rust: device_id: split out index support into a separate trait

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 the RawDeviceId trait.

The changes to acpi.rs and driver.rs were made by Danilo.

Reviewed-by: Trevor Gross <tmgross@umich.edu>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250711040947.1252162-2-fujita.tomonori@gmail.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

1 files changed, 10 insertions, 5 deletions

diff --git a/rust/kernel/of.rs b/rust/kernel/of.rs
index 52fe0c77b9a1..0888469bddb7 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>;
@@ -12,13 +16,14 @@ pub type IdTable<T> = &'static dyn kernel::device_id::IdTable<DeviceId, T>;
 #[derive(Clone, Copy)]
 pub struct DeviceId(bindings::of_device_id);
 
-// 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.
+// 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`.
 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 {