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Date:   Thu, 23 May 2019 12:26:08 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     "Koenig, Christian" <Christian.Koenig@amd.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Logan Gunthorpe <logang@deltatee.com>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: [PATCH] PCI/P2PDMA: Root complex whitelist should not apply
 when an IOMMU is present
Message-ID: <20190523102608.GA15800@lst.de>
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On Thu, May 23, 2019 at 10:06:28AM +0000, Koenig, Christian wrote:
> Ok, we certainly don't have a system which exercise this user case. 
> Could ask around if we have an ARM SOC with that properties somewhere.
> 
> But asking the other way around: Where is the right place to start 
> fixing all this? dma_map_resource()?

That is the the big gorrilla in the room.  The offset applies to the
device whos BARs/resources we map.  The current dma_map_resource API
does not even have the right information.  So I think we need to
enhance the API to pass a second struct device and we could fix it
there and then in the next steps add a map_sg version of
dma_map_resource and eventually also convert the PCIe P2P map_sg
over to that.