linux-kernel - Re: [PATCH 1/3] dt-bindings: iio: pressure: Support Honeywell mpr sensors

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Message-ID: <83faad26-bb59-14a9-23d8-9e53a235a18e@kernel.org>
Date:   Fri, 7 Apr 2023 08:45:41 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Andreas Klinger <ak@...klinger.de>,
        Jonathan Cameron <jic23@...nel.org>
Cc:     linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        Lars-Peter Clausen <lars@...afoo.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Angel Iglesias <ang.iglesiasg@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: iio: pressure: Support Honeywell mpr
 sensors

On 06/04/2023 22:15, Andreas Klinger wrote:
> Hi,
> 
> thanks to Krzysztof, Lars-Peter and Jonathan for the review and suggestions. I
> have one thing to clarify. See below.
> 
> Jonathan Cameron <jic23@...nel.org> schrieb am Sa, 01. Apr 16:27:
>> On Sat, 1 Apr 2023 11:42:15 +0200
>> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
>>
>>> On 01/04/2023 11:09, Andreas Klinger wrote:
> [...]
>>>> +  honeywell,pmin:
>>>> +    description:
>>>> +      Minimum pressure value the sensor can measure in pascal.  
>>>
>>> Use standard unit suffix:
>>> https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml
>>>
>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>> +
>>>> +  honeywell,pmax:
>>>> +    description:
>>>> +      Maximum pressure value the sensor can measure in pascal.
>>>> +    $ref: /schemas/types.yaml#/definitions/uint32  
>>>
>>> Same.
>>>
>>> Why these values are suitable for DT? Does it depend on type of sensor
>>> (thus it is implied from compatible) or on system setup?
>>
>> I think we'll end up with a lot of compatibles, but that's still better
>> than free form description.  May still need these as well though given
>> the datasheet helpfully adds a foot note.
>>
>> 1. Custom pressure ranges are available.
>>
>> Might not be worth including all the details though but unhelpfully the
>> bits we care about are after details like is the gel food grade or the port long.
>> Definitely can ignore the encoding of i2c address / spi in the last few bits but
>> may need the transfer function.
>>
>>
>> mpr-0025GA-A maybe as a form?
> 
> Just to clarify: There are 32 different pressure ranges and 3 transfer functions
> which means we'll end up with 96 compatibles and 96 I2C ids.

You anyway need compatibles per devices, don't you?
https://elixir.bootlin.com/linux/v6.1-rc1/source/Documentation/devicetree/bindings/writing-bindings.rst#L42

I already commented on this.

> 
> Would it be an option to have only one dt compatible and to add the pressure
> range as dt property?
> e. g.: honeywell,range = "0025PA";

Did you just decided to ignore my comment?

> 
> But because of "Custom pressure ranges" we still need the DT properties. In this
> case there's another "mpr-custom" compatible, right?

Please go to my email and respond to comments.

Best regards,
Krzysztof