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

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Message-ID: <CAFCwf13w74qFDchEsdCAtpOvnYkzvcsU0RAdBLNGJq-e5srfHA@mail.gmail.com>
Date:   Tue, 22 Jun 2021 18:40:44 +0300
From:   Oded Gabbay <oded.gabbay@...il.com>
To:     Christian König <christian.koenig@....com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        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 6:31 PM Christian König
<christian.koenig@....com> wrote:
>
>
>
> 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.
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

>
>
>
> >
> > Jason
>