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

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Message-ID: <20250924154534.cyyfi2aez46iu2sw@skbuf>
Date: Wed, 24 Sep 2025 18:45:34 +0300
From: Vladimir Oltean <vladimir.oltean@....com>
To: Rob Herring <robh@...nel.org>
Cc: linux-phy@...ts.infradead.org, Ioana Ciornei <ioana.ciornei@....com>,
	Vinod Koul <vkoul@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Josua Mayer <josua@...id-run.com>, linux-kernel@...r.kernel.org,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 phy 12/16] dt-bindings: phy: lynx-28g: add compatible
 strings per SerDes and instantiation

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@...0000 {
> > -        compatible = "fsl,lynx-28g";
> > +
> > +      serdes_1: serdes@...0000 {
> > +        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.