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``. 29