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Date:   Wed, 18 Oct 2017 08:53:16 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Jim Quinlan <jim2101024@gmail.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Robin Murphy <robin.murphy@arm.com>,
        linux-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
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        Kevin Cernekee <cernekee@gmail.com>,
        Will Deacon <will.deacon@arm.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        Rob Herring <robh+dt@kernel.org>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@broadcom.com>,
        Gregory Fong <gregory.0xf0@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Brian Norris <computersforpeace@gmail.com>,
        linux-arm-kernel@lists.infradead.org,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        iommu@lists.linux-foundation.org
Subject: Re: [PATCH 5/9] PCI: host: brcmstb: add dma-ranges for inbound
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On Tue, Oct 17, 2017 at 12:11:55PM -0400, Jim Quinlan wrote:
> My understanding is that dma_pfn_offset is that it is a single
> constant offset from RAM, in our case, to map to PCIe space.

Yes.

> But in
> my commit message I detail how our PCIe controller presents memory
> with multiple regions with multiple different offsets. If an EP device
> maps to a region on the host memory, yes we can set the dma_pfn_offset
> for that device for that location within that range,.  But if the
> device then unmaps and allocates from another region with a different
> offset, it won't work.  If  I set dma_pfn_offset I have to assume that
> the device is using only one region of memory only, not more than one,
> and that it is not unmapping that region and mapping another (with a
> different offset).  Can I make those assumptions?

No, we can't make that assumption unfortunately.  But how is your
code going to work if the mapping spans multiple of your translation
regions?

Also I really don't think the stacking of dma_ops as in this patch
is a good idea.  For MIPS you should do the variant suggested in
the patch description and hook into dma_to_phys/phys_to_dma helpers,
and for ARM/ARM64 you should talk to the maintainers on how they
want the translation integrated.