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

[Andrew Lunn]

> 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