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0b76335e8f
The common practice in C drivers is to store pointers into `driver_data` field of device IDs. The Rust code is however currently storing indices into the fields and then carry a side table that maps the index to pointers. It is much simpler to just have `DeviceId` carry the pointer like C code does. However, just doing so naively would cause a "pointers cannot be cast to integers during const eval" error, as kernel_ulong_t does not have provenance while pointers do, and Rust forbids `expose_provenance` during consteval. Work around this limitation by wrapping raw IDs in `MaybeUninit`. `MaybeUninit` is allowed to host arbitrary bytes with or without provenance, so we can just then use `unsafe` to store a pointer with provenance there. This has the same effect as changing the C-side definition to use `void*` instead of `kernel_ulong_t`, but without actually changing the C side. Signed-off-by: Gary Guo <gary@garyguo.net> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Link: https://patch.msgid.link/20260629-id_info-v2-8-56fccbe9c5ef@garyguo.net Signed-off-by: Danilo Krummrich <dakr@kernel.org>
56 lines
1.7 KiB
Rust
56 lines
1.7 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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//! Device Tree / Open Firmware abstractions.
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use crate::{
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bindings,
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device_id::{RawDeviceId, RawDeviceIdIndex},
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prelude::*,
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};
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/// IdTable type for OF drivers.
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pub type IdTable<T> = &'static dyn kernel::device_id::IdTable<DeviceId, T>;
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/// An open firmware device id.
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#[repr(transparent)]
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#[derive(Clone, Copy)]
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pub struct DeviceId(bindings::of_device_id);
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// SAFETY: `DeviceId` is a `#[repr(transparent)]` wrapper of `struct of_device_id` and
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// does not add additional invariants, so it's safe to transmute to `RawType`.
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unsafe impl RawDeviceId for DeviceId {
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type RawType = bindings::of_device_id;
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}
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// SAFETY: `DRIVER_DATA_OFFSET` is the offset to the `data` field.
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unsafe impl RawDeviceIdIndex for DeviceId {
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const DRIVER_DATA_OFFSET: usize = core::mem::offset_of!(bindings::of_device_id, data);
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}
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impl DeviceId {
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/// Create a new device id from an OF 'compatible' string.
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pub const fn new(compatible: &'static CStr) -> Self {
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let src = compatible.to_bytes_with_nul();
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// Replace with `bindings::of_device_id::default()` once stabilized for `const`.
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// SAFETY: FFI type is valid to be zero-initialized.
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let mut of: bindings::of_device_id = unsafe { core::mem::zeroed() };
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// TODO: Use `copy_from_slice` once stabilized for `const`.
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let mut i = 0;
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while i < src.len() {
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of.compatible[i] = src[i];
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i += 1;
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}
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Self(of)
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}
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}
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/// Create an OF `IdTable` with an "alias" for modpost.
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#[macro_export]
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macro_rules! of_device_table {
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($($tt:tt)*) => {
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$crate::module_device_table!("of", $crate::of::DeviceId, $($tt)*);
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};
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}
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