linux-kernel - Re: [PATCH v2 4/4] backlight: pwm_bl: switch to power-of-2 base for fixed-point math

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Message-ID: <20191014072745.GH4545@dell>
Date:   Mon, 14 Oct 2019 08:27:45 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-pwm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] backlight: pwm_bl: switch to power-of-2 base for
 fixed-point math

On Tue, 08 Oct 2019, Rasmus Villemoes wrote:

> Using a power-of-2 instead of power-of-10 base makes the computations
> much cheaper. 2^16 is safe; retval never becomes more than 2^48 +
> 2^32/2. On a 32 bit platform, the very expensive 64/32 division at the
> end of cie1931() instead becomes essentially free (a shift by 32 is
> just a register rename).
> 
> Reviewed-by: Daniel Thompson <daniel.thompson@...aro.org>
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  drivers/video/backlight/pwm_bl.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)

Applied, thanks.

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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