linux-kernel - Re: [PATCH 08/10] rust: property: Add property_get_reference

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Message-ID: <Z-VhgxJ5kyQbeVPi@cassiopeiae>
Date: Thu, 27 Mar 2025 15:32:35 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Remo Senekowitsch <remo@...nzli.dev>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Daniel Scally <djrscally@...il.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Rob Herring <robh@...nel.org>, Dirk Behme <dirk.behme@...bosch.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...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>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	devicetree@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 08/10] rust: property: Add property_get_reference_args

On Wed, Mar 26, 2025 at 06:13:47PM +0100, Remo Senekowitsch wrote:
> Signed-off-by: Remo Senekowitsch <remo@...nzli.dev>
> ---
>  rust/kernel/property.rs | 63 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
> 
> diff --git a/rust/kernel/property.rs b/rust/kernel/property.rs
> index dc927ad93..f1d0a33ba 100644
> --- a/rust/kernel/property.rs
> +++ b/rust/kernel/property.rs
> @@ -8,6 +8,7 @@
>  
>  use crate::{
>      alloc::KVec,
> +    arrayvec::ArrayVec,
>      bindings,
>      device::Device,
>      error::{to_result, Result},
> @@ -64,6 +65,20 @@ pub fn get_child_by_name(&self, name: &CStr) -> Option<ARef<FwNode>> {
>      pub fn children<'a>(&'a self) -> impl Iterator<Item = ARef<FwNode>> + 'a {
>          self.fwnode().children()
>      }
> +
> +    /// Finds a reference with arguments.
> +    pub fn property_get_reference_args(
> +        &self,
> +        prop: &CStr,
> +        nargs: NArgs<'_>,
> +        index: u32,
> +    ) -> Result<(
> +        ARef<FwNode>,
> +        ArrayVec<{ bindings::NR_FWNODE_REFERENCE_ARGS as usize }, u64>,
> +    )> {
> +        self.fwnode()
> +            .property_get_reference_args(prop, nargs, index)
> +    }
>  }
>  
>  /// A reference-counted fwnode_handle.
> @@ -226,6 +241,45 @@ pub fn children<'a>(&'a self) -> impl Iterator<Item = ARef<FwNode>> + 'a {
>              Some(next)
>          })
>      }
> +
> +    /// Finds a reference with arguments.
> +    pub fn property_get_reference_args(
> +        &self,
> +        prop: &CStr,
> +        nargs: NArgs<'_>,
> +        index: u32,
> +    ) -> Result<(
> +        ARef<Self>,
> +        ArrayVec<{ bindings::NR_FWNODE_REFERENCE_ARGS as usize }, u64>,
> +    )> {
> +        let mut out_args = bindings::fwnode_reference_args::default();
> +
> +        let (nargs_prop, nargs) = match nargs {
> +            NArgs::Prop(nargs_prop) => (nargs_prop.as_char_ptr(), 0),
> +            NArgs::N(nargs) => (ptr::null(), nargs),
> +        };
> +
> +        let ret = unsafe {
> +            bindings::fwnode_property_get_reference_args(
> +                self.0.get(),
> +                prop.as_char_ptr(),
> +                nargs_prop,
> +                nargs,
> +                index,
> +                &mut out_args,
> +            )
> +        };
> +        to_result(ret)?;
> +
> +        let node = unsafe { FwNode::from_raw(out_args.fwnode) };
> +        let mut args = ArrayVec::default();
> +
> +        for i in 0..out_args.nargs {
> +            args.push(out_args.args[i as usize]);
> +        }

Why the copy? Can't you just write an abstraction for struct
fwnode_reference_args and just return an instance of that?