netdev - Re: [net-next,v2,01/12] net: phy: phy_port: Correctly recompute the port's linkmodes

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Message-ID: <20260130040009.707764-1-kuba@kernel.org>
Date: Thu, 29 Jan 2026 20:00:09 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: maxime.chevallier@...tlin.com
Cc: Jakub Kicinski <kuba@...nel.org>,
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Subject: Re: [net-next,v2,01/12] net: phy: phy_port: Correctly recompute the port's linkmodes

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 patch changes phy_port_update_supported() from OR'ing medium-specific
modes into port->supported to AND'ing (filtering) port->supported against
the accumulated medium modes.

Fixes: 589e934d2735 ("net: phy: Introduce PHY ports representation")

> diff --git a/drivers/net/phy/phy_port.c b/drivers/net/phy/phy_port.c
> index ec93c8ca051e..68a0068220ed 100644
> --- a/drivers/net/phy/phy_port.c
> +++ b/drivers/net/phy/phy_port.c
> @@ -118,11 +118,14 @@ void phy_port_update_supported(struct phy_port *port)
>  	int i;
>
>  	for_each_set_bit(i, &port->mediums, __ETHTOOL_LINK_MEDIUM_LAST) {
> -		linkmode_zero(supported);
> -		phy_caps_medium_get_supported(supported, i, port->pairs);
> -		linkmode_or(port->supported, port->supported, supported);
> +		__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);

When port->supported starts empty (all zeros), this AND operation will
always produce an empty result regardless of what modes are in supported.

Tracing the call path of_phy_ports() -> phy_of_parse_port() -> phy_add_port()
-> phy_port_update_supported(): phy_of_parse_port() creates the port via
phy_port_alloc() which zeros port->supported, and phy_of_parse_port()
only sets port->mediums and port->pairs without populating port->supported.

The attach_mdi_port() callbacks for drivers like dp83822 and marvell10g
also do not set port->supported before phy_port_update_supported() runs.

Does this leave port->supported empty for ports described in device tree?

The docstring above this function at line 112 states "Any mode that was
manually set in the port's supported list remains set" - but for the DT
path where port->supported starts at zero, the AND with zero produces
zero regardless of what medium modes were computed.
-- 
pw-bot: cr