[PATCH v5 0/2] dma-buf: heaps: Support carved-out heaps

Maxime Ripard
2025-06-17T12:25:49Z

Hi,

This series is the follow-up of the discussion that John and I had some
time ago here:

https://lore.kernel.org/all/CANDhNCquJn6bH3KxKf65BWiTYLVqSd9892-xtFDHHqqyrroCMQ@mail.gmail.com/

The initial problem we were discussing was that I'm currently working on
a platform which has a memory layout with ECC enabled. However, enabling
the ECC has a number of drawbacks on that platform: lower performance,
increased memory usage, etc. So for things like framebuffers, the
trade-off isn't great and thus there's a memory region with ECC disabled
to allocate from for such use cases.

After a suggestion from John, I chose to first start using heap
allocations flags to allow for userspace to ask for a particular ECC
setup. This is then backed by a new heap type that runs from reserved
memory chunks flagged as such, and the existing DT properties to specify
the ECC properties.

After further discussion, it was considered that flags were not the
right solution, and relying on the names of the heaps would be enough to
let userspace know the kind of buffer it deals with.

Thus, even though the uAPI part of it has been dropped in this second
version, we still need a driver to create heaps out of carved-out memory
regions. In addition to the original usecase, a similar driver can be
found in BSPs from most vendors, so I believe it would be a useful
addition to the kernel.

Let me know what you think,
Maxime

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
Changes in v5:
- Rebased on 6.16-rc2
- Switch from property to dedicated binding
- Link to v4: https://lore.kernel.org/r/20250520-dma-buf-ecc-heap-v4-1-bd2e1f1bb42c@kernel.org

Changes in v4:
- Rebased on 6.15-rc7
- Map buffers only when map is actually called, not at allocation time
- Deal with restricted-dma-pool and shared-dma-pool
- Reword Kconfig options
- Properly report dma_map_sgtable failures
- Link to v3: https://lore.kernel.org/r/20250407-dma-buf-ecc-heap-v3-0-97cdd36a5f29@kernel.org

Changes in v3:
- Reworked global variable patch
- Link to v2: https://lore.kernel.org/r/20250401-dma-buf-ecc-heap-v2-0-043fd006a1af@kernel.org

Changes in v2:
- Add vmap/vunmap operations
- Drop ECC flags uapi
- Rebase on top of 6.14
- Link to v1: https://lore.kernel.org/r/20240515-dma-buf-ecc-heap-v1-0-54cbbd049511@kernel.org

---
Maxime Ripard (2):
dt-bindings: reserved-memory: Introduce carved-out memory region binding
dma-buf: heaps: Introduce a new heap for reserved memory

.../bindings/reserved-memory/carved-out.yaml | 49 +++
drivers/dma-buf/heaps/Kconfig | 8 +
drivers/dma-buf/heaps/Makefile | 1 +
drivers/dma-buf/heaps/carveout_heap.c | 362 +++++++++++++++++++++
4 files changed, 420 insertions(+)
---
base-commit: d076bed8cb108ba2236d4d49c92303fda4036893
change-id: 20240515-dma-buf-ecc-heap-28a311d2c94e

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