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doc: dma-buf: List the heaps by name

Since we're going to introduce multiple instances of the CMA heap
driver, there's no single CMA heap anymore.

Let's use the heap name instead to differentiate between all the heaps
available in the system.

While we're at it, let's also rework the backward compatibility part to
make it easier to amend later on.

Reviewed-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
[sumits: rebased to latest Doc]
Link: https://lore.kernel.org/r/20251013-dma-buf-ecc-heap-v8-1-04ce150ea3d9@kernel.org

authored by

Maxime Ripard and committed by
Sumit Semwal 2034134d 7910d693

+12 -10
+12 -10
Documentation/userspace-api/dma-buf-heaps.rst
··· 16 16 17 17 - The ``system`` heap allocates virtually contiguous, cacheable, buffers. 18 18 19 - - The ``cma`` heap allocates physically contiguous, cacheable, 20 - buffers. Only present if a CMA region is present. Such a region is 21 - usually created either through the kernel commandline through the 22 - ``cma`` parameter, a memory region Device-Tree node with the 23 - ``linux,cma-default`` property set, or through the ``CMA_SIZE_MBYTES`` or 24 - ``CMA_SIZE_PERCENTAGE`` Kconfig options. The heap's name in devtmpfs is 25 - ``default_cma_region``. For backwards compatibility, when the 26 - ``DMABUF_HEAPS_CMA_LEGACY`` Kconfig option is set, a duplicate node is 27 - created following legacy naming conventions; the legacy name might be 28 - ``reserved``, ``linux,cma``, or ``default-pool``. 19 + - The ``default_cma_region`` heap allocates physically contiguous, 20 + cacheable, buffers. Only present if a CMA region is present. Such a 21 + region is usually created either through the kernel commandline 22 + through the ``cma`` parameter, a memory region Device-Tree node with 23 + the ``linux,cma-default`` property set, or through the 24 + ``CMA_SIZE_MBYTES`` or ``CMA_SIZE_PERCENTAGE`` Kconfig options. Prior 25 + to Linux 6.17, its name wasn't stable and could be called 26 + ``reserved``, ``linux,cma``, or ``default-pool``, depending on the 27 + platform. From Linux 6.17 onwards, the creation of these heaps is 28 + controlled through the ``DMABUF_HEAPS_CMA_LEGACY`` Kconfig option for 29 + backwards compatibility. 30 + 29 31 Naming Convention 30 32 ================= 31 33