linux-kernel - Re: [PATCH v3 1/2] dt-bindings: thermal: generic-adc: Add optional io-channel-cells property

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Message-ID: <1796a9c5-4eb4-4120-a1fb-be773aace202@arm.com>
Date: Wed, 5 Mar 2025 14:51:57 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: Svyatoslav Ryhel <clamor95@...il.com>
Cc: linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
 Laxman Dewangan <ldewangan@...dia.com>, Conor Dooley <conor+dt@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Rob Herring <robh@...nel.org>,
 Zhang Rui <rui.zhang@...el.com>, Daniel Lezcano <daniel.lezcano@...aro.org>,
 linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v3 1/2] dt-bindings: thermal: generic-adc: Add optional
 io-channel-cells property

On 3/5/25 10:03, Svyatoslav Ryhel wrote:
> ср, 5 бер. 2025 р. о 12:00 Lukasz Luba <lukasz.luba@....com> пише:
>>
>>
>>
>> On 3/3/25 12:21, Svyatoslav Ryhel wrote:
>>> This implements a mechanism to derive temperature values from an existing ADC IIO
>>> channel, effectively creating a temperature IIO channel. This approach avoids adding
>>> a new sensor and its associated conversion table, while providing IIO-based temperature
>>> data for devices that may not utilize hwmon.
>>>
>>> Signed-off-by: Svyatoslav Ryhel <clamor95@...il.com>
>>> ---
>>>    .../devicetree/bindings/thermal/generic-adc-thermal.yaml      | 4 ++++
>>>    1 file changed, 4 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/thermal/generic-adc-thermal.yaml b/Documentation/devicetree/bindings/thermal/generic-adc-thermal.yaml
>>> index 12e6418dc24d..4bc2cff0593c 100644
>>> --- a/Documentation/devicetree/bindings/thermal/generic-adc-thermal.yaml
>>> +++ b/Documentation/devicetree/bindings/thermal/generic-adc-thermal.yaml
>>> @@ -30,6 +30,9 @@ properties:
>>>      io-channel-names:
>>>        const: sensor-channel
>>>
>>> +  '#io-channel-cells':
>>> +    const: 1
>>> +
>>>      temperature-lookup-table:
>>>        description: |
>>>          Lookup table to map the relation between ADC value and temperature.
>>> @@ -60,6 +63,7 @@ examples:
>>>            #thermal-sensor-cells = <0>;
>>>            io-channels = <&ads1015 1>;
>>>            io-channel-names = "sensor-channel";
>>> +        #io-channel-cells = <1>;
>>>            temperature-lookup-table = <
>>>                  (-40000) 2578
>>>                  (-39000) 2577
>>
>> Do we really need this change in the DT?
>> Won't the code in the thermal driver that registers a new iio device
>> would just be enough?
>>
>> I agree with Rob that it looks odd.
> 
> Building tree will complain on missing cells property if you try to
> bind it. It is not in required category anyway.

Fair enough, then I will leave it to DT folks.

For me it's looks OK-ish, assuming you add this property with the
comment describing it like Rob asked.

UUIC it will always be only 1 channel - with that temperature,
so shouldn't harm much the design in DT.