Re: [PATCH] thermal: rcar: reduce inaccuracy in calculate rounding

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello!

On 8/30/2018 5:39 AM, Nguyen An Hoan wrote:

> From: Hoan Nguyen An <na-hoan@jinso.co.jp>
> 
> About the formula for temperature calculation
> [reg] = [temp] * a + b <=> [temp] = ([reg] - b) / a
> 
> Using "(mcelsius * tsc-> coef.aX) / 1000" instead of "DIV_ROUND_CLOSEST(mcelsius, 1000) * tsc-> coef.aX"
> to avoid and reduce inaccuracy due to rounding the integer division.
> 
> Signed-off-by: Hoan Nguyen An <na-hoan@jinso.co.jp>
> ---
>   drivers/thermal/rcar_gen3_thermal.c | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/thermal/rcar_gen3_thermal.c b/drivers/thermal/rcar_gen3_thermal.c
> index 7aed533..dbb31b8 100644
> --- a/drivers/thermal/rcar_gen3_thermal.c
> +++ b/drivers/thermal/rcar_gen3_thermal.c
> @@ -185,11 +185,10 @@ static int rcar_gen3_thermal_get_temp(void *devdata, int *temp)
>   static int rcar_gen3_thermal_mcelsius_to_temp(struct rcar_gen3_thermal_tsc *tsc,
>   					      int mcelsius)
>   {
> -	int celsius, val1, val2;
> +	int val1, val2;
>   
> -	celsius = DIV_ROUND_CLOSEST(mcelsius, 1000);
> -	val1 = celsius * tsc->coef.a1 + tsc->coef.b1;
> -	val2 = celsius * tsc->coef.a2 + tsc->coef.b2;
> +	val1 = (mcelsius * tsc->coef.a1)/1000 + tsc->coef.b1;
> +	val2 = (mcelsius * tsc->coef.a2)/1000 + tsc->coef.b2;

    Please be consistent and enclose / in sopaces the same as you do for other 
operators.

[...]

MBR, Sergei