Re: [RFC net-next v2 1/6] ethtool: Add loopback netlink UAPI definitions

[Andrew Lunn]

On Tue, Mar 10, 2026 at 11:23:48AM +0100, Maxime Chevallier wrote:
> 
> 
> On 09/03/2026 17:45, Andrew Lunn wrote:
> >>> +    doc: |
> >>> +      Loopback component. Identifies where in the network path the
> >>> +      loopback is applied.
> >>> +    entries:
> >>> +      -
> >>> +        name: mac
> >>> +        doc: MAC loopback
> >>> +      -
> >>> +        name: pcs
> >>> +        doc: PCS loopback
> >>> +      -
> >>> +        name: phy
> >>> +        doc: PHY loopback
> >>> +      -
> >>> +        name: module
> >>> +        doc: Pluggable module (e.g. CMIS (Q)SFP) loopback
> >>
> >> Should we also add "serdes" ?
> > 
> > What is the difference between SERDES and PCS?
> 
> By Serdes I mean "generic PHY", but as you state below I don't really
> want to use the word "PHY" as it's very prone to confusion with Ethernet
> PHYs.

We probably want more than a minimum for doc: We actually want a full
sentence, maybe a paragraph, clearly defining what we mean by each
entry.

We also need to the careful with generic PHY and serdes. Marvell's
comment was that they have multiple loopback points, and named some of
those with -serdes. Is that actually a PCS? Or is it the same
functionality as a generic PHY, just not implemented as a Linux
generic PHY?

We have to assume vendors will get names wrong, because vendors often
get names wrong. Ideally we want to point to clauses in 802.3, since
it is very hard to argue against that.

	Andrew