linux-kernel - Re: [PATCH v3 2/3] arm64: dts: qcom: trogdor: Add brightness-levels

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Message-ID: <20201028145617.ermdpqomthxxj7qe@holly.lan>
Date:   Wed, 28 Oct 2020 14:56:17 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Alexandru Stan <amstan@...omium.org>
Cc:     Heiko Stuebner <heiko@...ech.de>, Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Douglas Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] arm64: dts: qcom: trogdor: Add brightness-levels

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@...omium.org>

Acked-by: Daniel Thompson <daniel.thompson@...aro.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