Re: [PATCH net-next v3 1/2] dt-bindings: net: pse-pd: Add bindings for LTC4266 PSE Controller

[Kyle Swenson <kyle.swenson@est.tech>]

Hello Rob,

On Wed, Oct 07, 2026 at 04:04:54PM -0500, Rob Herring wrote:
> On Sun, Sep 27, 2026 at 09:29:48PM +0000, Kyle Swenson wrote:
> > Add the LTC4266 Power Sourcing Equipment controller device tree bindings
> > documentation.
> > 
> > Signed-off-by: Kyle Swenson <kyle.swenson@est.tech>
> > ---
> >  .../bindings/net/pse-pd/lltc,ltc4266.yaml     | 180 ++++++++++++++++++
> >  1 file changed, 180 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.yaml b/Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.yaml
> > new file mode 100644
> > index 000000000000..e11c9d601eee
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.yaml
> > @@ -0,0 +1,180 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/net/pse-pd/lltc,ltc4266.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Linear Technology LTC4266 Power Sourcing Equipment controller
> > +
> > +maintainers:
> > +  - Kyle Swenson <kyle.swenson@est.tech>
> > +
> > +allOf:
> > +  - $ref: pse-controller.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - lltc,ltc4266
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  interrupts:
> > +    maxItems: 1
> > +
> > +  channels:
> > +    type: object
> > +    additionalProperties: false
> > +    description:
> > +      Defines the 4 physical delivery channels on the controller that can be
> > +      referenced by PSE PIs through their "pairsets" property. The actual port
> > +      matrix mapping is created when PSE PIs reference these channels in their
> > +      pairsets.
> > +
> > +    properties:
> > +      '#address-cells':
> > +        const: 1
> > +
> > +      '#size-cells':
> > +        const: 0
> > +
> > +    patternProperties:
> > +      '^channel@[0-3]$':
> > +        type: object
> > +        additionalProperties: false
> > +
> > +        properties:
> > +          reg:
> > +            maxItems: 1
> > +
> > +          sense-resistor-micro-ohms:
> > +            description: Sense resistor connected to the channel's MOSFET, used
> > +              for current measurement and for overcurrent detection. The I_CUT
> > +              and I_LIM register encodings depend on which value is fitted, so
> > +              a wrong value programs the wrong thresholds.
> > +            enum: [250000, 500000]
> > +
> > +        required:
> > +          - reg
> > +          - sense-resistor-micro-ohms
> > +
> > +    required:
> > +      - '#address-cells'
> > +      - '#size-cells'
> > +
> > +  pse-pis:
> > +    type: object
> > +    additionalProperties: false
> > +
> > +    properties:
> > +      '#address-cells':
> > +        const: 1
> > +
> > +      '#size-cells':
> > +        const: 0
> > +
> > +    patternProperties:
> > +      '^pse-pi@[0-3]$':
> > +        type: object
> > +        additionalProperties: true
> 
> This cannot be true. That allows adding any property.
> 

So my intent with the additionalProperties: true was to avoid
replicating the entire pse-pis node from pse-controller.yaml.
Conceptually, my goal was to inherit everything from the
pse-controller.yaml binding, except limit the maxItems to 1 (since the
LTC4266 only supports power over a single PI).

Is there a better way to express this?

> > +        properties:
> > +          pairsets:
> > +            description: The LTC4266 delivers power to a PI over a single
> > +              pairset, driven by one of the controller's four channels. There
> > +              is no 4-pair mode spreading a PI over two channels, so exactly
> > +              one channel phandle is expected.
> > +            maxItems: 1
> > +          pairset-names:
> > +            maxItems: 1
> 
> An empty node is valid? Needs 'required'.

I thought the 'required' comes from the pse-controller.yaml binding.
If I adjust the example dts in the binding with something like

           pse_pi2: pse-pi@2 {
-            reg = <2>;
-            #pse-cells = <0>;
-            pairset-names = "alternative-a";
-            pairsets = <&phys2>;
-            polarity-supported = "MDI";
-            vpwr-supply = <&vreg_pse>;
           };

Then make dt_binding_check will fail with 

  DTEX    Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.example.dts
  DTC [C] Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.example.dtb
Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.example.dts:83.33-84.17: Warning (unit_address_vs_reg): /example-0/i2c/ethernet-pse@2f/pse-pis/pse-pi@2: node has a unit name, but no reg or ranges property
Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.example.dtb: ethernet-pse@2f (lltc,ltc4266): pse-pis:pse-pi@2: 'reg' is a required property
	from schema $id: http://devicetree.org/schemas/net/pse-pd/lltc,ltc4266.yaml
Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.example.dtb: ethernet-pse@2f (lltc,ltc4266): pse-pis:pse-pi@2: '#pse-cells' is a required property
	from schema $id:
	http://devicetree.org/schemas/net/pse-pd/lltc,ltc4266.yaml

But I'm probably missing something obvious, so please don't hesitate to
point it out or point me to docs.

> 
> Rob

Thanks so much for the review!
Kyle