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    SubjectRe: [RFC 0/6] iommu: generic api migration and grouping
    On Mon, Jun 06, 2011 at 12:36:13PM -0400, Ohad Ben-Cohen wrote:
    > On Mon, Jun 6, 2011 at 6:35 PM, Roedel, Joerg <> wrote:
    > > On Mon, Jun 06, 2011 at 11:15:30AM -0400, Ohad Ben-Cohen wrote:
    > >
    > >> This is insufficient; users need somehow to tell what page sizes are
    > >> supported by the underlying hardware (we can't assume host page-sizes,
    > >> and we want to use bigger pages whenever possible, to relax the TLB
    > >> pressure).
    > > /
    > > What does the IOMMU-API user need this info for? On the x86 IOMMUs these
    > > details are handled transparently by the IOMMU driver.
    > That's one way to do that, but then it means duplicating this logic
    > inside the different IOMMU implementations.
    > Take the OMAP (and seemingly MSM too) example: we have 4KB, 64KB, 1MB
    > and 16MB page-table entries. When we map a memory region, we need to
    > break it up to a minimum number of pages (while validating
    > sizes/alignments are sane). It's not complicated, but it can be nice
    > if it'd be implemented only once.

    Well, it certainly makes sense to have a single implementation for this.
    But I want to hide this complexity to the user of the IOMMU-API. The
    best choice is to put this into the layer between the IOMMU-API and the
    backend implementation.

    > In addition, unless we require 'va' and 'pa' to have the exact same
    > alignment, we might run into specific page configuration that the
    > IOMMU implementation cannot restore on ->unmap, since unmap only takes
    > 'va' and 'order'. So we will either have to supply 'pa' too, or have
    > the implementation remember the mapping in order to unmap it later.
    > That begins to be a bit messy...

    That interface is not put into stone. There were other complains about
    the ->unmap part recently, so there is certainly room for improvement



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