netdev - Re: [PATCH net 3/3] net: phylink: disable autoneg for interfaces that have no inband

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Message-ID: <20250902225137.6h2ank6itrgeln6w@skbuf>
Date: Wed, 3 Sep 2025 01:51:37 +0300
From: Vladimir Oltean <olteanv@...il.com>
To: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Mathew McBride <matt@...verse.com.au>, netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net 3/3] net: phylink: disable autoneg for interfaces
 that have no inband

On Sun, Aug 31, 2025 at 06:34:43PM +0100, Russell King (Oracle) wrote:
> Mathew reports that as a result of commit 6561f0e547be ("net: pcs:
> pcs-lynx: implement pcs_inband_caps() method"), 10G SFP modules no
> longer work with the Lynx PCS.
> 
> This problem is not specific to the Lynx PCS, but is caused by commit
> df874f9e52c3 ("net: phylink: add pcs_inband_caps() method") which added
> validation of the autoneg state to the optical SFP configuration path.
> 
> Fix this by handling interface modes that fundamentally have no
> inband negotiation more correctly - if we only have a single interface
> mode, clear the Autoneg support bit and the advertising mask. If the
> module can operate with several different interface modes, autoneg may
> be supported for other modes, so leave the support mask alone and just
> clear the Autoneg bit in the advertising mask.
> 
> This restores 10G optical module functionality with PCS that supply
> their inband support, and makes ethtool output look sane.
> 
> Reported-by: Mathew McBride <matt@...verse.com.au>
> Closes: https://lore.kernel.org/r/025c0ebe-5537-4fa3-b05a-8b835e5ad317@app.fastmail.com
> Fixes: df874f9e52c3 ("net: phylink: add pcs_inband_caps() method")
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> ---

Tested-by: Vladimir Oltean <vladimir.oltean@....com>

I had missed this discussion and was about to report the same problem as
Mathew again.