linux-kernel - Re: [PATCH v3 2/3] dt-bindings: iio: adc: Add support for QCOM PMIC5 Gen3 ADC

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Date: Fri, 16 Feb 2024 16:09:38 +0530
From: Jishnu Prakash <quic_jprakash@...cinc.com>
To: Jonathan Cameron <jic23@...nel.org>
CC: <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <conor+dt@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <lee@...nel.org>,
        <andriy.shevchenko@...ux.intel.com>, <daniel.lezcano@...aro.org>,
        <dmitry.baryshkov@...aro.org>, <lars@...afoo.de>, <luca@...tu.xyz>,
        <marijn.suijten@...ainline.org>, <agross@...nel.org>,
        <sboyd@...nel.org>, <rafael@...nel.org>, <rui.zhang@...el.com>,
        <lukasz.luba@....com>, <linus.walleij@...aro.org>,
        <quic_subbaram@...cinc.com>, <quic_collinsd@...cinc.com>,
        <quic_amelende@...cinc.com>, <quic_kamalw@...cinc.com>,
        <kernel@...cinc.com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-arm-msm-owner@...r.kernel.org>,
        <linux-iio@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <cros-qcom-dts-watchers@...omium.org>
Subject: Re: [PATCH v3 2/3] dt-bindings: iio: adc: Add support for QCOM PMIC5
 Gen3 ADC

Hi Jonathan,

On 1/1/2024 11:32 PM, Jonathan Cameron wrote:
> On Sun, 31 Dec 2023 22:42:36 +0530
> Jishnu Prakash <quic_jprakash@...cinc.com> wrote:
>
>> For the PMIC5-Gen3 type PMICs, ADC peripheral is present in HW for the

>> +
>> +      label:
>> +        $ref: /schemas/types.yaml#/definitions/string
>> +        description: |
>> +            ADC input of the platform as seen in the schematics.
>> +            For thermistor inputs connected to generic AMUX or GPIO inputs
>> +            these can vary across platform for the same pins. Hence select
>> +            the platform schematics name for this channel.
> defined in adc.yaml, so should just have a reference to that here.
>
>> +
>> +      qcom,decimation:
>> +        $ref: /schemas/types.yaml#/definitions/uint32
>> +        description: |
>> +            This parameter is used to decrease ADC sampling rate.
>> +            Quicker measurements can be made by reducing decimation ratio.
> Why is this in DT rather than as a userspace control?


We don't intend this property to be something that can be controlled 
from userspace - if a client wants to read an ADC channel from 
userspace, we only intend to provide them the processed value, 
calculated with a fixed set of ADC properties mentioned in the 
corresponding channel node in DT.


>> +        enum: [ 85, 340, 1360 ]
>> +        default: 1360
>> +

>> +
>> +      qcom,hw-settle-time:
>> +        $ref: /schemas/types.yaml#/definitions/uint32
>> +        description: |
>> +            Time between AMUX getting configured and the ADC starting
>> +            conversion. The 'hw_settle_time' is an index used from valid values
>> +            and programmed in hardware to achieve the hardware settling delay.
>> +        enum: [ 15, 100, 200, 300, 400, 500, 600, 700, 1000, 2000, 4000,
>> +                8000, 16000, 32000, 64000, 128000 ]
>> +        default: 15
> only currently defined for muxes but we have settle-time-us which has benefit of
> providing the units (which are missing here from the description as well)
>
>> +
>> +      qcom,avg-samples:
>> +        $ref: /schemas/types.yaml#/definitions/uint32
>> +        description: |
>> +            Number of samples to be used for measurement.
>> +            Averaging provides the option to obtain a single measurement
>> +            from the ADC that is an average of multiple samples. The value
>> +            selected is 2^(value).
> Why is this in dt?  Why not just userspace control (in_voltageX_oversampling_ratio
>
> If it needs to be, we do have standard DT bindings for it in adc.yaml


avg-samples is also something we don't want the client to modify from 
userspace. As for using adc.yaml, I think I could use settling-time-us 
and oversampling-ratio from it for the above two properties.

However, Krzysztof has mentioned in another comment that I should put 
properties common to ADC5 Gen3 and older QCOM VADC devices in a common 
schema. If I now try replacing the existing qcom,hw-settle-time and 
qcom,avg-samples properties with settling-time-us and oversampling-ratio 
for older devices too, I would have to make several DT changes for 
existing devices...are you fine with this? Or should I just replace 
these two properties for ADC5 Gen3?


I'll address your other comments in the next patchset.


Thanks,

Jishnu