Re: [PATCH v3 net] net: phylink: add missing supported link modes for the fixed-link

[Russell King (Oracle)]

On Mon, Nov 17, 2025 at 06:29:43PM +0800, Wei Fang wrote:
> Pause, Asym_Pause and Autoneg bits are not set when pl->supported is
> initialized, so these link modes will not work for the fixed-link. This
> leads to a TCP performance degradation issue observed on the i.MX943
> platform.
> 
> The switch CPU port of i.MX943 is connected to an ENETC MAC, this link
> is a fixed link and the link speed is 2.5Gbps. And one of the switch
> user ports is the RGMII interface, and its link speed is 1Gbps. If the
> flow-control of the fixed link is not enabled, we can easily observe
> the iperf performance of TCP packets is very low. Because the inbound
> rate on the CPU port is greater than the outbound rate on the user port,
> the switch is prone to congestion, leading to the loss of some TCP
> packets and requiring multiple retransmissions.
> 
> Solving this problem should be as simple as setting the Asym_Pause and
> Pause bits. The reason why the Autoneg bit needs to be set, Russell
> has gave a very good explanation in the thread [1], see below.
> 
> "As the advertising and lp_advertising bitmasks have to be non-empty,
> and the swphy reports aneg capable, aneg complete, and AN enabled, then
> for consistency with that state, Autoneg should be set. This is how it
> was prior to the blamed commit."
> 
> [1] https://lore.kernel.org/all/aRjqLN8eQDIQfBjS@xxxxxxxxxxxxxxxxxxxxx/
> 
> Fixes: de7d3f87be3c ("net: phylink: Use phy_caps_lookup for fixed-link configuration")
> Signed-off-by: Wei Fang <wei.fang@xxxxxxx>
> Reviewed-by: Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx>

NAK. I give up.

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