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Date: Tue, 16 Apr 2024 16:48:33 +0100
From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Stefan Eichenberger <eichest@gmail.com>
Cc: Andrew Lunn <andrew@lunn.ch>, davem@davemloft.net, edumazet@google.com,
	kuba@kernel.org, pabeni@redhat.com, robh@kernel.org,
	krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
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	netdev@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 2/2] net: phy: mxl-gpy: add new device tree property
 to disable SGMII autoneg
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Sender: Russell King (Oracle) <linux@armlinux.org.uk>

On Tue, Apr 16, 2024 at 05:43:16PM +0200, Stefan Eichenberger wrote:
> Hi Andrew,
> 
> Thanks a lot for the feedback.
> 
> On Tue, Apr 16, 2024 at 03:46:19PM +0200, Andrew Lunn wrote:
> > On Tue, Apr 16, 2024 at 02:10:32PM +0200, Stefan Eichenberger wrote:
> > > Add a new device tree property to disable SGMII autonegotiation and
> > > instead use the option to match the SGMII speed to what was negotiated
> > > on the twisted pair interface (tpi).
> > 
> > Could you explain this is more detail.
> > 
> > SGMII always runs its clocks at 1000Mbps. The MAC needs to duplicate
> > the symbols 100 times when running at 10Mbs, and 10 times when running
> > at 100Mbps.
> 
> Currently, the mxl-gpy driver uses SGMII autonegotiation for 10 Mbps,
> 100 Mbps, and 1000 Mbps. For our Ethernet controller, which is on an
> Octeon TX2 SoC, this means that we have to enable "in-band-status" on
> the controller. This will work for all three speed settings. However, if
> we have a link partner that can do 2.5 Gbps, the mxl-gpy driver will
> disable SGMII autonegotiation in gpy_update_interface. This is not
> supported by this Ethernet controller because in-band-status is still
> enabled. Therefore, we will not be able to transfer data at 2.5 Gbps,
> the SGMII link will not go into a working state.

I have been working on a phylink/phylib patch set to address this. As
I've been busy with health-based appointments during last week and this
week, I haven't been able to spend enough time to get that to a point
that I'm happy to publish it yet.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!