Claude review: rust: auxiliary: replace drvdata() with registration data

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Overall Series Review

Subject: rust: auxiliary: replace drvdata() with registration data
Author: Danilo Krummrich <dakr@kernel.org>
Patches: 4
Reviewed: 2026-04-28T13:51:40.253354

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This is a well-designed 2-patch series that replaces the general-purpose `drvdata()` mechanism for inter-driver data sharing with a purpose-built `registration_data` pointer on `struct auxiliary_device`. The architectural rationale is sound: by tying the shared data to the auxiliary device registration rather than the parent driver's drvdata, the lifetime constraints become structural (enforced by the type system and drop ordering) rather than conventional.

The `TypeId`-based runtime type checking via a `#[repr(C)]` wrapper is a clean pattern that preserves memory safety while allowing type-erased storage in the C struct. The drop ordering in `Registration::drop()` — delete device first (unbinding the child), then free data, then uninit — correctly ensures no concurrent access to the registration data after it's freed.

The series is correct and clean. I have a few minor observations but no blocking issues.

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