Claude review: rust: add `bitfield!` macro

[Claude Code Review Bot <claude-review@example.com>]

Overall Series Review

Subject: rust: add `bitfield!` macro
Author: Alexandre Courbot <acourbot@nvidia.com>
Patches: 4
Reviewed: 2026-04-12T11:27:05.511057

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This is a well-structured 3-patch series that extracts the `bitfield!` macro from the `register!` macro in the Rust kernel infrastructure, making it available as a standalone, reusable module. The work is motivated by enabling dependencies from other subsystems (notably the Nova MM series) and is a clean factoring that doesn't introduce any fundamentally new abstractions.

**Strengths:**
- Comprehensive, high-quality documentation with examples covering all usage patterns (plain fields, infallible `=>`, fallible `?=>` conversions)
- The `Bounded` type provides compile-time safety for field values, preventing silent truncation
- Thorough KUnit test coverage across all storage types (u8, u16, u64)
- Clean migration of the nova-core consumer
- The `register!` macro properly delegates to `bitfield!` rather than duplicating code

**Minor concerns:**
- MAINTAINERS entry placement is not alphabetically sorted (BITFIELD before ALLOC)
- No overlap detection between fields -- this is a design choice but should be documented
- The old nova-core `Default` impl is dropped (only `Zeroable` is provided now), which is a subtle behavioral difference worth mentioning in the commit message

Overall: **The series looks good for merging with minor nits.**

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Generated by Claude Code Patch Reviewer