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

[Alexandre Courbot]

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.

But if we add a sample driver, we need to make sure it is exercised.