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Date:   Tue, 28 Sep 2021 16:17:41 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Logan Gunthorpe <logang@deltatee.com>
Cc:     linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
        linux-mm@kvack.org, iommu@lists.linux-foundation.org,
        Stephen Bates <sbates@raithlin.com>,
        Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Don Dutile <ddutile@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Jakowski Andrzej <andrzej.jakowski@intel.com>,
        Minturn Dave B <dave.b.minturn@intel.com>,
        Jason Ekstrand <jason@jlekstrand.net>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Xiong Jianxin <jianxin.xiong@intel.com>,
        Bjorn Helgaas <helgaas@kernel.org>,
        Ira Weiny <ira.weiny@intel.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Martin Oliveira <martin.oliveira@eideticom.com>,
        Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
Subject: Re: [PATCH v3 11/20] RDMA/core: introduce
 ib_dma_pci_p2p_dma_supported()
Message-ID: <20210928191741.GQ3544071@ziepe.ca>
References: <20210916234100.122368-1-logang@deltatee.com>
 <20210916234100.122368-12-logang@deltatee.com>
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On Thu, Sep 16, 2021 at 05:40:51PM -0600, Logan Gunthorpe wrote:
> Introduce the helper function ib_dma_pci_p2p_dma_supported() to check
> if a given ib_device can be used in P2PDMA transfers. This ensures
> the ib_device is not using virt_dma and also that the underlying
> dma_device supports P2PDMA.
> 
> Use the new helper in nvme-rdma to replace the existing check for
> ib_uses_virt_dma(). Adding the dma_pci_p2pdma_supported() check allows
> switching away from pci_p2pdma_[un]map_sg().
> 
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> ---
>  drivers/nvme/target/rdma.c |  2 +-
>  include/rdma/ib_verbs.h    | 11 +++++++++++
>  2 files changed, 12 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

> +/*
> + * Check if a IB device's underlying DMA mapping supports P2PDMA transfers.
> + */
> +static inline bool ib_dma_pci_p2p_dma_supported(struct ib_device *dev)
> +{
> +	if (ib_uses_virt_dma(dev))
> +		return false;

If someone wants to make rxe/hfi/qib use this stuff then they will
have to teach the the driver to do all the p2p checks and add some
struct ib_device flag

Jason