netdev - Re: [net-next: PATCH v3 1/6] Documentation: ACPI: DSD: describe additional MAC configuration

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Date:   Wed, 23 Jun 2021 23:00:42 +0200
From:   Marcin Wojtas <mw@...ihalf.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Grzegorz Jaszczyk <jaz@...ihalf.com>,
        Grzegorz Bernacki <gjb@...ihalf.com>, upstream@...ihalf.com,
        Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@....com>,
        Jon Nettleton <jon@...id-run.com>,
        Tomasz Nowicki <tn@...ihalf.com>, rjw@...ysocki.net,
        lenb@...nel.org
Subject: Re: [net-next: PATCH v3 1/6] Documentation: ACPI: DSD: describe
 additional MAC configuration

Hi Andrew,

śr., 23 cze 2021 o 22:18 Andrew Lunn <andrew@...n.ch> napisał(a):
>
> > +MAC node example with a "fixed-link" subnode.
> > +---------------------------------------------
> > +
> > +.. code-block:: none
> > +
> > +     Scope(\_SB.PP21.ETH1)
> > +     {
> > +       Name (_DSD, Package () {
> > +         ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> > +              Package () {
> > +                  Package () {"phy-mode", "sgmii"},
> > +              },
> > +         ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
> > +              Package () {
> > +                  Package () {"fixed-link", "LNK0"}
> > +              }
> > +       })
>
> At least in the DT world, it is pretty unusual to see both fixed-link
> and phy-mode.

I did a quick experiment:
git grep -C 8 fixed-link arch/arm64/boot/dts/
git grep -C 8 fixed-link arch/arm/boot/dts/
almost all MAC nodes (i.e. not switch ports) containing 'fixed-link'
have an adjacent 'phy-mode' property defined. How else would the
drivers know how to configure the HW connection type in its registers?

> You might have one of the four RGMII modes, in order to
> set the delays when connecting to a switch. But sgmii and fixed link
> seems very unlikely, how is sgmii autoneg going to work?
>

Indeed most cases in the tree are "rgmii*", but we can also see e.g.
10gbase-r, sgmii and 2500base-x. You can find sgmii + fixed-link on
the eth1 of the armada-388-clearfog. Regarding the autoneg - I'm
mostly familiar with the mvneta/mvpp2, but in this mode the
autonegotiation is disabled and the link is forcibly set up/down in
MAC registers during the netedev_open/close accordingly. FYI, along
with the 10G ports on CN913x-DB, I tested fixed-link on Macchiatobin
sgmii port.

Anyway - all above is a bit side discussion to the actual DSDT
description and how the fixed-link subnode looks like. I think
phy-mode set to "sgmii" is not incorrect, but we can change it to
whatever other type of your preference, as well.

Best regards,
Marcin

> > +       Name (LNK0, Package(){ // Data-only subnode of port
> > +         ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> > +              Package () {
> > +                  Package () {"speed", 1000},
> > +                  Package () {"full-duplex", 1}
> > +              }
> > +       })
> > +     }
> > +
>
>   Andrew