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

Rob Herring
2025-09-25T13:05:11Z

On Wed, Sep 24, 2025 at 06:45:34PM +0300, Vladimir Oltean wrote:
> 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.

That's all I can base my conclusion on if you don't tell me more...

> 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.

That's unfortunate that binding wasn't designed to support more than
1 instance. You could do:

lane@0 {
reg = <0>;
tx-p2p-microvolt = <123>;
};

lane@1 {
reg = <1>;
tx-p2p-microvolt = <123>;
};

Yeah, that's about what you had, but it avoids changing the cell size.
That should be a bit simpler to implement in the driver and to add to
existing DTs as a fixup (because you don't have to change 'phys' entries
everywhere).

Another option is go to cell size of 2 and stick the voltage in a cell.
That approach doesn't work well if you have a 3rd, 4th, etc. cell to add
later for more properties.

Your overlaying the old and new bindings approach works too. That
approach is fine with me.

Rob