[PATCH v2 1/3] rust: device_id: split out index support into a separate trait
From: FUJITA Tomonori
Date: Tue Jul 01 2025 - 10:18:00 EST
Introduce a new trait `RawDeviceIdIndex`, which extends `RawDeviceId`
to provide support for device ID types that include an index or
context field (e.g., `driver_data`). This separates the concerns of
layout compatibility and index-based data embedding, and allows
`RawDeviceId` to be implemented for types that do not contain a
`driver_data` field. Several such structures are defined in
include/linux/mod_devicetable.h.
Refactor `IdArray::new()` into a generic `build()` function, which
takes an optional offset. Based on the presence of `RawDeviceIdIndex`,
index writing is conditionally enabled. A new `new_without_index()`
constructor is also provided for use cases where no index should be
written.
This refactoring is a preparation for enabling the PHY abstractions to
use device_id trait.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxx>
---
rust/kernel/auxiliary.rs | 7 +++-
rust/kernel/device_id.rs | 80 +++++++++++++++++++++++++++++++---------
rust/kernel/of.rs | 11 +++++-
rust/kernel/pci.rs | 7 +++-
4 files changed, 81 insertions(+), 24 deletions(-)
diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
index d2cfe1eeefb6..655ed61247d0 100644
--- a/rust/kernel/auxiliary.rs
+++ b/rust/kernel/auxiliary.rs
@@ -6,7 +6,7 @@
use crate::{
bindings, container_of, device,
- device_id::RawDeviceId,
+ device_id::{RawDeviceId, RawDeviceIdIndex},
driver,
error::{to_result, Result},
prelude::*,
@@ -143,10 +143,13 @@ pub const fn new(modname: &'static CStr, name: &'static CStr) -> Self {
// SAFETY:
// * `DeviceId` is a `#[repr(transparent)`] wrapper of `auxiliary_device_id` and does not add
// additional invariants, so it's safe to transmute to `RawType`.
-// * `DRIVER_DATA_OFFSET` is the offset to the `driver_data` field.
unsafe impl RawDeviceId for DeviceId {
type RawType = bindings::auxiliary_device_id;
+}
+// SAFETY:
+// * `DRIVER_DATA_OFFSET` is the offset to the `driver_data` field.
+unsafe impl RawDeviceIdIndex for DeviceId {
const DRIVER_DATA_OFFSET: usize =
core::mem::offset_of!(bindings::auxiliary_device_id, driver_data);
diff --git a/rust/kernel/device_id.rs b/rust/kernel/device_id.rs
index 3dc72ca8cfc2..3bcab2310087 100644
--- a/rust/kernel/device_id.rs
+++ b/rust/kernel/device_id.rs
@@ -24,22 +24,36 @@
/// Ideally, this should be achieved using a const function that does conversion instead of
/// transmute; however, const trait functions relies on `const_trait_impl` unstable feature,
/// which is broken/gone in Rust 1.73.
-///
-/// - `DRIVER_DATA_OFFSET` is the offset of context/data field of the device ID (usually named
-/// `driver_data`) of the device ID, the field is suitable sized to write a `usize` value.
-///
-/// Similar to the previous requirement, the data should ideally be added during `Self` to
-/// `RawType` conversion, but there's currently no way to do it when using traits in const.
pub unsafe trait RawDeviceId {
/// The raw type that holds the device id.
///
/// Id tables created from [`Self`] are going to hold this type in its zero-terminated array.
type RawType: Copy;
+}
- /// The offset to the context/data field.
+/// Extension trait for [`RawDeviceId`] for devices that embed an index or context value.
+///
+/// This is typically used when the device ID struct includes a field like `driver_data`
+/// that is used to store a pointer-sized value (e.g., an index or context pointer).
+///
+/// # Safety
+///
+/// Implementers must ensure that:
+/// - `DRIVER_DATA_OFFSET` is the correct offset (in bytes) to the context/data field (e.g., the
+/// `driver_data` field) within the raw device ID structure. This field must be correctly sized
+/// to hold a `usize`.
+///
+/// Ideally, the data should ideally be added during `Self` to `RawType` conversion,
+/// but there's currently no way to do it when using traits in const.
+///
+/// - The `index` method must return the value stored at the location specified
+/// by `DRIVER_DATA_OFFSET`, assuming `self` is layout-compatible with `RawType`.
+pub unsafe trait RawDeviceIdIndex: RawDeviceId {
+ /// The offset (in bytes) to the context/data field in the raw device ID.
const DRIVER_DATA_OFFSET: usize;
- /// The index stored at `DRIVER_DATA_OFFSET` of the implementor of the [`RawDeviceId`] trait.
+ /// The index stored at `DRIVER_DATA_OFFSET` of the implementor of the [`RawDeviceIdIndex`]
+ /// trait.
fn index(&self) -> usize;
}
@@ -68,7 +82,14 @@ impl<T: RawDeviceId, U, const N: usize> IdArray<T, U, N> {
/// Creates a new instance of the array.
///
/// The contents are derived from the given identifiers and context information.
- pub const fn new(ids: [(T, U); N]) -> Self {
+ ///
+ /// # Safety
+ ///
+ /// If `offset` is `Some(offset)`, then:
+ /// - `offset` must be the correct offset (in bytes) to the context/data field
+ /// (e.g., the `driver_data` field) within the raw device ID structure.
+ /// - The field at `offset` must be correctly sized to hold a `usize`.
