Re: [RFC PATCH net-next v2 1/2] dt-bindings: net: pse-pd: Add bindings for LTC4266 PSE Controller

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

Hello Kory,

On Mon, Aug 24, 2026 at 12:46:35PM +0200, Kory Maincent wrote:
> Hello Kyle,
> 
> Glad to see the v2 landing in the mailing list.
Sure has taken a while, but finally here....

> 
> On 8/20/26 16:25, 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..b3da8fea0b07
> > --- /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
> > +
> > +  reset-gpios:
> > +    maxItems: 1
> 
> The reset-gpios is currently not implemented in your driver. Maybe add it in
> the binding when it will be the case.

I was trying to follow the "bindings document hardware" model but I've
no problem dropping it in future versions.  I would have added the
reset-gpios support in the driver, but the hardware I've got with the
LTC4266 has the LTC4266 reset connected to the board level reset and so
I can't test this functionality if I were to add it.

> 
> > +  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 for overcurrent detection.
> > +            enum: [250000, 500000]
> > +
> > +        required:
> > +          - reg
> > +          - sense-resistor-micro-ohms
> 
> I am bit skeptical about having sense-resistor-micro-ohms as a mandatory
> parameter. As you have described it's only for current measurement so it's
> not a requirement for PSE functioning. Maybe set it as a default value if
> not specified.
Well, on the LTC4266, the chipset depends on this current measurement to
enforce per-class current limits, which is required for power budgeting.
Maybe it'd be good for me to expclitly state that instead.

> 
> Else LGTM.
Ack.
> 
> > +    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
> > +        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
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - interrupts
> > +  - channels
> > +  - pse-pis
> > +
> > +unevaluatedProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/interrupt-controller/irq.h>
> > +
> > +    i2c {
> > +      #address-cells = <1>;
> > +      #size-cells = <0>;
> > +
> > +      ethernet-pse@2f {
> > +        compatible = "lltc,ltc4266";
> > +        reg = <0x2f>;
> > +        interrupts = <8 IRQ_TYPE_LEVEL_LOW>;
> > +        interrupt-parent = <&gpio>;
> > +
> > +        channels {
> > +          #address-cells = <1>;
> > +          #size-cells = <0>;
> > +
> > +          phys0: channel@0 {
> > +            reg = <0>;
> > +            sense-resistor-micro-ohms = <500000>;
> > +          };
> > +
> > +          phys1: channel@1 {
> > +            reg = <1>;
> > +            sense-resistor-micro-ohms = <500000>;
> > +          };
> > +
> > +          phys2: channel@2 {
> > +            reg = <2>;
> > +            sense-resistor-micro-ohms = <500000>;
> > +          };
> > +
> > +          phys3: channel@3 {
> > +            reg = <3>;
> > +            sense-resistor-micro-ohms = <500000>;
> > +          };
> > +        };
> > +
> > +        pse-pis {
> > +          #address-cells = <1>;
> > +          #size-cells = <0>;
> > +
> > +          pse_pi0: pse-pi@0 {
> > +            reg = <0>;
> > +            #pse-cells = <0>;
> > +            pairset-names = "alternative-a";
> > +            pairsets = <&phys0>;
> > +            polarity-supported = "MDI";
> > +            vpwr-supply = <&vreg_pse>;
> > +          };
> > +
> > +          pse_pi1: pse-pi@1 {
> > +            reg = <1>;
> > +            #pse-cells = <0>;
> > +            pairset-names = "alternative-a";
> > +            pairsets = <&phys1>;
> > +            polarity-supported = "MDI";
> > +            vpwr-supply = <&vreg_pse>;
> > +          };
> > +
> > +          pse_pi2: pse-pi@2 {
> > +            reg = <2>;
> > +            #pse-cells = <0>;
> > +            pairset-names = "alternative-a";
> > +            pairsets = <&phys2>;
> > +            polarity-supported = "MDI";
> > +            vpwr-supply = <&vreg_pse>;
> > +          };
> > +
> > +          pse_pi3: pse-pi@3 {
> > +            reg = <3>;
> > +            #pse-cells = <0>;
> > +            pairset-names = "alternative-a";
> > +            pairsets = <&phys3>;
> > +            polarity-supported = "MDI";
> > +            vpwr-supply = <&vreg_pse>;
> > +          };
> > +        };
> > +      };
> > +    };
> 
> -- 
> Köry Maincent, Bootlin
> Embedded Linux and kernel engineering
> https://bootlin.com
> 
Thanks for the review!

Thanks,
Kyle