[PATCH 01/10] rust: Move property_present to property.rs

[Remo Senekowitsch <remo@buenzli.dev>]

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,
the APIs has to be duplicated on a fwnode as they are in C.

A related discussion can be found on the R4L Zulip[1].

[1] https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/DS90UB954.20driver.20done.2C.20ready.20to.20upstream.3F/near/505415697

Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
 rust/helpers/helpers.c  |  1 +
 rust/helpers/property.c | 13 ++++++++
 rust/kernel/device.rs   |  7 ----
 rust/kernel/lib.rs      |  1 +
 rust/kernel/property.rs | 73 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 88 insertions(+), 7 deletions(-)
 create mode 100644 rust/helpers/property.c
 create mode 100644 rust/kernel/property.rs

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..c37c74488
--- /dev/null
+++ b/rust/helpers/property.c
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/property.h>
+
+struct fwnode_handle *rust_helper_dev_fwnode(struct device *dev)
+{
+	return dev_fwnode(dev);
+}
+
+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..b0a4bb63a
--- /dev/null
+++ b/rust/kernel/property.rs
@@ -0,0 +1,73 @@
+// 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.
+        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