[PATCH v7 0/9] More Rust bindings for device property reads

[PATCH v7 0/9] More Rust bindings for device property reads

[Remo Senekowitsch]

changes in v7:
* Fix a typo in a commit message.
* Fix bug in `FwNode::display_path`. I took a slightly different
  approach than the one suggested, using `Either` to handle the
  owned and borrowed case. That also removes the conditional
  `fwnode_handle_put` at the end.
* Move `FwNode::from_raw` to the commit which first introduces the
  `FwNode` abstraction. It is needed in an earlier commit than before
  and I think it fits better there.

Best regards,
Remo

Remo Senekowitsch (9):
  rust: device: Create FwNode abstraction for accessing device
    properties
  rust: device: Enable accessing the FwNode of a Device
  rust: device: Add property_present() to FwNode
  rust: device: Enable printing fwnode name and path
  rust: device: Introduce PropertyGuard
  rust: device: Implement accessors for firmware properties
  rust: device: Add child accessor and iterator
  rust: device: Add property_get_reference_args
  samples: rust: platform: Add property read examples

 MAINTAINERS                                  |   1 +
 drivers/of/unittest-data/tests-platform.dtsi |   3 +
 rust/helpers/helpers.c                       |   1 +
 rust/helpers/property.c                      |   8 +
 rust/kernel/device.rs                        |  17 +
 rust/kernel/device/property.rs               | 590 +++++++++++++++++++
 samples/rust/rust_driver_platform.rs         |  60 +-
 7 files changed, 679 insertions(+), 1 deletion(-)
 create mode 100644 rust/helpers/property.c
 create mode 100644 rust/kernel/device/property.rs

-- 
2.49.0

[PATCH v7 1/9] rust: device: Create FwNode abstraction for accessing device properties

[Remo Senekowitsch]

Accessing device properties is currently done via methods on `Device`
itself, using bindings to device_property_* functions. This is
sufficient for the existing method property_present. However, it's not
sufficient for other device properties we want to access. For example,
iterating over child nodes of a device will yield a fwnode_handle.
That's not a device, so it wouldn't be possible to read the properties
of that child node. Thus, we need an abstraction over fwnode_handle and
methods for reading its properties.

Add a struct FwNode which abstracts over the C struct fwnode_handle.
Implement its reference counting analogous to other Rust abstractions
over reference-counted C structs.

Subsequent patches will add functionality to access FwNode and read
properties with it.

Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
 MAINTAINERS                    |  1 +
 rust/helpers/helpers.c         |  1 +
 rust/helpers/property.c        |  8 ++++
 rust/kernel/device.rs          |  2 +
 rust/kernel/device/property.rs | 73 ++++++++++++++++++++++++++++++++++
 5 files changed, 85 insertions(+)
 create mode 100644 rust/helpers/property.c
 create mode 100644 rust/kernel/device/property.rs

diff --git a/MAINTAINERS b/MAINTAINERS
index e58cafb019e63..52e2cff786cac 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7249,6 +7249,7 @@ F:	include/linux/property.h
 F:	include/linux/sysfs.h
 F:	lib/kobj*
 F:	rust/kernel/device.rs
+F:	rust/kernel/device/
 F:	rust/kernel/device_id.rs
 F:	rust/kernel/devres.rs
 F:	rust/kernel/driver.rs
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 80785b1e7a63e..b5cffc08190da 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -25,6 +25,7 @@
 #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 0000000000000..08f68e2dac4a9
--- /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 1edebb88e496f..56ee463a4bd11 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -14,6 +14,8 @@
 #[cfg(CONFIG_PRINTK)]
 use crate::c_str;
 
+pub mod property;
+
 /// A reference-counted device.
 ///
 /// This structure represents the Rust abstraction for a C `struct device`. This implementation
diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
new file mode 100644
index 0000000000000..03850b7bb8087
--- /dev/null
+++ b/rust/kernel/device/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,
+    types::{ARef, Opaque},
+};
+
+/// 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 {
+    /// # Safety
+    ///
+    /// Callers must ensure that:
+    /// - The reference count was incremented at least once.
+    /// - They relinquish that increment. That is, if there is only one
+    ///   increment, callers must not use the underlying object anymore -- it is
+    ///   only safe to do so via the newly created `ARef<FwNode>`.
+    unsafe fn from_raw(raw: *mut bindings::fwnode_handle) -> ARef<Self> {
+        // SAFETY: As per the safety requirements of this function:
+        // - `NonNull::new_unchecked`:
+        //   - `raw` is not null.
+        // - `ARef::from_raw`:
+        //   - `raw` has an incremented refcount.
+        //   - that increment is relinquished, i.e. it won't be decremented
+        //     elsewhere.
+        // CAST: It is safe to cast from a `*mut fwnode_handle` to
+        // `*mut FwNode`, because `FwNode` is  defined as a
+        // `#[repr(transparent)]` wrapper around `fwnode_handle`.
+        unsafe { ARef::from_raw(ptr::NonNull::new_unchecked(raw.cast())) }
+    }
+
+    /// Obtain the raw `struct fwnode_handle *`.
+    pub(crate) fn as_raw(&self) -> *mut bindings::fwnode_handle {
+        self.0.get()
+    }
+}
+
+// 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

[PATCH v7 2/9] rust: device: Enable accessing the FwNode of a Device

[Remo Senekowitsch]

Subsequent patches will add methods for reading properties to FwNode.
The first step to accessing these methods will be to access the "root"
FwNode of a Device.

Add the method `fwnode` to `Device`.

Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
 rust/kernel/device.rs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 56ee463a4bd11..0018b37de4a29 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -186,6 +186,21 @@ unsafe fn printk(&self, klevel: &[u8], msg: fmt::Arguments<'_>) {
         };
     }
 
+    /// Obtain the [`FwNode`](property::FwNode) corresponding to the device.
+    pub fn fwnode(&self) -> Option<&property::FwNode> {
+        // SAFETY: `self` is valid.
+        let fwnode_handle = unsafe { bindings::__dev_fwnode(self.as_raw()) };
+        if fwnode_handle.is_null() {
+            return None;
+        }
+        // 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`.
+        Some(unsafe { &*fwnode_handle.cast() })
+    }
+
     /// 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

[PATCH v7 3/9] rust: device: Add property_present() to FwNode

[Remo Senekowitsch]

The new FwNode abstraction will be used for accessing all device
properties, so it must have the property_present method.

