rust: of: Add Node::address_as_resource()

Used for hand-rolled of_reserved_mem handling.

Signed-off-by: Asahi Lina <lina@asahilina.net>
Signed-off-by: Janne Grunau <j@jannau.net>

Author: hoshinolina

rust/kernel/io/resource.rs

@@ -105,6 +105,17 @@ impl Resource {
         unsafe { &*ptr.cast() }
     }
 
+    /// Creates a [`Resource`] from a valid pointer.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that the pointer points at a valid `bindings::resource`
+    pub(crate) fn new_from_ptr(ptr: *const bindings::resource) -> Self {
+        Resource {
+            0: unsafe { Opaque::<bindings::resource>::new(*ptr) },
+        }
+    }
+
     /// A helper to abstract the common pattern of requesting a region.
     fn request_region_checked(
         &self,

rust/kernel/of.rs

@@ -2,7 +2,9 @@
 
 //! Device Tree / Open Firmware abstractions.
 
-use crate::{bindings, device_id::RawDeviceId, prelude::*};
+use crate::{
+    bindings, device_id::RawDeviceId, error::to_result, io::resource::Resource, prelude::*,
+};
 // Note: Most OF functions turn into inline dummies with CONFIG_OF(_*) disabled.
 // We have to either add config conditionals to helpers.c or here; let's do it
 // here for now. In the future, once bindgen can auto-generate static inline
@@ -251,6 +253,27 @@ impl Node {
         }
     }
 
+    /// Translate device tree address and return as resource
+    pub fn address_as_resource(&self, index: usize) -> Result<Resource> {
+        #[cfg(not(CONFIG_OF))]
+        {
+            Err(EINVAL)
+        }
+        #[cfg(CONFIG_OF)]
+        {
+            let mut res = core::mem::MaybeUninit::<bindings::resource>::uninit();
+            // SAFETY: This function is safe to call as long as the arguments are valid pointers.
+            let ret = unsafe {
+                bindings::of_address_to_resource(self.raw_node, index.try_into()?, res.as_mut_ptr())
+            };
+            to_result(ret)?;
+            // SAFETY: We have checked the return value above, so the resource must be initialized now
+            let res = unsafe { res.assume_init() };
+
+            Ok(Resource::new_from_ptr(&res))
+        }
+    }
+
     #[allow(unused_variables)]
     /// Look up a node property by name, returning a `Property` object if found.
     pub fn find_property(&self, propname: &CStr) -> Option<Property<'_>> {