Re: [PATCH v2 phy 12/16] dt-bindings: phy: lynx-28g: add compatible strings per SerDes and instantiation

Vladimir Oltean
2025-09-24T15:45:40Z

Hi Rob,

On Wed, Sep 24, 2025 at 08:54:29AM -0500, Rob Herring wrote:
> > +description: |
>
> Don't need '|' if no formatting to preserve.

Thanks, will drop.

> > + "#address-cells":
> > + const: 1
> > + description: "Address cells for child lane nodes"
>
> You don't need generic descriptions of common properties.

Ok, I'll also drop the description from #size-cells but keep it in
#phy-cells (less obvious).

> > +
> > + "#size-cells":
> > + const: 0
> > + description: "Size cells for child lane nodes"
> > +
> > "#phy-cells":
> > + description: "Number of cells in PHY specifier (legacy binding only)"
> > const: 1
> >
> > @@ -32,9 +124,51 @@ examples:
> > soc {
> > #address-cells = <2>;
> > #size-cells = <2>;
> > - serdes_1: phy@1ea0000 {
> > - compatible = "fsl,lynx-28g";
> > +
> > + serdes_1: serdes@1ea0000 {
> > + compatible = "fsl,lx2160a-serdes1";
> > reg = <0x0 0x1ea0000 0x0 0x1e30>;
> > - #phy-cells = <1>;
> > + #address-cells = <1>;
> > + #size-cells = <0>;
> > +
> > + phy@0 {
> > + reg = <0>;
> > + #phy-cells = <0>;
> > + };
>
> There's really no difference between having child nodes 0-7 and 8 phy
> providers vs. putting 0-7 into a phy cell arg and 1 phy provider.
>
> The only difference I see is it is more straight-forward to determine
> what lanes are present in the phy driver if the driver needs to know
> that. But you can also just read all 'phys' properties in the DT with a
> &serdes_1 phandle and determine that. Is that efficient? No, but you
> have to do that exactly once and probably has no measurable impact.
>
> With that, then can't you simply just add a more specific compatible:
>
> compatible = "fsl,lx2160a-serdes1", "fsl,lynx-28g";
>
> Then you maintain some compatibility.
>
> Rob

With the patches that have been presented to you thus far -- yes, this
is the correct conclusion, there is not much of a difference. But this
is not all.

If I want in the future to apply the properties from
Documentation/devicetree/bindings/phy/transmit-amplitude.yaml to just
one of the lanes, how would I do that with just 1 phy provider? It's not
so clear. Compared to 8 phy providers, each with its OF node => much
easier to structure and to understand.

This is essentially what the discussion with Josua from v1 boils down to.