Date: Thu, 24 Aug 2017 18:19:45 +0200
From: Antoine Tenart <antoine.tenart@free-electrons.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Antoine Tenart <antoine.tenart@free-electrons.com>,
        davem@davemloft.net, kishon@ti.com, jason@lakedaemon.net,
        sebastian.hesselbarth@gmail.com, gregory.clement@free-electrons.com,
        thomas.petazzoni@free-electrons.com, nadavh@marvell.com,
        linux@armlinux.org.uk, linux-kernel@vger.kernel.org, mw@semihalf.com,
        stefanc@marvell.com, miquel.raynal@free-electrons.com,
        netdev@vger.kernel.org
Subject: Re: [PATCH net-next 09/13] net: mvpp2: dynamic reconfiguration of
 the PHY mode
Message-ID: <20170824161945.GG28443@kwain>
References: <20170824083823.16826-1-antoine.tenart@free-electrons.com>
 <20170824083823.16826-10-antoine.tenart@free-electrons.com>
 <20170824145609.GJ8022@lunn.ch>
 <20170824155241.GF28443@kwain>
 <20170824160124.GA18700@lunn.ch>
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On Thu, Aug 24, 2017 at 06:01:24PM +0200, Andrew Lunn wrote:
> On Thu, Aug 24, 2017 at 05:52:41PM +0200, Antoine Tenart wrote:
> > On Thu, Aug 24, 2017 at 04:56:09PM +0200, Andrew Lunn wrote:
> > > On Thu, Aug 24, 2017 at 10:38:19AM +0200, Antoine Tenart wrote:
> > > > This patch adds logic to reconfigure the comphy/gop when the link s=
tatus
> > > > change at runtime. This is very useful on boards such as the mcbin =
which
> > > > have SFP and Ethernet ports connected to the same MAC port: dependi=
ng on
> > > > what the user connects the driver will automatically reconfigure the
> > > > link mode.
> > >=20
> > > I would expect each of these external Ethernet ports to have its own
> > > Ethernet PHY. Don't you need to disconnect from one Ethernet phy and
> > > connect to the other Ethernet PHY when you change external Ethernet
> > > port?
> >=20
> > That's the other way around. The engines outputs (say GoP#) are
> > connected to the comphy inputs. In the SoC. Then there's a single output
> > of this comphy lane to the board. So when switching modes, you do not
> > have to connect to a different Ethernet PHY, it's the same.
>=20
> I think there is a mixup here between generic PHY and Ethernet PHY.
>=20
> When you swap from the copper RJ45 to the fibre SFP, the phylib needs
> to swap from the Copper Ethernet PHY driving the RJ45, to the PHY
> driving the SFP module, which is probably a fixed-phy.

Or on the mcbin the Alaska X 88X3310 which can operate from 10G to 10M.
This PHY changes its interface mode depending on what speed is
negotiated.

> I actually think this is why you have the carrier_on/off calls in the
> link modify callback.

Well, I still do not know if these calls are *really* needed. At least
in our case.

> Imagine phylib is using the copper Ethernet PHY, but the MAC is using
> the SFP port. Somebody pulls out the copper cable, phylib says the
> link is down, turns the carrier off and calls the callback. Not good,
> since your SFP cable is still plugged in...  Ethtool is
> returning/setting stuff in the Copper Ethernet PHY, when in fact you
> intend to be setting SFP settings.

I see what could be the issue but I do not understand one aspect though:
how could we switch from one PHY to another, as there's only one output
between the SoC (and so a given GoP#) and the board. So if a given PHY
can handle multiple modes I see, but in the other case a muxing
somewhere would be needed? Or did I miss something?

Thanks!
Antoine

--=20
Antoine T=E9nart, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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