Re: [PATCH v2 2/3] dt-bindings: dp83867: add binding for output-impedance

[Steffen Trumtrar <s.trumtrar@pengutronix.de>]

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On 2026-08-26 at 17:01 +01, Conor Dooley <conor@kernel.org> wrote:

> On Wed, Aug 26, 2026 at 02:48:40PM +0200, Steffen Trumtrar wrote:
> > Currently, the output-impedance can only be set to default, minimum or
> > maximum or via a nvmem cell.
> > In cases where there is no backend for a nvmem cell, a value can not be
> > set.
> > 
> > Add a DT binding, 'ti,output-impedance-ohms', for specifying the
> > output-impedance via a fixed value. The existing boolean values for
> > minimum and maximum still take precedence over the new value.
> > 
> > Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
> > ---
> >  Documentation/devicetree/bindings/net/ti,dp83867.yaml | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/net/ti,dp83867.yaml b/Documentation/devicetree/bindings/net/ti,dp83867.yaml
> > index 7a6fe516bab27..49fafe3ce6f47 100644
> > --- a/Documentation/devicetree/bindings/net/ti,dp83867.yaml
> > +++ b/Documentation/devicetree/bindings/net/ti,dp83867.yaml
> > @@ -38,6 +38,16 @@ properties:
> >      items:
> >        - const: io_impedance_ctrl
> >  
> > +  ti,output-impedance-ohms:
> > +    description: |
> > +      MAC Interface Impedance control to set the programmable output impedance.
> > +      Valid range is 0x00 to 0x1f (32 steps).
> > +      - 0x1f = 35 ohms (minimum impedance)
> > +      - 0x00 = 70 ohms (maximum impedance)
> > +      - Step size varies with process.
> > +    minimum: 0
> > +    maximum: 31
> 
> Your property is named in ohms, but not implemented in ohms.

So without the -ohms?

> pw-bot: changes-requested
> 
> Can't you just achieve the same result using the existing max property?

The max property is a boolean which just says "use 70ohms".

> I don't get the use case where you specify a max, but then don't want to
> use that max. Just set the max to what you actually want?

That's why I added the exclusion in the binding, because having nvmem-cells and/or any of the other output-impedance bindings doesn't make any sense.

Best regards,
Steffen

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