netdev - Re: [REGRESSION] net: pcs-lynx: 10G SFP no longer links up

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Message-Id: <681ec035-65f5-4aba-a448-cdb589fa5161@app.fastmail.com>
Date: Mon, 18 Aug 2025 19:59:21 +1000
From: "Mathew McBride" <matt@...verse.com.au>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: netdev@...r.kernel.org, regressions@...ts.linux.dev,
 "Thorsten Leemhuis" <regressions@...mhuis.info>
Subject: Re: [REGRESSION] net: pcs-lynx: 10G SFP no longer links up

Hi Russell,

On Wed, Aug 13, 2025, at 2:42 AM, Russell King (Oracle) wrote:

> 
> Yes, the reminder was sent during July when I wasn't looking at email,
> and as you can imagine, if I spend three weeks on vacation, I am _not_
> going to catch up with that pile of email - if I were, there'd be no
> point taking vacation because the mental effort would be just the same
> as having no vacation.
> 
No problem. I was not sure if you were on vacation or not.

> I have been debating whether we should actually do something like this,
> especially given the issues with 2500base-X:
> 
> -       if (!phylink_validate_pcs_inband_autoneg(pl, interface,
> -                                                config.advertising)) {
> -               phylink_err(pl, "autoneg setting not compatible with PCS");
> -               return -EINVAL;
> +       while (!phylink_validate_pcs_inband_autoneg(pl, interface,
> +                                                   config.advertising)) {
> +               if (!test_bit(ETHTOOL_LINK_MODE_Autoneg_BIT,
> +                             config.advertising)) {
> +                       phylink_err(pl, "autoneg setting is not compatible with PCS");
> +                       return -EINVAL;
> +               }
> +
> +               __clear_bit(ETHTOOL_LINK_MODE_Autoneg_BIT, config.advertising);
>         }
> 

I have just given this version a quick test with (at 10G only, I have not tested 1 or 2.5G configs), and it seems to work.

My board doesn't natively support 2.5G (due to a component in the signal path) but I can modify a board to work with 2.5G if testing these GPON or other imitator modules is helpful to you.

> which turns it into something generic - but my problem with that is..
> what if the module (e.g. a GPON module immitating a fibre module)
> requires Autoneg but the PCS doesn't support Autoneg for the selected
> interface mode.
> 

Many Thanks,
Matt

> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
>