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

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Date:   Mon, 17 Oct 2022 13:22:27 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Caleb Connolly <caleb.connolly@...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 11:29, Caleb Connolly wrote:

>>> +		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.

If it is connected to some line - e.g. to the battery - then it is
operational and there is no reason to disable it.


Best regards,
Krzysztof