linux-kernel - Re: [PATCH v2 4/4] arm64: dts: qcom: sdm845: mtp: Add vadc channels and thermal zones

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Date:   Mon, 4 Oct 2021 13:15:26 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Matthias Kaehlcke <mka@...omium.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Andy Gross <agross@...nel.org>, Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] arm64: dts: qcom: sdm845: mtp: Add vadc channels
 and thermal zones

On Wed 29 Sep 11:40 PDT 2021, Matthias Kaehlcke wrote:

> On Thu, Sep 23, 2021 at 02:23:11PM -0700, Bjorn Andersson wrote:
> > Downstream defines four ADC channels related to thermal sensors external
> > to the PM8998 and two channels for internal voltage measurements.
> > 
> > Add these to the upstream SDM845 MTP, describe the thermal monitor
> > channels and add thermal_zones for these.
> > 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > ---
> > 
> > In addition to the iio channels exposed by v1, Daniel wanted thermal_zones...
> > 
> > Changes since v1:
> > - Enable the pm8998_adc_tm and describe the ADC channels
> > - Add thermal-zones for the new channels
> > 
> >  arch/arm64/boot/dts/qcom/sdm845-mtp.dts | 128 ++++++++++++++++++++++++
> >  1 file changed, 128 insertions(+)
> > 
> > diff --git a/arch/arm64/boot/dts/qcom/sdm845-mtp.dts b/arch/arm64/boot/dts/qcom/sdm845-mtp.dts
[..]
> > +&pm8998_adc {
> > +	adc-chan@4c {
> > +		reg = <ADC5_XO_THERM_100K_PU>;
> > +		label = "xo_therm";
> > +	};
> > +
> > +	adc-chan@4d {
> > +		reg = <ADC5_AMUX_THM1_100K_PU>;
> > +		label = "msm_therm";
> > +	};
> > +
> > +	adc-chan@4f {
> > +		reg = <ADC5_AMUX_THM3_100K_PU>;
> > +		label = "pa_therm1";
> > +	};
> > +
> > +	adc-chan@51 {
> > +		reg = <ADC5_AMUX_THM5_100K_PU>;
> > +		label = "quiet_therm";
> > +	};
> > +
> > +	adc-chan@83 {
> > +		reg = <ADC5_VPH_PWR>;
> > +		label = "vph_pwr";
> > +	};
> > +
> > +	adc-chan@85 {
> > +		reg = <ADC5_VCOIN>;
> > +		label = "vcoin";
> > +	};
> > +};
> > +
> > +&pm8998_adc_tm {
> > +	status = "okay";
> > +
> > +	xo-thermistor@1 {
> > +		reg = <1>;
> > +		io-channels = <&pm8998_adc ADC5_XO_THERM_100K_PU>;
> > +		qcom,ratiometric;
> > +		qcom,hw-settle-time-us = <200>;
> > +	};
> > +
> > +	msm-thermistor@2 {
> > +		reg = <2>;
> > +		io-channels = <&pm8998_adc ADC5_AMUX_THM1_100K_PU>;
> > +		qcom,ratiometric;
> > +		qcom,hw-settle-time-us = <200>;
> > +	};
> > +
> > +	pa-thermistor@3 {
> > +		reg = <3>;
> > +		io-channels = <&pm8998_adc ADC5_AMUX_THM3_100K_PU>;
> > +		qcom,ratiometric;
> > +		qcom,hw-settle-time-us = <200>;
> > +	};
> > +
> > +	quiet-thermistor@4 {
> > +		reg = <4>;
> > +		io-channels = <&pm8998_adc ADC5_AMUX_THM5_100K_PU>;
> > +		qcom,ratiometric;
> > +		qcom,hw-settle-time-us = <200>;
> > +	};
> > +};
> > +
> 
> The example in the 'qcom,spmi-adc-tm5' binding specifies 'qcom,ratiometric'
> and 'qcom,hw-settle-time-us' for both the ADC and the thermal monitor, so do
> several board files (e.g. sm8250-mtp.dts and qrb5165-rb5.dts). This apparent
> redundancy bothered me earlier, it's not really clear to me whether it's
> needed/recommended or not. Do you happen to have any insights on this?

Hmm, you're right and I missed this in defining my channels. I've not
looked at this detail, just got reasonable readings from my thermal
zones and was happy about that.

Dmitry, do you have any further insights why these properties are
supposed to be duplicated between the adc channel and the thermal zones?

Thanks,
Bjorn