Re: [PATCH v1 1/2] dt-bindings: hwmon: Add starfive,jhb100-fan-tach

[Rob Herring]

On Wed, May 6, 2026 at 8:36 PM Changhuang Liang
<changhuang.liang@xxxxxxxxxxxxxxxx> wrote:
>
> Hi, Rob
>
> Thanks for the review.
>
> > On Tue, Apr 28, 2026 at 01:23:36AM -0700, Changhuang Liang wrote:
> > > Add compatible "starfive,jhb100-fan-tach" for StarFive JHB100 Fan-Tach
> > > controller.
> > >
> > > Signed-off-by: Changhuang Liang <changhuang.liang@xxxxxxxxxxxxxxxx>
> > > ---
> > >  .../hwmon/starfive,jhb100-fan-tach.yaml       | 98
> > +++++++++++++++++++
> > >  1 file changed, 98 insertions(+)
> > >  create mode 100644
> > > Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml
> > >
> > > diff --git
> > >
> > a/Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yam
> > > l
> > >
> > b/Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yam
> > > l
> > > new file mode 100644
> > > index 000000000000..fdc8539ec804
> > > --- /dev/null
> > > +++
> > b/Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach
> > > +++ .yaml
> > > @@ -0,0 +1,98 @@
> > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause %YAML 1.2
> > > +---
> > > +$id:
> > > +http://devicetree.org/schemas/hwmon/starfive,jhb100-fan-tach.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: StarFive JHB100 Fan-Tach controller
> > > +
> > > +maintainers:
> > > +  - Changhuang Liang <changhuang.liang@xxxxxxxxxxxxxxxx>
> > > +
> > > +description:
> > > +  The StarFive Fan-Tach controller can support up to 16 fan tach input.
> > > +
> > > +properties:
> > > +  compatible:
> > > +    enum:
> > > +      - starfive,jhb100-fan-tach
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  clocks:
> > > +    maxItems: 1
> > > +
> > > +  resets:
> > > +    maxItems: 1
> > > +
> > > +  interrupts:
> > > +    maxItems: 1
> > > +
> > > +  '#address-cells':
> > > +    const: 1
> > > +
> > > +  '#size-cells':
> > > +    const: 0
> > > +
> > > +patternProperties:
> > > +  "^fan@[0-9]+$":
> >
> > Unit-addresses are hex.
> >
> > > +    $ref: fan-common.yaml#
> > > +    unevaluatedProperties: false
> > > +    required:
> > > +      - reg
> > > +      - tach-ch
> >
> > You need constraints on the 'reg' values. Also, what does 'reg'
> > represent in this case?
>
> "reg" is only used to distinguish between different fan instances.
>
> >
> > > +
> > > +required:
> > > +  - compatible
> > > +  - reg
> > > +  - clocks
> > > +  - resets
> > > +  - interrupts
> > > +
> > > +additionalProperties: false
> > > +
> > > +examples:
> > > +  - |
> > > +    fan-tach-controller@11be0000 {
> > > +        compatible = "starfive,jhb100-fan-tach";
> > > +        reg = <0x11be0000 0x400>;
> > > +        interrupts = <128>;
> > > +        clocks = <&per2crg 33>;
> > > +        resets = <&per2crg 5>;
> > > +        #address-cells = <1>;
> > > +        #size-cells = <0>;
> > > +
> > > +        fan@0 {
> > > +            reg = <0>;
> > > +            tach-ch = /bits/ 8 <0x0>, <0x8>;
> >
> > How do you have 1 fan with 2 tach signals?
>
> On our platform, two fans share one PWM channel. It seems there was a misunderstanding earlier.
> I will change it to the form of one tach per fan.

I think you have to leave it like this as you can't have 2 fan nodes
at the same address. Just need to fix the size.

Rob