Re: [PATCH RFC 06/12] dma: direct: Provide accessor to dmem region

Maxime Ripard
2025-03-10T16:28:29Z

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On Mon, Mar 10, 2025 at 02:56:37PM +0000, Robin Murphy wrote:
> On 2025-03-10 12:06 pm, Maxime Ripard wrote:
> > Consumers of the direct DMA API will have to know which region their
> > device allocate from in order for them to charge the memory allocation
> > in the right one.
>
> This doesn't seem to make much sense - dma-direct is not an allocator
> itself, it just provides the high-level dma_alloc_attrs/dma_alloc_pages/etc.
> interfaces wherein the underlying allocations _could_ come from CMA, but
> also a per-device coherent/restricted pool, or a global coherent/atomic
> pool, or the regular page allocator, or in one weird corner case the SWIOTLB
> buffer, or...

I guess it wasn't super clear, but what I meant is that it's an
allocator to the consumer: it gets called, and returns a buffer. How it
does so is transparent to the device, and on the other side of the
abstraction.

I do agree that the logic is complicated to follow, and that's what I
was getting at in the cover letter.

Maxime

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