[PATCH 2/5] dt-bindings: connector: Add fsl,io-connector binding

[Frank Li]

On Wed, May 20, 2026 at 09:08:42AM +0200, Krzysztof Kozlowski wrote:
> On 20/05/2026 07:02, Chancel Liu (OSS) wrote:
> >>>>>>> +description:
> >>>>>>> +  The NXP I/O connector represents a physically present I/O
> >>>>>>> +connector on the
> >>>>>>> +  base board. It acts as a nexus that exposes a constrained set
> >> of
> >>>>>>> +I/O
> >>>>>>> +  resources, such as GPIOs, clocks, PWMs and interrupts, through
> >>>>>>> +fixed
> >>>>>>> +  electrical wiring. All actual hardware providers reside on the
> >> base
> >>>> board.
> >>>>>>> +  The connector node only defines index-based mappings to those
> >>>>>> providers.
> >>>>>>> +
> >>>>>>> +properties:
> >>>>>>> +  compatible:
> >>>>>>> +    const: fsl,io-connector
> >>>>>>
> >>>>>> Everything is IO. Everything is connector, so your compatible does
> >>>>>> not match requirements from writing bindings.
> >>>>>>
> >>>>>
> >>>>> Yes, this compatible is too generic. I will rename the compatible to
> >>>>> fsl,aud-io-connector.
> >>>>
> >>>> aud is not much better. Which boards have it? What's the pinout?
> >> What's
> >>>> standard? Is it described anywhere? If so, provide reference to
> >> spec/docs.
> >>>>
> >>>
> >>> This is not an industry standard electrical interface. This connector
> >>
> >> Then if you do not have standard, then you have board specific layouts
> >> thus you need board-specific compatibles. You can use fallbacks. Generic
> >> fallback could work, but both io-connector and aud-io-connector are just
> >> too generic. Every connector is "connector" and "io", thus absolutely
> >> anything can be "io-connector". "aud" improves it only a bit, thus
> >> honestly I would go with board specific fallback as well.
> >>
> >
> > How about board specific + common fallback compatible like this:
> >   compatible:
> >     items:
> >       - enum:
> >           - fsl,imx95-19x19-evk-aud-io-connector
> >           - fsl,imx952-evk-aud-io-connector
> >       - const: fsl,imx-aud-io-connector
> > Since the daughter board is named “IMX-AUD-IO” in publicly available
>
> I don't think it is named like that.
>
> git grep -i imx-aud-io
>
> > documentation, common compatible clearly indicates that this connector
> > is intended for that.
> >
> > Also, I want to talk about the topic of generic connector. It's a common
> > design that daughter board is connected to base board through a
> > connector. This connector more often acts as a nexus that exposes a
> > constrained subset of GPIO, clock, PWM and interrupt resources to the
> > daughter board. Can we document this kind of connector as a generic
> > binding?
>
> So this binding is the connector between carrier and some addon? Then
> you don't get a compatible for that at all, because it is not necessary,
> not useful and NEVER used. Do you see socket LGA "connector" bindings? No.

Not exactly. Any connector connects a carrier board with an add-on board.
The key point here is that this connector type is reused across different
boards, even though it is not an industry-standard connector. Both the
signal definitions and the mechanical layout are defined.

The same add-on boards can therefore be reused across different base boards
that use this type of connector.

There are also GPIO mappings involved. For example, pin 1 on the connector
may represent reset-gpios, but it could be connected to GPIO0 on board A
and GPIO1 on board B.

Without a connector definition layer, this would create an N × M
combination problem. The Nexus node discussion already covered this topic:
https://osseu2025.sched.com/event/25Vrw

An LGA socket is a CPU socket, where the signals are completely transparent
to software, so it is not a good comparison. A PCIe M.2 Key-M/E connector
would be a more appropriate comparison.

Frank

>
>
> Best regards,
> Krzysztof