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Date: Wed, 14 Feb 2024 18:41:54 +0100
From: Andrew Lunn <andrew@lunn.ch>
To: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: Rob Herring <robh@kernel.org>,
	Kory Maincent <kory.maincent@bootlin.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Russ Weight <russ.weight@linux.dev>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>, Mark Brown <broonie@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Heiner Kallweit <hkallweit1@gmail.com>,
	Russell King <linux@armlinux.org.uk>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-doc@vger.kernel.org, devicetree@vger.kernel.org,
	Dent Project <dentproject@linuxfoundation.org>
Subject: Re: [PATCH net-next v3 14/17] dt-bindings: net: pse-pd: Add bindings
 for PD692x0 PSE controller
Message-ID: <618be4b1-c52c-4b8f-8818-1e4150867cad@lunn.ch>
References: <20240208-feature_poe-v3-0-531d2674469e@bootlin.com>
 <20240208-feature_poe-v3-14-531d2674469e@bootlin.com>
 <20240209145727.GA3702230-robh@kernel.org>
 <ZciUQqjM4Z8Tc6Db@pengutronix.de>
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> 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.

And what happens for 1000BaseT when all four pairs are in use?

    Andrew