rust: of: add of::DeviceId abstraction

`of::DeviceId` is an abstraction around `struct of_device_id`.

This is used by subsequent patches, in particular the platform bus
abstractions, to create OF device ID tables.

Reviewed-by: Rob Herring (Arm) <[email protected]>
Signed-off-by: Danilo Krummrich <[email protected]>
Tested-by: Dirk Behme <[email protected]>
Tested-by: Fabien Parent <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Danilo Krummrich

MAINTAINERS

@@ -17505,6 +17505,7 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git
 F:	Documentation/ABI/testing/sysfs-firmware-ofw
 F:	drivers/of/
 F:	include/linux/of*.h
+F:	rust/kernel/of.rs
 F:	scripts/dtc/
 F:	tools/testing/selftests/dt/
 K:	of_overlay_notifier_

rust/kernel/lib.rs

@@ -56,6 +56,7 @@ pub mod list;
 pub mod miscdevice;
 #[cfg(CONFIG_NET)]
 pub mod net;
+pub mod of;
 pub mod page;
 pub mod pid_namespace;
 pub mod prelude;

rust/kernel/of.rs

@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Device Tree / Open Firmware abstractions.
+
+use crate::{bindings, device_id::RawDeviceId, prelude::*};
+
+/// IdTable type for OF drivers.
+pub type IdTable<T> = &'static dyn kernel::device_id::IdTable<DeviceId, T>;
+
+/// An open firmware device id.
+#[repr(transparent)]
+#[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.
+unsafe impl RawDeviceId for DeviceId {
+    type RawType = bindings::of_device_id;
+
+    const DRIVER_DATA_OFFSET: usize = core::mem::offset_of!(bindings::of_device_id, data);
+
+    fn index(&self) -> usize {
+        self.0.data as _
+    }
+}
+
+impl DeviceId {
+    /// Create a new device id from an OF 'compatible' string.
+    pub const fn new(compatible: &'static CStr) -> Self {
+        let src = compatible.as_bytes_with_nul();
+        // Replace with `bindings::of_device_id::default()` once stabilized for `const`.
+        // SAFETY: FFI type is valid to be zero-initialized.
+        let mut of: bindings::of_device_id = unsafe { core::mem::zeroed() };
+
+        // TODO: Use `clone_from_slice` once the corresponding types do match.
+        let mut i = 0;
+        while i < src.len() {
+            of.compatible[i] = src[i] as _;
+            i += 1;
+        }
+
+        Self(of)
+    }
+}
+
+/// Create an OF `IdTable` with an "alias" for modpost.
+#[macro_export]
+macro_rules! of_device_table {
+    ($table_name:ident, $module_table_name:ident, $id_info_type: ty, $table_data: expr) => {
+        const $table_name: $crate::device_id::IdArray<
+            $crate::of::DeviceId,
+            $id_info_type,
+            { $table_data.len() },
+        > = $crate::device_id::IdArray::new($table_data);
+
+        $crate::module_device_table!("of", $module_table_name, $table_name);
+    };
+}