.. SPDX-License-Identifier: GPL-2.0
==============================
Allocating dma-buf using heaps
==============================
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 ``cma`` 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. The heap's name in devtmpfs is
``default_cma_region``. For backwards compatibility, when the
``DMABUF_HEAPS_CMA_LEGACY`` Kconfig option is set, a duplicate node is
created following legacy naming conventions; the legacy name might be
``reserved``, ``linux,cma``, or ``default-pool``.
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