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

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

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