Re: [PATCH 06/12] IB/core: Add optional PCI P2P flag to rdma_rw_ctx_[init|destroy]()

Christoph Hellwig
2018-01-09T16:55:49Z

On Mon, Jan 08, 2018 at 12:01:16PM -0700, Jason Gunthorpe wrote:
> > So I very much disagree about where to place that workaround - the
> > RDMA code is exactly the right place.
>
> But why? RDMA is using core code to do this. It uses dma_ops in struct
> device and it uses normal dma_map SG. How is it RDMA's problem that
> some PCI drivers provide strange DMA ops?

Because RDMA uses the dma_virt_ops to pretend a device does DMA when
in fact it doesn't - at least not for the exact data mapped, or
as far as I can tell often not all - e.g. the QIB/HFI devices
might do mmio access for data mapped.

This whole problem only exist because a few RDMA HCA drivers lie
with the help of the RDMA core.
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