netdev - Re: [PATCH net-next v2 7/8] dt-bindings: net: pse-pd: Add bindings for PD692x0 PSE controller

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Date: Tue, 5 Dec 2023 11:15:01 +0100
From: Köry Maincent <kory.maincent@...tlin.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, Jonathan Corbet <corbet@....net>, Luis Chamberlain
 <mcgrof@...nel.org>, Russ Weight <russ.weight@...ux.dev>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, Rob Herring <robh+dt@...nel.org>, Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 devicetree@...r.kernel.org, Dent Project <dentproject@...uxfoundation.org>,
 Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH net-next v2 7/8] dt-bindings: net: pse-pd: Add bindings
 for PD692x0 PSE controller

On Tue, 5 Dec 2023 07:36:06 +0100
Oleksij Rempel <o.rempel@...gutronix.de> wrote:

> > > +examples:
> > > +  - |
> > > +    i2c {
> > > +        #address-cells = <1>;
> > > +        #size-cells = <0>;
> > > +
> > > +        ethernet-pse@3c {
> > > +          compatible = "microchip,pd69200";
> > > +          reg = <0x3c>;
> > > +          #pse-cells = <1>;
> > > +          ports-matrix = <0 2 5
> > > +                          1 3 6
> > > +                          2 0 0xff
> > > +                          3 1 0xff>;  
> > 
> > Hm... this will probably not scale.  PSE is kind of PMIC for ethernet. I
> > has bunch of regulators which can be grouped to one more powerful
> > regulator. Since it is regulators, we will wont to represent them in a
> > system as regulators too. We will probably have physical, board
> > specific limitation, so we will need to describe regulator limits for
> > each separate channel.  
> 
> After diving a bit deeper to the chip manual and communication protocol
> manual I would recommend to recreate system topology as good as possible
> in the devicetree. The reason is that we actually able to communicate
> with with "manager" behind the "controller" and the "port-matrix" is all
> about the "managers" and physical ports layout.

Ok, but the "managers communication" implementation will be added later as
for now only the basics of the the PSE controller is implemented.

> Typical system architecture looks like this:
> 
> SoC   --- i2c/uart --> controller -- spi --> manager0 -- phys_port0 -->
> log_port0 (PoE4) |           \- phys_port1 -/
> 					 |	     \- phys_port2 -->
> log_port1 (PoE2) |	     \- phys_port3 --> log_port2 (PoE2)
>                                          \- manager1 -- phys_port0 ..
> 					....
> 
> Please include some ASCII topology to the documentation :)

Ok. 

> I would expect a devicetree like this:
> 
>         ethernet-pse@3c {
> 	  // controller compatible should be precise
>           compatible = "microchip,pd69210";
>           reg = <0x3c>;
>           #pse-cells = <1>;
>           
> 	  managers {
> 	    manager@0 {
> 	      // manager compatible should be included, since we are
> 	      // able to campare it with communication results
> 	      compatible = "microchip,pd69208t4"
> 	      // addressing corresponding to the chip select addressing
> 	      reg = <0>;
> 
> 	      physical-ports {
> 	        phys0: port@0 {
> 		  // each of physical ports is actually a regulator
> 		  reg = <0>;
> 		};
> 	        phys1: port@1 {
> 		  reg = <1>;
> 		};
> 	        phys2: port@2 {
> 		  reg = <2>;
> 		};
> 
>                ...
> 	      }
> 
>           // port matrix can be calculated by using this information
>           logical-ports {
> 	    log_port0: port@0 {
> 	      // PoE4 port
> 	      physical-ports = <&phys0, &phys1>;
> 	    };
> 	    log_port1: port@1 {
> 	      // PoE2 port
> 	      physical-ports = <&phys2>;
> 	    };
> 	  };
> 
> ....
>    ethernet-phy@1 {
>      reg = <1>;
>      pses = <&log_port0>;
>    }
>    ethernet-phy@2 {
>      reg = <2>;
>      pses = <&log_port1>;
>    }

The pse node will become massive (more than 140 subnodes) but indeed this will
fit the real topology architecture.

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com