Claude review: dma-buf: heaps: Turn heaps into modules

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Overall Series Review

Subject: dma-buf: heaps: Turn heaps into modules
Author: Maxime Ripard <mripard@kernel.org>
Patches: 9
Reviewed: 2026-03-04T07:41:35.266050

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**Author**: Maxime Ripard <mripard@kernel.org>
**Series**: dma-buf: heaps: Turn heaps into modules (v3, 8 patches)

This series enables the CMA and system dma-buf heaps to be compiled as loadable modules (tristate). The approach is well-structured: patches 1-6 prepare the prerequisites (inverting the CMA registration logic, exporting necessary symbols), and patches 7-8 make the actual `bool` → `tristate` Kconfig changes.

The overall design is sound. Inverting the registration so the heap queries the contiguous DMA code (rather than the contiguous code calling into the heap) is the right way to break the built-in → module dependency. The patches are generally well-separated with clear commit messages.

**However, there is a build-breaking bug:** patch 1 removes the `dma_heap_cma_register_heap()` function definition from `cma_heap.c`, but the call site at `kernel/dma/contiguous.c:276` and the header declaration in `include/linux/dma-buf/heaps/cma.h` are left behind. This causes a **link error** when `CONFIG_DMABUF_HEAPS_CMA=y`. Details below.

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