[PATCH RFC net-next 0/9] net: introduce Qualcomm XPCS support and add Nord Ethernet plumbing

[Coia Prant]

Andrew Lunn <andrew at lunn.ch> 于2026年9月24日周四 02:35写道：
>
> > Non-existent MMDs
> > -----------------
> > Returning 0xffff on reads and silently discarding writes is what a
> > floating bus / unimplemented feature looks like, so I agree with that
> > direction. My pcs-xpcs-rk does the same.
>
> Did you read 802.3?
>
>   45.2:
>
>   If a device supports the MDIO interface it shall respond to all
>   possible register addresses for the device and return a value of
>   zero for undefined and unsupported registers. Writes to undefined
>   registers and read-only registers shall have no effect. The
>   operation of an MMD shall not be affected by writes to reserved and
>   unsupported register bits, and such register bits shall return a
>   value of zero when read.
>
> This is what i was commenting about in my review, returning EOPNOTSUPP
> is not correct according to the standard.
>
>         Andrew

I hadn't gone back to 45.2 when I wrote that, so fair enough on the
standard. For what it's worth, pcs-xpcs already treats 0 and 0xff as
the "no device" values in the identity path, so the glue follows that
convention rather than inventing a new one.

Sorry for that.
Coia