linux-kernel - Re: [PATCH net-next v4 14/17] dt-bindings: net: pse-pd: Add bindings for PD692x0 PSE controller

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Date: Wed, 21 Feb 2024 16:06:25 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Rob Herring <robh@...nel.org>
Cc: Kory Maincent <kory.maincent@...tlin.com>,
	"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>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, Mark Brown <broonie@...nel.org>,
	Frank Rowand <frowand.list@...il.com>, Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	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>
Subject: Re: [PATCH net-next v4 14/17] dt-bindings: net: pse-pd: Add bindings
 for PD692x0 PSE controller

On Wed, Feb 21, 2024 at 07:41:35AM -0700, Rob Herring wrote:
> On Sat, Feb 17, 2024 at 01:14:29PM +0100, Oleksij Rempel wrote:
> > On Thu, Feb 15, 2024 at 05:02:55PM +0100, Kory Maincent wrote:
> > > Add the PD692x0 I2C Power Sourcing Equipment controller device tree
> > > bindings documentation.
> > > 
> > > This patch is sponsored by Dent Project <dentproject@...uxfoundation.org>.
> > > 
> > > Signed-off-by: Kory Maincent <kory.maincent@...tlin.com>
> > > ---
> > ...
> > > +        pse_pis {
> > > +          #address-cells = <1>;
> > > +          #size-cells = <0>;
> > > +
> > > +          pse_pi0: pse_pi@0 {
> > > +            reg = <0>;
> > > +            #pse-cells = <0>;
> > > +            pairset-names = "alternative-a", "alternative-b";
> > > +            pairsets = <&phys0>, <&phys1>;
> > > +          };
> > > +          pse_pi1: pse_pi@1 {
> > > +            reg = <1>;
> > > +            #pse-cells = <0>;
> > > +            pairset-names = "alternative-a";
> > > +            pairsets = <&phys2>;
> > 
> > According to latest discussions, PSE PI nodes will need some
> > additional, board specific, information:
> > - this controller do not implements polarity switching, we need to know
> >   what polarity is implemented on this board. The 802.3 spec provide not
> >   really consistent names for polarity configurations:
> >   - Alternative A MDI-X
> >   - Alternative A MDI
> >   - Alternative B X
> >   - Alternative B S
> >   The board may implement one of polarity configurations per alternative
> >   or have additional helpers to switch them without using PSE
> >   controller.
> >   Even if specification explicitly say:
> >   "The PD shall be implemented to be insensitive to the polarity of the power
> >    supply and shall be able to operate per the PD Mode A column and the PD
> >    Mode B column in Table 33–13"
> >   it is possible to find reports like this:
> >   https://community.ui.com/questions/M5-cant-take-reversed-power-polarity-/d834d9a8-579d-4f08-80b1-623806cc5070
> > 
> >   Probably this kind of property is a good fit:
> >   polarity-supported = "MDI-X", "MDI", "X", "S";
> 
> Where does that live? Looks like a property of the consumers defined in 
> the provider. Generally, that's not the right way for DT. 

This is property of PSE PI (Power Interface)

                                             Ethernet PHY --\
PSE (provider) ----> PSE PI (consumer of multiple PSE's) ----> Physial port


PSE - provides power lines.
PSE PI - switches (or not) power lines in different configurations. This
is different part of the board/system. PSE PI can have combination or
one of following configurations: "MDI-X", "MDI", "X", "S";
This is not something what PSE actually do. PSE PI and PSE are described
in IEEE802.3 specification.

> I'll say it 
> again, I think you should be expanding #pse-cells (>1), not getting rid 
> of them (==0).

Did you took time to read my last explanation? Sorry for making it long
description, this topic is a bit complex.

Regards,
Oleksij
-- 
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