On Wed, Apr 23, 2025, at 22:41, Ben Collins wrote:
> On Wed, Apr 23, 2025 at 03:49:16PM -0500, Arnd Bergmann wrote:
>> Looking at the current code I don't see that any more, so it's
>> possible that now any DMA is allowed even if there is no
>> dma-ranges property at all.
>
> It's still there. It hardcodes zone_dma_limit to 31-bits:
>
> arch/powerpc/mm/mem.c: paging_init()
>
> I'm digging into this more. I'll check back when I have a better
> understanding.
zone_dma_limit is the other side of this: you need a ZONE_DMA
and/or ZONE_DMA32 memory zone that lets a driver allocate buffers
from low addresses if the DMA mask is smaller than the available
memory.
Arnd
