[Intel-gfx] [PATCH] drm/i915/gem: Allow importing of shmemfs objects into any device

[Chris Wilson]

Quoting Chris Wilson (2021-01-20 18:06:08)
> Quoting Matthew Auld (2021-01-20 17:46:10)
> > On Wed, 20 Jan 2021 at 15:40, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > >
> > > If we import a shmemfs object between devices, for example from
> > > Tigerlake to DG1, we can simply reuse the native object and its backing
> > > store.
> > 
> > Hmmm interesting, so does that include re-using the actual sg mapping
> > for the backing pages? Does that work out-of-the-box between different
> > devices assuming we have iommu enabled?
> 
> Indeed interesting; the dma_addr_t are supposed to be local to a device.

On reflection, we are expected to use cross-device dma_addr_t with
dma-buf. It's the exporter who assigns the dma_addr_t for the importer
to use, and they are always given from the original device.

Maybe not so bad. Definitely needs testing to see what happens in
practice.
-Chris