On Sat, 3 Jul 2021 20:01:31 +0200
Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> The kernel has a helper function for linear interpolation so
> use it. It incidentally makes the code easier to read as well.
>
> Cc: Peter Rosin <peda@xxxxxxxxxx>
> Cc: Chris Lesiak <chris.lesiak@xxxxxxxxx>
> Cc: linux-iio@xxxxxxxxxxxxxxx
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Potential precision problem because the multiplication by 1000 is now done
post division whereas before it was before it?
I'm only eyeballing the code so no idea if it makes a practical difference.
> ---
> drivers/hwmon/ntc_thermistor.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c
> index 8587189c7f15..61bd0e074ec9 100644
> --- a/drivers/hwmon/ntc_thermistor.c
> +++ b/drivers/hwmon/ntc_thermistor.c
> @@ -14,6 +14,7 @@
> #include <linux/err.h>
> #include <linux/of.h>
> #include <linux/of_device.h>
> +#include <linux/fixp-arith.h>
>
> #include <linux/platform_data/ntc_thermistor.h>
>
> @@ -557,10 +558,12 @@ static int get_temp_mc(struct ntc_data *data, unsigned int ohm)
> /* Unable to use linear approximation */
> temp = data->comp[low].temp_c * 1000;
> } else {
> - temp = data->comp[low].temp_c * 1000 +
> - ((data->comp[high].temp_c - data->comp[low].temp_c) *
> - 1000 * ((int)ohm - (int)data->comp[low].ohm)) /
> - ((int)data->comp[high].ohm - (int)data->comp[low].ohm);
> + temp = fixp_linear_interpolate(data->comp[low].ohm,
> + data->comp[low].temp_c,
> + data->comp[high].ohm,
> + data->comp[high].temp_c,
> + ohm);
> + temp *= 1000;
> }
> return temp;
> }
