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

Joel Fernandes
2025-09-29T19:36:15Z

On 9/29/2025 8:16 AM, Alexandre Courbot wrote:
> 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>

Thanks.

>
>> ---
>> 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/

Ah nice, looking forward to it!!

>
>> +//!
>> +//! #[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?
>

Ah, sure, I will add the setter into an example as well.

- Joel