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* [PATCH v2] rust: of: Add basic DeviceNode abstractions,
@ 2025-09-29 14:00 Markus Probst
  2025-09-29 14:31 ` Danilo Krummrich
  0 siblings, 1 reply; 3+ messages in thread
From: Markus Probst @ 2025-09-29 14:00 UTC (permalink / raw)
  To: devicetree, rust-for-linux, Rob Herring, Saravana Kannan,
	Miguel Ojeda, Alex Gaynor
  Cc: Boqun Feng, Gary Guo, Björn Roy Baron, Benno Lossin,
	Andreas Hindborg, Alice Ryhl, Trevor Gross, Danilo Krummrich

Add a safe wrapper arround `struct device_node`, which is capable of:

* reading string, u32 and bool properties

* iterating over children

Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers/of.c               |  10 +++
 rust/kernel/of.rs               | 150 ++++++++++++++++++++++++++++++++
 3 files changed, 161 insertions(+)

diff --git a/rust/bindings/bindings_helper.h
b/rust/bindings/bindings_helper.h
index 81796d5e16e8..e670b8e42787 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -59,6 +59,7 @@
 #include <linux/jump_label.h>
 #include <linux/mdio.h>
 #include <linux/miscdevice.h>
+#include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/pci.h>
 #include <linux/phy.h>
diff --git a/rust/helpers/of.c b/rust/helpers/of.c
index 86b51167c913..293cc43452aa 100644
--- a/rust/helpers/of.c
+++ b/rust/helpers/of.c
@@ -6,3 +6,13 @@ bool rust_helper_is_of_node(const struct fwnode_handle
*fwnode)
 {
 	return is_of_node(fwnode);
 }
+
+struct device_node *rust_helper_of_node_get(struct device_node *node)
+{
+	return of_node_get(node);
+}
+
+void rust_helper_of_node_put(struct device_node *node)
+{
+	of_node_put(node);
+}
diff --git a/rust/kernel/of.rs b/rust/kernel/of.rs
index b76b35265df2..e1a3114de686 100644
--- a/rust/kernel/of.rs
+++ b/rust/kernel/of.rs
@@ -1,12 +1,16 @@
 // SPDX-License-Identifier: GPL-2.0
 
 //! Device Tree / Open Firmware abstractions.
+//!
+//! C header: [`include/linux/of.h`](srctree/include/linux/of.h)
 
 use crate::{
     bindings,
     device_id::{RawDeviceId, RawDeviceIdIndex},
     prelude::*,
+    types::{ARef, Opaque},
 };
+use core::ptr::NonNull;
 
 /// IdTable type for OF drivers.
 pub type IdTable<T> = &'static dyn
kernel::device_id::IdTable<DeviceId, T>;
@@ -16,6 +20,20 @@
 #[derive(Clone, Copy)]
 pub struct DeviceId(bindings::of_device_id);
 
