614_CONST_SCALE;
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_CALIBEMISSIVITY: /* 1/65535 / LSB */
 		mlx90614_power_get(data, false);
@@ -221,12 +228,12 @@ static int mlx90614_read_raw(struct iio_dev *indio_dev,
 		if (ret < 0)
 			return ret;
 
-		if (ret == 65535) {
+		if (ret == MLX90614_CONST_RAW_EMISSIVITY_MAX) {
 			*val = 1;
 			*val2 = 0;
 		} else {
 			*val = 0;
-			*val2 = ret * 15259; /* 1/65535 ~ 0.000015259 */
+			*val2 = ret * MLX90614_CONST_EMISSIVITY_RESOLUTION;
 		}
 		return IIO_VAL_INT_PLUS_NANO;
 	default:
@@ -245,7 +252,8 @@ static int mlx90614_write_raw(struct iio_dev *indio_dev,
 	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 */
+		val = val * MLX90614_CONST_RAW_EMISSIVITY_MAX +
+			val2 / MLX90614_CONST_EMISSIVITY_RESOLUTION;
 
 		mlx90614_power_get(data, false);
 		mutex_lock(&data->lock);