Re: [PATCH v2 3/3] riscv: dts: thead: Add TH1520 ethernet nodes

[Emil Renner Berthing <emil.renner.berthing@canonical.com>]

Drew Fustini wrote:
> On Thu, Sep 26, 2024 at 09:30:32PM +0200, Andrew Lunn wrote:
> > On Thu, Sep 26, 2024 at 12:13:06PM -0700, Drew Fustini wrote:
> > > On Thu, Sep 26, 2024 at 08:39:29PM +0200, Andrew Lunn wrote:
> > > > > +&mdio0 {
> > > > > +	phy0: ethernet-phy@1 {
> > > > > +		reg = <1>;
> > > > > +	};
> > > > > +
> > > > > +	phy1: ethernet-phy@2 {
> > > > > +		reg = <2>;
> > > > > +	};
> > > > > +};
> > > >
> > > > Two PHYs on one bus...
> > >
> > > Thanks for pointing this out. I will move phy1 to mdio1.
> >
> > ???
> >
> > Are you saying the two PHYs are not on the same bus?
>
> Sorry, this is my first time working on an Ethernet driver and I
> misunderstood.
>
> Sipeed only shares the schematic of the baseboard for the LPi4a [1].
> There are pages for GMAC Ethernet0 and GMAC Ethernet1. Each shows 4 MDIO
> differential pairs going into a SG4301G transformer.
>
> I believe that RTL8211F-CG phy chips are on the LM4A SoM board which
> contains the TH1520 SoC. Unfortunately, Sipeed does not provide a
> schematic of the SoM so its hard for me to inspect how the phy chips are
> wired up.
>
> Vendor kernel [2] that Sipeed uses has:
>
> 	mdio0 {
> 		#address-cells = <1>;
> 		#size-cells = <0>;
> 		compatible = "snps,dwmac-mdio";
>
> 		phy_88E1111_0: ethernet-phy@0 {
> 			reg = <0x1>;
> 		};
>
> 		phy_88E1111_1: ethernet-phy@1 {
> 			reg = <0x2>;
> 		};
> 	};
>
> so I think that does mean they are on the same MDIO bus.

It depends how you look at it. The SoC has two MACs and they can both
control their own MDIO bus. However MDIO of both MACs are pinmux'ed to
the same pins on the SoC. So the solution above just mux the pins to
GMAC0 and let that control both PHYs. Alternatively I guess one could
let each GMAC control their own phy on their own MDIO bus and then
switch pinmux settings everytime you need to need to talk to one or
the other.

/Emil