.. SPDX-License-Identifier: GPL-2.0

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Allocating dma-buf using heaps
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Dma-buf Heaps are a way for userspace to allocate dma-buf objects. They are
typically used to allocate buffers from a specific allocation pool, or to share
buffers across frameworks.

Heaps
=====

A heap represents a specific allocator. The Linux kernel currently supports the
following heaps:

 - The ``system`` heap allocates virtually contiguous, cacheable, buffers.

 - The ``default_cma_region`` heap allocates physically contiguous,
   cacheable, buffers. Only present if a CMA region is present. Such a
   region is usually created either through the kernel commandline
   through the ``cma`` parameter, a memory region Device-Tree node with
   the ``linux,cma-default`` property set, or through the
   ``CMA_SIZE_MBYTES`` or ``CMA_SIZE_PERCENTAGE`` Kconfig options. Prior
   to Linux 6.17, its name wasn't stable and could be called
   ``reserved``, ``linux,cma``, or ``default-pool``, depending on the
   platform.

 - A heap will be created for each reusable region in the device tree
   with the ``shared-dma-pool`` compatible, using the full device tree
   node name as its name. The buffer semantics are identical to
   ``default-cma-region``.

Naming Convention