Re: [PATCH v4 1/6] nova-core: bitfield: Move bitfield-specific code from register! into new macro

Alexandre Courbot
2025-09-29T06:17:02Z

On Sun Sep 21, 2025 at 3:22 AM JST, Joel Fernandes wrote:
> The bitfield-specific into new macro. This will be used to define
> structs with bitfields, similar to C language.
>
> Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>
> Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>

Very clean. One nit remains below, in any case:

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>

> ---
> drivers/gpu/nova-core/bitfield.rs | 314 +++++++++++++++++++++++++++
> drivers/gpu/nova-core/nova_core.rs | 3 +
> drivers/gpu/nova-core/regs/macros.rs | 259 +---------------------
> 3 files changed, 327 insertions(+), 249 deletions(-)
> create mode 100644 drivers/gpu/nova-core/bitfield.rs
>
> diff --git a/drivers/gpu/nova-core/bitfield.rs b/drivers/gpu/nova-core/bitfield.rs
> new file mode 100644
> index 000000000000..ba6b7caa05d9
> --- /dev/null
> +++ b/drivers/gpu/nova-core/bitfield.rs
> @@ -0,0 +1,314 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Bitfield library for Rust structures
> +//!
> +//! Support for defining bitfields in Rust structures. Also used by the [`register!`] macro.
> +//!
> +//! # Syntax
> +//!
> +//! ```rust
> +//! #[derive(Debug, Clone, Copy)]
> +//! enum Mode {
> +//! Low = 0,
> +//! High = 1,
> +//! Auto = 2,
> +//! }
> +//!
> +//! impl TryFrom<u8> for Mode {
> +//! type Error = u8;
> +//! fn try_from(value: u8) -> Result<Self, Self::Error> {
> +//! match value {
> +//! 0 => Ok(Mode::Low),
> +//! 1 => Ok(Mode::High),
> +//! 2 => Ok(Mode::Auto),
> +//! _ => Err(value),
> +//! }
> +//! }
> +//! }
> +//!
> +//! impl From<Mode> for u32 {
> +//! fn from(mode: Mode) -> u32 {
> +//! mode as u32
> +//! }
> +//! }

Jesung's `TryFrom` and `Into` derive macros [1] would be greatly useful
here, I hope we can merge them soon.

[1] https://lore.kernel.org/all/cover.1755235180.git.y.j3ms.n@gmail.com/

> +//!
> +//! #[derive(Debug, Clone, Copy)]
> +//! enum State {
> +//! Inactive = 0,
> +//! Active = 1,
> +//! }
> +//!
> +//! impl From<bool> for State {
> +//! fn from(value: bool) -> Self {
> +//! if value { State::Active } else { State::Inactive }
> +//! }
> +//! }
> +//!
> +//! impl From<State> for u32 {
> +//! fn from(state: State) -> u32 {
> +//! state as u32
> +//! }
> +//! }
> +//!
> +//! bitfield! {
> +//! struct ControlReg {
> +//! 3:0 mode as u8 ?=> Mode;
> +//! 7 state as bool => State;
> +//! }
> +//! }
> +//! ```
> +//!
> +//! This generates a struct with:
> +//! - Field accessors: `mode()`, `state()`, etc.
> +//! - Field setters: `set_mode()`, `set_state()`, etc. (supports chaining with builder pattern).
> +//! - Debug and Default implementations
> +//!
> +//! The field setters can be used with the builder pattern, example:
> +//! ControlReg::default().set_mode(mode).set_state(state);

Missing code block for the example?