linux-kernel - Re: [net-next,v3,01/11] net: phy: phy_port: Correctly recompute the port's linkmodes

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Message-ID: <fd033a0e-4154-47e0-a15e-df92dd114f27@bootlin.com>
Date: Tue, 3 Feb 2026 19:13:25 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Simon Horman <horms@...nel.org>
Cc: christophe.leroy@...roup.eu, thomas.petazzoni@...tlin.com,
 andrew@...n.ch, kuba@...nel.org, mwojtas@...omium.org, kabel@...nel.org,
 linux-kernel@...r.kernel.org, pabeni@...hat.com, davem@...emloft.net,
 nicveronese@...il.com, hkallweit1@...il.com, linux@...linux.org.uk,
 edumazet@...gle.com, dimitri.fedrau@...bherr.com, herve.codina@...tlin.com,
 o.rempel@...gutronix.de, romain.gantois@...tlin.com, netdev@...r.kernel.org,
 daniel@...rotopia.org, vladimir.oltean@....com, f.fainelli@...il.com,
 kory.maincent@...tlin.com
Subject: Re: [net-next,v3,01/11] net: phy: phy_port: Correctly recompute the
 port's linkmodes

Hi Simon

On 03/02/2026 18:58, Simon Horman wrote:
> This is an AI-generated review of your patch. The human sending this
> email has considered the AI review valid, or at least plausible.
> 
> For local reproduction steps see https://netdev-ai.bots.linux.dev/ai-local.html
> ---
> net: phy: phy_port: Correctly recompute the port's linkmodes
> 
> This commit fixes phy_port_update_supported() to properly filter linkmodes
> instead of incorrectly or'ing medium-specific modes to the existing support.
> It moves the medium iteration inside a check for empty port->supported.
> 
> Fixes: 589e934d2735 ("net: phy: Introduce PHY ports representation")
> 
>> diff --git a/drivers/net/phy/phy_port.c b/drivers/net/phy/phy_port.c
>> --- a/drivers/net/phy/phy_port.c
>> +++ b/drivers/net/phy/phy_port.c
> 
> [ ... ]
> 
>> @@ -132,6 +126,19 @@ void phy_port_update_supported(struct phy_port *port)
>>  			port->pairs = max_t(int, port->pairs,
>>  					    ethtool_linkmode_n_pairs(mode));
>>
>> +	if (linkmode_empty(port->supported)) {
>> +		for_each_set_bit(i, &port->mediums,
>> +				 __ETHTOOL_LINK_MEDIUM_LAST) {
>> +			__ETHTOOL_DECLARE_LINK_MODE_MASK(med_supported) = {0};
>> +
>> +			phy_caps_medium_get_supported(med_supported, i,
>> +						      port->pairs);
>> +			linkmode_or(supported, supported, med_supported);
>> +		}
>> +
>> +		linkmode_and(port->supported, port->supported, supported);

Yeah :(

>> +	}
> 
> Jakub Kicinski raised a concern in v2 about the AND operation when
> port->supported starts empty. The v3 fix adds the
> 'if (linkmode_empty(port->supported))' check, but then still performs:
> 
>     linkmode_and(port->supported, port->supported, supported);
> 
> inside that block. Since we just confirmed port->supported is empty,
> ANDing it with anything will always produce an empty result.
> 
> Should this be linkmode_copy() or linkmode_or() instead of linkmode_and()
> when port->supported starts empty?
> 
> Reference: https://lore.kernel.org/all/20260130040009.707764-1-kuba@kernel.org/

True, that's already addressed in V4 :)

Maxime