Subject: Re: net: phy: Dealing with 88e1543 dual-port mode

From: Andrew Lunn <[email-masked]>
Date: Fri, 20 Nov 2020 14:55:17 +0100

On Fri, Nov 20, 2020 at 10:25:38AM +0000, Russell King - ARM Linux admin wrote:
> On Fri, Nov 20, 2020 at 10:36:01AM +0100, Maxime Chevallier wrote:
> > So maybe we could be a bit more generic, with something along these lines :
> > 
> >     ethernet-phy@0 {
> >         ...
> > 
> >         mdi {
> >             port@0 {
> >                 media = "10baseT", "100baseT", "1000baseT";
> >                 pairs = <1>;
> > 	    };
> > 
> >             port@1 {
> >                 media = "1000baseX", "10gbaseR"
> >             };
> >         };
> >     };
> 
> Don't forget that TP requires a minimum of two pairs.

Hi Russell

Well, actually, there are automotive PHYs which use just one pair, so
called T1 PHYs. We have drivers for i think two so far, with one more
on the way.

You also have to watch out for 'clever' PHYs. The Aquantia PHY can do
1000Base-T2, i.e. 1G over two pairs. This might be a proprietary
extension, rather than standardized, but it shows it can be done. So
you have to be careful about assumptions based on the number of pairs.

    Andrew