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    SubjectRe: [PATCH v3 1/2] habanalabs: define uAPI to export FD for DMA-BUF
    On Mon, Jun 21, 2021 at 7:55 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
    > On Mon, Jun 21, 2021 at 07:26:14PM +0300, Oded Gabbay wrote:
    > > On Mon, Jun 21, 2021 at 5:12 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
    > > >
    > > > On Mon, Jun 21, 2021 at 03:02:10PM +0200, Greg KH wrote:
    > > > > On Mon, Jun 21, 2021 at 02:28:48PM +0200, Daniel Vetter wrote:
    > > >
    > > > > > Also I'm wondering which is the other driver that we share buffers
    > > > > > with. The gaudi stuff doesn't have real struct pages as backing
    > > > > > storage, it only fills out the dma_addr_t. That tends to blow up with
    > > > > > other drivers, and the only place where this is guaranteed to work is
    > > > > > if you have a dynamic importer which sets the allow_peer2peer flag.
    > > > > > Adding maintainers from other subsystems who might want to chime in
    > > > > > here. So even aside of the big question as-is this is broken.
    > > > >
    > > > > From what I can tell this driver is sending the buffers to other
    > > > > instances of the same hardware,
    > > >
    > > > A dmabuf is consumed by something else in the kernel calling
    > > > dma_buf_map_attachment() on the FD.
    > > >
    > > > What is the other side of this? I don't see any
    > > > dma_buf_map_attachment() calls in drivers/misc, or added in this patch
    > > > set.
    > >
    > > This patch-set is only to enable the support for the exporter side.
    > > The "other side" is any generic RDMA networking device that will want
    > > to perform p2p communication over PCIe with our GAUDI accelerator.
    > > An example is indeed the mlnx5 card which has already integrated
    > > support for being an "importer".
    >
    > It raises the question of how you are testing this if you aren't using
    > it with the only intree driver: mlx5.

    For p2p dma-buf there's also amdgpu as a possible in-tree candiate
    driver, that's why I added amdgpu folks. Otoh I'm not aware of AI+GPU
    combos being much in use, at least with upstream gpu drivers (nvidia
    blob is a different story ofc, but I don't care what they do in their
    own world).
    -Daniel
    --
    Daniel Vetter
    Software Engineer, Intel Corporation
    http://blog.ffwll.ch

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