Re: [hwmon-next PATCH v3 1/4] dt-bindings: hwmon: adi,adt7470

[Krzysztof Kozlowski <krzk@kernel.org>]

On 29/07/2026 06:45, Luiz Angelo Daros de Luca wrote:
> Hi Krzysztof,
> 
> Thanks for the review.
> 
>> On Tue, Jul 28, 2026 at 12:07:09AM -0300, Luiz Angelo Daros de Luca wrote:
>>> The Analog Devices ADT7470 is a multichannel temperature sensor and
>>> PWM fan controller. It supports monitoring up to 10 external
>>> temperature sensors and controlling up to 4 fans.
>>>
>>> Add the device tree binding documentation for it. This includes
>>> support for the thermal framework by defining the "#thermal-sensor-cells"
>>> property, and models the fan control lines as PWM channels by
>>> defining the "#pwm-cells" property.
>>>
>>> Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
>>> ---
>>>  .../devicetree/bindings/hwmon/adi,adt7470.yaml     | 55 ++++++++++++++++++++++
>>>  1 file changed, 55 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/hwmon/adi,adt7470.yaml b/Documentation/devicetree/bindings/hwmon/adi,adt7470.yaml
>>> new file mode 100644
>>> index 000000000000..bb2375a4a490
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/hwmon/adi,adt7470.yaml
>>> @@ -0,0 +1,55 @@
>>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/hwmon/adi,adt7470.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: Analog Devices ADT7470 hwmon sensor
>>> +
>>> +maintainers:
>>> +  - Luiz Angelo Daros de Luca <luizluca@gmail.com>
>>> +
>>> +description:
>>> +  Multi-channel temperature monitor and PWM fan controller.
>>> +  It supports monitoring up to 10 external temperature sensors and
>>> +  controlling up to four fans. The fan control lines are modeled
>>> +  as standard PWM channels.
>>> +
>>> +properties:
>>> +  compatible:
>>> +    const: adi,adt7470
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>> +  "#pwm-cells":
>>> +    const: 3
>>> +    description:
>>> +      See Documentation/devicetree/bindings/pwm/pwm.yaml for the
>>> +      generic PWM binding description.
>>
>> Drop description.
>>
>> You OTOH, miss ref to pwm schema. Referencing here in description should
>> raise you questions... And then use unevaluatedProperties.
> 
> I will drop the description and change to `unevaluatedProperties: false`.
> 
> Regarding the reference to the PWM schema, adding `$ref:
> /schemas/pwm/pwm.yaml#` enforces the `$nodename` to match
> `^pwm(@.*|-([0-9a-f]+))?$`. Since the ADT7470 is primarily a hardware
> monitor, its node is typically named `sensor@...`,
> `fan-controller@...` or `hwmon@...`. Importing `pwm.yaml` causes
> `dtbs_check` to fail on existing node names because of this mismatch.

If it is a fan-controller then it should use common fan schema, because
you might be missing several properties.

Device having PWM outputs alone does not make it a fan controller, though.

> 
> Since we cannot override the `$nodename` from an imported schema, what
> is the preferred approach here? Should I skip the `$ref` to `pwm.yaml`
> in this specific case, or is there an accepted workaround for sensors
> acting as PWM providers?

You can skip the pwm.yaml in such case.

> 
>> You most likely miss ref to thermal-sensor.yaml as well, but that would
>> change the ABI since hwmon would fail on missing cells, right?
> 
> Yes, you are right. It would require #thermal-sensor-cells and the
> device might not have a thermal sensor connected if it is used as a
> pure fan controller. Likewise, it can also be used as a simple
> analog-to-digital temperature adapter, with no fans connected (and
> "#pwm-cells" might be missing).
> 
> To address this without breaking the ABI, we could add the ref
> conditionally if "#thermal-sensor-cells" is present.
> 
> allOf:
>  - if:
>      required:
>        - "#thermal-sensor-cells"
>    then:
>      $ref: /schemas/thermal/thermal-sensor.yaml#
> 
> I just don't know if it is ok to ref thermal-sensor but not pwm.

Feels ok.


Best regards,
Krzysztof