Re: [PATCH 3/3] sample: rust: Add GPIO consumer sample driver

[Bartosz Golaszewski]

On Mon, 14 Sep 2026 03:41:29 +0200, Alexandre Courbot
<acourbot@xxxxxxxxxx> said:
> On Sun Sep 13, 2026 at 5:46 PM JST, Kohei Ito wrote:
>> Hi, Bartosz,
>>
>> On Thu, Sep 10, 2026 at 12:37:17AM -0700, Bartosz Golaszewski wrote:
>>> On Sun, 6 Sep 2026 10:45:51 +0200, Kohei Ito <koheiito.dev@xxxxxxxxx> said:
>>> > Add a sample driver to demonstrate the use of the Rust GPIO APIs.
>>> >
>>> > Signed-off-by: Kohei Ito <koheiito.dev@xxxxxxxxx>
>>> > ---
>>>
>>> I don't like samples as they rarely get built or tested. We seem to already
>>> have kunit support for rust, wouldn't it make more sense to implement a kunit
>>> module for rust GPIO abstractions? If we don't have provider abstractions, you
>>> should be able to reuse gpio-sim as the GPIO controller for testing just by
>>> instantiating simulated GPIO devices.
>>
>> Thank you for your suggestion.
>>
>> I assume the kunit module you have in mind would be implemented like
>> `gpiolib-kunit.c`. Based on your comment, I agree that a kunit-based
>> approach is more appropriate than a sample driver.
>>
>> However, as far as I know, we don't yet have Rust abstractions for
>> platform_device registration and software_node, which are required to
>> implement a kunit-based module for testing GPIO consumer APIs. Given the
>> current state of Rust for Linux, I think creating a sample driver is a
>> more practical approach for now. I would like to consider migrating to a
>> kunit-based module as future work.
>
> The problem is that this sample driver never probes, so in effect it is
> only ever compile-tested. Without support for the provider API, you need
> to include a small C fixture providing a GPIO chip for it to be actually
> runtime-tested.
>
> Doing the same using KUnit would involve building the `gpio_chip` using a
> bunch of unsafe statements working with the C bindings (which would then
> in turn require `gpio/driver.h` to be added), so I guess we'll want to
> wait until we have a proper Rust provider API to go that direction.
>

No, I was thinking about the gpio-sim module which is implemented as a platform
driver which you can describe with a software node and then register to create
a simulated GPIO provider against which the consumer APIs in rust could be
tested.

To that end, we'd need to just register a platform device from rust and AFAICT,
there are already APIs for that, except for the software nodes.

Bart