[2/5] backlight: pwm_bl: eliminate a 64/32 division
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Message ID 20190919140620.32407-2-linux@rasmusvillemoes.dk
State New
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Series
  • [1/5] backlight: pwm_bl: fix cie1913 comments and constant
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Commit Message

Rasmus Villemoes Sept. 19, 2019, 2:06 p.m. UTC
lightness*1000 is nowhere near overflowing 32 bits, so we can just use
an ordinary 32/32 division, which is much cheaper than the 64/32 done
via do_div().

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 drivers/video/backlight/pwm_bl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Daniel Thompson Oct. 7, 2019, 3:13 p.m. UTC | #1
On Thu, Sep 19, 2019 at 04:06:17PM +0200, Rasmus Villemoes wrote:
> lightness*1000 is nowhere near overflowing 32 bits, so we can just use
> an ordinary 32/32 division, which is much cheaper than the 64/32 done
> via do_div().
> 
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>

Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>

> ---
>  drivers/video/backlight/pwm_bl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index be36be1cacb7..9252d51f31b9 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -177,7 +177,7 @@ static u64 cie1931(unsigned int lightness, unsigned int scale)
>  	 */
>  	lightness *= 100;
>  	if (lightness <= (8 * scale)) {
> -		retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9033);
> +		retval = DIV_ROUND_CLOSEST(lightness * 10, 9033);
>  	} else {
>  		retval = int_pow((lightness + (16 * scale)) / 116, 3);
>  		retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale));
> -- 
> 2.20.1

Patch
diff mbox series

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index be36be1cacb7..9252d51f31b9 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -177,7 +177,7 @@  static u64 cie1931(unsigned int lightness, unsigned int scale)
 	 */
 	lightness *= 100;
 	if (lightness <= (8 * scale)) {
-		retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9033);
+		retval = DIV_ROUND_CLOSEST(lightness * 10, 9033);
 	} else {
 		retval = int_pow((lightness + (16 * scale)) / 116, 3);
 		retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale));