linux-kernel - Re: [PATCH net-next v2 4/4] net: mvpp2: 2500baseX support

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Date:   Wed, 3 Jan 2018 16:53:11 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Antoine Tenart <antoine.tenart@...e-electrons.com>
Cc:     davem@...emloft.net, kishon@...com,
        gregory.clement@...e-electrons.com, linux@...linux.org.uk,
        mw@...ihalf.com, stefanc@...vell.com, ymarkman@...vell.com,
        thomas.petazzoni@...e-electrons.com,
        miquel.raynal@...e-electrons.com, nadavh@...vell.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 4/4] net: mvpp2: 2500baseX support

On Wed, Jan 03, 2018 at 04:32:27PM +0100, Antoine Tenart wrote:
> Hi Andrew,
> 
> On Wed, Jan 03, 2018 at 04:20:36PM +0100, Andrew Lunn wrote:
> > > @@ -4612,6 +4616,9 @@ static int mvpp22_comphy_init(struct mvpp2_port *port)
> > >  	case PHY_INTERFACE_MODE_1000BASEX:
> > >  		mode = PHY_MODE_SGMII;
> > >  		break;
> > > +	case PHY_INTERFACE_MODE_2500BASEX:
> > > +		mode = PHY_MODE_2500SGMII;
> > > +		break;
> > 
> > I think this is the source of confusion with linux/phy.h and
> > linux/phy/phy.h.
> > 
> > What would PHY_INTERFACE_MODE_2500SGMII use?
> > 
> > Where is this all getting confused? Should the caller to
> > mvpp22_comphy_init() actually be passing PHY_INTERFACE_MODE_2500SGMII?
> > What is the MAC actually doing at this point? 2500BASEX or 2500SGMII?
> 
> PHY_INTERFACE_MODE_2500BASEX is the PHY mode whereas PHY_MODE_2500SGMII
> is the mode used by the common PHY driver (i.e. the one configuring the
> serdes lanes).

> There's no PHY_INTERFACE_MODE_2500SGMII mode.

Hi Antoine

At the moment there is no PHY_INTERFACE_MODE_2500SGMII. However,
there are some devices which can do 2.5G SGMII. So it will appear
sometime. This piece of code then looks even stranger.

> Sure, I can add a comment to state this function is a translation
> between the net PHY mode and the generic PHY mode (it's a n-to-1
> translation).

I think from an API design point of view, passing PHY_MODE_2500BASEX
to comphy makes more sense. That is what the MAC wants to do. How the
comphy achieves that should be internal to the comphy.

       Andrew