Re: [PATCH net-next v2 2/4] dt-bindings: net: dsa: Add SoC-e SWIP switch

[Andrew Lunn <andrew@lunn.ch>]

On Tue, Sep 08, 2026 at 08:15:35PM +0200, Vasilij Strassheim wrote:
> On Mon, 2026-09-07 at 21:04 +0200, Andrew Lunn wrote:
> > > +    patternProperties:
> > > +      '^mdio@[0-9a-f]+$':
> > > +        $ref: /schemas/net/mdio.yaml#
> > > +        unevaluatedProperties: false
> > > +
> > > +        properties:
> > > +          reg:
> > > +            maximum: 30
> > > +            description:
> > > +              MDIO controller output index, which must be lower than the
> > > +              number of implemented switch ports.
> > 
> > Is there a relationship between an MDIO bus and a port?
> 
> Yes, there is a one-to-one relationship for this IP. The MDIO bus
> selector corresponds to the switch port index.
> 
> > 
> > I'm just wondering if the MDIO bus should be a property of the
> > port. There are switch which have an MDIO bus per port.
> > 
> 
> I see this model in the new NETC switch binding. I will move the
> optional mdio node below the corresponding ethernet-port@N and derive
> the selector from the port's reg.

Since this is an FPGA, i assume there are no internal PHYs. Mixed mode
is not something FPGAs do. There are sometime "interesting"
relationships between port number and address on the MDIO bus. But
without internal PHYs you don't need to worry about this.

> > > +patternProperties:
> > > +  '^(ethernet-)?ports$':
> > > +    patternProperties:
> > > +      '^(ethernet-)?port@[0-9a-f]+$':
> > > +        $ref: dsa-port.yaml#
> > > +        unevaluatedProperties: false
> > > +
> > > +        properties:
> > > +          reg:
> > > +            maximum: 30
> > > +            description:
> > > +              Switch port index. Supported switch configurations have
> > > +              up to 31 ports, numbered from 0 through 30.
> > 
> > 30 seems odd. Is 31 something special? 
> > 
> 
> The hardware stores the port count directly in a 5-bit field, so 31 is
> the maximum representable count. Therefore, valid zero-based port
> indices range from 0 to 30. The switch documentation is unclear about
> the encoding, but I tested a three-port configuration and the field
> contained 3.

So in theory, a 0 port switch is possible!

   Andrew