It's possible to duplicate the methods on the device itself, but since
some of the methods on Device would have different type sigatures as
the ones on FwNode, this would only lead to inconsistency and confusion.
So, in the future, property_present will be removed from Device. However,
there's a user about to be merged, so the method is left to make merging
easier.

Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
 rust/kernel/device/property.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
index 03850b7bb8087..50c61aa056e6b 100644
--- a/rust/kernel/device/property.rs
+++ b/rust/kernel/device/property.rs
@@ -8,6 +8,7 @@
 
 use crate::{
     bindings,
+    str::CStr,
     types::{ARef, Opaque},
 };
 
@@ -55,6 +56,12 @@ unsafe fn from_raw(raw: *mut bindings::fwnode_handle) -> ARef<Self> {
     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.
-- 
2.49.0

[PATCH v7 4/9] rust: device: Enable printing fwnode name and path

[Remo Senekowitsch]

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 | 79 +++++++++++++++++++++++++++++++++-
 1 file changed, 78 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
index 50c61aa056e6b..8e0414b0517e4 100644
--- a/rust/kernel/device/property.rs
+++ b/rust/kernel/device/property.rs
@@ -9,7 +9,7 @@
 use crate::{
     bindings,
     str::CStr,
-    types::{ARef, Opaque},
+    types::{ARef, Either, Opaque},
 };
 
 /// A reference-counted fwnode_handle.
@@ -57,6 +57,83 @@ 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.
+                // - `name` was checked to be non-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).
+
+                // SAFETY: `self.0.as_raw()` is valid by its type invariant.
+                let num_parents = unsafe { bindings::fwnode_count_parents(self.0.as_raw()) };
+
+                for depth in (0..=num_parents).rev() {
+                    let fwnode = if depth == 0 {
+                        Either::Left(self.0)
+                    } else {
+                        // SAFETY: `self.0.as_raw()` is valid.
+                        let ptr =
+                            unsafe { bindings::fwnode_get_nth_parent(self.0.as_raw(), depth) };
+                        // SAFETY:
+                        // - The depth passed to `fwnode_get_nth_parent` is
+                        //   within the valid range, so the returned pointer is
+                        //   not null.
+                        // - The reference count was incremented by
+                        //   `fwnode_get_nth_parent`.
+                        // - That increment is relinquished to
+                        //   `FwNode::from_raw`.
+                        Either::Right(unsafe { FwNode::from_raw(ptr) })
+                    };
+                    // Take a reference to the owned or borrowed `FwNode`.
+                    let fwnode: &FwNode = match &fwnode {
+                        Either::Left(f) => f,
+                        Either::Right(f) => f,
+                    };
+
+                    // SAFETY: `fwnode` is valid by its type invariant.
+                    let prefix = unsafe { bindings::fwnode_get_name_prefix(fwnode.as_raw()) };
+                    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}")?;
+                    }
+                    write!(f, "{}", fwnode.display_name())?;
+                }
+
+                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

[PATCH v7 5/9] rust: device: Introduce PropertyGuard

[Remo Senekowitsch]

This abstraction is a way to force users to specify whether a property
is supposed to be required or not. This allows us to move error
logging of missing required properties into core, preventing a lot of
boilerplate in drivers.

It will be used by upcoming methods for reading device properties.

Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
 rust/kernel/device/property.rs | 59 ++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
index 8e0414b0517e4..b789fbbd0e6cc 100644
--- a/rust/kernel/device/property.rs
+++ b/rust/kernel/device/property.rs
@@ -155,3 +155,62 @@ unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
         unsafe { bindings::fwnode_handle_put(obj.cast().as_ptr()) }
     }
 }
+
+/// A helper for reading device properties.
+///
+/// Use [`Self::required_by`] if a missing property is considered a bug and
+/// [`Self::optional`] otherwise.
+///
+/// For convenience, [`Self::or`] and [`Self::or_default`] are provided.
+pub struct PropertyGuard<'fwnode, 'name, T> {
+    /// The result of reading the property.
+    inner: Result<T>,
+    /// The fwnode of the property, used for logging in the "required" case.
+    fwnode: &'fwnode FwNode,
+    /// The name of the property, used for logging in the "required" case.
+    name: &'name CStr,
+}
+
+impl<T> PropertyGuard<'_, '_, T> {
+    /// Access the property, indicating it is required.
+    ///
+    /// If the property is not present, the error is automatically logged. If a
+    /// missing property is not an error, use [`Self::optional`] instead. The
+    /// device is required to associate the log with it.
+    pub fn required_by(self, dev: &super::Device) -> Result<T> {
+        if self.inner.is_err() {
+            dev_err!(
+                dev,
+                "{}: property '{}' is missing\n",
+                self.fwnode.display_path(),
+                self.name
+            );
+        }
+        self.inner
+    }
+
+    /// Access the property, indicating it is optional.
+    ///
+    /// In contrast to [`Self::required_by`], no error message is logged if
+    /// the property is not present.
+    pub fn optional(self) -> Option<T> {
+        self.inner.ok()
+    }
+
+    /// Access the property or the specified default value.
+    ///
+    /// Do not pass a sentinel value as default to detect a missing property.
+    /// Use [`Self::required_by`] or [`Self::optional`] instead.
+    pub fn or(self, default: T) -> T {
+        self.inner.unwrap_or(default)
+    }
+}
+
+impl<T: Default> PropertyGuard<'_, '_, T> {
+    /// Access the property or a default value.
+    ///
+    /// Use [`Self::or`] to specify a custom default value.
+    pub fn or_default(self) -> T {
+        self.inner.unwrap_or_default()
+    }
+}
-- 
2.49.0

[PATCH v7 6/9] rust: device: Implement accessors for firmware properties

[Remo Senekowitsch]

Add methods to FwNode for reading several firmware property types like
strings, integers and arrays.

