linux-kernel - Re: [PATCH v2 3/3] arm64: dts: qcom: sa8295p-adp: Add max20411 on i2c12

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Date:   Thu, 26 Jan 2023 16:54:46 -0600
From:   Andrew Halaney <ahalaney@...hat.com>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 3/3] arm64: dts: qcom: sa8295p-adp: Add max20411 on
 i2c12

On Tue, Jan 24, 2023 at 10:44:40AM -0800, Bjorn Andersson wrote:
> From: Bjorn Andersson <bjorn.andersson@...aro.org>
> 
> The SA8295P ADP has a Maxim max20411 step-down converter on i2c12.
> 
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>
> ---
> 
> Changes since v1:
> - i2c node had changed name
> 
>  arch/arm64/boot/dts/qcom/sa8295p-adp.dts | 41 ++++++++++++++++++++++++
>  1 file changed, 41 insertions(+)

I realized today this has to do with the comment over at:

    https://lore.kernel.org/all/30166208-ba9d-e6e6-1cd2-807a80536052@quicinc.com/

and I just didn't realize that the schematic I've started looking at
black boxes the SOM/SIP which holds this... darn I thought I could see
more than I could :(

I took a similiar patch for a spin on sa8540p-ride (which I'll later
submit), and things worked fine (I'm not really consuming the output of
the regulator mind you).

Downstream devicetree indicates all of this looks ok except for possibly
the below comment:

> 
> diff --git a/arch/arm64/boot/dts/qcom/sa8295p-adp.dts b/arch/arm64/boot/dts/qcom/sa8295p-adp.dts
> index bb4270e8f551..642000d95812 100644
> --- a/arch/arm64/boot/dts/qcom/sa8295p-adp.dts
> +++ b/arch/arm64/boot/dts/qcom/sa8295p-adp.dts
> @@ -266,6 +266,27 @@ &dispcc1 {
>  	status = "okay";
>  };
>  
> +&i2c12 {
> +	pinctrl-names = "default";
> +	pinctrl-0 = <&i2c12_state>;
> +
> +	status = "okay";
> +
> +	vdd_gfx: regulator@39 {
> +		compatible = "maxim,max20411";
> +		reg = <0x39>;
> +
> +		regulator-name = "vdd_gfx";
> +		regulator-min-microvolt = <800000>;

Is there a reason you chose this instead of the 500000 I see downstream?

> +		regulator-max-microvolt = <968750>;

Likewise, I see in this brief description of the regulator
that the upper bound is higher than this (1.275 V). I am not sure if
the values in the devicetree are supposed to describe the
min/max of the regulator itself, or of what your board can really
handle/needs (the latter I guess makes more sense since you wouldn't want to
accidentally request a current draw that could melt something.. that can
be fun). I do see you've got that min/max in the driver itself (now that
I peaked at that patch).

https://www.analog.com/en/products/MAX20411.html#product-overview

For what it is worth, I also see a SIP document that states vdd_gfx min/max
is 0.56/1.03 V, which is ultimately what you'd feed this into. The
downstream devicetree uses the max value you provide though.

No idea how much faith I should put into the SIP document's bounds, or
downstream, but I thought I should at least highlight them.

Thanks,
Andrew