linux-kernel - Re: [PATCH v2 2/5] rust: Add bindings for reading device properties

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Message-ID: <8fc82ddb-fe5c-43e2-928e-efd3ebaec3e6@de.bosch.com>
Date: Wed, 23 Apr 2025 14:34:30 +0200
From: Dirk Behme <dirk.behme@...bosch.com>
To: Remo Senekowitsch <remo@...nzli.dev>, Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>, 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>, "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
	<rafael@...nel.org>
CC: <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] rust: Add bindings for reading device properties

Hi Remo,

On 14/04/2025 17:26, Remo Senekowitsch wrote:
> The device property API is a firmware agnostic API for reading
> properties from firmware (DT/ACPI) devices nodes and swnodes.
> 
> While the C API takes a pointer to a caller allocated variable/buffer,
> the rust API is designed to return a value and can be used in struct
> initialization. Rust generics are also utilized to support different
> types of properties where appropriate.
> 
> The PropertyGuard is a way to force users to specify whether a property
> is supposed to be required or not. This allows us to move error
> logging of missing required properties into core, preventing a lot of
> boilerplate in drivers.
> 
> Co-developed-by: Rob Herring (Arm) <robh@...nel.org>
> Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> Signed-off-by: Remo Senekowitsch <remo@...nzli.dev>
> ---
>  rust/kernel/property.rs | 385 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 383 insertions(+), 2 deletions(-)
> 
> diff --git a/rust/kernel/property.rs b/rust/kernel/property.rs
> index f6e6c980d..0d4ea3168 100644
> --- a/rust/kernel/property.rs
> +++ b/rust/kernel/property.rs
> @@ -4,9 +4,17 @@
....
> +    /// Returns the value of firmware property `name`.
> +    ///
> +    /// This method is generic over the type of value to read. Informally,
> +    /// the types that can be read are booleans, strings, unsigned integers and
> +    /// arrays of unsigned integers.
> +    ///
> +    /// Reading a `KVec` of integers is done with the separate
> +    /// method [`Self::property_read_array_vec`], because it takes an
> +    /// additional `len` argument.
> +    ///
> +    /// When reading a boolean, this method never fails. A missing property
> +    /// is interpreted as `false`, whereas a present property is interpreted
> +    /// as `true`.
> +    ///
> +    /// For more precise documentation about what types can be read, see
> +    /// the [implementors of Property][Property#implementors] and [its
> +    /// implementations on foreign types][Property#foreign-impls].
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```
> +    /// # use crate::{device::Device, types::CString};
> +    /// fn examples(dev: &Device) -> Result {
> +    ///     let fwnode = dev.fwnode();
> +    ///     let b: bool = fwnode.property_read("some-bool").required()?;
> +    ///     if let Some(s) = fwnode.property_read::<CString>("some-str").optional() {
> +    ///         // ...
> +    ///     }
> +    /// }
> +    /// ```

With CONFIG_RUST_KERNEL_DOCTESTS=y I had to change this example to [1]
to make it buildable.

Best regards

Dirk

[1]

diff --git a/rust/kernel/property.rs b/rust/kernel/property.rs
index 17ad176378206..bd43c910786d6 100644
--- a/rust/kernel/property.rs
+++ b/rust/kernel/property.rs
@@ -214,11 +214,10 @@ pub fn property_count_elem<T: PropertyInt>(&self,
name: &CStr) -> Result<usize>
     /// # Examples
     ///
     /// ```
-    /// # use crate::{device::Device, types::CString};
-    /// fn examples(dev: &Device) -> Result {
-    ///     let fwnode = dev.fwnode();
-    ///     let b: bool = fwnode.property_read("some-bool").required()?;
-    ///     if let Some(s) =
fwnode.property_read::<CString>("some-str").optional() {
+    /// # use kernel::{c_str, property::FwNode, str::CString};
+    /// fn examples(fwnode: &FwNode) -> () {
+    ///     let b: bool = fwnode.property_read_bool(c_str!("some-bool"));
+    ///     if let Some(s) =
fwnode.property_read::<CString>(c_str!("some-str")).optional() {
     ///         // ...
     ///     }
     /// }