To solve that sanely, every PHY-based ethtool probably needs a way
to specify which PHY the command is intended for, but then there's
the question of how userspace users react to that - because it's
likely more than just modifying the ethtool utility, ethtool
commands are probably used from many programs.

This idea of extending ethtool with a PHY ID has discussed last
year. It helps solve some of the problems discussed here. You can then
enumerate all the PHYs connected to a MAC, and operate on each PHY
independently.

https://lore.kernel.org/netdev/20221017105100.0cb33490@pc-8.home/ (local)

	Andrew