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

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

On Mon, 4 Oct 2021 at 23:13, Bjorn Andersson <bjorn.andersson@linaro.org> wrote:
>
> 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@linaro.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?

Because both ADC channel and thermal zone registers should be
programmed accordingly.

One not-so-perfect approach would be to use io-channels property to
locate the adc's adc-chan node and to parse it. However this way
thermal driver would have to know the exact structure of adc's device
tree nodes.
Another (even worse) solution would be to introduce qcom-specific API
to query these properties from the IIO channel.

Selecting between these two options I decided to follow the downstream
path and just to duplicate these few properties.

-- 
With best wishes
Dmitry