This adds support for allocating DMA buffers on systems that support it,
i.e. Linux and Android.
On mainline Linux, starting version 5.6 (equivalent to Android 12),
there is a new kernel module framework available called [DMA-BUF
Heaps](https://github.com/torvalds/linux/blob/master/drivers/dma-buf/dma-heap.c).
The goal of this framework is to provide a standardised way for user
applications to allocate and share memory buffers between different
devices, subsystems, etc. The main feature of interest is that the
framework provides device-agnostic allocation; it abstracts away the
underlying hardware, and provides a single IOCTL,
`DMA_HEAP_IOCTL_ALLOC`. Mainline implementation provides two heaps that
act as character devices that can allocate DMA buffers; system, which
uses the buddy allocator, and cma, which uses the
[CMA](https://developer.toradex.com/software/linux-resources/linux-features/contiguous-memory-allocator-cma-linux/)
(Contiguous Memory Allocator). Both of these are [kernel configuration
options](https://github.com/torvalds/linux/blob/master/drivers/dma-buf/heaps/Kconfig)
that need to be enabled when building the Linux kernel. Generally, any
kernel module implementing this framework is made available under
/dev/dma_heaps/<heap_name>, e.g. /dev/dma_heaps/system.
The implementation currently only supports one type of DMA heaps;
`system`, the default device path for which is `/dev/dma_heap/system`.
The path can be overridden at runtime using an environment variable,
`OCL_CTS_DMA_HEAP_PATH_SYSTEM`, if needed. Extending this in the future
should be trivial (subject to platform support), by adding an entry to
the enum `dma_buf_heap_type`, and an appropriate default path and
overriding environment variable name.
The proposed implementation will conditionally compile if the conditions
are met (i.e. building for Linux or Android, using kernel headers >=
5.6.0), and will provide a compile-time warning otherwise, and return
`-1` as the DMA handle in runtime if not.
To demonstrate the functionality, a new test is added for the
`cl_khr_external_memory_dma_buf` extension. If the extension is
supported by the device, a DMA buffer will be allocated and used to
create a CL buffer, that is then used by a simple kernel.
This should provide a way forward for adding more tests that depend on
DMA buffers.
---------
Signed-off-by: Gorazd Sumkovski <gorazd.sumkovski@arm.com>
Signed-off-by: Ahmed Hesham <ahmed.hesham@arm.com>
Co-authored-by: Gorazd Sumkovski <gorazd.sumkovski@arm.com>
