netdev - Re: [PATCH net-next] net: mvpp2: phylink support

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Message-ID: <20170925130610.GE19364@kwain>
Date:   Mon, 25 Sep 2017 15:06:10 +0200
From:   Antoine Tenart <antoine.tenart@...e-electrons.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Antoine Tenart <antoine.tenart@...e-electrons.com>,
        davem@...emloft.net, andrew@...n.ch,
        gregory.clement@...e-electrons.com,
        thomas.petazzoni@...e-electrons.com,
        miquel.raynal@...e-electrons.com, nadavh@...vell.com,
        linux-kernel@...r.kernel.org, mw@...ihalf.com, stefanc@...vell.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: mvpp2: phylink support

On Mon, Sep 25, 2017 at 01:13:43PM +0100, Russell King - ARM Linux wrote:
> On Mon, Sep 25, 2017 at 01:53:03PM +0200, Antoine Tenart wrote:
> > On Mon, Sep 25, 2017 at 11:45:32AM +0100, Russell King - ARM Linux wrote:
> > > Can you describe what the GoP link IRQ is doing please?
> > 
> > In cases where there is no PHY connected to the MAC and no SFP cage is
> > used. One example is when a SOHO switch is connected directly to a
> > serdes lane. In such cases we still need to have a minimal link
> > management. The GoP link interrupt helps doing so as it raises when the
> > serdes is in sync and AN succeeded.
> 
> Isn't this just like a fixed link scenario, or an in-band
> autonegotiation scenario (both of which phylink supports natively)?
> 
> The situation on Clearfog with the 88E6176 switch is pretty similar -
> a switch connected directly via serdes to the MAC.  Currently, we
> configure stuff there as a fixed link, but in actual fact the 88E6176
> is configured to run the CPU facing port in 1000base-X mode, and with
> appropriate tweaks, switching phylink to 1000base-X mode also works.

Hmm, I think you're right, we should be able to represent the link
between the MAC and the switch as a fixed link. And when it's not fixed,
it could be done with in-band AN. I cannot test this myself but I've
asked someone who can to.

Antoine

-- 
Antoine Ténart, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com