Re: [PATCH] iio: mlx90614: Define magic numbers

[Jonathan Cameron <jic23@kernel.org>]

On 20/07/15 20:38, Crt Mori wrote:
> 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>
Applied to the togreg branch of iio.git - initially pushed out as
testing for the autobuilders to play with it.
Should get a pull request out to Greg later in the week,

Jonathan
> ---
>  drivers/iio/temperature/mlx90614.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iio/temperature/mlx90614.c b/drivers/iio/temperature/mlx90614.c
> index cb2e8ad..4590f83 100644
> --- a/drivers/iio/temperature/mlx90614.c
> +++ b/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);
>