Re: [PATCH net-next 2/2] dt-bindings: net: microchip,ksz: document microchip,rmii-clk-internal

[Conor Dooley <conor@kernel.org>]

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On Mon, Oct 16, 2023 at 09:53:49AM +0200, Ante Knezic wrote:
> On Thu, 12 Oct 2023 16:18:09 +0100, Conor Dooley wrote:
> > On Thu, Oct 12, 2023 at 12:55:56PM +0200, Ante Knezic wrote:
> > > Add documentation for selecting reference rmii clock on KSZ88X3 devices
> > > 
> > > Signed-off-by: Ante Knezic <ante.knezic@helmholz.de>
> > > ---
> > >  .../devicetree/bindings/net/dsa/microchip,ksz.yaml    | 19 +++++++++++++++++++
> > >  1 file changed, 19 insertions(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/net/dsa/microchip,ksz.yaml b/Documentation/devicetree/bindings/net/dsa/microchip,ksz.yaml
> > > index 41014f5c01c4..eaa347b04db1 100644
> > > --- a/Documentation/devicetree/bindings/net/dsa/microchip,ksz.yaml
> > > +++ b/Documentation/devicetree/bindings/net/dsa/microchip,ksz.yaml
> > > @@ -72,6 +72,25 @@ properties:
> > >    interrupts:
> > >      maxItems: 1
> > >  
> > > +  microchip,rmii-clk-internal:
> > > +    $ref: /schemas/types.yaml#/definitions/flag
> > > +    description:
> > > +      Set if the RMII reference clock is provided internally. Otherwise
> > > +      reference clock should be provided externally.
> > 
> > I regret not asking this on the previous iteration - how come you need a
> > custom property? In the externally provided case would there not be a
> > clocks property pointing to the RMII reference clock, that would be
> > absent when provided by the itnernal reference?

> In both cases (external and internal), the KSZ88X3 is actually providing the
> RMII reference clock.
> Difference is only will the clock be routed as external
> copper track (pin REFCLKO -> pin REFCLKI), or will it be routed internally.

The switch always provides it's own external reference, wut? Why would
anyone actually bother doing this instead of just using the internal
reference?

> So, this should not affect the clock relation between the uC and the switch
> device?

> This property has no effect if KSZ88X3 is not providing the reference clock.

This appears to contradict with the above, unless I am misunderstanding
something.

> Maybe I should provide more info in the commit message of both patches as well?

What I would have expected to see is that when the reference clock is
provided externally that there would be a clocks property in the DT
node, pointing at that external clock & when there was not, then
no property. Likely that ship has already said, as I don't see clocks
present in the current binding. How does the driver get the frequency of
the RMII reference clock when an external reference is provided?

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