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

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Message-ID: <20170925115303.GC19364@kwain>
Date:   Mon, 25 Sep 2017 13:53:03 +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 11:45:32AM +0100, Russell King - ARM Linux wrote:
> On Mon, Sep 25, 2017 at 11:55:14AM +0200, Antoine Tenart wrote:
> > On Fri, Sep 22, 2017 at 12:07:31PM +0100, Russell King - ARM Linux wrote:
> > > On Thu, Sep 21, 2017 at 03:45:22PM +0200, Antoine Tenart wrote:
> > > > Convert the PPv2 driver to use phylink, which models the MAC to PHY
> > > > link. The phylink support is made such a way the GoP link IRQ can still
> > > > be used: the two modes are incompatible and the GoP link IRQ will be
> > > > used if no PHY is described in the device tree. This is the same
> > > > behaviour as before.
> > > 
> > > This makes no sense.  The point of phylink is to be able to support SFP
> > > cages, and SFP cages do not have a PHY described in DT.  So, when you
> > > want to use phylink because of SFP, you can't, because if you omit
> > > the PHY the driver avoids using phylink.
> > 
> > Yes that's an issue. However we do need to support the GoP link IRQ
> > which is also needed in some cases where there is no PHY (and when
> > phylink cannot be used). What would you propose to differentiate those
> > two cases: no PHY using phylink, and no PHY using the GoP link IRQ?
> 
> 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.

I also wonder if this is needed when using passive cables?

Antoine

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