Hi Hoan,
On Thu, Aug 30, 2018 at 4:39 AM Nguyen An Hoan <na-hoan@xxxxxxxxxxx> wrote:
> From: Hoan Nguyen An <na-hoan@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxx>
Thanks for your patch!
> --- 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;
No rounding anymoe?
val1 = DIV_ROUND_CLOSEST(mcelsius * tsc->coef.a1, 1000) + tsc->coef.b1;
val2 = DIV_ROUND_CLOSEST(mcelsius * tsc->coef.a2, 1000) + tsc->coef.b2;
Can the multiplication overflow?
I know mcelsius = -40000..120000/
What is the range of a1 and a2?
>
> return INT_FIXPT((val1 + val2) / 2);
BTW, do we want to introduce rounding here, too?
(for INT_FIXPT(), it doesn't matter much for /2)?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
