linux-kernel - Re: [PATCH 1/5] arm64: dts: qcom: pmi8998: add rradc node

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Date:   Mon, 17 Oct 2022 16:29:28 +0100
From:   Caleb Connolly <caleb.connolly@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Luca Weiss <luca@...tu.xyz>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        devicetree@...r.kernel.org,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH 1/5] arm64: dts: qcom: pmi8998: add rradc node



On 17/10/2022 02:10, Krzysztof Kozlowski wrote:
> On 16/10/2022 14:03, Caleb Connolly wrote:
>> Add a DT node for the Round Robin ADC found in the PMI8998 PMIC.
>>
>> Signed-off-by: Caleb Connolly <caleb.connolly@...aro.org>
>> ---
>>   arch/arm64/boot/dts/qcom/pmi8998.dtsi | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/arch/arm64/boot/dts/qcom/pmi8998.dtsi b/arch/arm64/boot/dts/qcom/pmi8998.dtsi
>> index 6d3d212560c1..5a479259c041 100644
>> --- a/arch/arm64/boot/dts/qcom/pmi8998.dtsi
>> +++ b/arch/arm64/boot/dts/qcom/pmi8998.dtsi
>> @@ -18,6 +18,14 @@ pmi8998_gpio: gpios@...0 {
>>   			interrupt-controller;
>>   			#interrupt-cells = <2>;
>>   		};
>> +
>> +		pmi8998_rradc: adc@...0 {
>> +			compatible = "qcom,pmi8998-rradc";
>> +			reg = <0x4500>;
>> +			#io-channel-cells = <1>;
>> +
>> +			status = "disabled";
> 
> Why disabling it? It does not need any external/board resources, so
> maybe it should be just like other adcs - enabled by default? What does
> it measure? What is its input?

The RRADC mostly reports values which only make sense on mobile devices, battery 
ID and temperature, USB and DC input voltage/current as well as a (duplicate?) 
die temperature of the PMIC - I guess closer to the SMB/FG block.

When I last tested the DC input readings didn't work on db845c, as it just 
produces the 4.2v you'd get from a battery.

Enabling it by default should be fine (and would certainly simplify this series :P).
> 
> Best regards,
> Krzysztof
> 

-- 
Kind Regards,
Caleb (they/them)