DMA-buf and uncached system memory

[Rob Clark]

On Mon, Feb 15, 2021 at 12:58 AM Christian König
<christian.koenig at amd.com> wrote:
>
> Hi guys,
>
> we are currently working an Freesync and direct scan out from system
> memory on AMD APUs in A+A laptops.
>
> On problem we stumbled over is that our display hardware needs to scan
> out from uncached system memory and we currently don't have a way to
> communicate that through DMA-buf.
>
> For our specific use case at hand we are going to implement something
> driver specific, but the question is should we have something more
> generic for this?

I'm a bit late to this party (and sorry, I didn't read the entire
thread), but it occurs to me that dmabuf mmap_info[1] would also get
you what you need, ie. display importing dma-buf could check whether
the exporter is mapping cached or not, and reject the import if
needed?

[1] https://patchwork.freedesktop.org/patch/496069/?series=106847&rev=2

> After all the system memory access pattern is a PCIe extension and as
> such something generic.
>
> Regards,
> Christian.
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