linux-kernel - Re: [PATCH net-next v3 14/17] dt-bindings: net: pse-pd: Add bindings for PD692x0 PSE controller

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Date: Thu, 15 Feb 2024 13:04:01 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Köry Maincent <kory.maincent@...tlin.com>
Cc: Andrew Lunn <andrew@...n.ch>, Rob Herring <robh@...nel.org>,
	"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>,
	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 v3 14/17] dt-bindings: net: pse-pd: Add bindings
 for PD692x0 PSE controller

On Thu, Feb 15, 2024 at 11:41:23AM +0100, Köry Maincent wrote:
> On Thu, 15 Feb 2024 09:17:48 +0100
> Oleksij Rempel <o.rempel@...gutronix.de> wrote:
> 
> > On Wed, Feb 14, 2024 at 06:41:54PM +0100, Andrew Lunn wrote:
> > > > Alternative A and B Overview
> > > > ----------------------------
> > > > 
> > > > - **Alternative A:** Utilizes the data-carrying pairs for power
> > > > transmission in 10/100BaseT networks. The power delivery's polarity in
> > > > this alternative can vary based on the MDI (Medium Dependent Interface)
> > > > or MDI-X (Medium Dependent Interface Crossover) configuration.
> > > > 
> > > > - **Alternative B:** Delivers power over the spare pairs not used for
> > > > data in 10/100BaseT networks. Unlike Alternative A, Alternative B's
> > > > method separates power from data lines within the cable. Though it is
> > > > less influenced by data transmission direction, Alternative B includes
> > > > two configurations with different polarities, known as variant X and
> > > > variant S, to accommodate different network requirements and device
> > > > specifications.  
> > > 
> > > Thanks for this documentation.
> > > 
> > > It might be worth pointing out that RJ-45 supports up to 4
> > > pairs. However, 10/100BaseT only makes use of two pairs for data
> > > transfer from the four. 1000BaseT and above make use of all four pairs
> > > for data transfer. If you don't know this, it is not so obvious what
> > > 'data-carrying pairs' and 'spare pairs' mean.  
> > 
> > @Kory, can you please update it.
> > 
> > > And what happens for 1000BaseT when all four pairs are in use?  
> > 
> > Hm.. good question. I didn't found the answer in the spec. By combining all
                                                               ^^^^^^^^^^^^^^^^

> > puzzle parts I assume, different Alternative configurations are designed
    ^^^^^^^^^^^^^^^^^^^^^^

> > to handle conflict between "PSE Physical Layer classification" and PHY
> > autoneg.
> 
> Oleksij how did you get the definition of Alternative A uses the "data-carrying"
> pairs for power transmission and Alternative B Delivers power over the "spare
> pairs"?
> 
> On my understanding of the 2022 standard the definition is: 
> - Alternative A is for pinout conductors 1, 2, 3 and 6
> - Alternative B is for pinout conductors 4, 5, 7, 8.
> 
> Then indeed if we are in 10/100BaseT Alternative A are "data-carrying
> pairs" and Alternative B are "spare pairs" but that's not the case on
> 1000BaseT.
> 
> You can see it in the figures in the paragraph 145.2.3.

Please, re-read my answer :)

Autoneg for 1000Mbit is not done on all 4 pairs. The only MDI/-X
dependent transfer processes only on one pair is autoneg. Every thing
else is extrapolated out of it.

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