linux-kernel - Re: [PATCH 2/3] dt-bindings: trivial-devices: add asair,ags02ma

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Date:   Wed, 8 Nov 2023 13:29:42 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Anshul Dalal <anshulusr@...il.com>, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Shuah Khan <skhan@...uxfoundation.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH 2/3] dt-bindings: trivial-devices: add asair,ags02ma

On 08/11/2023 13:15, Anshul Dalal wrote:
> On 11/8/23 17:31, Krzysztof Kozlowski wrote:
>> On 08/11/2023 12:54, Anshul Dalal wrote:
>>>
>>> Hello Krzysztof,
>>>
>>> On 11/7/23 23:17, Krzysztof Kozlowski wrote:
>>>> On 07/11/2023 18:30, Anshul Dalal wrote:
>>>>> Add bindings for Asair AGS02MA TVOC sensor to trivial devices.
>>>>>
>>>>> The sensor communicates over i2c with the default address 0x1a.
>>>>> TVOC values can be read in the units of ppb and ug/m^3 at register 0x00.
>>>>>
>>>>> Datasheet:
>>>>>   https://asairsensors.com/wp-content/uploads/2021/09/AGS02MA.pdf
>>>>> Product-Page:
>>>>>   http://www.aosong.com/m/en/products-33.html
>>>>>
>>>>> Signed-off-by: Anshul Dalal <anshulusr@...il.com>
>>>>> ---
>>>>>  Documentation/devicetree/bindings/trivial-devices.yaml | 2 ++
>>>>>  1 file changed, 2 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/trivial-devices.yaml b/Documentation/devicetree/bindings/trivial-devices.yaml
>>>>> index cd58179ae337..9cd67b758a88 100644
>>>>> --- a/Documentation/devicetree/bindings/trivial-devices.yaml
>>>>> +++ b/Documentation/devicetree/bindings/trivial-devices.yaml
>>>>> @@ -47,6 +47,8 @@ properties:
>>>>>            - adi,lt7182s
>>>>>              # AMS iAQ-Core VOC Sensor
>>>>>            - ams,iaq-core
>>>>> +            # TVOC (Total Volatile Organic Compounds) i2c sensor
>>>>> +          - asair,ags02ma
>>>>
>>>> I think you miss VDD supply.
>>>
>>> I am sorry but I'm not sure what you meant. Are you referring to the
>>> addition of some information in the commit description?
>>
>> I meant that your device might not be trivial. Your device takes VDD
>> supply, which is now not described in the bindings. Do you want to say
>> that VDD supply in all possible designs is hard-wired to
>> non-controllable regulator supply?
> 
> I can't speak for all possible designs but for testing this driver I had
> just connected the VDD pin to 5V out of the Raspberry Pi. I have since
> verified 3.3V to also work.
> Could you explain why `vdd-supply` is a property or point me to further
> sources. Wouldn't almost all devices have a VDD/VCC pin for power in?

Most of the devices have such pin. For most of the devices we include it
in the bindings.

git grep regulator_get -- drivers/iio/
git grep vdd -- drivers/iio/

If you do not describe it in the bindings, then your device will have to
be supplied by always-on regulators (and marking controllable regulator
as always-on because of this is not correct).

If you are unsure and you just work on some sensor not used for final
product, I think it's fine as is, so to add the regulator later if ever
needed.

Best regards,
Krzysztof