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Date:   Wed, 20 Apr 2022 15:11:26 -0500
From:   Rob Herring <robh@...nel.org>
To:     Clément Léger <clement.leger@...tlin.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Herve Codina <herve.codina@...tlin.com>,
        Miquèl Raynal <miquel.raynal@...tlin.com>,
        Milan Stevanovic <milan.stevanovic@...com>,
        Jimmy Lalande <jimmy.lalande@...com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 03/12] dt-bindings: net: pcs: add bindings for
 Renesas RZ/N1 MII converter

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@...nel.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@...30000 {
>   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@...50000 {
>     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

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