Most types are read with the generic `property_read` method. There are
two exceptions:

* `property_read_bool` cannot fail, so the fallible function signature
  of `property_read` would not make sense for reading booleans.

* `property_read_array_vec` can fail because of a dynamic memory
  allocation. This error must be handled separately, leading to a
  different function signature than `property_read`.

The traits `Property` and `PropertyInt` drive the generic behavior
of `property_read`. `PropertyInt` is necessary to associate
specific integer types with the C functions to read them. While
there is a C function to read integers of generic sizes called
`fwnode_property_read_int_array`, it was preferred not to make this
public.

Co-developed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
 rust/kernel/device/property.rs | 255 ++++++++++++++++++++++++++++++++-
 1 file changed, 253 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
index b789fbbd0e6cc..46884c433606a 100644
--- a/rust/kernel/device/property.rs
+++ b/rust/kernel/device/property.rs
@@ -4,11 +4,15 @@
 //!
 //! C header: [`include/linux/property.h`](srctree/include/linux/property.h)
 
-use core::ptr;
+use core::{mem::MaybeUninit, ptr};
 
 use crate::{
+    alloc::KVec,
     bindings,
-    str::CStr,
+    error::{to_result, Result},
+    prelude::*,
+    private::Sealed,
+    str::{CStr, CString},
     types::{ARef, Either, Opaque},
 };
 
@@ -139,6 +143,104 @@ 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()) }
     }
+
+    /// Returns firmware property `name` boolean value.
+    pub fn property_read_bool(&self, name: &CStr) -> bool {
+        // SAFETY:
+        // - `name` is non-null and null-terminated.
+        // - `self.as_raw()` is valid because `self` is valid.
+        unsafe { bindings::fwnode_property_read_bool(self.as_raw(), name.as_char_ptr()) }
+    }
+
+    /// Returns the index of matching string `match_str` for firmware string
+    /// property `name`.
+    pub fn property_match_string(&self, name: &CStr, match_str: &CStr) -> Result<usize> {
+        // SAFETY:
+        // - `name` and `match_str` are non-null and null-terminated.
+        // - `self.as_raw` is valid because `self` is valid.
+        let ret = unsafe {
+            bindings::fwnode_property_match_string(
+                self.as_raw(),
+                name.as_char_ptr(),
+                match_str.as_char_ptr(),
+            )
+        };
+        to_result(ret)?;
+        Ok(ret as usize)
+    }
+
+    /// Returns firmware property `name` integer array values in a [`KVec`].
+    pub fn property_read_array_vec<'fwnode, 'name, T: PropertyInt>(
+        &'fwnode self,
+        name: &'name CStr,
+        len: usize,
+    ) -> Result<PropertyGuard<'fwnode, 'name, KVec<T>>> {
+        let mut val: KVec<T> = KVec::with_capacity(len, GFP_KERNEL)?;
+
+        let res = T::read_array_from_fwnode_property(self, name, val.spare_capacity_mut());
+        let res = match res {
+            Ok(_) => {
+                // SAFETY:
+                // - `len` is equal to `val.capacity - val.len`, because
+                //   `val.capacity` is `len` and `val.len` is zero.
+                // - All elements within the interval [`0`, `len`) were initialized
+                //   by `read_array_from_fwnode_property`.
+                unsafe { val.inc_len(len) }
+                Ok(val)
+            }
+            Err(e) => Err(e),
+        };
+        Ok(PropertyGuard {
+            inner: res,
+            fwnode: self,
+            name,
+        })
+    }
+
+    /// Returns integer array length for firmware property `name`.
+    pub fn property_count_elem<T: PropertyInt>(&self, name: &CStr) -> Result<usize> {
+        T::read_array_len_from_fwnode_property(self, name)
+    }
+
+    /// Returns the value of firmware property `name`.
+    ///
+    /// This method is generic over the type of value to read. The types that
+    /// can be read are strings, integers and arrays of integers.
+    ///
+    /// Reading a [`KVec`] of integers is done with the separate
+    /// method [`Self::property_read_array_vec`], because it takes an
+    /// additional `len` argument.
+    ///
+    /// Reading a boolean is done with the separate method
+    /// [`Self::property_read_bool`], because this operation is infallible.
+    ///
+    /// For more precise documentation about what types can be read, see
+    /// the [implementors of Property][Property#implementors] and [its
+    /// implementations on foreign types][Property#foreign-impls].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use kernel::{c_str, device::{Device, property::FwNode}, str::CString};
+    /// fn examples(dev: &Device) -> Result {
+    ///     let fwnode = dev.fwnode().ok_or(ENOENT)?;
+    ///     let b: u32 = fwnode.property_read(c_str!("some-number")).required_by(dev)?;
+    ///     if let Some(s) = fwnode.property_read::<CString>(c_str!("some-str")).optional() {
+    ///         // ...
+    ///     }
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn property_read<'fwnode, 'name, T: Property>(
+        &'fwnode self,
+        name: &'name CStr,
+    ) -> PropertyGuard<'fwnode, 'name, T> {
+        PropertyGuard {
+            inner: T::read_from_fwnode_property(self, name),
+            fwnode: self,
+            name,
+        }
+    }
 }
 
 // SAFETY: Instances of `FwNode` are always reference-counted.
@@ -156,6 +258,155 @@ unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
     }
 }
 
