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

[Jens Emil Schulz Ostergaard]

On Wed, 2026-03-04 at 19:06 +0000, Conor Dooley wrote:
> 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>;
> 


I will go with the genuine example. I was not sure if it was appropriate 
to mention the spi node from here. But this is what it would look like with
the mfd driver. I will also fix the addresses.

Thanks,
Emil