Re: [PATCH net-next 2/8] dt-bindings: net: lan9645x: add LAN9645X switch bindings

[Conor Dooley]

On Wed, Mar 04, 2026 at 06:14:57PM +0200, Vladimir Oltean wrote:
> On Wed, Mar 04, 2026 at 05:10:11PM +0100, Jens Emil Schulz Ostergaard wrote:
> > On Tue, 2026-03-03 at 18:56 +0000, Conor Dooley wrote:
> > > On Tue, Mar 03, 2026 at 01:22:28PM +0100, Jens Emil Schulz Østergaard wrote:
> > > > +examples:
> > > > +  - |
> > > > +    soc {
> > > > +        #address-cells = <1>;
> > > > +        #size-cells = <0>;
> > > > +
> > > > +      ethernet-switch@0 {
> > > > +        reg = <0>;
> > > 
> > > Also, this is an odd example, why are you at address 0 on a "soc" bus,
> > > which usually means that this device on an AXI/AHB bus, and 0 is very
> > > unusual for that. Obviously the example doesn't have to match the real
> > > user, but this stands out.
> > > I may have some follow up questions I think depending on your answer.
> > 
> > The intended way to bind this driver is via a parent MFD driver which sets
> > up the SPI register protocol, initiates regmaps and distributes them to child
> > devices (like this DSA driver).
> > 
> > Similar to mscc,vsc7512 in drivers/mfd/ocelot-spi.c.
> > 
> > This MFD would be the soc node. All child nodes perform register IO over
> > spi, using the regmaps requested from this parent so I think the addresses
> > on the bus are purely ornamental. Should I write the smallest register
> > address in all regions used by the DSA driver instead?
> 
> They are not ornamental, they should be the same addresses you'd put if
> Linux had direct access to the SoC interconnect for MMIO, rather than to
> an SPI bridge to the SoC interconnect. Or at least I don't see why it
> wouldn't be that way.

I don't mind if they're made up addresses, but the example should be
realistic. 0 is likely not realistic, but if it was 0x4000_0000 when the
real thing is 0x8123_1234 then I don't really care. Since the parent is
not actually a soc bus, can't you just remove this fake parent entirely,
like the ocelot switch example does? Or insert something more genuine,
like:
spi {
  #address-cells = <1>;
  #size-cells = <0>;

  soc@0 {
    compatible = "microchip,lan96455s";
    reg = <0>;
    #address-cells = <1>;
    #size-cells = <1>;

    ethernet-switch@4000000 {
      reg = <4000000 44>;

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