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

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Date:   Thu, 21 Apr 2022 09:35:42 +0200
From:   Clément Léger <clement.leger@...tlin.com>
To:     Rob Herring <robh@...nel.org>
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

Le Wed, 20 Apr 2022 15:11:26 -0500,
Rob Herring <robh@...nel.org> a écrit :

> 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?

'port' represent the port index in the MII converter IP. I went with reg
first, but according to Andrew feedback, it looked like it was a bad
idea since it was not really a "bus".  However, this pattern is already
used for dsa ports.

> > > 
> > > 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.

Acked.

> 
> 
> >             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.

Yep, it seems to be used in some other driver as a single phandle too.
I'll kept that.

> 
> > 
> >  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.

No worries.

> 
> Rob



-- 
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com