netdev - Re: [PATCH] net: ethernet: mvneta: add support for 2.5G DRSGMII mode

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Message-ID: <20200609131216.GJ1022955@lunn.ch>
Date:   Tue, 9 Jun 2020 15:12:16 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Sascha Hauer <s.hauer@...gutronix.de>
Cc:     Russell King <rmk+kernel@...linux.org.uk>,
        devicetree@...r.kernel.org, kernel@...gutronix.de,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] net: ethernet: mvneta: add support for 2.5G DRSGMII mode

On Tue, Jun 09, 2020 at 02:55:35PM +0200, Sascha Hauer wrote:
> On Mon, Jun 08, 2020 at 04:57:37PM +0200, Andrew Lunn wrote:
> > On Mon, Jun 08, 2020 at 09:47:16AM +0200, Sascha Hauer wrote:
> > > The Marvell MVNETA Ethernet controller supports a 2.5 Gbps SGMII mode
> > > called DRSGMII.
> > > 
> > > This patch adds a corresponding phy-mode string 'drsgmii' and parses it
> > > from DT. The MVNETA then configures the SERDES protocol value
> > > accordingly.
> > > 
> > > It was successfully tested on a MV78460 connected to a FPGA.
> > 
> > Hi Sascha
> > 
> > Is this really overclocked SGMII, or 2500BaseX? How does it differ
> > from 2500BaseX, which mvneta already supports?
> 
> I think it is overclocked SGMII or 2500BaseX depending on the Port MAC
> Control Register0 PortType setting bit.
> As said to Russell we have a fixed link so nobody really cares if it's
> SGMII or 2500BaseX. This boils down the patch to fixing the Serdes
> configuration setting for 2500BaseX.

Hi Sascha

Does 2500BaseX work for your use case? Since this drsmgii mode is not
well defined, i would prefer to not add it, unless it is really
needed.

	Andrew