[PATCH v4 2/6] nova-core: bitfield: Add support for different storage widths

Joel Fernandes
2025-09-20T18:23:01Z

Previously, bitfields were hardcoded to use u32 as the underlying
storage type. Add support for different storage types (u8, u16, u32,
u64) to the bitfield macro.

New syntax is: struct Name: <type ex., u32> { ... }

Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
drivers/gpu/nova-core/bitfield.rs | 71 +++++++++++++++++-----------
drivers/gpu/nova-core/regs/macros.rs | 16 +++----
2 files changed, 52 insertions(+), 35 deletions(-)

diff --git a/drivers/gpu/nova-core/bitfield.rs b/drivers/gpu/nova-core/bitfield.rs
index ba6b7caa05d9..687ef234be75 100644
--- a/drivers/gpu/nova-core/bitfield.rs
+++ b/drivers/gpu/nova-core/bitfield.rs
@@ -51,7 +51,7 @@
//! }
//!
//! bitfield! {
-//! struct ControlReg {
+//! struct ControlReg: u32 {
//! 3:0 mode as u8 ?=> Mode;
//! 7 state as bool => State;
//! }
@@ -61,6 +61,8 @@
//! This generates a struct with:
//! - Field accessors: `mode()`, `state()`, etc.
//! - Field setters: `set_mode()`, `set_state()`, etc. (supports chaining with builder pattern).
+//! Note that the compiler will error out if the size of the setter's arg exceeds the
+//! struct's storage size.
//! - Debug and Default implementations
//!
//! The field setters can be used with the builder pattern, example:
@@ -77,21 +79,21 @@
//!
macro_rules! bitfield {
// Main entry point - defines the bitfield struct with fields
- (struct $name:ident $(, $comment:literal)? { $($fields:tt)* }) => {
- bitfield!(@core $name $(, $comment)? { $($fields)* });
+ (struct $name:ident : $storage:ty $(, $comment:literal)? { $($fields:tt)* }) => {
+ bitfield!(@core $name $storage $(, $comment)? { $($fields)* });
};

// All rules below are helpers.

// Defines the wrapper `$name` type, as well as its relevant implementations (`Debug`,
// `Default`, `BitOr`, and conversion to the value type) and field accessor methods.
- (@core $name:ident $(, $comment:literal)? { $($fields:tt)* }) => {
+ (@core $name:ident $storage:ty $(, $comment:literal)? { $($fields:tt)* }) => {
$(
#[doc=$comment]
)?
#[repr(transparent)]
#[derive(Clone, Copy)]
- pub(crate) struct $name(u32);
+ pub(crate) struct $name($storage);

impl ::core::ops::BitOr for $name {
type Output = Self;
@@ -101,20 +103,26 @@ fn bitor(self, rhs: Self) -> Self::Output {
}
}

- impl ::core::convert::From<$name> for u32 {
- fn from(val: $name) -> u32 {
+ impl ::core::convert::From<$name> for $storage {
+ fn from(val: $name) -> $storage {
val.0
}
}

- bitfield!(@fields_dispatcher $name { $($fields)* });
+ impl ::core::convert::From<$storage> for $name {
+ fn from(val: $storage) -> Self {
+ Self(val)
+ }
+ }
+
+ bitfield!(@fields_dispatcher $name $storage { $($fields)* });
};

// Captures the fields and passes them to all the implementers that require field information.
//
// Used to simplify the matching rules for implementers, so they don't need to match the entire
// complex fields rule even though they only make use of part of it.
- (@fields_dispatcher $name:ident {
+ (@fields_dispatcher $name:ident $storage:ty {
$($hi:tt:$lo:tt $field:ident as $type:tt
$(?=> $try_into_type:ty)?
$(=> $into_type:ty)?
@@ -123,7 +131,7 @@ fn from(val: $name) -> u32 {
)*
}
) => {
- bitfield!(@field_accessors $name {
+ bitfield!(@field_accessors $name $storage {
$(
$hi:$lo $field as $type
$(?=> $try_into_type)?
@@ -138,7 +146,7 @@ fn from(val: $name) -> u32 {

// Defines all the field getter/setter methods for `$name`.
(
- @field_accessors $name:ident {
+ @field_accessors $name:ident $storage:ty {
$($hi:tt:$lo:tt $field:ident as $type:tt
$(?=> $try_into_type:ty)?
$(=> $into_type:ty)?
@@ -154,7 +162,7 @@ fn from(val: $name) -> u32 {
#[allow(dead_code)]
impl $name {
$(
- bitfield!(@field_accessor $name $hi:$lo $field as $type
+ bitfield!(@field_accessor $name $storage, $hi:$lo $field as $type
$(?=> $try_into_type)?
$(=> $into_type)?
$(, $comment)?
@@ -188,11 +196,11 @@ impl $name {

