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

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Date:   Fri, 2 Apr 2021 14:34:59 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     "Voon, Weifeng" <weifeng.voon@...el.com>
Cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        "Sit, Michael Wei Hong" <michael.wei.hong.sit@...el.com>,
        "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
        "alexandre.torgue@...com" <alexandre.torgue@...com>,
        "joabreu@...opsys.com" <joabreu@...opsys.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        "Ong, Boon Leong" <boon.leong.ong@...el.com>,
        "qiangqing.zhang@....com" <qiangqing.zhang@....com>,
        "Wong, Vee Khee" <vee.khee.wong@...el.com>,
        "fugang.duan@....com" <fugang.duan@....com>,
        "Chuah, Kim Tatt" <kim.tatt.chuah@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>
Subject: Re: [PATCH net-next 1/2] net: stmmac: enable 2.5Gbps link speed

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