netdev - Re: [PATCH net-next 02/10] net: phy: phylink: allow 10GKR interface to use in-band negotiation

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Message-ID: <20180319131804.GD2743@n2100.armlinux.org.uk>
Date:   Mon, 19 Mar 2018 13:18:05 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Antoine Tenart <antoine.tenart@...tlin.com>
Cc:     Andrew Lunn <andrew@...n.ch>, davem@...emloft.net, kishon@...com,
        gregory.clement@...tlin.com, jason@...edaemon.net,
        sebastian.hesselbarth@...il.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com,
        maxime.chevallier@...tlin.com, miquel.raynal@...tlin.com,
        nadavh@...vell.com, stefanc@...vell.com, ymarkman@...vell.com,
        mw@...ihalf.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net-next 02/10] net: phy: phylink: allow 10GKR interface
 to use in-band negotiation

On Mon, Mar 19, 2018 at 02:10:09PM +0100, Antoine Tenart wrote:
> Hi Andrew,
> 
> On Mon, Mar 19, 2018 at 01:59:53PM +0100, Andrew Lunn wrote:
> > 
> > If they don't have PHYs, how are the connected to the outside world?
> 
> On 7k/8k you have the following scheme for 10G only interfaces:
> 
>    MAC -- Comphy -- PHY -- SFP cage -- ...
> 
> Or
> 
>    MAC -- Comphy -- SFP cage -- ...
> 
> The comphy provides serdes lanes, and can be configured in various
> modes (SGMII, 2500SGMII, 10GKR...).

Right - the correct mode is dependent on the SFP module plugged into
the cage.  Trying to describe this by ignoring the SFP cage isn't
going to work out well for end-user functionality, though is fine if
you're just hacking a configuration to test (which would not be
suitable for mainline kernels!)

As I've recently replied to Yan, this is a configuration I haven't
tested yet, and it's entirely possible that phylink may need some
tweaks for it.

What you have is a very similar setup to what is on Clearfog with
its SFP cage, where the SFP cage is connected directly to the
Armada 388.  That only has to deal with 2500base-X / 1000base-X /
SGMII and not 10G.

What I want is to avoid hacks as much as possible here - if there is
a short-coming with SFP/phylink here, we need to address that
properly.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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