Re: [RFC net-next v2 0/6] ethtool: Generic loopback support

[Naveen Mamindlapalli]

On 2026-03-09 at 20:25:51, Björn Töpel (bjorn@xxxxxxxxxx) wrote:
> Naveen!
> 
> Naveen Mamindlapalli <naveenm@xxxxxxxxxxx> writes:
> 
> >> Open questions
> >> ==============
> >> 
> >>  - Is this the right extensibility model? I'd appreciate input from
> >>    other NIC vendors on whether component/name/direction is flexible
> >>    enough for their loopback implementations. Also, from the PHY/port
> >>    folks (Maxime, Russell)!
> >
> > Hi Bjorn,
> >
> > The component/name/direction model in v2 fits our hardware well.
> >
> > I am working on loopback support for Marvell OcteonTX2.
> > The MAC (RPM block) supports a PCS-level loopback. In addition,
> > the on-chip SerDes (GSERM) is managed by embedded firmware and
> > supports three more loopback modes:
> >   NED (Near-End Digital) -- digital domain, before the analog front-end
> >   NEA (Near-End Analog) -- through the full analog front-end
> >   FED (Far-End Digital) -- line-side traffic looped back
> >
> > Since the GSERM is not a phylib phy_device, both the MAC PCS
> > loopback and the SerDes loopbacks fall under the MAC component
> > in your model.
> >
> > Mapped to the v2 model:
> >   component  name         supported    description
> >   MAC        mac          near-end     PCS-level loopback
> >   MAC        serdes-ned   near-end     digital only
> >   MAC        serdes-nea   near-end     analog
> >   MAC        serdes-fed   far-end      line-side
> >
> > The SerDes NED and NEA both have the same (component, direction).
> > Both are (MAC, near-end) -- but exercise fundamentally different
> > hardware paths. The name field distinguishes them as per your model,
> 
> Ok! ...and MAC+serdes makes sense from your PoV? Or do we need a new
> component "SERDES" (as Maxime points out in another reply)?
> 

In my earlier comment I mapped the SerDes loopbacks under the MAC
component to fit the current model, but a separate SERDES component
as Maxime suggests would be a better fit for our hardware.

On OcteonTX2 SoC, MAC (PCS) and SerDes are separate hardware blocks.
Each block has its own loopback controls.

With a SERDES component, the mapping becomes cleaner:
  component  name         supported
  MAC        mac          near-end
  SERDES     serdes-ned   near-end
  SERDES     serdes-nea   near-end
  SERDES     serdes-fed   far-end

Thanks,
Naveen

> > I can work on MAC + SerDes loopback driver support for CN10K and
> > post patches on top of your series once MAC component dispatch is
> > in place.
> 
> Got it! Thanks!
> 
>