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

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Date:   Tue, 22 Jun 2021 12:28:27 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Christian König <christian.koenig@....com>
Cc:     Oded Gabbay <oded.gabbay@...il.com>,
        Christian König <ckoenig.leichtzumerken@...il.com>,
        Gal Pressman <galpress@...zon.com>, sleybo@...zon.com,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Oded Gabbay <ogabbay@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        Doug Ledford <dledford@...hat.com>,
        Tomer Tayar <ttayar@...ana.ai>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Alex Deucher <alexander.deucher@....com>,
        Leon Romanovsky <leonro@...dia.com>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>
Subject: Re: [Linaro-mm-sig] [PATCH v3 1/2] habanalabs: define uAPI to export
 FD for DMA-BUF

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