// Catches fields defined as `bool` and convert them into a boolean value.
(
- @field_accessor $name:ident $hi:tt:$lo:tt $field:ident as bool => $into_type:ty
+ @field_accessor $name:ident $storage:ty, $hi:tt:$lo:tt $field:ident as bool => $into_type:ty
$(, $comment:literal)?;
) => {
bitfield!(
- @leaf_accessor $name $hi:$lo $field
+ @leaf_accessor $name $storage, $hi:$lo $field
{ |f| <$into_type>::from(if f != 0 { true } else { false }) }
$into_type => $into_type $(, $comment)?;
);
@@ -200,17 +208,17 @@ impl $name {

// Shortcut for fields defined as `bool` without the `=>` syntax.
(
- @field_accessor $name:ident $hi:tt:$lo:tt $field:ident as bool $(, $comment:literal)?;
+ @field_accessor $name:ident $storage:ty, $hi:tt:$lo:tt $field:ident as bool $(, $comment:literal)?;
) => {
- bitfield!(@field_accessor $name $hi:$lo $field as bool => bool $(, $comment)?;);
+ bitfield!(@field_accessor $name $storage, $hi:$lo $field as bool => bool $(, $comment)?;);
};

// Catches the `?=>` syntax for non-boolean fields.
(
- @field_accessor $name:ident $hi:tt:$lo:tt $field:ident as $type:tt ?=> $try_into_type:ty
+ @field_accessor $name:ident $storage:ty, $hi:tt:$lo:tt $field:ident as $type:tt ?=> $try_into_type:ty
$(, $comment:literal)?;
) => {
- bitfield!(@leaf_accessor $name $hi:$lo $field
+ bitfield!(@leaf_accessor $name $storage, $hi:$lo $field
{ |f| <$try_into_type>::try_from(f as $type) } $try_into_type =>
::core::result::Result<
$try_into_type,
@@ -221,29 +229,38 @@ impl $name {

// Catches the `=>` syntax for non-boolean fields.
(
- @field_accessor $name:ident $hi:tt:$lo:tt $field:ident as $type:tt => $into_type:ty
+ @field_accessor $name:ident $storage:ty, $hi:tt:$lo:tt $field:ident as $type:tt => $into_type:ty
$(, $comment:literal)?;
) => {
- bitfield!(@leaf_accessor $name $hi:$lo $field
+ bitfield!(@leaf_accessor $name $storage, $hi:$lo $field
{ |f| <$into_type>::from(f as $type) } $into_type => $into_type $(, $comment)?;);
};

// Shortcut for non-boolean fields defined without the `=>` or `?=>` syntax.
(
- @field_accessor $name:ident $hi:tt:$lo:tt $field:ident as $type:tt
+ @field_accessor $name:ident $storage:ty, $hi:tt:$lo:tt $field:ident as $type:tt
$(, $comment:literal)?;
) => {
- bitfield!(@field_accessor $name $hi:$lo $field as $type => $type $(, $comment)?;);
+ bitfield!(@field_accessor $name $storage, $hi:$lo $field as $type => $type $(, $comment)?;);
};

// Generates the accessor methods for a single field.
(
- @leaf_accessor $name:ident $hi:tt:$lo:tt $field:ident
+ @leaf_accessor $name:ident $storage:ty, $hi:tt:$lo:tt $field:ident
{ $process:expr } $to_type:ty => $res_type:ty $(, $comment:literal)?;
) => {
::kernel::macros::paste!(
const [<$field:upper _RANGE>]: ::core::ops::RangeInclusive<u8> = $lo..=$hi;
- const [<$field:upper _MASK>]: u32 = ((((1 << $hi) - 1) << 1) + 1) - ((1 << $lo) - 1);
+ const [<$field:upper _MASK>]: $storage = {
+ // Generate mask for shifting
+ match ::core::mem::size_of::<$storage>() {
+ 1 => ::kernel::bits::genmask_u8($lo..=$hi) as $storage,
+ 2 => ::kernel::bits::genmask_u16($lo..=$hi) as $storage,
+ 4 => ::kernel::bits::genmask_u32($lo..=$hi) as $storage,
+ 8 => ::kernel::bits::genmask_u64($lo..=$hi) as $storage,
+ _ => ::kernel::build_error!("Unsupported storage type size")
+ }
+ };
const [<$field:upper _SHIFT>]: u32 = Self::[<$field:upper _MASK>].trailing_zeros();
);

