linux-kernel - [PATCH v3 6/7] rust: property: Add property_get_reference

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Message-ID: <20250425150130.13917-7-remo@buenzli.dev>
Date: Fri, 25 Apr 2025 17:01:29 +0200
From: Remo Senekowitsch <remo@...nzli.dev>
To: 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>,
	Dirk Behme <dirk.behme@...bosch.com>,
	Remo Senekowitsch <remo@...nzli.dev>
Cc: linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org,
	rust-for-linux@...r.kernel.org
Subject: [PATCH v3 6/7] rust: property: Add property_get_reference_args

Allow Rust code to read reference args from device properties. The
wrapper type `FwNodeReferenceArgs` allows callers to access the buffer
of read args safely.

Signed-off-by: Remo Senekowitsch <remo@...nzli.dev>
---
 rust/kernel/device/property.rs | 68 ++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
index 0a0cb0c02..475b916d0 100644
--- a/rust/kernel/device/property.rs
+++ b/rust/kernel/device/property.rs
@@ -315,6 +315,65 @@ 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<FwNodeReferenceArgs> {
+        let mut out_args = FwNodeReferenceArgs::default();
+
+        let (nargs_prop, nargs) = match nargs {
+            NArgs::Prop(nargs_prop) => (nargs_prop.as_char_ptr(), 0),
+            NArgs::N(nargs) => (ptr::null(), nargs),
+        };
+
+        // SAFETY: `self.0.get()` is valid. `prop.as_char_ptr()` is valid and
+        // zero-terminated. `nargs_prop` is valid and zero-terminated if `nargs`
+        // is zero, otherwise it is allowed to be a null-pointer.
+        let ret = unsafe {
+            bindings::fwnode_property_get_reference_args(
+                self.0.get(),
+                prop.as_char_ptr(),
+                nargs_prop,
+                nargs,
+                index,
+                &mut out_args.0,
+            )
+        };
+        to_result(ret)?;
+
+        Ok(out_args)
+    }
+}
+
+/// The return value of `property_get_reference_args`.
+///
+/// - [`Device::property_get_reference_args`]
+/// - [`FwNode::property_get_reference_args`]
+#[repr(transparent)]
+#[derive(Copy, Clone, Default)]
+pub struct FwNodeReferenceArgs(bindings::fwnode_reference_args);
+
+impl FwNodeReferenceArgs {
+    /// Returns the slice of reference arguments.
+    pub fn as_slice(&self) -> &[u64] {
+        // SAFETY: As per the safety invariant of FwNodeReferenceArgs, `nargs`
+        // is the number of elements in `args` that is valid.
+        unsafe { core::slice::from_raw_parts(self.0.args.as_ptr(), self.0.nargs as usize) }
+    }
+
+    /// Returns the number of reference arguments.
+    pub fn len(&self) -> usize {
+        self.0.nargs as usize
+    }
+
+    /// Returns `true` if there are no reference arguments.
+    pub fn is_empty(&self) -> bool {
+        self.0.nargs == 0
+    }
 }
 
 // SAFETY: Instances of `FwNode` are always reference-counted.
@@ -452,6 +511,15 @@ fn read_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<Self> {
     }
 }
 
+/// The number of arguments of a reference.
+pub enum NArgs<'a> {
+    /// The name of the property of the reference indicating the number of
+    /// arguments.
+    Prop(&'a CStr),
+    /// The known number of arguments.
+    N(u32),
+}
+
 /// A helper for reading device properties.
 ///
 /// Use [`Self::required`] if a missing property is considered a bug and
-- 
2.49.0