[PATCH v4 0/8] dma-buf: heaps: Turn heaps into modules

Maxime Ripard
2026-03-31T10:00:25Z

Hi,

The recent introduction of heaps in the optee driver [1] made possible
the creation of heaps as modules.

It's generally a good idea if possible, including for the already
existing system and CMA heaps.

The system one is pretty trivial, the CMA one is a bit more involved,
especially since we have a call from kernel/dma/contiguous.c to the CMA
heap code. This was solved by turning the logic around and making the
CMA heap call into the contiguous DMA code.

Let me know what you think,
Maxime

1: https://lore.kernel.org/dri-devel/20250911135007.1275833-4-jens.wiklander@linaro.org/

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
Changes in v4:
- Fix compilation failure
- Rework to take into account OF_RESERVED_MEM
- Fix regression making the default CMA area disappear if not created
through the DT
- Added some documentation and comments
- Link to v3: https://lore.kernel.org/r/20260303-dma-buf-heaps-as-modules-v3-0-24344812c707@kernel.org

Changes in v3:
- Squashed cma_get_name and cma_alloc/release patches
- Fixed typo in Export dev_get_cma_area commit title
- Fixed compilation failure with DMA_CMA but not OF_RESERVED_MEM
- Link to v2: https://lore.kernel.org/r/20260227-dma-buf-heaps-as-modules-v2-0-454aee7e06cc@kernel.org

Changes in v2:
- Collect tags
- Don't export dma_contiguous_default_area anymore, but export
dev_get_cma_area instead
- Mentioned that heap modules can't be removed
- Link to v1: https://lore.kernel.org/r/20260225-dma-buf-heaps-as-modules-v1-0-2109225a090d@kernel.org

---
Maxime Ripard (8):
dma: contiguous: Turn heap registration logic around
dma: contiguous: Make dev_get_cma_area() a proper function
dma: contiguous: Make dma_contiguous_default_area static
dma: contiguous: Export dev_get_cma_area()
mm: cma: Export cma_alloc(), cma_release() and cma_get_name()
dma-buf: heaps: Export mem_accounting parameter
dma-buf: heaps: cma: Turn the heap into a module
dma-buf: heaps: system: Turn the heap into a module

drivers/dma-buf/dma-heap.c | 1 +
drivers/dma-buf/heaps/Kconfig | 4 +--
drivers/dma-buf/heaps/cma_heap.c | 22 +++----------
drivers/dma-buf/heaps/system_heap.c | 5 +++
include/linux/dma-buf/heaps/cma.h | 16 ---------
include/linux/dma-map-ops.h | 14 ++++----
kernel/dma/contiguous.c | 66 +++++++++++++++++++++++++++++++++----
mm/cma.c | 3 ++
8 files changed, 82 insertions(+), 49 deletions(-)
---
base-commit: c081b71f11732ad2c443f170ab19c3ebe8a1a422
change-id: 20260225-dma-buf-heaps-as-modules-1034b3ec9f2a

Best regards,
--
Maxime Ripard <mripard@kernel.org>