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

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Message-Id: <DD52CATR8C30.1SXPZH285XBPN@nvidia.com>
Date: Mon, 29 Sep 2025 15:16:55 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Joel Fernandes" <joelagnelf@...dia.com>,
 <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>,
 <dri-devel@...ts.freedesktop.org>, <dakr@...nel.org>, <acourbot@...dia.com>
Cc: "Alistair Popple" <apopple@...dia.com>, "Miguel Ojeda"
 <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun Feng"
 <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 <bjorn3_gh@...tonmail.com>, "Benno Lossin" <lossin@...nel.org>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>,
 "Trevor Gross" <tmgross@...ch.edu>, "David Airlie" <airlied@...il.com>,
 "Simona Vetter" <simona@...ll.ch>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>, "John Hubbard"
 <jhubbard@...dia.com>, "Timur Tabi" <ttabi@...dia.com>,
 <joel@...lfernandes.org>, "Elle Rhumsaa" <elle@...thered-steel.dev>, "Yury
 Norov" <yury.norov@...il.com>, "Daniel Almeida"
 <daniel.almeida@...labora.com>, <nouveau@...ts.freedesktop.org>
Subject: Re: [PATCH v4 1/6] nova-core: bitfield: Move bitfield-specific code
 from register! into new macro

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@...thered-steel.dev>
> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>

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

Reviewed-by: Alexandre Courbot <acourbot@...dia.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?