netdev - Re: [PATCH net-next 3/3] net: phylink: add phylink_sfp_select_interface

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Message-ID: <14b442ad-c0ab-4276-8491-c692f0b7c5c9@lunn.ch>
Date: Wed, 9 Jul 2025 17:54:44 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Alexander Duyck <alexander.duyck@...il.com>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next 3/3] net: phylink: add
 phylink_sfp_select_interface_speed()

> Settings for enp1s0:
>         Supported ports: [  ]
>         Supported link modes:   50000baseCR/Full
>                                 100000baseCR2/Full
>         Supported pause frame use: Symmetric Receive-only
>         Supports auto-negotiation: No
>         Supported FEC modes: RS
>         Advertised link modes:  100000baseCR2/Full
>         Advertised pause frame use: Symmetric Receive-only
>         Advertised auto-negotiation: No
>         Advertised FEC modes: RS
>         Link partner advertised link modes:  100000baseCR2/Full
>         Link partner advertised pause frame use: No
>         Link partner advertised auto-negotiation: No
>         Link partner advertised FEC modes: RS

This all looks suspicious. If it does not support autoneg, how can it
know what the link partner is advertising?

If you look at what phylib does, for plain old 1G devices:

genphy_read_status() calls genphy_read_lpa()

genphy_read_lpa() then looks to see if autoneg is enabled, and if not
it does linkmode_zero(phydev->lp_advertising).

So it will not report any link partner information.

What is wrong, that it is reporting LP information, or that it is
reporting it does not support autoneg when in fact it is actually
doing autoneg?

	Andrew