[PATCH v3 2/7] rust: property: Enable printing fwnode name and path

Remo Senekowitsch
2025-04-25T15:02:11Z

Add two new public methods `display_name` and `display_path` to
`FwNode`. They can be used by driver authors for logging purposes. In
addition, they will be used by core property abstractions for automatic
logging, for example when a driver attempts to read a required but
missing property.

Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
rust/kernel/device/property.rs | 78 ++++++++++++++++++++++++++++++++++
1 file changed, 78 insertions(+)

diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
index d89715f7d..28850aa3b 100644
--- a/rust/kernel/device/property.rs
+++ b/rust/kernel/device/property.rs
@@ -49,6 +49,84 @@ pub(crate) fn as_raw(&self) -> *mut bindings::fwnode_handle {
self.0.get()
}

+ /// Returns an object that implements [`Display`](core::fmt::Display) for
+ /// printing the name of a node.
+ pub fn display_name(&self) -> impl core::fmt::Display + '_ {
+ struct FwNodeDisplayName<'a>(&'a FwNode);
+
+ impl core::fmt::Display for FwNodeDisplayName<'_> {
+ fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+ // SAFETY: self is valid by its type invariant
+ let name = unsafe { bindings::fwnode_get_name(self.0.as_raw()) };
+ if name.is_null() {
+ return Ok(());
+ }
+ // SAFETY: fwnode_get_name returns null or a valid C string and
+ // name is not null
+ let name = unsafe { CStr::from_char_ptr(name) };
+ write!(f, "{name}")
+ }
+ }
+
+ FwNodeDisplayName(self)
+ }
+
+ /// Returns an object that implements [`Display`](core::fmt::Display) for
+ /// printing the full path of a node.
+ pub fn display_path(&self) -> impl core::fmt::Display + '_ {
+ struct FwNodeDisplayPath<'a>(&'a FwNode);
+
+ impl core::fmt::Display for FwNodeDisplayPath<'_> {
+ fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+ // The logic here is the same as the one in lib/vsprintf.c
+ // (fwnode_full_name_string).
+
+ let num_parents = unsafe { bindings::fwnode_count_parents(self.0.as_raw()) };
+
+ for depth in (0..=num_parents).rev() {
+ let fwnode = if depth == 0 {
+ self.0.as_raw()
+ } else {
+ // SAFETY: `self.0.as_raw()` is valid
+ unsafe { bindings::fwnode_get_nth_parent(self.0.as_raw(), depth) }
+ };
+
+ // SAFETY: fwnode is valid, it is either `self.0.as_raw()` or
+ // the return value of `bindings::fwnode_get_nth_parent` which
+ // returns a valid pointer to a fwnode_handle if the provided
+ // depth is within the valid range, which we know to be true.
+ let prefix = unsafe { bindings::fwnode_get_name_prefix(fwnode) };
+ if !prefix.is_null() {
+ // SAFETY: fwnode_get_name_prefix returns null or a
+ // valid C string
+ let prefix = unsafe { CStr::from_char_ptr(prefix) };
+ write!(f, "{prefix}")?;
+ }
+ // SAFETY: fwnode is valid for the reasons stated above
+ let name = unsafe { bindings::fwnode_get_name(fwnode) };
+ if !name.is_null() {
+ // SAFETY: fwnode_get_name returns null or a valid
+ // C string
+ let name = unsafe { CStr::from_char_ptr(name) };
+ write!(f, "{name}")?;
+ }
+
+ if depth != 0 {
+ // SAFETY: `fwnode` is valid, because `depth` is
+ // a valid depth of a parent of `self.0.as_raw()`.
+ // `fwnode_get_nth_parent` increments the refcount and
+ // we are responsible to decrement it.
+ unsafe { bindings::fwnode_handle_put(fwnode) }
+ }
+ }
+
+ Ok(())
+ }
+ }
+
+ FwNodeDisplayPath(self)
+ }
+
/// 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.
--
2.49.0