On Tue, Mar 31, 2026 at 12:46:26AM +0200, Nicolai Buchwitz wrote:

Implement the standard ETHTOOL_PHY_DOWNSHIFT tunable for the LAN88xx
PHY. This allows runtime configuration of the auto-downshift feature
via ethtool:

  ethtool --set-phy-tunable eth0 downshift on count 3

The LAN88xx PHY supports downshifting from 1000BASE-T to 100BASE-TX
after 2-5 failed auto-negotiation attempts. Valid count values are
2, 3, 4 and 5.

This is based on an earlier downstream implementation by Phil Elwell.

Signed-off-by: Nicolai Buchwitz <redacted>

I didn't see a cover message. Please always include a cover message with
patch series.

Reviewed-by: Russell King (Oracle) <redacted>

Thanks!

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