[PATCH v2 1/5] rust: Move property_present to separate file

Remo Senekowitsch
2025-04-14T15:33:24Z

Not all property-related APIs can be exposed directly on a device.
For example, iterating over child nodes of a device will yield
fwnode_handle. Thus, in order to access properties on these child nodes,
duplicate the APIs on a fwnode as they are in C.

Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
MAINTAINERS | 1 +
rust/helpers/helpers.c | 1 +
rust/helpers/property.c | 8 +++++
rust/kernel/device.rs | 7 ----
rust/kernel/lib.rs | 1 +
rust/kernel/property.rs | 75 +++++++++++++++++++++++++++++++++++++++++
6 files changed, 86 insertions(+), 7 deletions(-)
create mode 100644 rust/helpers/property.c
create mode 100644 rust/kernel/property.rs

diff --git a/MAINTAINERS b/MAINTAINERS
index c8d9e8187..a34471662 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7117,6 +7117,7 @@ F: rust/kernel/device_id.rs
F: rust/kernel/devres.rs
F: rust/kernel/driver.rs
F: rust/kernel/platform.rs
+F: rust/kernel/property.rs
F: samples/rust/rust_driver_platform.rs

DRIVERS FOR OMAP ADAPTIVE VOLTAGE SCALING (AVS)
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 0640b7e11..b4eec5bf2 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -23,6 +23,7 @@
#include "platform.c"
#include "pci.c"
#include "pid_namespace.c"
+#include "property.c"
#include "rbtree.c"
#include "rcu.c"
#include "refcount.c"
diff --git a/rust/helpers/property.c b/rust/helpers/property.c
new file mode 100644
index 000000000..08f68e2da
--- /dev/null
+++ b/rust/helpers/property.c
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/property.h>
+
+void rust_helper_fwnode_handle_put(struct fwnode_handle *fwnode)
+{
+ fwnode_handle_put(fwnode);
+}
diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index db2d9658b..d5e6a19ff 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -6,7 +6,6 @@

use crate::{
bindings,
- str::CStr,
types::{ARef, Opaque},
};
use core::{fmt, ptr};
@@ -181,12 +180,6 @@ unsafe fn printk(&self, klevel: &[u8], msg: fmt::Arguments<'_>) {
)
};
}
-
- /// Checks if property is present or not.
- pub fn property_present(&self, name: &CStr) -> bool {
- // SAFETY: By the invariant of `CStr`, `name` is null-terminated.
- unsafe { bindings::device_property_present(self.as_raw().cast_const(), name.as_char_ptr()) }
- }
}

// SAFETY: Instances of `Device` are always reference-counted.
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 496ed32b0..ca233fd20 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -67,6 +67,7 @@
pub mod platform;
pub mod prelude;
pub mod print;
+pub mod property;
pub mod rbtree;
pub mod revocable;
pub mod security;
diff --git a/rust/kernel/property.rs b/rust/kernel/property.rs
new file mode 100644
index 000000000..f6e6c980d
--- /dev/null
+++ b/rust/kernel/property.rs
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Unified device property interface.
+//!
+//! C header: [`include/linux/property.h`](srctree/include/linux/property.h)
+
+use core::ptr;
+
+use crate::{bindings, device::Device, str::CStr, types::Opaque};
+
+impl Device {
+ /// Obtain the fwnode corresponding to the device.
+ fn fwnode(&self) -> &FwNode {
+ // SAFETY: `self` is valid.
+ let fwnode_handle = unsafe { bindings::__dev_fwnode(self.as_raw()) };
+ if fwnode_handle.is_null() {
+ panic!("fwnode_handle cannot be null");
+ }
+ // SAFETY: `fwnode_handle` is valid. Its lifetime is tied to `&self`. We
+ // return a reference instead of an `ARef<FwNode>` because `dev_fwnode()`
+ // doesn't increment the refcount. It is safe to cast from a
+ // `struct fwnode_handle*` to a `*const FwNode` because `FwNode` is
+ // defined as a `#[repr(transparent)]` wrapper around `fwnode_handle`.
+ unsafe { &*fwnode_handle.cast() }
+ }
+
+ /// Checks if property is present or not.
+ pub fn property_present(&self, name: &CStr) -> bool {
+ self.fwnode().property_present(name)
+ }
+}
+
+/// A reference-counted fwnode_handle.
+///
+/// This structure represents the Rust abstraction for a
+/// C `struct fwnode_handle`. This implementation abstracts the usage of an
+/// already existing C `struct fwnode_handle` within Rust code that we get
+/// passed from the C side.
+///
+/// # Invariants
+///
+/// A `FwNode` instance represents a valid `struct fwnode_handle` created by the
+/// C portion of the kernel.
+///
+/// Instances of this type are always reference-counted, that is, a call to
+/// `fwnode_handle_get` ensures that the allocation remains valid at least until
+/// the matching call to `fwnode_handle_put`.
+#[repr(transparent)]
+pub struct FwNode(Opaque<bindings::fwnode_handle>);
+
+impl FwNode {
+ /// Obtain the raw `struct fwnode_handle *`.
+ pub(crate) fn as_raw(&self) -> *mut bindings::fwnode_handle {
+ self.0.get()
+ }
+
+ /// Checks if property is present or not.
+ pub fn property_present(&self, name: &CStr) -> bool {
+ // SAFETY: By the invariant of `CStr`, `name` is null-terminated.
+ unsafe { bindings::fwnode_property_present(self.as_raw().cast_const(), name.as_char_ptr()) }
+ }
+}
+
+// SAFETY: Instances of `FwNode` are always reference-counted.
+unsafe impl crate::types::AlwaysRefCounted for FwNode {
+ fn inc_ref(&self) {
+ // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
+ unsafe { bindings::fwnode_handle_get(self.as_raw()) };
+ }
+
+ unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
+ // SAFETY: The safety requirements guarantee that the refcount is non-zero.
+ unsafe { bindings::fwnode_handle_put(obj.cast().as_ptr()) }
+ }
+}
--
2.49.0