linux-kernel - Re: [PATCH net-next RFC 0/5] net: phy: Introduce a port representation

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Message-ID: <Z31OHYsfZc8fT--Z@pengutronix.de>
Date: Tue, 7 Jan 2025 16:54:05 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Kory Maincent <kory.maincent@...tlin.com>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com,
	Andrew Lunn <andrew@...n.ch>, Jakub Kicinski <kuba@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	linux-arm-kernel@...ts.infradead.org,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Herve Codina <herve.codina@...tlin.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Marek Behún <kabel@...nel.org>,
	Nicolò Veronese <nicveronese@...il.com>,
	Simon Horman <horms@...nel.org>, mwojtas@...omium.org,
	Antoine Tenart <atenart@...nel.org>
Subject: Re: [PATCH net-next RFC 0/5] net: phy: Introduce a port
 representation

On Tue, Jan 07, 2025 at 03:14:43PM +0000, Russell King (Oracle) wrote:
> On Tue, Jan 07, 2025 at 03:02:46PM +0100, Oleksij Rempel wrote:
> > On Tue, Jan 07, 2025 at 02:26:05PM +0100, Kory Maincent wrote:
> > > On Thu, 2 Jan 2025 18:03:52 +0100
> > > Oleksij Rempel <o.rempel@...gutronix.de> wrote:
> > The IEEE 802.3 - 2022 has following variants:
> > 14.5.2 Crossover function - only A<>B swap is supported
> > 40.4.4 Automatic MDI/MDI-X Configuration - only A<>B swap is supported?
> > 55.4.4 Automatic MDI/MDI-X configuration - 4 swap variants are supported
> > 113.4.4 Automatic MDI/MDI-X configuration - 4 swap variants are supported
> > 126.4.4 Automatic MDI/MDI-X configuration - 4 swap variants are supported
> > 
> > This was only the pair swap. How to reflect the polarity swap withing
> > the pairs?
> 
> 802.3 supports this because of the problems caused by miswired cables,
> which are typically a user thing. It's not really there to give freedom
> to designers to wire their sockets incorrectly.
> 
> Do we have any real cases where a socket has been wired incorrectly?

Yes. I tested some low cost adapter using same driver but reporting
incorrect results, depending on board. I can explain it only by
incorrect PCB design.

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