linux-kernel - Re: [PATCH net-next v2 05/14] net: mvpp2: do not force the link mode

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Message-ID: <20170828085152.GF20805@n2100.armlinux.org.uk>
Date:   Mon, 28 Aug 2017 09:51:52 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Marcin Wojtas <mw@...ihalf.com>
Cc:     Antoine Tenart <antoine.tenart@...e-electrons.com>,
        "David S. Miller" <davem@...emloft.net>, kishon@...com,
        Andrew Lunn <andrew@...n.ch>,
        Jason Cooper <jason@...edaemon.net>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Gregory Clément 
        <gregory.clement@...e-electrons.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        nadavh@...vell.com, linux-kernel@...r.kernel.org,
        Stefan Chulski <stefanc@...vell.com>,
        Miquèl Raynal 
        <miquel.raynal@...e-electrons.com>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 05/14] net: mvpp2: do not force the link mode

On Mon, Aug 28, 2017 at 10:38:37AM +0200, Marcin Wojtas wrote:
> Hi Antoine,
>
> Can you be 100% sure that when using SGMII with PHY's (like Marvell
> Alaska 88E1xxx series), is in-band link information always available?
> I'd be very cautious with such assumption and use in-band management
> only when set in the DT, like mvneta. I think phylib can properly can
> do its work when MDIO connection is provided on the board.

There is another issue to be aware of: if you're wanting to use flow
control autonegotiation, that is not carried across SGMII's in-band
signalling.  If you want to use SGMII's in-band signalling for the
duplex and speed information, you still need phylib's notification
to properly set the flow control.

<plug>
Switching mvpp2 to use phylink (which is needed for the 1G SFP slot on
mcbin) will handle all this for you - dealing with both in-band and
out-of-band negotiation methods, and combining them in the appropriate
manner for the selected operation mode.
</plug>

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