| Message ID | 1535596744-16598-2-git-send-email-na-hoan@jinso.co.jp (mailing list archive) |
|---|---|
| State | Under Review |
| Delegated to: | Geert Uytterhoeven |
| Headers | show |
| Series | thermal: rcar: reduce inaccuracy in calculate rounding | expand |
Hi Hoan, On Thu, Aug 30, 2018 at 4:39 AM Nguyen An Hoan <na-hoan@jinso.co.jp> 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> 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
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
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; return INT_FIXPT((val1 + val2) / 2); }