+/// Implemented for types that can be read as properties.
+///
+/// This is implemented for strings, integers and arrays of integers. It's used
+/// to make [`FwNode::property_read`] generic over the type of property being
+/// read. There are also two dedicated methods to read other types, because they
+/// require more specialized function signatures:
+/// - [`property_read_bool`](FwNode::property_read_bool)
+/// - [`property_read_array_vec`](FwNode::property_read_array_vec)
+///
+/// It must be public, because it appears in the signatures of other public
+/// functions, but its methods shouldn't be used outside the kernel crate.
+pub trait Property: Sized + Sealed {
+    /// Used to make [`FwNode::property_read`] generic.
+    fn read_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<Self>;
+}
+
+impl Sealed for CString {}
+
+impl Property for CString {
+    fn read_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<Self> {
+        let mut str: *mut u8 = ptr::null_mut();
+        let pstr: *mut _ = &mut str;
+
+        // SAFETY:
+        // - `name` is non-null and null-terminated.
+        // - `fwnode.as_raw` is valid because `fwnode` is valid.
+        let ret = unsafe {
+            bindings::fwnode_property_read_string(fwnode.as_raw(), name.as_char_ptr(), pstr.cast())
+        };
+        to_result(ret)?;
+
+        // SAFETY:
+        // - `pstr` is a valid pointer to a NUL-terminated C string.
+        // - It is valid for at least as long as `fwnode`, but it's only used
+        //   within the current function.
+        // - The memory it points to is not mutated during that time.
+        let str = unsafe { CStr::from_char_ptr(*pstr) };
+        Ok(str.try_into()?)
+    }
+}
+
+/// Implemented for all integers that can be read as properties.
+///
+/// This helper trait is needed on top of the existing [`Property`]
+/// trait to associate the integer types of various sizes with their
+/// corresponding `fwnode_property_read_*_array` functions.
+///
+/// It must be public, because it appears in the signatures of other public
+/// functions, but its methods shouldn't be used outside the kernel crate.
+pub trait PropertyInt: Copy + Sealed {
+    /// Reads a property array.
+    fn read_array_from_fwnode_property<'a>(
+        fwnode: &FwNode,
+        name: &CStr,
+        out: &'a mut [MaybeUninit<Self>],
+    ) -> Result<&'a mut [Self]>;
+
+    /// Reads the length of a property array.
+    fn read_array_len_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<usize>;
+}
+// This macro generates implementations of the traits `Property` and
+// `PropertyInt` for integers of various sizes. Its input is a list
+// of pairs separated by commas. The first element of the pair is the
+// type of the integer, the second one is the name of its corresponding
+// `fwnode_property_read_*_array` function.
+macro_rules! impl_property_for_int {
+    ($($int:ty: $f:ident),* $(,)?) => { $(
+        impl Sealed for $int {}
+        impl<const N: usize> Sealed for [$int; N] {}
+
+        impl PropertyInt for $int {
+            fn read_array_from_fwnode_property<'a>(
+                fwnode: &FwNode,
+                name: &CStr,
+                out: &'a mut [MaybeUninit<Self>],
+            ) -> Result<&'a mut [Self]> {
+                // SAFETY:
+                // - `fwnode`, `name` and `out` are all valid by their type
+                //   invariants.
+                // - `out.len()` is a valid bound for the memory pointed to by
+                //   `out.as_mut_ptr()`.
+                // CAST: It's ok to cast from `*mut MaybeUninit<$int>` to a
+                // `*mut $int` because they have the same memory layout.
+                let ret = unsafe {
+                    bindings::$f(
+                        fwnode.as_raw(),
+                        name.as_char_ptr(),
+                        out.as_mut_ptr().cast(),
+                        out.len(),
+                    )
+                };
+                to_result(ret)?;
+                // SAFETY: Transmuting from `&'a mut [MaybeUninit<Self>]` to
+                // `&'a mut [Self]` is sound, because the previous call to a
+                // `fwnode_property_read_*_array` function (which didn't fail)
+                // fully initialized the slice.
+                Ok(unsafe { core::mem::transmute(out) })
+            }
+
+            fn read_array_len_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<usize> {
+                // SAFETY:
+                // - `fwnode` and `name` are valid by their type invariants.
+                // - It's ok to pass a null pointer to the
+                //   `fwnode_property_read_*_array` functions if `nval` is zero.
+                //   This will return the length of the array.
+                let ret = unsafe {
+                    bindings::$f(
+                        fwnode.as_raw(),
+                        name.as_char_ptr(),
+                        ptr::null_mut(),
+                        0,
+                    )
+                };
+                to_result(ret)?;
+                Ok(ret as usize)
+            }
+        }
+
+        impl Property for $int {
+            fn read_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<Self> {
+                let val: [_; 1] = <[$int; 1]>::read_from_fwnode_property(fwnode, name)?;
+                Ok(val[0])
+            }
+        }
+
+        impl<const N: usize> Property for [$int; N] {
+            fn read_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<Self> {
+                let mut val: [MaybeUninit<$int>; N] = [const { MaybeUninit::uninit() }; N];
+
+                <$int>::read_array_from_fwnode_property(fwnode, name, &mut val)?;
+
+                // SAFETY: `val` is always initialized when
+                // `fwnode_property_read_*_array` is successful.
+                Ok(val.map(|v| unsafe { v.assume_init() }))
+            }
+        }
+    )* };
+}
+impl_property_for_int! {
+    u8: fwnode_property_read_u8_array,
+    u16: fwnode_property_read_u16_array,
+    u32: fwnode_property_read_u32_array,
+    u64: fwnode_property_read_u64_array,
+    i8: fwnode_property_read_u8_array,
+    i16: fwnode_property_read_u16_array,
+    i32: fwnode_property_read_u32_array,
+    i64: fwnode_property_read_u64_array,
+}
+
 /// A helper for reading device properties.
 ///
 /// Use [`Self::required_by`] if a missing property is considered a bug and
-- 
2.49.0

[PATCH v7 7/9] rust: device: Add child accessor and iterator

[Remo Senekowitsch]

Allow Rust drivers to access children of a fwnode either by name or by
iterating over all of them.

In C, there is the function `fwnode_get_next_child_node` for iteration
and the macro `fwnode_for_each_child_node` that helps with handling the
pointers. Instead of a macro, a native iterator is used in Rust such
that regular for-loops can be used.

Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
 rust/kernel/device/property.rs | 56 ++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
index 46884c433606a..743f296bfb03c 100644
--- a/rust/kernel/device/property.rs
+++ b/rust/kernel/device/property.rs
@@ -241,6 +241,62 @@ pub fn property_read<'fwnode, 'name, T: Property>(
             name,
         }
     }
+
+    /// Returns first matching named child node handle.
+    pub fn get_child_by_name(&self, name: &CStr) -> Option<ARef<Self>> {
+        // SAFETY: `self` and `name` are valid by their type invariants.
+        let child =
+            unsafe { bindings::fwnode_get_named_child_node(self.as_raw(), name.as_char_ptr()) };
+        if child.is_null() {
+            return None;
+        }
+        // SAFETY:
+        // - `fwnode_get_named_child_node` returns a pointer with its refcount
+        //   incremented.
+        // - That increment is relinquished, i.e. the underlying object is not
+        //   used anymore except via the newly created `ARef`.
+        Some(unsafe { Self::from_raw(child) })
+    }
+
+    /// Returns an iterator over a node's children.
+    pub fn children<'a>(&'a self) -> impl Iterator<Item = ARef<FwNode>> + 'a {
+        let mut prev: Option<ARef<FwNode>> = None;
+
+        core::iter::from_fn(move || {
+            let prev_ptr = match prev.take() {
+                None => ptr::null_mut(),
+                Some(prev) => {
+                    // We will pass `prev` to `fwnode_get_next_child_node`,
+                    // which decrements its refcount, so we use
+                    // `ARef::into_raw` to avoid decrementing the refcount
+                    // twice.
+                    let prev = ARef::into_raw(prev);
+                    prev.as_ptr().cast()
+                }
+            };
+            // SAFETY:
+            // - `self.as_raw()` is valid by its type invariant.
+            // - `prev_ptr` may be null, which is allowed and corresponds to
+            //   getting the first child. Otherwise, `prev_ptr` is valid, as it
+            //   is the stored return value from the previous invocation.
+            // - `prev_ptr` has its refount incremented.
+            // - The increment of `prev_ptr` is relinquished, i.e. the
+            //   underlying object won't be used anymore.
+            let next = unsafe { bindings::fwnode_get_next_child_node(self.as_raw(), prev_ptr) };
+            if next.is_null() {
+                return None;
+            }
+            // SAFETY:
+            // - `next` is valid because `fwnode_get_next_child_node` returns a
+            //   pointer with its refcount incremented.
+            // - That increment is relinquished, i.e. the underlying object
+            //   won't be used anymore, except via the newly created
+            //   `ARef<Self>`.
+            let next = unsafe { FwNode::from_raw(next) };
+            prev = Some(next.clone());
+            Some(next)
+        })
+    }
 }
 
 // SAFETY: Instances of `FwNode` are always reference-counted.
-- 
2.49.0

[PATCH v7 8/9] rust: device: Add property_get_reference_args

[Remo Senekowitsch]

Allow Rust code to read reference args from device properties. The
wrapper type `FwNodeReferenceArgs` allows callers to access the buffer
of read args safely.

Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
 rust/kernel/device/property.rs | 67 ++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)

diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
index 743f296bfb03c..4dec6ef591620 100644
--- a/rust/kernel/device/property.rs
+++ b/rust/kernel/device/property.rs
@@ -297,6 +297,64 @@ pub fn children<'a>(&'a self) -> impl Iterator<Item = ARef<FwNode>> + 'a {
             Some(next)
         })
     }
+
+    /// Finds a reference with arguments.
+    pub fn property_get_reference_args(
+        &self,
+        prop: &CStr,
+        nargs: NArgs<'_>,
+        index: u32,
+    ) -> Result<FwNodeReferenceArgs> {
+        let mut out_args = FwNodeReferenceArgs::default();
+
+        let (nargs_prop, nargs) = match nargs {
+            NArgs::Prop(nargs_prop) => (nargs_prop.as_char_ptr(), 0),
+            NArgs::N(nargs) => (ptr::null(), nargs),
+        };
+
+        // SAFETY:
+        // - `self.0.get()` is valid.
+        // - `prop.as_char_ptr()` is valid and zero-terminated.
+        // - `nargs_prop` is valid and zero-terminated if `nargs`
+        //   is zero, otherwise it is allowed to be a null-pointer.
+        let ret = unsafe {
+            bindings::fwnode_property_get_reference_args(
+                self.0.get(),
+                prop.as_char_ptr(),
+                nargs_prop,
+                nargs,
+                index,
+                &mut out_args.0,
+            )
+        };
+        to_result(ret)?;
+
+        Ok(out_args)
+    }
+}
+
+/// The return value of [`FwNode::property_get_reference_args`].
+#[repr(transparent)]
+#[derive(Copy, Clone, Default)]
+pub struct FwNodeReferenceArgs(bindings::fwnode_reference_args);
+
+impl FwNodeReferenceArgs {
+    /// Returns the slice of reference arguments.
+    pub fn as_slice(&self) -> &[u64] {
+        // SAFETY: As per the safety invariant of `FwNodeReferenceArgs`, `nargs`
+        // is the number of elements in `args` that is valid.
+        unsafe { core::slice::from_raw_parts(self.0.args.as_ptr(), self.0.nargs as usize) }
+    }
+
+    /// Returns the number of reference arguments.
+    pub fn len(&self) -> usize {
+        self.0.nargs as usize
+    }
+
+    /// Returns `true` if there are no reference arguments.
+    pub fn is_empty(&self) -> bool {
+        self.0.nargs == 0
+    }
 }
 
 // SAFETY: Instances of `FwNode` are always reference-counted.
@@ -463,6 +521,15 @@ fn read_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<Self> {
     i64: fwnode_property_read_u64_array,
 }
 
+/// The number of arguments of a reference.
+pub enum NArgs<'a> {
+    /// The name of the property of the reference indicating the number of
+    /// arguments.
+    Prop(&'a CStr),
+    /// The known number of arguments.
+    N(u32),
+}
+
 /// A helper for reading device properties.
 ///
 /// Use [`Self::required_by`] if a missing property is considered a bug and
-- 
2.49.0

[PATCH v7 9/9] samples: rust: platform: Add property read examples

[Remo Senekowitsch]

Add some example usage of the device property read methods for
DT/ACPI/swnode properties.

