Re: [PATCH v12 2/2] arm: dts: aspeed: ventura: add Meta Ventura BMC

[Andrew Lunn]

On Tue, Apr 07, 2026 at 05:05:12PM +0800, PK Lee wrote:
> > > +&mac3 {
> > > +     status = "okay";
> > > +     phy-mode = "rmii";
> > > +     pinctrl-names = "default";
> > > +     pinctrl-0 = <&pinctrl_rmii4_default>;
> > > +     fixed-link {
> > > +             speed = <100>;
> > > +             full-duplex;
> > > +     };
> >
> > What is on the other end of this fixed link?
> 
> The other end of this fixed link is the CPU port of a Marvell 88E6393X
> switch. We are using this switch in unmanaged mode rather than using
> the DSA subsystem. Therefore, we use a fixed-link to force the mac3 to
> 100Mbps full-duplex RMII to match the CPU port configuration.

You are mixing up terms. The 88E6393X does not have a dedicated port
for connecting to the host CPU. Any port can be connected to the host,
using DSA tags. And all the ports are 1G or faster, so it seems odd to
limit it to 100Mbps. There is something consider a CPU port, but that
connects the internal Z80 CPU to the switch fabric.

> > > +};
> > > +
> > > +&mdio0 {
> > > +     status = "okay";
> > > +};
> >
> > If there are no devices on the bus, why enable it?
> 
> We intentionally enable it so user-space tools can access the switch
> registers. I have added a comment in v13 to clarify this.

Why would user space want to access the switch registers for an
unmanaged switch? It sounds like you are using Marvells SDK in
userspace to manage the switch, rather than using DSA.

	Andrew