Re: PCIe P2P access to GPU memory

From: Daniel Vetter <daniel@ffwll.ch>
To: "Koenig, Christian" <Christian.Koenig@amd.com>
Cc: "dirk.eibach@googlemail.com" <dirk.eibach@googlemail.com>,
	dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: PCIe P2P access to GPU memory
Date: Wed, 3 Oct 2018 11:06:07 +0200	[thread overview]
Message-ID: <20181003090607.GA23685@phenom.ffwll.local> (raw)
In-Reply-To: <856f3ee3-5f5c-f8a3-d9e2-d8f894aaf967@amd.com>

On Wed, Oct 03, 2018 at 08:54:44AM +0000, Koenig, Christian wrote:
> Am 03.10.2018 um 09:14 schrieb Daniel Vetter:
> > On Sat, Sep 29, 2018 at 9:27 AM Koenig, Christian
> > <Christian.Koenig@amd.com> wrote:
> >> This is work in progress.
> >>
> >> I published patches to enable DMA_buf P2P a few months ago, but now I'm waiting for the PCI subsystem to pick up core support for this.
> >>
> >> I can prepare you a branch based on current upstream kernel next week if you want to test this.
> > Thread hijack, since I just read the lwn article on p2p for storage folks:
> >
> > https://lwn.net/Articles/767281/
> >
> > Totally doesn't match what I remember of your dma-buf p2p work. Do we
> > need to rework, or is this some kind of higher-level interface on top
> > of the raw p2p pci stuff? Or do I misremember.
> 
> The P2P from the storage folks are some mix of raw p2p capability 
> detection for PCI and higher level interface.
> 
> I'm actually waiting for that stuff to land to extract the p2p 
> capability detection and use it for this DMA-buf stuff as well.
> 
> Alternative would be to convince Logan to extract the capability 
> detection in his patch set as well, but so far he wasn't very keen about 
> that.

So no plan to make dma-buf some kind of orchestrator and use the p2p
map_sg stuff? That seems to be the new/additional bits I haven't seen yet,
and I'm wondered how we should fit dma-buf into that picture.
-Daniel

> 
> Christian.
> 
> >
> > Thanks, Daniel
> >
> >> Regards,
> >> Christian.
> >>
> >> Am 29.09.2018 09:01 schrieb Dirk Eibach <dirk.eibach@googlemail.com>:
> >> I want to access GPU VRAM via PCIe P2P access, like DirectGMA but with
> >> mainline drivers.
> >> I can acquire a dmabuf from the GPU and pass it to my PCIe
> >> framegrabber. But I don't see a way to get the PCIe bus address of the
> >> video memory which I need for the P2P transfer. Is there already any
> >> infrastructure in place for doing this? If not, what would be the
> >> right way to implement this? Add another callback to the dmabuf
> >> struct?
> >>
> >> Cheers
> >> Dirk
> >> _______________________________________________
> >> dri-devel mailing list
> >> dri-devel@lists.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >
> >
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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