netdev - Re: [PATCH 2/2] net: phy: Associate device node with fixed PHY

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Date:   Sat, 1 Aug 2020 17:11:07 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Vikas Singh <vikas.singh@...esoftware.com>, f.fainelli@...il.com,
        hkallweit1@...il.com, netdev@...r.kernel.org,
        "Calvin Johnson (OSS)" <calvin.johnson@....nxp.com>,
        Kuldip Dwivedi <kuldip.dwivedi@...esoftware.com>,
        "Madalin Bucur (OSS)" <madalin.bucur@....nxp.com>,
        Vikas Singh <vikas.singh@....com>
Subject: Re: [PATCH 2/2] net: phy: Associate device node with fixed PHY

On Sat, Aug 01, 2020 at 10:41:32AM +0100, Russell King - ARM Linux admin wrote:
> On Sat, Aug 01, 2020 at 09:52:52AM +0530, Vikas Singh wrote:
> > Hi Andrew,
> > 
> > Please refer to the "fman" node under
> > linux/arch/arm64/boot/dts/freescale/fsl-ls1046a-rdb.dts
> > I have two 10G ethernet interfaces out of which one is of fixed-link.
> 
> Please do not top post.
> 
> How does XGMII (which is a 10G only interface) work at 1G speed?  Is
> what is in DT itself a hack because fixed-phy doesn't support 10G
> modes?

My gut feeling is there is some hack going on here, which is why i'm
being persistent at trying to understand what is actually going on
here.

So Vikas, as Russell pointed out, fixed-link is limited to 1G. It
seems odd you are running a 10G link at 1G. It is also unclear what
you have on the other end of that fixed link? Is it an SFP and you are
afraid of the work needed to get phylink working with ACPI? Is it an
Ethernet switch, and you are afraid of the work needed to get DSA
working with ACPI?

Looking at
https://www.nxp.com/docs/en/quick-reference-guide/LS1046AQRS.pdf

I see a XFI/2-5G SGMII port connected to a PHY, which i guess is

       ethernet@...00 { /* 10GEC1 */
                phy-handle = <&aqr106_phy>;
                phy-connection-type = "xgmii";
        };

and
                aqr106_phy: ethernet-phy@0 {
                        compatible = "ethernet-phy-ieee802.3-c45";
                        interrupts = <0 131 4>;
                        reg = <0x0>;
                };

Which leaves an XFI interface connected to a retimer and then to an
SFP cage? Is this where you are using fixed-link?

	Andrew