linux-kernel - Re: [PATCH v2 3/4] nova-core: bitstruct: Add support for custom visiblity

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Message-Id: <DCN3UXK0EQ1Q.KWGM7NKTCS13@nvidia.com>
Date: Mon, 08 Sep 2025 12:40:17 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Joel Fernandes" <joelagnelf@...dia.com>,
 <linux-kernel@...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>,
 "Daniel Almeida" <daniel.almeida@...labora.com>,
 <nouveau@...ts.freedesktop.org>, <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] nova-core: bitstruct: Add support for custom
 visiblity

On Thu Sep 4, 2025 at 6:54 AM JST, Joel Fernandes wrote:
> Add support for custom visiblity to allow for users to control visibility
> of the structure and helpers.
>
> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
> ---
>  drivers/gpu/nova-core/bitstruct.rs   | 46 ++++++++++++++--------------
>  drivers/gpu/nova-core/regs/macros.rs | 16 +++++-----
>  2 files changed, 31 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/bitstruct.rs b/drivers/gpu/nova-core/bitstruct.rs
> index 068334c86981..1047c5c17e2d 100644
> --- a/drivers/gpu/nova-core/bitstruct.rs
> +++ b/drivers/gpu/nova-core/bitstruct.rs
> @@ -9,7 +9,7 @@
>  ///
>  /// ```rust
>  /// bitstruct! {
> -///     struct ControlReg: u32 {
> +///     pub struct ControlReg: u32 {
>  ///         3:0       mode        as u8 ?=> Mode;
>  ///         7:4       state       as u8 => State;
>  ///     }

Maybe mention in the documentation that the field accessors are given
the same visibility as the type - otherwise one might be led into
thinking that they can specify visibility for individual fields as well
(I'm wondering whether we might ever want that in the future?).

> @@ -34,21 +34,21 @@
>  ///   and returns the result. This is useful with fields for which not all values are valid.
>  macro_rules! bitstruct {
>      // Main entry point - defines the bitfield struct with fields
> -    (struct $name:ident : $storage:ty $(, $comment:literal)? { $($fields:tt)* }) => {
> -        bitstruct!(@core $name $storage $(, $comment)? { $($fields)* });
> +    ($vis:vis struct $name:ident : $storage:ty $(, $comment:literal)? { $($fields:tt)* }) => {
> +        bitstruct!(@core $name $vis $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 $storage:ty $(, $comment:literal)? { $($fields:tt)* }) => {
> +    (@core $name:ident $vis:vis $storage:ty $(, $comment:literal)? { $($fields:tt)* }) => {

Being very nitpicky here, but for consistency why not put `$vis` before
`$name` since it is the order they are given by the caller?

>          $(
>          #[doc=$comment]
>          )?
>          #[repr(transparent)]
>          #[derive(Clone, Copy)]
> -        pub(crate) struct $name($storage);
> +        $vis struct $name($vis $storage);

`$storage` should probably be kept private - we already have accessors
for it, and the visibility parameter is for the outer type, not its
internals.