linux-kernel - Re: [PATCH RESEND v2] rust: regulator: add a bare minimum regulator abstraction

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Message-ID: <opip2gbm6tpjqnx4hqk4mghbkhv7egexeqs5ukfn7oz3mm7nev@y7qffwz5ckdz>
Date: Thu, 27 Mar 2025 14:46:30 +0100
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, 
	Boris Brezillon <boris.brezillon@...labora.com>, lgirdwood@...il.com, broonie@...nel.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH RESEND v2] rust: regulator: add a bare minimum regulator
 abstraction

Hi,

On Wed, Mar 26, 2025 at 03:39:33PM -0300, Daniel Almeida wrote:
> +    pub fn get(dev: &Device, name: &CStr) -> Result<Self> {
> +        // SAFETY: It is safe to call `regulator_get()`, on a device pointer
> +        // received from the C code.
> +        let inner = from_err_ptr(unsafe { bindings::regulator_get(dev.as_raw(), name.as_ptr()) })?;
> +
> +        // SAFETY: We can safely trust `inner` to be a pointer to a valid
> +        // regulator if `ERR_PTR` was not returned.
> +        let inner = unsafe { NonNull::new_unchecked(inner) };
> +
> +        Ok(Self { inner })
> +    }

I think it's worth discussing using regulator_get() VS
regulator_get_optional(). We somehow ended up with the C regulator
API being more or less orthogonal to other in-kernel C APIs (clocks,
gpio, reset, LED) with the _optional suffixed version returning
-ENODEV for a missing regulator (and thus needing explicit handling)
and the normal version creating a dummy regulator (and a warning).

Considering the Rust API is new, it would be possible to let the
Rust get() function call regulator_get_optional() instead and then
introduce something like get_or_dummy() to call the normal
regulator_get() C function.

I see reasons in favor and against this. I just want to make sure it
has been considered before the API is being used, which makes it a
lot harder to change.

Greetings,

-- Sebastian

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