linux-kernel - Re: [PATCH RFC net-next] net: phylink: always config mac for (delayed) phy

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Message-ID: <b7705a4e-5559-4fe3-a302-4c60d7224e49@gmail.com>
Date: Tue, 7 Jan 2025 15:23:18 +0100
From: Eric Woudstra <ericwouds@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>,
 Heiner Kallweit <hkallweit1@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Frank Wunderlich <frank-w@...lic-files.de>,
 Daniel Golle <daniel@...rotopia.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
 coreteam@...filter.org, bridge@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH RFC net-next] net: phylink: always config mac for
 (delayed) phy

On 1/7/25 2:20 PM, Andrew Lunn wrote:
>> I think it is because pl->act_link_an_mode stays at MLO_AN_INBAND, but
>> it needs to be set to MLO_AN_PHY, so that only the phy determines the
>> link state:
>>
>> phylink_resolve() {
>>     ...
>> 	} else if (pl->act_link_an_mode == MLO_AN_PHY) {
>> 		link_state = pl->phy_state;
>>     ...
>> }
> 
> phylink tries to determine the whole chain is up. As Russell says, it
> could be the PCS has not got sync with the PHY for some reason. So
> even if you ignore the PCS state, it might not work. This is actually
> a useful pieces of information. Does the link actually work end to end
> if you only look at the media state? If it does, that would indicate
> the PCS is maybe missing an interrupt, or needs polling for change in
> state.
> 
> 	Andrew

After phylink_mac_initial_config() is re-triggered with the phy
attached, either by the patch, or even with:

ethtool -s eth1 advertise 0x28
(switches to sgmii)
ethtool -s eth1 advertise 0x800000000028
(switches mac back to 2500base-x)

mode is set to MLO_AN_PHY in phylink_pcs_neg_mode() and the link works
end to end.

So the an-mode can be 2 different values, one after link up and another
after these ethtool commands.