Co-developed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
---
 drivers/of/unittest-data/tests-platform.dtsi |  3 +
 samples/rust/rust_driver_platform.rs         | 60 +++++++++++++++++++-
 2 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/drivers/of/unittest-data/tests-platform.dtsi b/drivers/of/unittest-data/tests-platform.dtsi
index 4171f43cf01cc..50a51f38afb60 100644
--- a/drivers/of/unittest-data/tests-platform.dtsi
+++ b/drivers/of/unittest-data/tests-platform.dtsi
@@ -37,6 +37,9 @@ dev@100 {
 			test-device@2 {
 				compatible = "test,rust-device";
 				reg = <0x2>;
+
+				test,u32-prop = <0xdeadbeef>;
+				test,i16-array = /bits/ 16 <1 2 (-3) (-4)>;
 			};
 		};
 
diff --git a/samples/rust/rust_driver_platform.rs b/samples/rust/rust_driver_platform.rs
index 8b42b3cfb363a..c0abf78d0683b 100644
--- a/samples/rust/rust_driver_platform.rs
+++ b/samples/rust/rust_driver_platform.rs
@@ -2,7 +2,14 @@
 
 //! Rust Platform driver sample.
 
-use kernel::{c_str, device::Core, of, platform, prelude::*, types::ARef};
+use kernel::{
+    c_str,
+    device::{self, Core},
+    of, platform,
+    prelude::*,
+    str::CString,
+    types::ARef,
+};
 
 struct SampleDriver {
     pdev: ARef<platform::Device>,
@@ -31,12 +38,63 @@ fn probe(
             dev_info!(pdev.as_ref(), "Probed with info: '{}'.\n", info.0);
         }
 
+        Self::properties_parse(pdev.as_ref())?;
+
         let drvdata = KBox::new(Self { pdev: pdev.into() }, GFP_KERNEL)?;
 
         Ok(drvdata.into())
     }
 }
 
+impl SampleDriver {
+    fn properties_parse(dev: &device::Device) -> Result {
+        let fwnode = dev.fwnode().ok_or(ENOENT)?;
+
+        if let Ok(idx) =
+            fwnode.property_match_string(c_str!("compatible"), c_str!("test,rust-device"))
+        {
+            dev_info!(dev, "matched compatible string idx = {}\n", idx);
+        }
+
+        let name = c_str!("compatible");
+        let prop = fwnode.property_read::<CString>(name).required_by(dev)?;
+        dev_info!(dev, "'{name}'='{prop:?}'\n");
+
+        let name = c_str!("test,bool-prop");
+        let prop = fwnode.property_read_bool(c_str!("test,bool-prop"));
+        dev_info!(dev, "'{name}'='{prop}'\n");
+
+        if fwnode.property_present(c_str!("test,u32-prop")) {
+            dev_info!(dev, "'test,u32-prop' is present\n");
+        }
+
+        let name = c_str!("test,u32-optional-prop");
+        let prop = fwnode.property_read::<u32>(name).or(0x12);
+        dev_info!(dev, "'{name}'='{prop:#x}' (default = 0x12)\n",);
+
+        // A missing required property will print an error. Discard the error to
+        // prevent properties_parse from failing in that case.
+        let name = c_str!("test,u32-required-prop");
+        let _ = fwnode.property_read::<u32>(name).required_by(dev);
+
+        let name = c_str!("test,u32-prop");
+        let prop: u32 = fwnode.property_read(name).required_by(dev)?;
+        dev_info!(dev, "'{name}'='{prop:#x}'\n");
+
+        let name = c_str!("test,i16-array");
+        let prop: [i16; 4] = fwnode.property_read(name).required_by(dev)?;
+        dev_info!(dev, "'{name}'='{prop:?}'\n");
+        let len = fwnode.property_count_elem::<u16>(name)?;
+        dev_info!(dev, "'{name}' length is {len}\n",);
+
+        let name = c_str!("test,i16-array");
+        let prop: KVec<i16> = fwnode.property_read_array_vec(name, 4)?.required_by(dev)?;
+        dev_info!(dev, "'{name}'='{prop:?}' (KVec)\n");
+
+        Ok(())
+    }
+}
+
 impl Drop for SampleDriver {
     fn drop(&mut self) {
         dev_dbg!(self.pdev.as_ref(), "Remove Rust Platform driver sample.\n");
-- 
2.49.0

Re: [PATCH v7 0/9] More Rust bindings for device property reads

[Danilo Krummrich]

On Fri, May 30, 2025 at 09:28:47PM +0200, Remo Senekowitsch wrote:
> changes in v7:
> * Fix a typo in a commit message.
> * Fix bug in `FwNode::display_path`. I took a slightly different
>   approach than the one suggested, using `Either` to handle the
>   owned and borrowed case. That also removes the conditional
>   `fwnode_handle_put` at the end.

That's a good idea, but also a bit unfortunate; there are efforts to remove
Either [1] in favor of using - more descriptive - custom enum types.

Can you please replace this with e.g. an enum Node with a Borrowed and Owned
variant?

[1] https://lore.kernel.org/lkml/20250519124304.79237-1-lossin@kernel.org/

Re: [PATCH v7 0/9] More Rust bindings for device property reads

[Remo Senekowitsch]

On Fri May 30, 2025 at 9:56 PM CEST, Danilo Krummrich wrote:
> On Fri, May 30, 2025 at 09:28:47PM +0200, Remo Senekowitsch wrote:
>> changes in v7:
>> * Fix a typo in a commit message.
>> * Fix bug in `FwNode::display_path`. I took a slightly different
>>   approach than the one suggested, using `Either` to handle the
>>   owned and borrowed case. That also removes the conditional
>>   `fwnode_handle_put` at the end.
>
> That's a good idea, but also a bit unfortunate; there are efforts to remove
> Either [1] in favor of using - more descriptive - custom enum types.
>
> Can you please replace this with e.g. an enum Node with a Borrowed and Owned
> variant?
>
> [1] https://lore.kernel.org/lkml/20250519124304.79237-1-lossin@kernel.org/

Sure, that seems reasonable.

