linux-kernel - Re: [PATCH v2 4/4] rust: Move register and bitstruct macros out of Nova

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Message-ID: <a2c990ff-e05c-4d09-aaeb-5a2fc16ecb77@nvidia.com>
Date: Mon, 8 Sep 2025 13:06:12 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 dakr@...nel.org, acourbot@...dia.com, 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 4/4] rust: Move register and bitstruct macros out of
 Nova



On 9/7/2025 2:14 PM, Miguel Ojeda wrote:
> Hi Joel,
> 
> I didn't check the macros, but a couple nits I noticed in this patch
> in particular given it moved it to `kernel`...
> 
> On Wed, Sep 3, 2025 at 11:54 PM Joel Fernandes <joelagnelf@...dia.com> wrote:
>>
>> +//! A library that provides support for defining bit fields in Rust
> 
> What about just "Support for defining bit fields in ..." or similar?
> 
>> +//! structures. Also used from things that need bitfields like register macro.

Ok, I changed it to:
"Also used from things that need bitfields like [`register!`] macro." for next
revision.

> 
> The "register macro" part sounds like it should be formatted with
> Markdown plus an intra-doc link.
> 
>> -            ::kernel::build_assert!(
>> +            build_assert!(
> 
> Is this path unqualified for some reason? Does it mean the user needs
> to have imported the prelude?

Yes, for register macro importing prelude is required (I commented more below).

> 
>> +pub use super::{bitstruct, register};
> 
> Please justify in the commit message why we want them in the prelude,
> e.g. are they expected to be common? Does it simplify some code? etc.
> 
The issue I ran into is, without adding it to prelude, the users of register!
macro will have to import both bitfield! and register! macros explictly, even
though they're only using register!. I tried to make it work without adding to
prelude, but couldn't:

  use kernel::{bitfield, register};

Also not adding it to prelude, means register! macro has to invoke bitfield with
$crate prefixed  ($crate::bitfield).

I think the prelude-way is clean, but let me know if there's any other trick I
can try.

I will also add this rationale to the commit message as you suggested.

Thanks!

 - Joel