Re: [PATCH v6 4/5] dma-buf: heaps: Add CMA heap to dmabuf heaps

[Christoph Hellwig]

On Thu, Jul 25, 2019 at 09:31:50AM -0400, Andrew F. Davis wrote:
> But that's just it, dma-buf does not assume buffers are backed by normal
> kernel managed memory, it is up to the buffer exporter where and when to
> allocate the memory. The memory backed by this SRAM buffer does not have
> the normal struct page backing. So moving the map, sync, etc functions
> to common code would fail for this and many other heap types. This was a
> major problem with Ion that prompted this new design.

The code clearly shows it has page backing, e.g. this:

+	sg_set_page(table->sgl, pfn_to_page(PFN_DOWN(buffer->paddr)), buffer->len, 0);

and the fact that it (and the dma-buf API) uses scatterlists, which 
requires pages.