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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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