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

[Krzysztof Kozlowski <krzk@kernel.org>]

On 03/06/2026 00:18, Frank Li wrote:
> 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

Yes, could be a bit shorter like fsl,imx95-19x19-evk-aud-io-slot or even
without slot because prefixing it with board compatible makes it very
specific.

> 
> Frank
> 
>>
>> Best regards,
>> Krzysztof


Best regards,
Krzysztof