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

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Message-ID: <c299f30205b602031905ed972fc6ea9f@mainlining.org>
Date: Wed, 12 Feb 2025 23:36:58 +0100
From: barnabas.czeman@...nlining.org
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: 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>,
 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 2025-02-12 23:31, Konrad Dybcio wrote:
> 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?
Yes, 
https://github.com/Mi-Thorium/kernel_devicetree_xiaomi-msm8937/blob/dts/mi8937/4.9/master/wingtech/msm8917/common/pm8937.dtsi#L24-L31
>> +		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

It is for enabling pwm and not backlight,
it should be placed here otherwise backlight will not work correctly.
> 
> Konrad