Messages in this thread Patch in this message |  | | From | John Hubbard <> | | Subject | [PATCH v3 1/2] rust: sizes: add DeviceSize trait for device address space constants | | Date | Tue, 31 Mar 2026 15:43:18 -0700 |
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The SZ_* constants are usize, matching the CPU pointer width. But device address spaces have their own widths (32-bit MMIO windows, 64-bit GPU framebuffers, etc.), so drivers end up casting these constants with SZ_1M as u64 or helper functions. This adds boilerplate with no safety benefit.
Add a DeviceSize trait with associated SZ_* constants, implemented for u32, u64, and usize. With the trait in scope, callers write u64::SZ_1M or u32::SZ_4K to get the constant in their device's native width. All SZ_* values fit in a u32, so every implementation is lossless. Each impl has a const assert to catch any future constant that would overflow.
A define_sizes! macro generates everything from a single internal list of names. The macro takes the target types as arguments, so adding a new target type requires changing only the call site.
Suggested-by: Danilo Krummrich <dakr@kernel.org> Link: https://lore.kernel.org/all/DGB9G697GSWO.3VBFGU5MKFPMR@kernel.org/ Link: https://lore.kernel.org/all/DGHI8WRKBQS9.38910L6FIIZTE@kernel.org/ Signed-off-by: John Hubbard <jhubbard@nvidia.com> --- rust/kernel/sizes.rs | 166 +++++++++++++++++++++++++++++++------------ 1 file changed, 122 insertions(+), 44 deletions(-)
diff --git a/rust/kernel/sizes.rs b/rust/kernel/sizes.rs index 661e680d9330..cbf0a6c0a757 100644 --- a/rust/kernel/sizes.rs +++ b/rust/kernel/sizes.rs @@ -3,48 +3,126 @@ //! Commonly used sizes. //! //! C headers: [`include/linux/sizes.h`](srctree/include/linux/sizes.h). +//! +//! The top-level `SZ_*` constants are [`usize`]-typed, for use in kernel page +//! arithmetic and similar CPU-side work. +//! +//! The [`DeviceSize`] trait provides the same constants as associated constants +//! on [`u32`], [`u64`], and [`usize`], for use in device address spaces where +//! the address width depends on the hardware. Device drivers frequently need +//! these constants as [`u64`] (or [`u32`]) rather than [`usize`], because +//! device address spaces are sized independently of the CPU pointer width. +//! +//! # Examples +//! +//! ``` +//! use kernel::sizes::{DeviceSize, SZ_1M}; +//! +//! // usize constant (CPU-side) +//! let num_pages_in_1m: usize = SZ_1M / kernel::page::PAGE_SIZE; +//! +//! // Device-side constant via the trait +//! let heap_size: u64 = 14 * u64::SZ_1M; +//! let small: u32 = u32::SZ_4K; +//! ``` + +macro_rules! define_sizes { + ($($type:ty),* $(,)?) => { + define_sizes!(@internal [$($type),*] + /// 0x0000_0400 + SZ_1K, + /// 0x0000_0800 + SZ_2K, + /// 0x0000_1000 + SZ_4K, + /// 0x0000_2000 + SZ_8K, + /// 0x0000_4000 + SZ_16K, + /// 0x0000_8000 + SZ_32K, + /// 0x0001_0000 + SZ_64K, + /// 0x0002_0000 + SZ_128K, + /// 0x0004_0000 + SZ_256K, + /// 0x0008_0000 + SZ_512K, + /// 0x0010_0000 + SZ_1M, + /// 0x0020_0000 + SZ_2M, + /// 0x0040_0000 + SZ_4M, + /// 0x0080_0000 + SZ_8M, + /// 0x0100_0000 + SZ_16M, + /// 0x0200_0000 + SZ_32M, + /// 0x0400_0000 + SZ_64M, + /// 0x0800_0000 + SZ_128M, + /// 0x1000_0000 + SZ_256M, + /// 0x2000_0000 + SZ_512M, + /// 0x4000_0000 + SZ_1G, + /// 0x8000_0000 + SZ_2G, + ); + }; + + (@internal [$($type:ty),*] $($names_and_metas:tt)*) => { + define_sizes!