| .. 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``. |
