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

[Luiz Angelo Daros de Luca]

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@xxxxxxxxx>
> > ---
> >  .../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@xxxxxxxxx>
> > +
> > +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.

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 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.

> > +
> > +  "#thermal-sensor-cells":
> > +    const: 1
> > +    description:
> > +      Number of cells required to uniquely identify the temperature sensors.
>
> Drop sentence, you never need to explain standard properties. It only
> adds bloat and more places to fix/change if we do any refactoring.
>
> > +      Valid index values are 0 to 9, corresponding to temp1 through temp10.
>
> Only this is needed.

I'll keep only the sentence regarding the valid index values.

I'll send a v4 with the updates mostly because Sashiko-bot failed to
merge v3 with dependencies.

Regards,

Luiz