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

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Date:   Mon, 28 Aug 2017 10:38:37 +0200
From:   Marcin Wojtas <mw@...ihalf.com>
To:     Antoine Tenart <antoine.tenart@...e-electrons.com>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        "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

Hi Antoine,

2017-08-28 8:55 GMT+02:00 Antoine Tenart <antoine.tenart@...e-electrons.com>:
> Hi Russell,
>
> On Fri, Aug 25, 2017 at 11:43:13PM +0100, Russell King - ARM Linux wrote:
>> On Fri, Aug 25, 2017 at 04:48:12PM +0200, Antoine Tenart wrote:
>> > The link mode (speed, duplex) was forced based on what the phylib
>> > returns. This should not be the case, and only forced by ethtool
>> > functions manually. This patch removes the link mode enforcement from
>> > the phylib link_event callback.
>>
>> So how does RGMII work (which has no in-band signalling between the PHY
>> and MAC)?
>>
>> phylib expects the network driver to configure it according to the PHY
>> state at link_event time - I think you need to explain more why you
>> think that this is not necessary.
>
> Good catch, this won't work properly with RGMII. This could be done
> out-of-band according to the spec, but that would use PHY polling and we
> do not want that (the same concern was raised by Andrew on another
> patch).
>
> I'll keep this mode enforcement for RGMII then.
>

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.

Did you check the change also on A375?

Best regards,
Marcin