Re: [Linaro-mm-sig] [PATCH v3 1/2] habanalabs: define uAPI to export FD for DMA-BUF

[Oded Gabbay <oded.gabbay@gmail.com>]

On Tue, Jun 22, 2021 at 6:31 PM Christian König
<christian.koenig@amd.com> wrote:
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> Am 22.06.21 um 17:28 schrieb Jason Gunthorpe:
> > On Tue, Jun 22, 2021 at 05:24:08PM +0200, Christian König wrote:
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> >>>> I will take two GAUDI devices and use one as an exporter and one as an
> >>>> importer. I want to see that the solution works end-to-end, with real
> >>>> device DMA from importer to exporter.
> >>> I can tell you it doesn't. Stuffing physical addresses directly into
> >>> the sg list doesn't involve any of the IOMMU code so any configuration
> >>> that requires IOMMU page table setup will not work.
> >> Sure it does. See amdgpu_vram_mgr_alloc_sgt:
> >>
> >>          amdgpu_res_first(res, offset, length, &cursor);
> >           ^^^^^^^^^^
> >
> > I'm not talking about the AMD driver, I'm talking about this patch.
> >
> > +             bar_address = hdev->dram_pci_bar_start +
> > +                             (pages[cur_page] - prop->dram_base_address);
> > +             sg_dma_address(sg) = bar_address;
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> Yeah, that is indeed not working.
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> Oded you need to use dma_map_resource() for this.
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> Christian.
Yes, of course.
But will it be enough ?
Jason said that supporting IOMMU isn't nice when we don't have struct pages.
I fail to understand the connection, I need to dig into this.

Oded

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