linux-kernel - Re: [PATCH net-next v5 09/13] net: phylink: Use phy_caps

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Message-ID: <12e3b86d-27aa-420b-8676-97b603abb760@lunn.ch>
Date: Fri, 28 Mar 2025 22:45:05 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Alexander Duyck <alexander.duyck@...il.com>
Cc: Maxime Chevallier <maxime.chevallier@...tlin.com>, davem@...emloft.net,
	Jakub Kicinski <kuba@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Russell King <linux@...linux.org.uk>,
	Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.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>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Köry Maincent <kory.maincent@...tlin.com>,
	Oleksij Rempel <o.rempel@...gutronix.de>,
	Simon Horman <horms@...nel.org>,
	Romain Gantois <romain.gantois@...tlin.com>
Subject: Re: [PATCH net-next v5 09/13] net: phylink: Use phy_caps_lookup for
 fixed-link configuration

> Also I am not sure it makes sense to say we can't support multiple
> modes on a fixed connection. For example in the case of SerDes links
> and the like it isn't unusual to see support for CR/KR advertised at
> the same speed on the same link and use the exact same configuration
> so a fixed config could support both and advertise both at the same
> time if I am not mistaken.

Traditionally, fixed link has only supported one mode. The combination
of speed and duplex fully describes a base-T link. Even more
traditionally, it was implemented as an emulated C22 PHY, using the
genphy driver, so limited to just 1G. With multigige PHY we needed to
be a bit more flexible, so phylink gained its own fixed link
implementation which did not emulate a PHY, just the results of
talking to a multigige PHY.

But i don't think you are actually talking about a PHY. I think you
mean the PCS advertises CR/KR, and you want to emulate a fixed-link
PCS? That is a different beast.

	Andrew