Re: [PATCH v2 2/2] gpio: aggregator: add gpio-aggregator DT compatible

[James Hilliard]

On Thu, Feb 12, 2026 at 12:18 AM Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote:
>
> On 11/02/2026 22:49, James Hilliard wrote:
> >>>>>
> >>>>> Regardless of the DT bindings - this change is perfectly fine. We do
> >>>>
> >>>> You cannot have compatible without DT bindings, so this alone is not
> >>>> "perfectly fine". Maybe you wanted platform_device_id entry for
> >>>> ACPI/legacy/MFD devices?
> >>>>
> >>>
> >>> Sure you can, you just can't put it into upstream devicetree sources.
> >>> We have had a compatible for gpio-sim for testing purposes for years.
> >>> Why would it be illegal to enable matching of platform drivers over DT
> >>> for testing purposes?
> >>
> >> The primary issue is undocumented ones show up in 'make
> >> dt_compatible_check'. I would like that to be warning free.
> >
> > Would adding it here make sense?
> > https://github.com/torvalds/linux/blob/v6.19/Documentation/devicetree/bindings/incomplete-devices.yaml#L243-L245
>
> What would you like to achieve with that? The binding patch did not have
> rationale why do we want it and here is the same question - what sort of
> problem is being solved by adding it to incomplete (so wrong) devices?

See details for what I'm trying to accomplish with gpio-aggregator:
https://lore.kernel.org/all/CADvTj4oBtO0Yhib1rE8QQwgtJvy-x_hK46C63mjVAydtxHOV8g@xxxxxxxxxxxxxx/

I'm basically trying to use it for the reasons described here:
https://bootlin.com/blog/gpio-aggregator-a-virtual-gpio-chip/

Is there a different device tree mechanism that can be used to
name individual gpio lines on a gpiochip without having to name
all of them for non-hog lines?

I'm confused why a "gpio-delay" compatible is allowed but one
without the delay param is not?

Or is the issue just with the name of the compatible I used being
called "gpio-aggregator"?

> This is not a pure virtual device, but for use with actual hardware.
>
> Nacked-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

I'm trying to use this with actual hardware, I just called it "virtual"
because that's how it was described in the bootlin blog post.

I'm confused about what the issue is here as "gpio-delay" is also
a virtual device in the same way.

> Well, it is a virtual device in that there's no actual "aggregator"
> device on the board. It virtually aggregates GPIOs into a separate
> chip for user's convenience. While there's no such device as a
> gpio-aggregator - and so we must not put it into bindings nor into
> mainline devicetree sources - having a compatible matching in the
> driver is perfectly fine IMO. Just like gpio-sim.

There's no such "gpio-delay" device either right? I'm confused
why that compatible can exist but one without the delay param can
not in the mainline sources. Aren't they both virtual devices?