Re: [PATCH v3 1/9] dt-bindings: misc: Describe TI FPC202 dual port controller

Romain Gantois
2024-11-26T08:05:51Z

Hello Conor,

On lundi 25 novembre 2024 19:26:35 heure normale d’Europe centrale Conor Dooley wrote:
> On Mon, Nov 25, 2024 at 09:45:15AM +0100, Romain Gantois wrote:
> > The FPC202 dual port controller serves as a low speed signal aggregator
> > for
...
> > +
> > +required:
> > + - compatible
> > + - gpio-controller
> > + - "#gpio-cells"
> > + - reg
> > + - "#address-cells"
> > + - "#size-cells"
> > + - i2c@0
> > + - i2c@1
>
> btw, why are both downstream ports required?

It's because both downstream ports are always present in an FPC202 unit
so in my opinion, it doesn't make sense to describe an FPC202 with only one
downstream port.

I suppose you could also consider that ports would only be described in the DT
if they were connected to something in the hardware, but I don't think it would
make sense to use an FPC202 in this way. After all, the whole point of this
component is to act as an I2C ATR and low-speed signal aggregator for
downstream devices which would have address collisions if you placed them
on the same I2C bus.

But then again, you could consider that DT bindings should only describe what is
possible, and not only what makes sense as a use case. I don't really know how to
answer this question myself, so I'll refer to the maintainers' opinions.

Best Regards,

--
Romain Gantois, Bootlin
Embedded Linux and Kernel engineering