netdev - Re: [net-next PATCH 0/6] Add support for 25G, 50G, and 100G to fbnic

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Message-ID: <CAKgT0UfLCmZ9r6xqxH6NbOyVWJOMmVAJLEZwyCX41Hk99Tb=FQ@mail.gmail.com>
Date: Mon, 16 Jun 2025 07:39:05 -0700
From: Alexander Duyck <alexander.duyck@...il.com>
To: Leon Romanovsky <leon@...nel.org>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>, Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org, 
	hkallweit1@...il.com, davem@...emloft.net, pabeni@...hat.com, kuba@...nel.org, 
	Jiri Pirko <jiri@...dia.com>
Subject: Re: [net-next PATCH 0/6] Add support for 25G, 50G, and 100G to fbnic

On Mon, Jun 16, 2025 at 3:33 AM Leon Romanovsky <leon@...nel.org> wrote:
>
> On Fri, Jun 13, 2025 at 11:43:58PM +0100, Russell King (Oracle) wrote:
> > On Fri, Jun 13, 2025 at 07:00:24PM +0300, Leon Romanovsky wrote:
> > > Excellent, like you said, no one needs this code except fbnic, which is
> > > exactly as was agreed - no core in/out API changes special for fbnic.
> >
> > Rather than getting all religious about this, I'd prefer to ask a
> > different question.
> >
> > Is it useful to add 50GBASER, LAUI and 100GBASEP PHY interface modes,
> > and would anyone else use them? That's the real question here, and
> > *not* whomever is submitting the patches or who is the first user.
>
> Right now, the answer is no. There are no available devices in the
> market which implement it.
>
> Thanks

That's not really true. From what I can tell the XPCS driver is lying
about what it supports and is advertising an XLGMII interface as being
capable of doing 25, 50, and 100G speeds. Just take a look at the
xpcs_xlgmii feature set
(https://elixir.bootlin.com/linux/v6.15.1/source/drivers/net/pcs/pcs-xpcs.c#L40).
Somehow it is saying that XLGMII supports all those speeds, but only
the 40G ones really apply. The rest are a combination of most of the
modes I am calling out here.

One of the things on my list to fix is the XPCS driver as I am pretty
sure the DW IP we are using is the same IP. It is just that nobody
ever went through and enabled the correct interface modes as that
hardware is somewhat hacky in that the PMA configuration essentially
determines what the actual setup is and I suspect we may be the only
part that is allowing dynamic reconfiguration of the external pins to
allow it to switch between 10, 25, 40, 50, and 100G speeds and FEC
configurations.