Re: [PATCH net-next 1/2] dt-bindings: net: document Microchip PIC64-HPSC/HX MDIO controller

[Charles Perry]

On Wed, Mar 18, 2026 at 05:48:08PM +0000, Conor Dooley wrote:
> On Tue, Mar 17, 2026 at 11:46:09AM -0700, Charles Perry wrote:
> > This MDIO hardware is based on a Microsemi design supported in Linux by
> > mdio-mscc-miim.c. However, The register interface is completely different
> > with pic64hpsc, hence the need for separate documentation.
> > 
> > The hardware supports C22 and C45.
> > 
> > The documentation recommends an input clock of 156.25MHz and a prescaler
> > of 39, which yields an MDIO clock of 1.95MHz.
> > 
> > The hardware supports an interrupt pin to signal transaction completion
> > which is not strictly needed as the software can also poll a "TRIGGER"
> > bit for this.
> > 
> > Signed-off-by: Charles Perry <charles.perry@xxxxxxxxxxxxx>
> > ---
> >  .../net/microchip,pic64hpsc-mdio.yaml         | 61 +++++++++++++++++++
> >  1 file changed, 61 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/net/microchip,pic64hpsc-mdio.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/net/microchip,pic64hpsc-mdio.yaml b/Documentation/devicetree/bindings/net/microchip,pic64hpsc-mdio.yaml
> > new file mode 100644
> > index 000000000000..21c76199c11b
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/net/microchip,pic64hpsc-mdio.yaml
> > @@ -0,0 +1,61 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/net/microchip,pic64hpsc-mdio.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Microchip PIC64-HPSC/HX MDIO controller
> > +
> > +maintainers:
> > +  - Charles Perry <charles.perry@xxxxxxxxxxxxx>
> > +
> > +description: |
> > +  Microchip PIC64-HPSC/HX SoCs have two MDIO bus controller. This MDIO bus
> > +  controller supports C22 and C45 register access. It is named "MDIO Initiator"
> > +  in the documentation.
> > +
> > +allOf:
> > +  - $ref: mdio.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    oneOf:
> > +      - const: microchip,pic64hpsc-mdio
> > +      - items:
> > +          - const: microchip,pic64hx-mdio
> > +          - const: microchip,pic64hpsc-mdio
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  clocks:
> > +    maxItems: 1
> > +
> > +  clock-frequency: true
> 
> Does this genuinely have no constraints?

It's going to divide the input frequency by 2 to 512 (the prescaler is 8
bit long), so assuming an input clock of 156.25 MHz, the bounds are 305KHz
to 78MHz. The standard is 2.5MHz.

I can add a maximum and minimum here since I do have some validation on
this in the driver which will bail out if this is out of bound.

Thanks,
Charles