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

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Message-ID: <CAKgT0UfXRsVEgvJScapiXNWyqB8Yd07t5dgrKX82MRup78tXrw@mail.gmail.com>
Date: Thu, 10 Jul 2025 10:22:44 -0700
From: Alexander Duyck <alexander.duyck@...il.com>
To: Andrew Lunn <andrew@...n.ch>
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()

On Thu, Jul 10, 2025 at 9:11 AM Andrew Lunn <andrew@...n.ch> wrote:
>
> > 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?

I have some debug code on here that is reporting the FW config as the
"LP Advertised". I had borrowed that approach from the phylink
fixedlink config as I thought it was a good way for me to know what
the FW was requesting without having to report it out to a log file.