PCIe P2P access to GPU memory

[Christian König]

Am 03.10.2018 um 11:06 schrieb Daniel Vetter:
> 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 at 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?

Not sure about that yet. Didn't had time to take a closer look.

Christian.

>   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 at 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
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>>>