Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200721042522.2403410-1-amstan@chromium.org>
In-Reply-To: <20200721042522.2403410-1-amstan@chromium.org>
From:   Alexandru M Stan <amstan@chromium.org>
Date:   Wed, 5 Aug 2020 14:04:09 -0700
Message-ID: <CAHNYxRzwQ2jx99M0oyNv8CDE4h051jcdAdYFjRd8mhNjB19FgA@mail.gmail.com>
Subject: Re: [PATCH 0/3] PWM backlight interpolation adjustments
To:     Thierry Reding <thierry.reding@gmail.com>,
        =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>, Lee Jones <lee.jones@linaro.org>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Jingoo Han <jingoohan1@gmail.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Heiko Stuebner <heiko@sntech.de>,
        Rob Herring <robh+dt@kernel.org>
Cc:     Matthias Kaehlcke <mka@chromium.org>,
        Douglas Anderson <dianders@chromium.org>,
        Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-fbdev@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-pwm@vger.kernel.org,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Jul 20, 2020 at 9:27 PM Alexandru Stan <amstan@chromium.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