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

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Message-ID: <2c5734db-1e62-4aeb-9c6a-ef14939575c2@kernel.org>
Date: Wed, 11 Feb 2026 11:48:59 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Bartosz Golaszewski <brgl@...nel.org>,
 Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: James Hilliard <james.hilliard1@...il.com>, linux-gpio@...r.kernel.org,
 Linus Walleij <linusw@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Alexander Stein <linux@...tq-group.com>,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] gpio: aggregator: add gpio-aggregator DT
 compatible

On 11/02/2026 11:38, Bartosz Golaszewski wrote:
> On Wed, Feb 11, 2026 at 10:50 AM Geert Uytterhoeven
> <geert@...ux-m68k.org> wrote:
>>
>>>>
>>>>  static const struct of_device_id gpio_aggregator_dt_ids[] = {
>>>> +       {
>>>> +               .compatible = "gpio-aggregator",
>>>> +       },
>>>>         {
>>>>                 .compatible = "gpio-delay",
>>>>                 .data = (void *)FWD_FEATURE_DELAY,
>>>> --
>>>> 2.43.0
>>>>
>>>
>>> Regardless of the DT bindings - this change is perfectly fine. We do
>>> that for other "virtual" devices like gpio-sim, gpio-virtuser, etc. I
>>> would just ask you to document it under
>>> Documentation/admin-guide/gpio/gpio-aggregator.rst.
>>
>> This is not a pure virtual device, but for use with actual hardware.
>>
>> Nacked-by: Geert Uytterhoeven <geert+renesas@...der.be>
>>
> 
> 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.

I already wrote, you cannot have undocumented compatible. There are even
explicit checks for this - in schema and checkpatch - so with your
approach you accept known warnings. Really, no, and fact we need to keep
discussing it:

Nacked-by: Krzysztof Kozlowski <krzysztof.kozlowski@....qualcomm.com>

Best regards,
Krzysztof