[RPi5] How to Allocate DMA-Safe Memory and Perform VA↔PA Translation in Zephyr

[sb-cho]

I'm working on Raspberry Pi 5 using base Zephyr (no custom drivers), and I'm facing two fundamental challenges when trying to use DMA memory:

Questions

1. How can I allocate DMA-safe memory in Zephyr that:

Is guaranteed to be in a DMA-safe physical region (e.g., 0x40000000–0x80000000 on RPi5)?
Is non-cacheable or cache-coherent (as required by DMA engines)?

2. How can I perform address translation (VA → PA and PA → VA) for this DMA-safe memory?

There is no public API such as arch_mem_va_to_pa() or arch_mem_pa_to_va() in AArch64
In practice, it's often necessary to get the physical address to program a DMA engine, or map a PA buffer returned from a device

What I've tried

1. DTS reserved-memory at 0x40000000 using shared-dma-pool and zephyr,memory-region
2. Allocation via K_HEAP_DEFINE() in a custom section
3. Custom linker file to map .nocache_heap to desired memory
4. Zephyr APIs like k_heap_aligned_alloc, etc.
5. DEVICE_MMIO_MAP in the device driver

Environment

1. Raspberrypi_5
2. Zephyr OS build v4.1.0-6181
3. Modified samples/hello_world to have K_HEAP_DEFINE and k_heap_aligned_alloc

Test result
allocated memory addresses with k_heap_aligned_alloc from here
.nocache_heap 0x000000000021f940 0x400 .nocache_heap 0x000000000021f940 0x400 app/libapp.a(main.c.obj)

[sb-cho]

For the memory translation, I tried to use sys_mm_drv_page_phys_get, but I got a linking error for the RPI_5.