Subject: Re: [PATCH net-next 1/2] net: stmmac: enable 2.5Gbps link speed

From: Andrew Lunn <[email-masked]>
Date: Fri, 2 Apr 2021 14:34:59 +0200

On Fri, Apr 02, 2021 at 07:45:04AM +0000, Voon, Weifeng wrote:
> > > +	/* 2.5G mode only support 2500baseT full duplex only */
> > > +	if (priv->plat->has_gmac4 && priv->plat->speed_2500_en) {
> > > +		phylink_set(mac_supported, 2500baseT_Full);
> > > +		phylink_set(mask, 10baseT_Half);
> > > +		phylink_set(mask, 10baseT_Full);
> > > +		phylink_set(mask, 100baseT_Half);
> > > +		phylink_set(mask, 100baseT_Full);
> > > +		phylink_set(mask, 1000baseT_Half);
> > > +		phylink_set(mask, 1000baseT_Full);
> > > +		phylink_set(mask, 1000baseKX_Full);
> > 
> > Why? This seems at odds to the comment above?
> 
> > What about 2500baseX_Full ?
> 
> The comments explain that the PCS<->PHY link is in 2500BASE-X
> and why 10/100/1000 link speed is mutually exclusive with 2500.
> But the connected external PHY are twisted pair cable which only
> supports 2500baseT_full.

The PHY should indicate what modes its supports. The PHY drivers
get_features() call should set supported to only 2500baseT_Full, if
that is all it supports.

What modes are actually used should then be the intersect of what both
the MAC and the PHY indicate they can do.

     Andrew