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

From: Jason Gunthorpe <jgg@ziepe.ca>
To: "Christian König" <christian.koenig@amd.com>
Cc: "Oded Gabbay" <oded.gabbay@gmail.com>,
	linux-rdma <linux-rdma@vger.kernel.org>,
	"Christian König" <ckoenig.leichtzumerken@gmail.com>,
	sleybo@amazon.com, "Gal Pressman" <galpress@amazon.com>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	"Christoph Hellwig" <hch@lst.de>,
	"moderated list:DMA BUFFER SHARING FRAMEWORK"
	<linaro-mm-sig@lists.linaro.org>,
	"Doug Ledford" <dledford@redhat.com>,
	"Tomer Tayar" <ttayar@habana.ai>,
	"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
	"Greg KH" <gregkh@linuxfoundation.org>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Leon Romanovsky" <leonro@nvidia.com>,
	"Oded Gabbay" <ogabbay@kernel.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"open list:DMA BUFFER SHARING FRAMEWORK"
	<linux-media@vger.kernel.org>
Subject: Re: [Linaro-mm-sig] [PATCH v3 1/2] habanalabs: define uAPI to export FD for DMA-BUF
Date: Tue, 22 Jun 2021 12:28:27 -0300	[thread overview]
Message-ID: <20210622152827.GQ1096940@ziepe.ca> (raw)
In-Reply-To: <4a37216d-7c4c-081e-3325-82466f30b6eb@amd.com>

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;

Jason
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