linux-kernel - Re: [PATCH net-next 0/7] Allow controlling PHY loopback and isolate modes

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Message-ID: <aae18d69-fc00-47f2-85d8-2a45d738261b@lunn.ch>
Date: Thu, 12 Sep 2024 20:21:52 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com,
	Jakub Kicinski <kuba@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Russell King <linux@...linux.org.uk>,
	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>,
	Köry Maincent <kory.maincent@...tlin.com>,
	Oleksij Rempel <o.rempel@...gutronix.de>
Subject: Re: [PATCH net-next 0/7] Allow controlling PHY loopback and isolate
 modes

> The loopback control from that API is added as it fits the API
> well, and having the ability to easily set the PHY in MII-loopback
> mode is a helpful tool to have when bringing-up a new device and
> troubleshooting the link setup.

We might want to take a step back and think about loopback some more.

Loopback can be done at a number of points in the device(s). Some
Marvell PHYs can do loopback in the PHY PCS layer. Some devices also
support loopback in the PHY SERDES layer. I've not seen it for Marvell
devices, but maybe some PHYs allow loopback much closer to the line?
And i expect some MAC PCS allow loopback.

So when talking about loopback, we might also want to include the
concept of where the loopback occurs, and maybe it needs to be a NIC
wide concept, not a PHY concept?

	Andrew