jinxiuxu opened a new pull request, #21108:
URL: https://github.com/apache/nuttx/pull/21108
## Summary
This series adds a Linux-style DMA-BUF framework and a system heap allocator
to NuttX.
### 1. drivers/dma-buf: add DMA-BUF framework
* Shared buffer objects with fd-based export/import
* Userspace uAPI close to Linux (`DMA_BUF_IOCTL_SYNC`, `DMA_BUF_SET_NAME`)
* Atomic refcounting; `close()` drops the reference
* `mmap()` holds a reference for the lifetime of the mapping so the buffer
cannot be released while the mapping is still valid
### 2. drivers/dma-buf: add system heap allocator
* `/dev/dma_heap/system` with `DMA_BUF_HEAP_IOCTL_ALLOC` (Linux dma-heap
model)
* 32-byte aligned payloads for DMA-capable importers
* Device-mapped CPU access brackets dcache invalidate/flush
* On flat / non-addrenv builds, the CPU virtual address is used as the DMA
address
## Testing
On `sim:nsh` with `CONFIG_DMABUF_HEAPS=y`:
```
nsh> ls /dev/dma_heap
/dev/dma_heap:
system
nsh> dmabuf_test
ALLOC ok fd=4 len=4096
MMAP close-while-mapped ok
SYNC ok
dmabuf_test PASSED
```
`tools/checkpatch.sh -f` passes for all new files.
The smoke test covers ALLOC, mmap, close-while-mapped refcounting, and
`DMA_BUF_IOCTL_SYNC`.
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