netdev - Re: [PATCH net-next 5/6] arm64: dts: marvell: mcbin: enable the fourth network interface

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Message-ID: <20171228184642.GV10595@n2100.armlinux.org.uk>
Date:   Thu, 28 Dec 2017 18:46:42 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Antoine Tenart <antoine.tenart@...e-electrons.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        thomas.petazzoni@...e-electrons.com, ymarkman@...vell.com,
        jason@...edaemon.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kishon@...com, nadavh@...vell.com,
        miquel.raynal@...e-electrons.com,
        gregory.clement@...e-electrons.com, stefanc@...vell.com,
        mw@...ihalf.com, davem@...emloft.net,
        linux-arm-kernel@...ts.infradead.org,
        sebastian.hesselbarth@...il.com
Subject: Re: [PATCH net-next 5/6] arm64: dts: marvell: mcbin: enable the
 fourth network interface

On Thu, Dec 28, 2017 at 07:27:39PM +0100, Antoine Tenart wrote:
> Hi Florian,
> 
> On Thu, Dec 28, 2017 at 07:02:09AM -0800, Florian Fainelli wrote:
> > On 12/28/2017 02:05 AM, Antoine Tenart wrote:
> > > On Thu, Dec 28, 2017 at 08:46:23AM +0100, Andrew Lunn wrote:
> > >> On Wed, Dec 27, 2017 at 10:24:01PM +0000, Russell King - ARM Linux wrote:
> > >>> On Wed, Dec 27, 2017 at 11:14:45PM +0100, Antoine Tenart wrote:
> > >>>>  
> > >>>> +&cps_eth2 {
> > >>>> +	/* CPS Lane 5 */
> > >>>> +	status = "okay";
> > >>>> +	phy-mode = "2500base-x";
> > >>>> +	/* Generic PHY, providing serdes lanes */
> > >>>> +	phys = <&cps_comphy5 2>;
> > >>>> +};
> > >>>> +
> > >>>
> > >>> This is wrong.  This lane is connected to a SFP cage which can support
> > >>> more than just 2500base-X.  Tying it in this way to 2500base-X means
> > >>> that this port does not support conenctions at 1000base-X, despite
> > >>> that's one of the most popular and more standardised speeds.
> > >>>
> > >>
> > >> I agree with Russell here. SFP modules are hot pluggable, and support
> > >> a range of interface modes. You need to query what the SFP module is
> > >> in order to know how to configure the SERDES interface. The phylink
> > >> infrastructure does that for you.
> > > 
> > > Sure, I understand. We'll be able to support such interfaces only when
> > > the phylink PPv2 support lands in.
> > 
> > Should we expect PHYLINK support to make it as the first patch in your
> > v2 of this patch series, or is someone else doing that?
> 
> No, the phylink patch conflicts with Marcin's ACPI series and we agreed
> to let him get his series merged first. And I will probably work on a
> few other topics before having the chance to work on it. So it'll
> probably be me doing that, but not right now.

ACPI is going to be a problem with phylink for a while.  There's patches
queued in net-next which convert phylink and SFP mostly to the fwnode
and property based systems, but phylib and i2c do not seem to have the
necessary bits to be able to deal with those.

Specifically, in DT we have "of_find_i2c_adapter_by_node()" but afaics
there is no equivalent in ACPI - which means in an ACPI based system
we have no way to determine the I2C bus associated with a SFP socket,
which is a rather fundamental issue for SFP modules.

For phylib side, there's "of_phy_attach()" but again there is no
equivalent in ACPI. This should not be that much of a problem, because
network drivers using the DT phylib calls (eg, "of_phy_connect()") are
already restricted by this. That may have been solved by Marcin's
series, but I've not seen it to know.

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