Re: [PATCH v2 1/3] rust: extract `bitfield!` macro from `register!`

["Alexandre Courbot" <acourbot@nvidia.com>]

On Thu Apr 16, 2026 at 10:35 AM JST, Yury Norov wrote:
> On Thu, Apr 09, 2026 at 11:58:47PM +0900, Alexandre Courbot wrote:
>> Extract the bitfield-defining part of the `register!` macro into an
>> independent macro used to define bitfield types with bounds-checked
>> accessors.
>> 
>> Each field is represented as a `Bounded` of the appropriate bit width,
>> ensuring field values are never silently truncated.
>> 
>> Fields can optionally be converted to/from custom types, either fallibly
>> or infallibly.
>> 
>> Appropriate documentation is also added, and a MAINTAINERS entry created
>> for the new module.
>> 
>> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
>> ---
>>  MAINTAINERS                |   8 +
>>  rust/kernel/bitfield.rs    | 491 +++++++++++++++++++++++++++++++++++++++++++++
>>  rust/kernel/io/register.rs | 246 +----------------------
>>  rust/kernel/lib.rs         |   1 +
>>  4 files changed, 502 insertions(+), 244 deletions(-)
>> 
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index b01791963e25..77f2617ade5d 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -23186,6 +23186,14 @@ F:	scripts/*rust*
>>  F:	tools/testing/selftests/rust/
>>  K:	\b(?i:rust)\b
>>  
>> +RUST [BITFIELD]
>> +M:	Alexandre Courbot <acourbot@nvidia.com>
>> +M:	Joel Fernandes <joelagnelf@nvidia.com>
>> +R:	Yury Norov <yury.norov@gmail.com>
>> +L:	rust-for-linux@vger.kernel.org
>> +S:	Maintained
>> +F:	rust/kernel/bitfield.rs
>> +
>>  RUST [ALLOC]
>>  M:	Danilo Krummrich <dakr@kernel.org>
>>  R:	Lorenzo Stoakes <ljs@kernel.org>
>> diff --git a/rust/kernel/bitfield.rs b/rust/kernel/bitfield.rs
>> new file mode 100644
>> index 000000000000..f5948eec8a76
>> --- /dev/null
>> +++ b/rust/kernel/bitfield.rs
>> @@ -0,0 +1,491 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +//! Support for defining bitfields as Rust structures.
>> +//!
>> +//! The [`bitfield!`](kernel::bitfield!) macro declares integer types that are split into distinct
>> +//! bit fields of arbitrary length. Each field is typed using [`Bounded`](kernel::num::Bounded) to
>> +//! ensure values are properly validated and to avoid implicit data loss.
>> +//!
>> +//! # Example
>> +//!
>> +//! ```rust
>> +//! use kernel::bitfield;
>> +//! use kernel::num::Bounded;
>> +//!
>> +//! bitfield! {
>> +//!     pub struct Rgb(u16) {
>> +//!         15:11 blue;
>> +//!         10:5 green;
>> +//!         4:0 red;
>
> Hi Alex,
>
> Can you please describe those implied naming limitations we've
> discussed on the previous round, like with_blue, BLUE_SHIFT etc.
> in a separate top comment?

Yes, that was missing indeed. Added for v3.