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

[Jishnu Prakash]

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@xxxxxxxxxxx> 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