Re: [PATCH net-next v2 1/5] net: mdiobus: Scan buses in reverse order (31 -> 0)

[Andrew Lunn]

On Sun, Mar 01, 2026 at 12:22:37AM +0100, Jakub Vaněk wrote:
> Some PHY devices incorrectly treat address 0 as a broadcast address.
> As a result, accesses to address 0 may cause multiple PHYs to respond,
> making one or both PHYs work unreliably. In other cases, the PHY may be
> detected twice by Linux: once at address 0 and once at its actual
> address).
> 
> On several PHYs (e.g. Motorcomm YT8821 and Realtek RTL8221B), this
> behavior can be disabled via a vendor-specific internal register.
> However, for that to be useful, that register would have to be
> programmed before address 0 is accessed for the first time.
> 
> On non-Device Tree systems, MDIO buses are typically scanned in
> mdiobus_register(). Change the address scan order from 0->31 to 31->0
> so that PHY fixups are applied to addresses 1-31 before address 0
> is probed. This way the address collision can be avoided.

Please add a comment about phy_package_join() etc. You need to
indicate this change has not broken any assumptions. It might also be
good to extend the documentation about PHY packages.

     Andrew