Re: [PATCH net-next 03/12] dt-bindings: net: pcs: add bindings for Renesas RZ/N1 MII converter

Rob Herring
2022-04-20T20:11:38Z

On Tue, Apr 19, 2022 at 05:00:44PM +0200, Clément Léger wrote:
> Le Tue, 19 Apr 2022 08:43:47 -0500,
> Rob Herring <robh@kernel.org> a écrit :
>
> > > + clocks:
> > > + items:
> > > + - description: MII reference clock
> > > + - description: RGMII reference clock
> > > + - description: RMII reference clock
> > > + - description: AHB clock used for the MII converter register interface
> > > +
> > > + renesas,miic-cfg-mode:
> > > + description: MII mux configuration mode. This value should use one of the
> > > + value defined in dt-bindings/net/pcs-rzn1-miic.h.
> >
> > Describe possible values here as constraints. At present, I don't see
> > the point of this property if there is only 1 possible value and it is
> > required.
>
> The ethernet subsystem contains a number of internal muxes that allows
> to configure ethernet routing. This configuration option allows to set
> the register that configure these muxes.
>
> After talking with Andrew, I considered moving to something like this:
>
> eth-miic@44030000 {
> compatible = "renesas,rzn1-miic";
>
> mii_conv1: mii-conv-1 {
> renesas,miic-input = <MIIC_GMAC1_PORT>;
> port = <1>;

'port' is already used, find another name. Maybe 'reg' here. Don't know.
What do 1 and 2 represent?

> };
> mii_conv2: mii-conv-2 {
> renesas,miic-input = <MIIC_SWITCHD_PORT>;
> port = <2>;
> };
> ...
> };
>
> Which would allow embedding the configuration inside the port
> sub-nodes. Moreover, it allows a better validation of the values using
> the schema validation directly since only a limited number of values
> are allowed for each port.
>
> >
> > > + $ref: /schemas/types.yaml#/definitions/uint32
> > > +
> > > +patternProperties:
> > > + "^mii-conv@[0-4]$":
> > > + type: object
> >
> > additionalProperties: false
> >
> > > + description: MII converter port
> > > +
> > > + properties:
> > > + reg:
> > > + maxItems: 1
> >
> > Why do you need sub-nodes? They don't have any properties. A simple mask
> > property could tell you which ports are present/active/enabled if that's
> > what you are tracking. Or the SoC specific compatibles you need to add
> > can imply the ports if they are SoC specific.
>
> The MACs are using phandles to these sub-nodes to query a specific MII
> converter port PCS:
>
> switch@44050000 {
> compatible = "renesas,rzn1-a5psw";
>
> ports {
> port@0 {

ethernet-ports and ethernet-port so we don't collide with the graph
binding.

> reg = <0>;
> label = "lan0";
> phy-handle = <&switch0phy3>;
> pcs-handle = <&mii_conv4>;
> };
> };
> };
>
> According to Andrew, this is not a good idea to represent the PCS as a
> bus since it is indeed not a bus. I could also switch to something like
> pcs-handle = <&eth_mii 4> but i'm not sure what you'd prefer. We could
> also remove this from the device-tree and consider each driver to
> request the MII ouput to be configured using something like this for
> instance:

I'm pretty sure we already defined pcs-handle as only a phandle. If you
want variable cells, then it's got to be extended like all the other
properties using that pattern.

>
> miic_request_pcs(pcs_np, miic_port_nr, MIIC_SWITCHD_PORT);
>
> But I'm not really fan of this because it requires the drivers to
> assume some specificities of the MII converter (port number are not in
> the same order of the switch for instance) and thus I would prefer this
> to be in the device-tree.
>
> Let me know if you can think of something that would suit you
> better but keep in mind that I need to correctly match a switch/MAC
> port with a PCS port and that I also need to configure MII internal
> muxes.
>
> For more information, you can look at section 8 of the manual at [1].

I can't really. Other people want their bindings reviewed too.

Rob