Btw. what's the normal waiting time before posting a new version of a
patch series? The requested changes have been getting fewer and I could
crank these out much faster, but my gut feeling tells me not to spam the
list too much. Or is that wrong and people can deal with quick updates
just fine?

Best regards,
Remo

Re: [PATCH v7 0/9] More Rust bindings for device property reads

[Danilo Krummrich]

On Fri, May 30, 2025 at 11:45:38PM +0200, Remo Senekowitsch wrote:
> On Fri May 30, 2025 at 9:56 PM CEST, Danilo Krummrich wrote:
> > On Fri, May 30, 2025 at 09:28:47PM +0200, Remo Senekowitsch wrote:
> >> changes in v7:
> >> * Fix a typo in a commit message.
> >> * Fix bug in `FwNode::display_path`. I took a slightly different
> >>   approach than the one suggested, using `Either` to handle the
> >>   owned and borrowed case. That also removes the conditional
> >>   `fwnode_handle_put` at the end.
> >
> > That's a good idea, but also a bit unfortunate; there are efforts to remove
> > Either [1] in favor of using - more descriptive - custom enum types.
> >
> > Can you please replace this with e.g. an enum Node with a Borrowed and Owned
> > variant?
> >
> > [1] https://lore.kernel.org/lkml/20250519124304.79237-1-lossin@kernel.org/
> 
> Sure, that seems reasonable.
> 
> Btw. what's the normal waiting time before posting a new version of a
> patch series? The requested changes have been getting fewer and I could
> crank these out much faster, but my gut feeling tells me not to spam the
> list too much. Or is that wrong and people can deal with quick updates
> just fine?

I think the pace was appropriate. For the current state, I don't expect much
more feedback, so it'd be fine to send an update for the enum change rather
quicky.

However, we're anyways in the merge window currently, so I'd recomment to leave
the patch series as is and send a v8 once the merge window closes -- I'll pick
it up then unless there's some further feedback.

Re: [PATCH v7 0/9] More Rust bindings for device property reads

[Dirk Behme]

Hi Remo,

On 30/05/2025 21:28, Remo Senekowitsch wrote:
> changes in v7:
> * Fix a typo in a commit message.
> * Fix bug in `FwNode::display_path`. I took a slightly different
>   approach than the one suggested, using `Either` to handle the
>   owned and borrowed case. That also removes the conditional
>   `fwnode_handle_put` at the end.
> * Move `FwNode::from_raw` to the commit which first introduces the
>   `FwNode` abstraction. It is needed in an earlier commit than before
>   and I think it fits better there.
> 
> Best regards,
> Remo
> 
> Remo Senekowitsch (9):
>   rust: device: Create FwNode abstraction for accessing device
>     properties
>   rust: device: Enable accessing the FwNode of a Device
>   rust: device: Add property_present() to FwNode
>   rust: device: Enable printing fwnode name and path
>   rust: device: Introduce PropertyGuard
>   rust: device: Implement accessors for firmware properties
>   rust: device: Add child accessor and iterator
>   rust: device: Add property_get_reference_args
>   samples: rust: platform: Add property read examples
> 
>  MAINTAINERS                                  |   1 +
>  drivers/of/unittest-data/tests-platform.dtsi |   3 +
>  rust/helpers/helpers.c                       |   1 +
>  rust/helpers/property.c                      |   8 +
>  rust/kernel/device.rs                        |  17 +
>  rust/kernel/device/property.rs               | 590 +++++++++++++++++++
>  samples/rust/rust_driver_platform.rs         |  60 +-
>  7 files changed, 679 insertions(+), 1 deletion(-)
>  create mode 100644 rust/helpers/property.c
>  create mode 100644 rust/kernel/device/property.rs
I have tested this series with x86/Qemu running the sample. And the same
on real custom ARM64 hardware. Additionally, I ported a custom driver on
ARM64 to use this (well, it just uses the trivial
property_read().required_by()). So if it helps

Tested-by: Dirk Behme <dirk.behme@de.bosch.com>

for the whole series.

Btw, many thanks for working on this!

Dirk

Re: [PATCH v7 5/9] rust: device: Introduce PropertyGuard

[Rob Herring]

On Fri, May 30, 2025 at 09:28:52PM +0200, Remo Senekowitsch wrote:
> This abstraction is a way to force users to specify whether a property
> is supposed to be required or not. This allows us to move error
> logging of missing required properties into core, preventing a lot of
> boilerplate in drivers.
> 
> It will be used by upcoming methods for reading device properties.
> 
> Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
> ---
>  rust/kernel/device/property.rs | 59 ++++++++++++++++++++++++++++++++++
>  1 file changed, 59 insertions(+)
> 
> diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
> index 8e0414b0517e4..b789fbbd0e6cc 100644
> --- a/rust/kernel/device/property.rs
> +++ b/rust/kernel/device/property.rs
> @@ -155,3 +155,62 @@ unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
>          unsafe { bindings::fwnode_handle_put(obj.cast().as_ptr()) }
>      }
>  }
> +
> +/// A helper for reading device properties.
> +///
> +/// Use [`Self::required_by`] if a missing property is considered a bug and
> +/// [`Self::optional`] otherwise.
> +///
> +/// For convenience, [`Self::or`] and [`Self::or_default`] are provided.
> +pub struct PropertyGuard<'fwnode, 'name, T> {
> +    /// The result of reading the property.
> +    inner: Result<T>,
> +    /// The fwnode of the property, used for logging in the "required" case.
> +    fwnode: &'fwnode FwNode,
> +    /// The name of the property, used for logging in the "required" case.
> +    name: &'name CStr,
> +}
> +
> +impl<T> PropertyGuard<'_, '_, T> {
> +    /// Access the property, indicating it is required.
> +    ///
> +    /// If the property is not present, the error is automatically logged. If a
> +    /// missing property is not an error, use [`Self::optional`] instead. The
> +    /// device is required to associate the log with it.
> +    pub fn required_by(self, dev: &super::Device) -> Result<T> {
> +        if self.inner.is_err() {
> +            dev_err!(
> +                dev,
> +                "{}: property '{}' is missing\n",
> +                self.fwnode.display_path(),

Is it possible to make "{self.fwnode}: property..." work? Just need to 
implement Display trait on FwNode, right?