(@consts_and_trait $($names_and_metas)*); + define_sizes!(@impls [$($type),*] $($names_and_metas)*); + }; + + (@consts_and_trait $($(#[$meta:meta])* $name:ident,)*) => { + $( + $(#[$meta])* + pub const $name: usize = bindings::$name as usize; + )* + + /// Size constants for device address spaces. + /// + /// Implemented for [`u32`], [`u64`], and [`usize`] so drivers can + /// choose the width that matches their hardware. All `SZ_*` values fit + /// in a [`u32`], so all implementations are lossless. + /// + /// # Examples + /// + /// ``` + /// use kernel::sizes::DeviceSize; + /// + /// let gpu_heap: u64 = 14 * u64::SZ_1M; + /// let mmio_window: u32 = u32::SZ_16M; + /// ``` + pub trait DeviceSize { + $( + $(#[$meta])* + const $name: Self; + )* + } + }; + + (@impls [] $($(#[$meta:meta])* $name:ident,)*) => {}; + + (@impls [$first:ty $(, $rest:ty)*] $($(#[$meta:meta])* $name:ident,)*) => { + impl DeviceSize for $first { + $( + const $name: Self = { + assert!((self::$name as u128) <= (<$first>::MAX as u128)); + self::$name as $first + }; + )* + } + + define_sizes!(@impls [$($rest),*] $($(#[$meta])* $name,)*); + }; +} -/// 0x00000400 -pub const SZ_1K: usize = bindings::SZ_1K as usize; -/// 0x00000800 -pub const SZ_2K: usize = bindings::SZ_2K as usize; -/// 0x00001000 -pub const SZ_4K: usize = bindings::SZ_4K as usize; -/// 0x00002000 -pub const SZ_8K: usize = bindings::SZ_8K as usize; -/// 0x00004000 -pub const SZ_16K: usize = bindings::SZ_16K as usize; -/// 0x00008000 -pub const SZ_32K: usize = bindings::SZ_32K as usize; -/// 0x00010000 -pub const SZ_64K: usize = bindings::SZ_64K as usize; -/// 0x00020000 -pub const SZ_128K: usize = bindings::SZ_128K as usize; -/// 0x00040000 -pub const SZ_256K: usize = bindings::SZ_256K as usize; -/// 0x00080000 -pub const SZ_512K: usize = bindings::SZ_512K as usize; -/// 0x00100000 -pub const SZ_1M: usize = bindings::SZ_1M as usize; -/// 0x00200000 -pub const SZ_2M: usize = bindings::SZ_2M as usize; -/// 0x00400000 -pub const SZ_4M: usize = bindings::SZ_4M as usize; -/// 0x00800000 -pub const SZ_8M: usize = bindings::SZ_8M as usize; -/// 0x01000000 -pub const SZ_16M: usize = bindings::SZ_16M as usize; -/// 0x02000000 -pub const SZ_32M: usize = bindings::SZ_32M as usize; -/// 0x04000000 -pub const SZ_64M: usize = bindings::SZ_64M as usize; -/// 0x08000000 -pub const SZ_128M: usize = bindings::SZ_128M as usize; -/// 0x10000000 -pub const SZ_256M: usize = bindings::SZ_256M as usize; -/// 0x20000000 -pub const SZ_512M: usize = bindings::SZ_512M as usize; -/// 0x40000000 -pub const SZ_1G: usize = bindings::SZ_1G as usize; -/// 0x80000000 -pub const SZ_2G: usize = bindings::SZ_2G as usize; +define_sizes!(u32, u64, usize); -- 2.53.0
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