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// SPDX-License-Identifier: GPL-2.0
//! Generic implementation of device IDs.
//!
//! Each bus / subsystem that matches device and driver through a bus / subsystem specific ID is
//! expected to implement [`RawDeviceId`].
use core::mem::MaybeUninit;
/// Marker trait to indicate a Rust device ID type represents a corresponding C device ID type.
///
/// This is meant to be implemented by buses/subsystems so that they can use [`IdTable`] to
/// guarantee (at compile-time) zero-termination of device id tables provided by drivers.
///
/// # Safety
///
/// Implementers must ensure that:
/// - `Self` is layout-compatible with [`RawDeviceId::RawType`]; i.e. it's safe to transmute to
/// `RawDeviceId`.
///
/// This requirement is needed so `IdArray::new` can convert `Self` to `RawType` when building
/// the ID table.
///
/// 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.
const DRIVER_DATA_OFFSET: usize;
/// The index stored at `DRIVER_DATA_OFFSET` of the implementor of the [`RawDeviceId`] trait.
fn index(&self) -> usize;
}
/// A zero-terminated device id array.
#[repr(C)]
pub struct RawIdArray<T: RawDeviceId, const N: usize> {
ids: [T::RawType; N],
sentinel: MaybeUninit<T::RawType>,
}
impl<T: RawDeviceId, const N: usize> RawIdArray<T, N> {
#[doc(hidden)]
pub const fn size(&self) -> usize {
core::mem::size_of::<Self>()
}
}
/// A zero-terminated device id array, followed by context data.
#[repr(C)]
pub struct IdArray<T: RawDeviceId, U, const N: usize> {
raw_ids: RawIdArray<T, N>,
id_infos: [U; N],
}
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 {
let mut raw_ids = [const { MaybeUninit::<T::RawType>::uninit() }; N];
let mut infos = [const { MaybeUninit::uninit() }; N];
let mut i = 0usize;
while i < 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_offset(T::DRIVER_DATA_OFFSET as _)
.cast::<usize>()
.write(i);
}
// SAFETY: this is effectively a move: `infos[i] = ids[i].1`. We make a copy here but
// later forget `ids`.
infos[i] = MaybeUninit::new(unsafe { core::ptr::read(&ids[i].1) });
i += 1;
}
core::mem::forget(ids);
Self {
raw_ids: RawIdArray {
// SAFETY: this is effectively `array_assume_init`, which is unstable, so we use
// `transmute_copy` instead. We have initialized all elements of `raw_ids` so this
// `array_assume_init` is safe.
ids: unsafe { core::mem::transmute_copy(&raw_ids) },
sentinel: MaybeUninit::zeroed(),
},
// SAFETY: We have initialized all elements of `infos` so this `array_assume_init` is
// safe.
id_infos: unsafe { core::mem::transmute_copy(&infos) },
}
}
/// Reference to the contained [`RawIdArray`].
pub const fn raw_ids(&self) -> &RawIdArray<T, N> {
&self.raw_ids
}
}
/// A device id table.
///
/// This trait is only implemented by `IdArray`.
///
/// The purpose of this trait is to allow `&'static dyn IdArray<T, U>` to be in context when `N` in
/// `IdArray` doesn't matter.
pub trait IdTable<T: RawDeviceId, U> {
/// Obtain the pointer to the ID table.
fn as_ptr(&self) -> *const T::RawType;
/// Obtain the pointer to the bus specific device ID from an index.
fn id(&self, index: usize) -> &T::RawType;
/// Obtain the pointer to the driver-specific information from an index.
fn info(&self, index: usize) -> &U;
}
impl<T: RawDeviceId, U, const N: usize> IdTable<T, U> for IdArray<T, U, N> {
fn as_ptr(&self) -> *const T::RawType {
// This cannot be `self.ids.as_ptr()`, as the return pointer must have correct provenance
// to access the sentinel.
(self as *const Self).cast()
}
fn id(&self, index: usize) -> &T::RawType {
&self.raw_ids.ids[index]
}
fn info(&self, index: usize) -> &U {
&self.id_infos[index]
}
}
/// Create device table alias for modpost.
#[macro_export]
macro_rules! module_device_table {
($table_type: literal, $module_table_name:ident, $table_name:ident) => {
#[rustfmt::skip]
#[export_name =
concat!("__mod_device_table__", $table_type,
"__", module_path!(),
"_", line!(),
"_", stringify!($table_name))
]
static $module_table_name: [core::mem::MaybeUninit<u8>; $table_name.raw_ids().size()] =
unsafe { core::mem::transmute_copy($table_name.raw_ids()) };
};
}
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