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The CMA heap's name in devtmpfs can vary depending on how the heap is defined. Its name defaults to "reserved", but if a CMA area is defined in the devicetree, the heap takes on the devicetree node's name, such as "default-pool" or "linux,cma". To simplify naming, unconditionally name it "default_cma_region", but keep a legacy node in place backed by the same underlying allocator for backwards compatibility. Reviewed-by: Maxime Ripard <mripard@kernel.org> Signed-off-by: Jared Kangas <jkangas@redhat.com> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org> Link: https://lore.kernel.org/r/20250610131231.1724627-4-jkangas@redhat.com
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29 lines
1.2 KiB
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.. SPDX-License-Identifier: GPL-2.0
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==============================
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Allocating dma-buf using heaps
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==============================
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Dma-buf Heaps are a way for userspace to allocate dma-buf objects. They are
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typically used to allocate buffers from a specific allocation pool, or to share
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buffers across frameworks.
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Heaps
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=====
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A heap represents a specific allocator. The Linux kernel currently supports the
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following heaps:
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- The ``system`` heap allocates virtually contiguous, cacheable, buffers.
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- The ``cma`` heap allocates physically contiguous, cacheable,
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buffers. Only present if a CMA region is present. Such a region is
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usually created either through the kernel commandline through the
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``cma`` parameter, a memory region Device-Tree node with the
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``linux,cma-default`` property set, or through the ``CMA_SIZE_MBYTES`` or
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``CMA_SIZE_PERCENTAGE`` Kconfig options. The heap's name in devtmpfs is
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``default_cma_region``. For backwards compatibility, when the
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``DMABUF_HEAPS_CMA_LEGACY`` Kconfig option is set, a duplicate node is
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created following legacy naming conventions; the legacy name might be
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``reserved``, ``linux,cma``, or ``default-pool``.
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