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

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Message-ID: <20231205162321.4bd165eb@kmaincent-XPS-13-7390>
Date:   Tue, 5 Dec 2023 16:23:21 +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 15:21:47 +0100
Oleksij Rempel <o.rempel@...gutronix.de> wrote:

> On Tue, Dec 05, 2023 at 02:31:23PM +0100, Köry Maincent wrote:
> > On Tue, 5 Dec 2023 11:15:01 +0100
> > Köry Maincent <kory.maincent@...tlin.com> wrote:
> >   
> > > On Tue, 5 Dec 2023 07:36:06 +0100
> > > Oleksij Rempel <o.rempel@...gutronix.de> wrote:  
> >    
> > > > 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  
> > 
> > If this phys0 is a regulator, which device will be the consumer of this
> > regulator? log_port0 as the phys0 regulator consumer seems a bit odd!  
> 
> Why?
> 
> > A 8P8C node should be the consumer.  
> 
> PHY is not actual consumer of this regulator. State of the Ethernet PHY
> is not related to the power supply. We should deliver power independent
> of network interface state. There is no other local consumer we can
> use in this case.

Just to be clear, are you saying we should use the regulator framework or is it
simply a way of speaking as it behaves like regulator?

> > Finally, the devicetree would not know the matrix between logical port and
> > physical port, this would be cleaner.
> > 
> > Did I miss something?  
> 
> In case different PSE suppliers are linked withing the PHY node, we
> loose most of information needed for PSE functionality. For example how
> we will know if our log_port supports PoE4 and PoE2 mode, or only PoE2.
> This information is vital for proper PSE configuration, this is why I
> suggested to have logica-ports subnodes. With the price of hawing huge
> DT on a switch with 48 ports.

It could be known in the of_pse_control_get() function if there is two phandles
in the "pses" parameter. Then we add a new enum c33_pse_mode member in the
pse_control struct to store the mode.
PoE2 and PoE4 is not a parameter of the logical port, it depends of the number
of PSE ports wired to an 8P8C connector. 

In fact I am also working on the tps23881 driver which aimed to be added to
this series soon. In the tps23881 case the logical port can only be configured
to one physical port. Two physical ports (which mean two logical ports) can
still be used to have PoE4 mode.
For PoE4, in the pd692x0 driver we use one logical port (one pse_control->id)
configured to two physical ports but in the tps23881 we will need two logical
ports (two pse_control->id).

So with the tps23881 driver we will need two phandle in the "pses" parameter to
have PoE4, that's why my proposition seems relevant.

The same goes with your pse-regulator driver, you can't do PoE4 if two
regulators is needed for each two pairs group.

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