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 18:31:04 +0300
From:   Oded Gabbay <oded.gabbay@...il.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Christian König <christian.koenig@....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 6:28 PM Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> 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
Yes, you are correct of course, but what will happen Jason, If I will
add a call to dma_map_resource() like Christian said ?
Won't that solve that specific issue ?
That's why I want to try it...

Oded