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    SubjectRE: [PATCH 2/5] iommu/amd: Implement DOMAIN_ATTR_GEOMETRY attribute
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    > -----Original Message-----
    > From: Joerg Roedel [mailto:joerg.roedel@amd.com]
    > Sent: Friday, January 27, 2012 12:21 AM
    > To: Wood Scott-B07421
    > Cc: Sethi Varun-B16395; iommu@lists.linux-foundation.org; Ohad Ben-Cohen;
    > Tony Lindgren; Hiroshi DOYU; linux-kernel@vger.kernel.org; Laurent
    > Pinchart; Wood Scott-B07421; David Brown; David Woodhouse
    > Subject: Re: [PATCH 2/5] iommu/amd: Implement DOMAIN_ATTR_GEOMETRY
    > attribute
    >
    > On Thu, Jan 26, 2012 at 12:42:10PM -0600, Scott Wood wrote:
    > > On 01/26/2012 12:31 PM, Joerg Roedel wrote:
    > > > The force_aperture flag indicated whether DMA is only allowed
    > > > between aperture_start and apertuer_end or if DMA is allowed outside
    > > > of this range too (unmapped in this case).
    > > >
    > > > The AMD GART for example would set this flag to false because it
    > > > does not enforce DMA to be in the aperture-range.
    > >
    > > Why is this not an AMD GART specific attribute? Is there any feature
    > > reporting mechanism by which a user would know if that flag is
    > supported?
    >
    > Because this is a flag that makes sense for all IOMMU. Every IOMMU either
    > allows DMA outside its aperture or it doesn't.
    >
    > Another reason why it must be in the generic struct is the intended
    > generic dma-ops layer on-top. This code can decide on this flag wheter a
    > address needs to be remapped at all.


    Can you please explain how would IOMMU remapping be used, based on the force_aperture flag.

    -Varun




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