+ const unsafe fn build(ids: [(T, U); N], offset: Option<usize>) -> Self {
let mut raw_ids = [const { MaybeUninit::<T::RawType>::uninit() }; N];
let mut infos = [const { MaybeUninit::uninit() }; N];
@@ -77,14 +98,17 @@ impl<T: RawDeviceId, U, const N: usize> IdArray<T, U, N> {
// SAFETY: by the safety requirement of `RawDeviceId`, we're guaranteed that `T` is
// layout-wise compatible with `RawType`.
raw_ids[i] = unsafe { core::mem::transmute_copy(&ids[i].0) };
- // SAFETY: by the safety requirement of `RawDeviceId`, this would be effectively
- // `raw_ids[i].driver_data = i;`.
- unsafe {
- raw_ids[i]
- .as_mut_ptr()
- .byte_add(T::DRIVER_DATA_OFFSET)
- .cast::<usize>()
- .write(i);
+
+ if let Some(offset) = offset {
+ // SAFETY: by the safety requirement of this function, this would be effectively
+ // `raw_ids[i].driver_data = i;`.
+ unsafe {
+ raw_ids[i]
+ .as_mut_ptr()
+ .byte_add(offset)
+ .cast::<usize>()
+ .write(i);
+ }
}
// SAFETY: this is effectively a move: `infos[i] = ids[i].1`. We make a copy here but
@@ -92,7 +116,6 @@ impl<T: RawDeviceId, U, const N: usize> IdArray<T, U, N> {
infos[i] = MaybeUninit::new(unsafe { core::ptr::read(&ids[i].1) });
i += 1;
}
-
core::mem::forget(ids);
Self {
@@ -109,12 +132,33 @@ impl<T: RawDeviceId, U, const N: usize> IdArray<T, U, N> {
}
}
+ /// Creates a new instance of the array without writing index values.
+ ///
+ /// The contents are derived from the given identifiers and context information.
+ pub const fn new_without_index(ids: [(T, U); N]) -> Self {
+ // SAFETY: Calling `Self::build` with `offset = None` is always safe,
+ // because no raw memory writes are performed in this case.
+ unsafe { Self::build(ids, None) }
+ }
+
/// Reference to the contained [`RawIdArray`].
pub const fn raw_ids(&self) -> &RawIdArray<T, N> {
&self.raw_ids
}
}
+impl<T: RawDeviceId + RawDeviceIdIndex, U, const N: usize> IdArray<T, U, N> {
+ /// Creates a new instance of the array.
+ ///
+ /// The contents are derived from the given identifiers and context information.
+ pub const fn new(ids: [(T, U); N]) -> Self {
+ // SAFETY: by the safety requirement of `RawDeviceIdIndex`,
+ // `T::DRIVER_DATA_OFFSET` is guaranteed to be the correct offset (in bytes) to
+ // a field within `T::RawType`.
+ unsafe { Self::build(ids, Some(T::DRIVER_DATA_OFFSET)) }
+ }
+}
+
/// A device id table.
///
/// This trait is only implemented by `IdArray`.
diff --git a/rust/kernel/of.rs b/rust/kernel/of.rs
index 40d1bd13682c..c690bceb0d73 100644
--- a/rust/kernel/of.rs
+++ b/rust/kernel/of.rs
@@ -2,7 +2,11 @@
//! Device Tree / Open Firmware abstractions.
-use crate::{bindings, device_id::RawDeviceId, prelude::*};
+use crate::{
+ bindings,
+ device_id::{RawDeviceId, RawDeviceIdIndex},
+ prelude::*,
+};
/// IdTable type for OF drivers.
pub type IdTable<T> = &'static dyn kernel::device_id::IdTable<DeviceId, T>;
@@ -15,10 +19,13 @@
// SAFETY:
// * `DeviceId` is a `#[repr(transparent)` wrapper of `struct of_device_id` and does not add
// additional invariants, so it's safe to transmute to `RawType`.
-// * `DRIVER_DATA_OFFSET` is the offset to the `data` field.
unsafe impl RawDeviceId for DeviceId {
type RawType = bindings::of_device_id;
+}
+// SAFETY:
+// * `DRIVER_DATA_OFFSET` is the offset to the `data` field.
+unsafe impl RawDeviceIdIndex for DeviceId {
const DRIVER_DATA_OFFSET: usize = core::mem::offset_of!(bindings::of_device_id, data);
fn index(&self) -> usize {
diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index 6b94fd7a3ce9..96d6275c7afb 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -7,7 +7,7 @@
use crate::{
alloc::flags::*,
bindings, container_of, device,
- device_id::RawDeviceId,
+ device_id::{RawDeviceId, RawDeviceIdIndex},
devres::Devres,
driver,
error::{to_result, Result},
@@ -164,10 +164,13 @@ pub const fn from_class(class: u32, class_mask: u32) -> Self {
// SAFETY:
// * `DeviceId` is a `#[repr(transparent)` wrapper of `pci_device_id` and does not add
// additional invariants, so it's safe to transmute to `RawType`.
-// * `DRIVER_DATA_OFFSET` is the offset to the `driver_data` field.
unsafe impl RawDeviceId for DeviceId {
type RawType = bindings::pci_device_id;
+}
+// SAFETY:
+// * `DRIVER_DATA_OFFSET` is the offset to the `driver_data` field.
+unsafe impl RawDeviceIdIndex for DeviceId {
const DRIVER_DATA_OFFSET: usize = core::mem::offset_of!(bindings::pci_device_id, driver_data);
fn index(&self) -> usize {
--
2.43.0