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

[Frank Li <Frank.li@nxp.com>]

On Mon, May 25, 2026 at 02:28:32PM +0200, Krzysztof Kozlowski wrote:
> On 25/05/2026 08:26, 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.
> >>>
> >>
> >> So the terminology of daughter and carrier boards was confusing. If this
> >> is a hat, mezzanine or other addon, it's fine.
> >>
> >
> > The IMX-AUD-IO is an add-on board that attaches to the base board. To
> > make it clearer, I will replace "daughter board" with "add-on board"
> > throughout descriptions.
> >
> >> I still insist on board specific compatibles - fallback and specific.
> >>
> >
> > The base board has a slot component that is mechanically compatible
> > with a PCIe x8 connector. However, it carries no PCIe signals and the
> > pins are repurposed to carry fixed board-level audio I/O related
> > signals.
> >
> > I think we can name a compatible reflects a standard mechanical form
> > factor.
> > For the compatibles (specific + fallback) I propose:
> > - enum:
> >     - fsl,imx95-19x19-evk-aud-io-pcie-x8-slot
> >     - fsl,imx952-evk-aud-io-pcie-x8-slot
> > - const: fsl,aud-io-pcie-x8-slot
>
> Does not solve my request, so I won't ack it. Maybe you will get ack
> from other DT maintainer then.

Krzysztof:
	Thank you for your support. This type header/slot is difficult to
name it.

After read again previous comments

"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."

Do you means
oneOf
  - items:
      - enum:
          - fsl,imx943-evk-aud-io-pcie-x8-slot
          - fsl,imx952-evk-aud-io-pcie-x8-slot
      - const: fsl,imx95-19x19-evk-aud-io-pcie-x8-slot
 - const: fsl,imx95-19x19-evk-aud-io-pcie-x8-slot

Frank

>
> Best regards,
> Krzysztof