linux-kernel - Re: [PATCH 2/2] arm64: dts: qcom: msm8917-xiaomi-riva: Add display backlight

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Message-ID: <0d540105-1da7-459b-a812-dbc13097520e@oss.qualcomm.com>
Date: Wed, 12 Feb 2025 23:31:30 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Barnabás Czémán <barnabas.czeman@...nlining.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: dts: qcom: msm8917-xiaomi-riva: Add display
 backlight

On 12.02.2025 11:21 PM, Barnabás Czémán wrote:
> Redmi 5A display uses pwm backlight, add support for it.
> 
> Signed-off-by: Barnabás Czémán <barnabas.czeman@...nlining.org>
> ---
>  arch/arm64/boot/dts/qcom/msm8917-xiaomi-riva.dts | 25 ++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/qcom/msm8917-xiaomi-riva.dts b/arch/arm64/boot/dts/qcom/msm8917-xiaomi-riva.dts
> index f1d22535fedd94467ba3f0a88b2110ce5360e7e1..8808306c989f54116052667887f9bf36b63c4c64 100644
> --- a/arch/arm64/boot/dts/qcom/msm8917-xiaomi-riva.dts
> +++ b/arch/arm64/boot/dts/qcom/msm8917-xiaomi-riva.dts
> @@ -20,6 +20,14 @@ / {
>  	qcom,msm-id = <QCOM_ID_MSM8917 0>;
>  	qcom,board-id = <0x1000b 2>, <0x2000b 2>;
>  
> +	pwm_backlight: backlight {
> +		compatible = "pwm-backlight";
> +		pwms = <&pm8937_pwm 0 100000>;
> +		brightness-levels = <0 255>;
> +		num-interpolated-steps = <255>;
> +		default-brightness-level = <128>;
> +	};
> +
>  	battery: battery {
>  		compatible = "simple-battery";
>  		charge-full-design-microamp-hours = <3000000>;
> @@ -131,6 +139,23 @@ bq25601@6b{
>  	};
>  };
>  
> +&pm8937_gpios {
> +	pwm_enable_default: pwm-enable-default-state {
> +		pins = "gpio8";
> +		function = "dtest2";

Are you sure?
> +		output-low;
> +		bias-disable;
> +		qcom,drive-strength = <2>;
> +	};
> +};
> +
> +&pm8937_pwm {
> +	pinctrl-0 = <&pwm_enable_default>;
> +	pinctrl-names = "default";

We normally put this under the backlight node, but I'm not sure which
one is more correct.. it may be that this one is, given we're
controlling the pin that the PWM signal is sent through

Konrad