tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
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linux
1.. SPDX-License-Identifier: GPL-2.0
2
3==============================
4Allocating dma-buf using heaps
5==============================
6
7Dma-buf Heaps are a way for userspace to allocate dma-buf objects. They are
8typically used to allocate buffers from a specific allocation pool, or to share
9buffers across frameworks.
10
11Heaps
12=====
13
14A heap represents a specific allocator. The Linux kernel currently supports the
15following heaps:
16
17 - The ``system`` heap allocates virtually contiguous, cacheable, buffers.
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``.