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 17:43:54 -0600
From:   Andrew Halaney <ahalaney@...hat.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Bjorn Andersson <quic_bjorande@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.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 Fri, Jan 27, 2023 at 12:35:37AM +0100, Konrad Dybcio wrote:
> 
> 
> On 26.01.2023 23:54, Andrew Halaney wrote:
> > 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).
> Yes, your suspicions are correct and the DT sets the actual ranges
> for the voltage regulators on this specific board while the
> hardware reachable ranges are defined in the .c driver.
> 
> Konrad

Thanks Konrad, then I think:

Reviewed-by: Andrew Halaney <ahalaney@...hat.com>
Tested-by: Andrew Halaney <ahalaney@...hat.com>

is appropriate since things are within range on all accounts. I would
appreciate an explanation on the current min/max values though if possible!