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.