+/// The device node representation.
+///
+/// This structure represents the Rust abstraction for a C `struct
device_node`. The implementation
+/// abstracts the usage of an already existing C `struct device_node`
within Rust code that we get
+/// passed from the C side.
+///
+/// # Invariants
+///
+/// A [`DeviceNode`] instance represents a valid `struct device_node`
created by the C portion of the kernel.
+#[repr(transparent)]
+pub struct DeviceNode(Opaque<bindings::device_node>);
+
+struct DeviceNodeIterator<'a>(&'a DeviceNode,
Option<NonNull<bindings::device_node>>);
+
 // SAFETY: `DeviceId` is a `#[repr(transparent)]` wrapper of `struct
of_device_id` and
 // does not add additional invariants, so it's safe to transmute to
`RawType`.
 unsafe impl RawDeviceId for DeviceId {
@@ -63,3 +81,135 @@ macro_rules! of_device_table {
         $crate::module_device_table!("of", $module_table_name,
$table_name);
     };
 }
+
+impl DeviceNode {
+    const fn as_raw(&self) -> *mut bindings::device_node {
+        self.0.get()
+    }
+
+    /// Returns the device tree populated by the bootloader.
+    pub fn root() -> Option<&'static DeviceNode> {
+        // SAFETY: `of_root` is guaranteed to be a pointer to a valid
`struct device_node` or a null-pointer.
+        NonNull::new(unsafe { bindings::of_root })
+            // CAST: `DeviceNode` is a transparent wrapper of
`Opaque<bindings::device_node>`.
+            // SAFETY: `ptr` is guaranteed to be a pointer to a valid
`struct device_node`.
+            .map(|ptr| unsafe { ptr.cast().as_ref() })
+    }
+
+    /// Returns an iterator over the children of this device node.
+    pub fn children(&self) -> impl Iterator<Item = ARef<DeviceNode>> +
use<'_> {
+        // SAFETY: `self.as_raw` is guaranteed to be a pointer to a
valid `struct device_node`.
+        let initial = unsafe {
bindings::of_get_next_child(self.as_raw(), core::ptr::null_mut()) };
+        DeviceNodeIterator(self, NonNull::new(initial.cast()))
+    }
+
+    /// Returns the name of the device node.
+    pub fn name(&self) -> Option<&CStr> {
+        // SAFETY: `self.as_raw` is guaranteed to be a pointer to a
valid `struct device_node`.
+        let name = unsafe { (*self.as_raw()).name };
+        if name.is_null() {
+            None
+        } else {
+            // SAFETY: `name` is valid by the safety requirements.
+            Some(unsafe { CStr::from_char_ptr(name) })
+        }
+    }
+
+    /// Returns the full name (name including the full_name of the
parent) of the device node.
+    pub fn full_name(&self) -> Option<&CStr> {
+        // SAFETY: `self.as_raw` is guaranteed to be a pointer to a
valid `struct device_node`.
+        let full_name = unsafe { (*self.as_raw()).full_name };
+        if full_name.is_null() {
+            None
+        } else {
+            // SAFETY: `full_name` is valid by the safety
requirements.
+            Some(unsafe { CStr::from_char_ptr(full_name) })
+        }
+    }
+
+    /// Find and read a u32 from a multi-value property.
+    pub fn property_read_u32_index(&self, propname: &CStr, index: u32)
-> Result<u32> {
+        let mut value = 0;
+        // SAFETY: `self.as_raw` is guaranteed to be a pointer to a
valid `struct device_node`.
+        let ret = unsafe {
+            bindings::of_property_read_u32_index(
+                self.as_raw(),
+                propname.as_char_ptr(),
+                index,
+                &mut value,
+            )
+        };
+        if ret != 0 {
+            return Err(Error::from_errno(ret));
+        }
+        Ok(value)
+    }
+
+    /// Find and read a string from a property.
+    pub fn property_read_string(&self, propname: &CStr) ->
Result<&CStr> {
+        let mut value = core::ptr::null();
+        // SAFETY: `self.as_raw` is guaranteed to be a pointer to a
valid `struct device_node`.
+        let ret = unsafe {
+            bindings::of_property_read_string(self.as_raw(),
propname.as_char_ptr(), &mut value)
+        };
+        if ret != 0 {
+            return Err(Error::from_errno(ret));
+        }
+        // SAFETY: `value` is guaranteed to be a valid C string
pointer.
+        Ok(unsafe { CStr::from_char_ptr(value) })
+    }
+
+    /// Find a property.
+    ///
+    /// Returns true if the property exists false otherwise.
+    pub fn property_read_bool(&self, propname: &CStr) -> bool {
+        // SAFETY: `self.as_raw` is guaranteed to be a pointer to a
valid `struct device_node`.
+        unsafe { bindings::of_property_read_bool(self.as_raw(),
propname.as_char_ptr()) }
+    }
+
+    /// Find the child node by name for this device node.
+    pub fn child_by_name(&self, name: &CStr) ->
Option<ARef<DeviceNode>> {
+        // SAFETY: `self.as_raw` is guaranteed to be a pointer to a
valid `struct device_node`.
+        let node = unsafe {
bindings::of_get_child_by_name(self.as_raw(), name.as_char_ptr()) };
+        // SAFETY: `node` is guaranteed to be a pointer to a valid
`struct device_node` or a null-pointer.
+        Some(unsafe { ARef::from_raw(NonNull::new(node)?.cast()) })
+    }
+}
+
+// SAFETY: A `DeviceNode` is always reference-counted and can be
released from any thread.
+unsafe impl Send for DeviceNode {}
+
+// SAFETY: `DeviceNode` can be shared among threads because all
methods of `DeviceNode` are thread safe.
+unsafe impl Sync for DeviceNode {}
+
+// SAFETY: Instances of `DeviceNode` are always reference-counted.
+unsafe impl kernel::types::AlwaysRefCounted for DeviceNode {
+    fn inc_ref(&self) {
+        // SAFETY: The existence of a shared reference guarantees that
the refcount is non-zero.
+        unsafe { bindings::of_node_get(self.as_raw()) };
+    }
+
+    unsafe fn dec_ref(obj: NonNull<Self>) {
+        // SAFETY: The safety requirements guarantee that the refcount
is non-zero.
+        unsafe { bindings::of_node_put(obj.cast().as_ptr()) }
+    }
+}
+
+impl<'a> Iterator for DeviceNodeIterator<'a> {
+    type Item = ARef<DeviceNode>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let prev = self.1.take()?;
+
+        // CAST: `DeviceNode` is a transparent wrapper of
`Opaque<bindings::device_node>`.
+        // SAFETY: `ptr` is guaranteed to be a pointer to a valid
`struct device_node`.
+        let result = ARef::from(unsafe {
prev.cast::<DeviceNode>().as_ref() });
+
+        // SAFETY:
+        // - `self.0.as_raw` is guaranteed to be a pointer to a valid
`struct device_node`.
+        // - `prev` is guaranteed to be a pointer to a valid `struct
device_node`.
+        self.1 =
+            NonNull::new(unsafe {
bindings::of_get_next_child(self.0.as_raw(), prev.as_ptr()) });
+        Some(result)
+    }
+}
-- 
2.49.1

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2025-09-29 14:00 [PATCH v2] rust: of: Add basic DeviceNode abstractions, Markus Probst
2025-09-29 14:31 ` Danilo Krummrich
2025-09-29 14:57   ` Markus Probst

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