backlight: pwm_bl: Drop use of int_pow()

For a fixed small exponent of 3, it is more efficient to simply use
two explicit multiplications rather than calling the int_pow() library
function: Aside from the function call overhead, its implementation
using repeated squaring means it ends up doing four 64x64
multiplications.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 15d84da77ecde514e602e8a4cb4da5b6ab92e420..ee85055146dd7ebf40f079682a1afb6f407bb8be 100644 (file)
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -180,7 +180,8 @@ static u64 cie1931(unsigned int lightness, unsigned int scale)
        if (lightness <= (8 * scale)) {
                retval = DIV_ROUND_CLOSEST(lightness * 10, 9033);
        } else {
-               retval = int_pow((lightness + (16 * scale)) / 116, 3);
+               retval = (lightness + (16 * scale)) / 116;
+               retval *= retval * retval;
                retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale));
        }