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: <ae415df8-612b-4850-9749-660ae8629b1c@nvidia.com>
Date: Mon, 29 Sep 2025 15:36:09 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: Alexandre Courbot <acourbot@...dia.com>, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 dakr@...nel.org
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 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@...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>

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