@@ -254,7 +271,7 @@ impl $name {
#[inline(always)]
pub(crate) fn $field(self) -> $res_type {
::kernel::macros::paste!(
- const MASK: u32 = $name::[<$field:upper _MASK>];
+ const MASK: $storage = $name::[<$field:upper _MASK>];
const SHIFT: u32 = $name::[<$field:upper _SHIFT>];
);
let field = ((self.0 & MASK) >> SHIFT);
@@ -269,9 +286,9 @@ pub(crate) fn $field(self) -> $res_type {
)?
#[inline(always)]
pub(crate) fn [<set_ $field>](mut self, value: $to_type) -> Self {
- const MASK: u32 = $name::[<$field:upper _MASK>];
+ const MASK: $storage = $name::[<$field:upper _MASK>];
const SHIFT: u32 = $name::[<$field:upper _SHIFT>];
- let value = (u32::from(value) << SHIFT) & MASK;
+ let value = (<$storage>::from(value) << SHIFT) & MASK;
self.0 = (self.0 & !MASK) | value;

self
diff --git a/drivers/gpu/nova-core/regs/macros.rs b/drivers/gpu/nova-core/regs/macros.rs
index 945d15a2c529..d34c7f37fb93 100644
--- a/drivers/gpu/nova-core/regs/macros.rs
+++ b/drivers/gpu/nova-core/regs/macros.rs
@@ -276,25 +276,25 @@ pub(crate) trait RegisterBase<T> {
macro_rules! register {
// Creates a register at a fixed offset of the MMIO space.
($name:ident @ $offset:literal $(, $comment:literal)? { $($fields:tt)* } ) => {
- bitfield!(struct $name $(, $comment)? { $($fields)* } );
+ bitfield!(struct $name: u32 $(, $comment)? { $($fields)* } );
register!(@io_fixed $name @ $offset);
};

// Creates an alias register of fixed offset register `alias` with its own fields.
($name:ident => $alias:ident $(, $comment:literal)? { $($fields:tt)* } ) => {
- bitfield!(struct $name $(, $comment)? { $($fields)* } );
+ bitfield!(struct $name: u32 $(, $comment)? { $($fields)* } );
register!(@io_fixed $name @ $alias::OFFSET);
};

// Creates a register at a relative offset from a base address provider.
($name:ident @ $base:ty [ $offset:literal ] $(, $comment:literal)? { $($fields:tt)* } ) => {
- bitfield!(struct $name $(, $comment)? { $($fields)* } );
+ bitfield!(struct $name: u32 $(, $comment)? { $($fields)* } );
register!(@io_relative $name @ $base [ $offset ]);
};

// Creates an alias register of relative offset register `alias` with its own fields.
($name:ident => $base:ty [ $alias:ident ] $(, $comment:literal)? { $($fields:tt)* }) => {
- bitfield!(struct $name $(, $comment)? { $($fields)* } );
+ bitfield!(struct $name: u32 $(, $comment)? { $($fields)* } );
register!(@io_relative $name @ $base [ $alias::OFFSET ]);
};

@@ -305,7 +305,7 @@ macro_rules! register {
}
) => {
static_assert!(::core::mem::size_of::<u32>() <= $stride);
- bitfield!(struct $name $(, $comment)? { $($fields)* } );
+ bitfield!(struct $name: u32 $(, $comment)? { $($fields)* } );
register!(@io_array $name @ $offset [ $size ; $stride ]);
};

@@ -326,7 +326,7 @@ macro_rules! register {
$(, $comment:literal)? { $($fields:tt)* }
) => {
static_assert!(::core::mem::size_of::<u32>() <= $stride);
- bitfield!(struct $name $(, $comment)? { $($fields)* } );
+ bitfield!(struct $name: u32 $(, $comment)? { $($fields)* } );
register!(@io_relative_array $name @ $base [ $offset [ $size ; $stride ] ]);
};

@@ -348,7 +348,7 @@ macro_rules! register {
}
) => {
static_assert!($idx < $alias::SIZE);
- bitfield!(struct $name $(, $comment)? { $($fields)* } );
+ bitfield!(struct $name: u32 $(, $comment)? { $($fields)* } );
register!(@io_relative $name @ $base [ $alias::OFFSET + $idx * $alias::STRIDE ] );
};

@@ -357,7 +357,7 @@ macro_rules! register {
// to avoid it being interpreted in place of the relative register array alias rule.
($name:ident => $alias:ident [ $idx:expr ] $(, $comment:literal)? { $($fields:tt)* }) => {
static_assert!($idx < $alias::SIZE);
- bitfield!(struct $name $(, $comment)? { $($fields)* } );
+ bitfield!(struct $name: u32 $(, $comment)? { $($fields)* } );
register!(@io_fixed $name @ $alias::OFFSET + $idx * $alias::STRIDE );
};

--
2.34.1