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Date:   Wed, 28 Oct 2020 14:56:17 +0000
From:   Daniel Thompson <daniel.thompson@linaro.org>
To:     Alexandru Stan <amstan@chromium.org>
Cc:     Heiko Stuebner <heiko@sntech.de>, Rob Herring <robh+dt@kernel.org>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>, Lee Jones <lee.jones@linaro.org>,
        Jingoo Han <jingoohan1@gmail.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Douglas Anderson <dianders@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 2/3] arm64: dts: qcom: trogdor: Add brightness-levels
Message-ID: <20201028145617.ermdpqomthxxj7qe@holly.lan>
References: <20201022050445.930403-1-amstan@chromium.org>
 <20201021220404.v3.2.Ie4d84af5a85e8dcb8f575845518fa39f324a827d@changeid>
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On Wed, Oct 21, 2020 at 10:04:44PM -0700, Alexandru Stan wrote:
> We want userspace to represent the human perceived brightness.
> Since the led drivers and the leds themselves don't have a
> linear response to the value we give them in terms of perceived
> brightness, we'll bake the curve into the dts.
> 
> The panel also doesn't have a good response under 5%, so we'll avoid
> sending it anything lower than that.
> 
> Note: Ideally this patch should be coupled with the driver change from
> "backlight: pwm_bl: Fix interpolation", but it can work without it,
> without looking too ugly.
> 
> Signed-off-by: Alexandru Stan <amstan@chromium.org>

Acked-by: Daniel Thompson <daniel.thompson@linaro.org>


> ---
> 
>  arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> index bf875589d364..ccdabc6c4994 100644
> --- a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> +++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> @@ -179,6 +179,15 @@ pp3300_fp_tp: pp3300-fp-tp-regulator {
>  	backlight: backlight {
>  		compatible = "pwm-backlight";
>  
> +		/* The panels don't seem to like anything below ~ 5% */
> +		brightness-levels = <
> +			196 256 324 400 484 576 676 784 900 1024 1156 1296
> +			1444 1600 1764 1936 2116 2304 2500 2704 2916 3136
> +			3364 3600 3844 4096
> +		>;
> +		num-interpolated-steps = <64>;
> +		default-brightness-level = <951>;
> +
>  		pwms = <&cros_ec_pwm 1>;
>  		enable-gpios = <&tlmm 12 GPIO_ACTIVE_HIGH>;
>  		power-supply = <&ppvar_sys>;
> -- 
> 2.28.0