linux-kernel - Re: [PATCH 2/2] rust: regulator: add devm_regulator_get

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Message-Id: <DCFID32NEFH0.3JB41XV88JZ3F@nvidia.com>
Date: Sat, 30 Aug 2025 14:20:55 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Daniel Almeida" <daniel.almeida@...labora.com>, "Liam Girdwood"
 <lgirdwood@...il.com>, "Mark Brown" <broonie@...nel.org>, "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"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice
 Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "Danilo
 Krummrich" <dakr@...nel.org>
Cc: <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH 2/2] rust: regulator: add devm_regulator_get_enable API

On Sat Aug 30, 2025 at 6:11 AM JST, Daniel Almeida wrote:
> A lot of drivers only care about enabling the regulator for as long as
> the underlying Device is bound. This can be easily observed due to the
> extensive use of `devm_regulator_get_enable` and
> `devm_regulator_get_enable_optional` throughout the kernel.
>
> Therefore, make this helper available in Rust. Also add an example
> noting how it should be the default API unless the driver needs more
> fine-grained control over the regulator.
>
> Suggested-by: Danilo Krummrich <dakr@...nel.org>
> Signed-off-by: Daniel Almeida <daniel.almeida@...labora.com>
> ---
>  rust/helpers/regulator.c | 10 ++++++++++
>  rust/kernel/regulator.rs | 42 +++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/rust/helpers/regulator.c b/rust/helpers/regulator.c
> index cd8b7ba648ee33dd14326c9242fb6c96ab8e32a7..11bc332443bd064f4b5afd350ffc045badff9076 100644
> --- a/rust/helpers/regulator.c
> +++ b/rust/helpers/regulator.c
> @@ -40,4 +40,14 @@ int rust_helper_regulator_is_enabled(struct regulator *regulator)
>  	return regulator_is_enabled(regulator);
>  }
>  
> +int rust_helper_devm_regulator_get_enable(struct device *dev, const char *id)
> +{
> +	return devm_regulator_get_enable(dev, id);
> +}
> +
> +int rust_helper_devm_regulator_get_enable_optional(struct device *dev, const char *id)
> +{
> +	return devm_regulator_get_enable_optional(dev, id);
> +}
> +
>  #endif
> diff --git a/rust/kernel/regulator.rs b/rust/kernel/regulator.rs
> index 60993373f4d911f4f0cbec2510f0c67efa24a51b..73d4c9b56dca9c676793d78e35e5758d18eef3e8 100644
> --- a/rust/kernel/regulator.rs
> +++ b/rust/kernel/regulator.rs
> @@ -18,7 +18,7 @@
>  
>  use crate::{
>      bindings,
> -    device::Device,
> +    device::{Bound, Device},
>      error::{from_err_ptr, to_result, Result},
>      prelude::*,
>  };
> @@ -70,6 +70,26 @@ pub struct Error<State: RegulatorState> {
>      pub regulator: Regulator<State>,
>  }
>  
> +/// Enables a regulator whose lifetime is tied to the lifetime of `dev`.
> +///
> +/// This calls `regulator_disable()` and `regulator_put()` automatically on
> +/// driver detach.
> +///
> +/// This API is identical to `devm_regulator_get_enable()`, and should be
> +/// preferred if the caller only cares about the regulator being on.
> +pub fn enable(dev: &Device<Bound>, name: &CStr) -> Result {

The name `enable` sounds like it just enables a regulator, which is a bit
confusing IMHO. Maybe `get_enable` or `get_enable_for`? Not sure what
would be idiomatic here.

> +    // SAFETY: `dev` is a valid and bound device, while `name` is a valid C
> +    // string.
> +    to_result(unsafe { bindings::devm_regulator_get_enable(dev.as_raw(), name.as_ptr()) })
> +}
> +
> +/// Same as [`enable`], but calls `devm_regulator_get_enable_optional` instead.

Maybe explain in one sentence what `devm_regulator_get_enable_optional`
as it might not be completely obvious.

> +pub fn enable_optional(dev: &Device<Bound>, name: &CStr) -> Result {
> +    // SAFETY: `dev` is a valid and bound device, while `name` is a valid C
> +    // string.
> +    to_result(unsafe { bindings::devm_regulator_get_enable_optional(dev.as_raw(), name.as_ptr()) })
> +}
> +
>  /// A `struct regulator` abstraction.
>  ///
>  /// # Examples
> @@ -146,6 +166,26 @@ pub struct Error<State: RegulatorState> {
>  /// }
>  /// ```
>  ///
> +/// If a driver only cares about the regulator being on for as long it is bound
> +/// to a device, then it should use [`regulator::get_enabled`] or
> +/// [`regulator::get_enabled_optional`]. This should be the default use-case

I suppose you mean `enable` and `enable_optional` instead of
`get_enabled` and `get_enabled_optional` (although I personally would
favor the latter :)).