John Hubbard
2025-Aug-24 17:37 UTC
[PATCH 1/2] nova-core: Add a library for bitfields in Rust structs
+Cc: bitmap maintainer/reviewers: Yury Norov, Rasmus Villemoes On 8/24/25 6:59 AM, Joel Fernandes wrote:> Add a minimal bitfield library for defining in Rust structures (called > bitstruct), similar in concept to bit fields in C structs. This will be used > for defining page table entries and other structures in nova-core. > > Signed-off-by: Joel Fernandes <joelagnelf at nvidia.com> > --- > drivers/gpu/nova-core/bitstruct.rs | 149 +++++++++++++++++++++++++++++ > drivers/gpu/nova-core/nova_core.rs | 1 + > 2 files changed, 150 insertions(+) > create mode 100644 drivers/gpu/nova-core/bitstruct.rs > > diff --git a/drivers/gpu/nova-core/bitstruct.rs b/drivers/gpu/nova-core/bitstruct.rs > new file mode 100644 > index 000000000000..661a75da0a9c > --- /dev/null > +++ b/drivers/gpu/nova-core/bitstruct.rs > @@ -0,0 +1,149 @@ > +// SPDX-License-Identifier: GPL-2.0 > +// > +// bitstruct.rs ? C-style library for bitfield-packed Rust structures > +// > +// A library that provides support for defining bit fields in Rust > +// structures to circumvent lack of native language support for this. > +// > +// Similar usage syntax to the register! macro. > + > +use kernel::prelude::*; > + > +/// Macro for defining bitfield-packed structures in Rust. > +/// The size of the underlying storage type is specified with #[repr(TYPE)]. > +/// > +/// # Example (just for illustration) > +/// ```rust > +/// bitstruct! { > +/// #[repr(u64)] > +/// pub struct PageTableEntry { > +/// 0:0 present as bool, > +/// 1:1 writable as bool, > +/// 11:9 available as u8, > +/// 51:12 pfn as u64, > +/// 62:52 available2 as u16, > +/// 63:63 nx as bool, > +/// } > +/// } > +/// ``` > +/// > +/// This generates a struct with methods: > +/// - Constructor: `default()` sets all bits to zero. > +/// - Field accessors: `present()`, `pfn()`, etc. > +/// - Field setters: `set_present()`, `set_pfn()`, etc. > +/// - Builder methods: `with_present()`, `with_pfn()`, etc. > +/// - Raw conversion: `from_raw()`, `into_raw()` > +#[allow(unused_macros)] > +macro_rules! bitstruct { > + ( > + #[repr($storage:ty)] > + $vis:vis struct $name:ident { > + $( > + $hi:literal : $lo:literal $field:ident as $field_type:tt > + ),* $(,)? > + } > + ) => { > + #[repr(transparent)] > + #[derive(Copy, Clone, Default)] > + $vis struct $name($storage); > + > + impl $name { > + /// Create from raw value > + #[inline(always)] > + $vis const fn from_raw(val: $storage) -> Self { > + Self(val) > + } > + > + /// Get raw value > + #[inline(always)] > + $vis const fn into_raw(self) -> $storage { > + self.0 > + } > + } > + > + impl core::fmt::Debug for $name { > + fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { > + write!(f, "{}({:#x})", stringify!($name), self.0) > + } > + } > + > + // Generate all field methods > + $( > + bitstruct_field_impl!($vis, $name, $storage, $hi, $lo, $field as $field_type); > + )* > + }; > +} > + > +/// Helper to calculate mask for bit fields > +#[allow(unused_macros)] > +macro_rules! bitstruct_mask { > + ($hi:literal, $lo:literal, $storage:ty) => {{ > + let width = ($hi - $lo + 1) as usize; > + let storage_bits = 8 * core::mem::size_of::<$storage>(); > + if width >= storage_bits { > + <$storage>::MAX > + } else { > + ((1 as $storage) << width) - 1 > + } > + }}; > +} > + > +#[allow(unused_macros)] > +macro_rules! bitstruct_field_impl { > + ($vis:vis, $struct_name:ident, $storage:ty, $hi:literal, $lo:literal, $field:ident as $field_type:tt) => { > + impl $struct_name { > + #[inline(always)] > + $vis const fn $field(&self) -> $field_type { > + let field_val = (self.0 >> $lo) & bitstruct_mask!($hi, $lo, $storage); > + bitstruct_cast_value!(field_val, $field_type) > + } > + } > + bitstruct_make_setters!($vis, $struct_name, $storage, $hi, $lo, $field, $field_type); > + }; > +} > + > +/// Helper macro to convert extracted value to target type > +/// > +/// Special handling for bool types is required because the `as` keyword > +/// cannot be used to convert to bool in Rust. For bool fields, we check > +/// if the extracted value is non-zero. For all other types, we use the > +/// standard `as` conversion. > +#[allow(unused_macros)] > +macro_rules! bitstruct_cast_value { > + ($field_val:expr, bool) => { > + $field_val != 0 > + }; > + ($field_val:expr, $field_type:tt) => { > + $field_val as $field_type > + }; > +} > + > +#[allow(unused_macros)] > +macro_rules! bitstruct_write_bits { > + ($raw:expr, $hi:literal, $lo:literal, $val:expr, $storage:ty) => {{ > + let mask = bitstruct_mask!($hi, $lo, $storage); > + ($raw & !(mask << $lo)) | ((($val as $storage) & mask) << $lo) > + }}; > +} > + > +#[allow(unused_macros)] > +macro_rules! bitstruct_make_setters { > + ($vis:vis, $struct_name:ident, $storage:ty, $hi:literal, $lo:literal, $field:ident, $field_type:tt) => { > + ::kernel::macros::paste! { > + impl $struct_name { > + #[inline(always)] > + #[allow(dead_code)] > + $vis fn [<set_ $field>](&mut self, val: $field_type) { > + self.0 = bitstruct_write_bits!(self.0, $hi, $lo, val, $storage); > + } > + > + #[inline(always)] > + #[allow(dead_code)] > + $vis const fn [<with_ $field>](mut self, val: $field_type) -> Self { > + self.0 = bitstruct_write_bits!(self.0, $hi, $lo, val, $storage); > + self > + } > + } > + } > + }; > +} > diff --git a/drivers/gpu/nova-core/nova_core.rs b/drivers/gpu/nova-core/nova_core.rs > index cb2bbb30cba1..54505cad4a73 100644 > --- a/drivers/gpu/nova-core/nova_core.rs > +++ b/drivers/gpu/nova-core/nova_core.rs > @@ -2,6 +2,7 @@ > > //! Nova Core GPU Driver > > +mod bitstruct; > mod dma; > mod driver; > mod falcon;thanks, -- John Hubbard