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

[Krzysztof Kozlowski <krzk@kernel.org>]

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.

Best regards,
Krzysztof