Subject: Re: [PATCH net-next 10/12] net: stmmac: tc956x: add TC956x/QPS615 support

From: Daniel Thompson <[email-masked]>
Date: Fri, 8 May 2026 16:54:54 +0100

On Fri, May 08, 2026 at 03:34:42PM +0200, Andrew Lunn wrote:
> > BTW if you are bothered by SP_SEL_SGMII_2500M, that name comes directly
> > from the TRM and I'd prefer to keep it if I can. The enumerated value
> > we have to write into the SP_SEL for 2500base-X is "SGMII 2500M".
>
> We try to avoid anything to do with SGMII and 2500 because it is
> technically wrong. Cisco never defined SGMII for 2500, it is something
> silicon vendors have made up, without any foundation in any
> standardisation. We much prefer to refer to it as 2500BaseX with
> broken signalling, which is a much more accurate description.
>
> The TRM is also not a public document. If it was, i could see some
> value in keeping with the naming, but since ~0 developers have the
> document, this is less useful.

This is a pretty obscure register buried on some of the TC956x glue
logic (e.g. it's not part of the DWMAC's register set). I take the view
that if someone is debugging the hardware interactions deeply enough to
care what this is called then the odds of them having access to the TRM
are actually pretty good.

However having a different name would be only a minor irritant to the
poor soul trying to debug the thing! I'll rename to SP_SEL_2500BASEX
in the next rev of the patchset.

Daniel.