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

[Christian König]

Am 22.06.21 um 17:28 schrieb Jason Gunthorpe:
> On Tue, Jun 22, 2021 at 05:24:08PM +0200, Christian König wrote:
>
>>>> 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;

Yeah, that is indeed not working.

Oded you need to use dma_map_resource() for this.

Christian.



>
> Jason