Re: [PATCH net v1] net: phy: motorcomm: yt8821: disable MDIO broadcast address 0

[Andrew Lunn]

On Sun, Feb 22, 2026 at 03:32:45AM +0100, Jakub Vaněk wrote:
> Hello Daniel, Qingfang, SkyLake,
> 
> do you happen to know if the MediaTek Gigabit PHY in the MT7981B
> can be remapped to a MDIO address other than address 0?
> 
> I wasn't able to find public documentation describing the registers
> of internal PHY or whether its MDIO address is configurable.
> 
> Being able to move the internal PHY off address 0 in U-Boot could be
> a better way of resolving a MDIO address conflict between the internal
> PHY and the broadcast address used by an external Motorcomm YT8821 PHY.
> 
> Any pointers would be appreciated.

Even if you can avoid the conflict, you still need to handle the fact
the YT8821 appears on two addresses. phylib has no idea it is the same
device in two places, so it can instantiate two struct phy_device for
it. This can cause problems, i think suspend/resume will break, etc.

There is nothing in IEEE 802.3 clause 22 or 45 that allows for this
behaviour. So rather than living with all the issues it causes, you
really do want to get the PHY into standards conformance.

       Andrew