linux-kernel - Re: [PATCH 0/3] PWM backlight interpolation adjustments

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Message-ID: <CAHNYxRzwQ2jx99M0oyNv8CDE4h051jcdAdYFjRd8mhNjB19FgA@mail.gmail.com>
Date:   Wed, 5 Aug 2020 14:04:09 -0700
From:   Alexandru M Stan <amstan@...omium.org>
To:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-fbdev@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-pwm@...r.kernel.org,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH 0/3] PWM backlight interpolation adjustments

On Mon, Jul 20, 2020 at 9:27 PM Alexandru Stan <amstan@...omium.org> wrote:
>
> I was trying to adjust the brightness for a new chromebook:
> https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/2291209
> Like a lot of panels, the low end needs to be cropped,
> and now that we have the interpolation stuff I wanted to make use of it
> and bake in even the curve.
>
> I found the behavior a little unintuitive and non-linear. See patch 1
> for a suggested fix for this.
>
> Unfortunatelly a few veyron dts files were relying on this
> (perhaps weird) behavior. Those devices also want a minimum brightness.
> The issue is that they also want the 0% point for turning off the
> display.
> https://github.com/torvalds/linux/commit/6233269bce47bd450196a671ab28eb1ec5eb88d9#diff-e401ae20091bbfb311a062c464f4f47fL23
>
> So the idea here is to change those dts files to only say <3 255> (patch
> 3), and add in a virtual 0% point at the bottom of the scale (patch 2).
>
> We have to do this conditionally because it seems some devices like to
> have the scale inverted:
>   % git grep "brightness-levels\s*=\s*<\s*[1-9]"|cat
>   arch/arm/boot/dts/tegra124-apalis-eval.dts:             brightness-levels = <255 231 223 207 191 159 127 0>;
>
>
> Alexandru Stan (3):
>   backlight: pwm_bl: Fix interpolation
>   backlight: pwm_bl: Artificially add 0% during interpolation
>   ARM: dts: rockchip: Remove 0 point in backlight
>
>  arch/arm/boot/dts/rk3288-veyron-jaq.dts    |  2 +-
>  arch/arm/boot/dts/rk3288-veyron-minnie.dts |  2 +-
>  arch/arm/boot/dts/rk3288-veyron-tiger.dts  |  2 +-
>  drivers/video/backlight/pwm_bl.c           | 78 +++++++++++-----------
>  4 files changed, 42 insertions(+), 42 deletions(-)
>
> --
> 2.27.0
>

Hello,

Friendly ping.
Let me know if you would like me to make any changes to my patches.

Thanks,
Alexandru M Stan