Doesn't look to me like we can alter what we print like in C, but for 
dmesg it's usually the full path we want anyways.

Rob

Re: [PATCH v7 0/9] More Rust bindings for device property reads

[Rob Herring]

On Fri, May 30, 2025 at 11:50:39PM +0200, Danilo Krummrich wrote:
> On Fri, May 30, 2025 at 11:45:38PM +0200, Remo Senekowitsch wrote:
> > On Fri May 30, 2025 at 9:56 PM CEST, Danilo Krummrich wrote:
> > > On Fri, May 30, 2025 at 09:28:47PM +0200, Remo Senekowitsch wrote:
> > >> changes in v7:
> > >> * Fix a typo in a commit message.
> > >> * Fix bug in `FwNode::display_path`. I took a slightly different
> > >>   approach than the one suggested, using `Either` to handle the
> > >>   owned and borrowed case. That also removes the conditional
> > >>   `fwnode_handle_put` at the end.
> > >
> > > That's a good idea, but also a bit unfortunate; there are efforts to remove
> > > Either [1] in favor of using - more descriptive - custom enum types.
> > >
> > > Can you please replace this with e.g. an enum Node with a Borrowed and Owned
> > > variant?
> > >
> > > [1] https://lore.kernel.org/lkml/20250519124304.79237-1-lossin@kernel.org/
> > 
> > Sure, that seems reasonable.
> > 
> > Btw. what's the normal waiting time before posting a new version of a
> > patch series? The requested changes have been getting fewer and I could
> > crank these out much faster, but my gut feeling tells me not to spam the
> > list too much. Or is that wrong and people can deal with quick updates
> > just fine?
> 
> I think the pace was appropriate. For the current state, I don't expect much
> more feedback, so it'd be fine to send an update for the enum change rather
> quicky.

Yes. General rules are no more frequent than 24 hours, but generally 1-2 
weeks. It also is a function of amount of review. No review, wait. If 
there's enough review that the current version isn't going to get more 
review, then go ahead and send another version. When things are close to 
merging and the changes are small, you can pick up the pace a little 
(outside of the merge window). 

> 
> However, we're anyways in the merge window currently, so I'd recomment to leave
> the patch series as is and send a v8 once the merge window closes -- I'll pick
> it up then unless there's some further feedback.

You'll need to fixup the user drivers/cpufreq/rcpufreq_dt.rs that 
landed in the merge window.

Overall, this all looks great to me. Thanks for continuing to push this 
forward.

Rob

Re: [PATCH v7 5/9] rust: device: Introduce PropertyGuard

[Remo Senekowitsch]

On Thu Jun 5, 2025 at 5:08 PM CEST, Rob Herring wrote:
> On Fri, May 30, 2025 at 09:28:52PM +0200, Remo Senekowitsch wrote:
>> This abstraction is a way to force users to specify whether a property
>> is supposed to be required or not. This allows us to move error
>> logging of missing required properties into core, preventing a lot of
>> boilerplate in drivers.
>> 
>> It will be used by upcoming methods for reading device properties.
>> 
>> Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
>> ---
>>  rust/kernel/device/property.rs | 59 ++++++++++++++++++++++++++++++++++
>>  1 file changed, 59 insertions(+)
>> 
>> diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
>> index 8e0414b0517e4..b789fbbd0e6cc 100644
>> --- a/rust/kernel/device/property.rs
>> +++ b/rust/kernel/device/property.rs
>> @@ -155,3 +155,62 @@ unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
>>          unsafe { bindings::fwnode_handle_put(obj.cast().as_ptr()) }
>>      }
>>  }
>> +
>> +/// A helper for reading device properties.
>> +///
>> +/// Use [`Self::required_by`] if a missing property is considered a bug and
>> +/// [`Self::optional`] otherwise.
>> +///
>> +/// For convenience, [`Self::or`] and [`Self::or_default`] are provided.
>> +pub struct PropertyGuard<'fwnode, 'name, T> {
>> +    /// The result of reading the property.
>> +    inner: Result<T>,
>> +    /// The fwnode of the property, used for logging in the "required" case.
>> +    fwnode: &'fwnode FwNode,
>> +    /// The name of the property, used for logging in the "required" case.
>> +    name: &'name CStr,
>> +}
>> +
>> +impl<T> PropertyGuard<'_, '_, T> {
>> +    /// Access the property, indicating it is required.
>> +    ///
>> +    /// If the property is not present, the error is automatically logged. If a
>> +    /// missing property is not an error, use [`Self::optional`] instead. The
>> +    /// device is required to associate the log with it.
>> +    pub fn required_by(self, dev: &super::Device) -> Result<T> {
>> +        if self.inner.is_err() {
>> +            dev_err!(
>> +                dev,
>> +                "{}: property '{}' is missing\n",
>> +                self.fwnode.display_path(),
>
> Is it possible to make "{self.fwnode}: property..." work? Just need to 
> implement Display trait on FwNode, right?
>
> Doesn't look to me like we can alter what we print like in C, but for 
> dmesg it's usually the full path we want anyways.

Well, field access is not allowed directly in the format string. But if
there is a variable `fwnode`, then yes, one can do "{fwnode}" directly.
Implementing Display directly on FwNode seems like a good idea if the
full path is the intuitive default.

I tried it with an `ARef<FwNode>`, but that didn't work. I had to force
the dereference with `&*fwnode`. Maybe an `impl<T: Display> for ARef<T>`
could be added, the standard library does that for its smart pointers.

Remo