Re: [PATCH 2/5] backlight: pwm_bl: eliminate a 64/32 division

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