linux-kernel - Re: [PATCH V7 3/5] dt-bindings: iio: adc: Add support for QCOM PMIC5 Gen3 ADC

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Message-ID: <CAGE=qrrCvq28pr9Y7it-CGMW=szKUnU+XBj1TmpoUwuASM05ig@mail.gmail.com>
Date: Sat, 4 Oct 2025 15:52:46 +0900
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Jishnu Prakash <jishnu.prakash@....qualcomm.com>
Cc: Jonathan Cameron <jic23@...nel.org>, Krzysztof Kozlowski <krzk@...nel.org>, robh@...nel.org, 
	krzk+dt@...nel.org, conor+dt@...nel.org, agross@...nel.org, 
	andersson@...nel.org, lumag@...nel.org, dmitry.baryshkov@....qualcomm.com, 
	konradybcio@...nel.org, daniel.lezcano@...aro.org, sboyd@...nel.org, 
	amitk@...nel.org, thara.gopinath@...il.com, lee@...nel.org, rafael@...nel.org, 
	subbaraman.narayanamurthy@....qualcomm.com, david.collins@....qualcomm.com, 
	anjelique.melendez@....qualcomm.com, kamal.wadhwa@....qualcomm.com, 
	rui.zhang@...el.com, lukasz.luba@....com, devicetree@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, linux-iio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	cros-qcom-dts-watchers@...omium.org, quic_kotarake@...cinc.com, 
	neil.armstrong@...aro.org, stephan.gerhold@...aro.org, 
	Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH V7 3/5] dt-bindings: iio: adc: Add support for QCOM PMIC5
 Gen3 ADC

On Sat, 4 Oct 2025 at 11:42, Jishnu Prakash
<jishnu.prakash@....qualcomm.com> wrote:
>
> Hi Jonathan,
>
> On 9/27/2025 7:17 PM, Jonathan Cameron wrote:
> > On Fri, 19 Sep 2025 20:17:43 +0530
> > Jishnu Prakash <jishnu.prakash@....qualcomm.com> wrote:
> >
> >> Hi Krzysztof,
> >>
> >> On 9/18/2025 5:45 AM, Krzysztof Kozlowski wrote:
> >>> On 18/09/2025 04:47, Jishnu Prakash wrote:
> >>>> Hi Krzysztof,
> >>>>
> >>>> On 9/17/2025 5:59 AM, Krzysztof Kozlowski wrote:
> >>>>> On 16/09/2025 16:28, Jishnu Prakash wrote:
> >>>>>>> You cannot have empty spaces in ID constants. These are abstract
> >>>>>>> numbers.
> >>>>>>>
> >>>>>>> Otherwise please point me to driver using this constant.
> >>>>>>
> >>>>>> These constants are for ADC channel numbers, which are fixed in HW.
> >>>>>>
> >>>>>> They are used in this driver: drivers/iio/adc/qcom-spmi-adc5-gen3.c,
> >>>>>> which is added in patch 4 of this series.
> >>>>>>
> >>>>>> They can be found in the array named adc5_gen3_chans_pmic[].
> >>>>>
> >>>>> Really? So point me to the line there using ADC5_GEN3_VREF_BAT_THERM.
> >>>>>
> >>>>
> >>>> We may not be using all of these channels right now - we can add them
> >>>> later based on requirements coming up. For now, I'll remove the channels
> >>>> not used in adc5_gen3_chans_pmic[].
> >>>
> >>> You are not implementing the feedback then. Please read it carefully.
> >>>
> >>
> >> Sorry, I misunderstood - so you actually meant I should remove the
> >> empty spaces in the definitions, like this?
> >>
> >> -#define ADC5_GEN3_VREF_BAT_THERM               0x15
> >> +#define ADC5_GEN3_VREF_BAT_THERM 0x15
> >>
> >> I thought this at first, but I somehow doubted this later, as I saw some
> >> other recently added files with empty spaces in #define lines, like:
> >>
> >> include/dt-bindings/iio/adc/mediatek,mt6373-auxadc.h
> >> include/dt-bindings/regulator/st,stm32mp15-regulator.h
> >>
> >> I can make this change, if you prefer this. Please let me know
> >> if I'm still missing something.
> >>
> >> Also please let me know if you want me to remove the unused
> >> channels - I would prefer to keep them if there's no issue,
> >> as we might need them later.
> >>
> > He is referring to 0x14 and below not being defined values.  So what
> > do they mean if they turn up in the DT?
> >
>
> Thanks for your clarification. To address your first point above, the macros
> added here only represent the ADC channel numbers which are supported for
> ADC5 Gen3 devices. If there are numbers missing in between (like 0x14),
> that is because there exist no valid ADC channels in HW matching those
> channel numbers.
>
> For your question above, if any of the undefined channels are used in the DT,
> they should ideally be treated as invalid when parsed in the driver probe and
> lead to an error. When I checked the code again, I saw we do not have such an
> explicit check right now, so I will add that in the next patch series.
>
> And to be clear on which channel numbers are supported, I think it may be
> best if, for now, we only add support for the channel numbers referenced in
> the array adc5_gen3_chans_pmic[] in drivers/iio/adc/qcom-spmi-adc5-gen3.c.
>
> There are only 18 channel numbers used in this array and I would remove
> all channels except for these from the binding files. During parsing, we
> would use this array to confirm if an ADC channel added in DT is supported.
>
> In case we need to add support for any more channels later, we could add
> their macros in the binding file and update the array correspondingly at
> that time.
>
> Does all this sound fine? Please let me know if you have any more concerns
> or queries.

No, it doesn't.  You keep ignoring my arguments and responding to
something else. I prefer not to store hardware values as bindings,
because these are not bindings (and you failed to prove which SW
interface they bind) and it's really not necessary.