From: Daniel Thompson <daniel.thompson@linaro.org>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Lee Jones <lee.jones@linaro.org>,
Jingoo Han <jingoohan1@gmail.com>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org,
linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/5] backlight: pwm_bl: eliminate a 64/32 division
Date: Mon, 7 Oct 2019 16:13:19 +0100 [thread overview]
Message-ID: <20191007151319.de6ko7n5dypqgyce@holly.lan> (raw)
In-Reply-To: <20190919140620.32407-2-linux@rasmusvillemoes.dk>
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
next prev parent reply other threads:[~2019-10-07 15:13 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-19 14:06 [PATCH 1/5] backlight: pwm_bl: fix cie1913 comments and constant Rasmus Villemoes
2019-09-19 14:06 ` [PATCH 2/5] backlight: pwm_bl: eliminate a 64/32 division Rasmus Villemoes
2019-10-07 15:13 ` Daniel Thompson [this message]
2019-09-19 14:06 ` [PATCH 3/5] backlight: pwm_bl: drop use of int_pow() Rasmus Villemoes
2019-10-07 15:28 ` Daniel Thompson
2019-10-07 18:43 ` Rasmus Villemoes
2019-10-08 9:31 ` Daniel Thompson
2019-10-08 10:02 ` Rasmus Villemoes
2019-10-08 10:43 ` Daniel Thompson
2019-09-19 14:06 ` [PATCH 4/5] backlight: pwm_bl: switch to power-of-2 base for fixed-point math Rasmus Villemoes
2019-10-07 15:32 ` Daniel Thompson
2019-09-19 14:06 ` [PATCH 5/5] lib/math: remove int_pow() Rasmus Villemoes
2019-09-19 14:36 ` Andy Shevchenko
2019-09-21 15:19 ` kbuild test robot
2019-09-21 15:22 ` kbuild test robot
2019-09-20 10:14 ` [PATCH 1/5] backlight: pwm_bl: fix cie1913 comments and constant Daniel Thompson
2019-09-20 10:36 ` Rasmus Villemoes
2019-10-07 15:08 ` Daniel Thompson
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