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    SubjectRe: Question about iommu on x86_64 and radeon driver.
    On Wed, May 25, 2011 at 09:21:21PM +0100, Daniel Haid wrote:
    > >Only if you allow 3GB or less in the machine. So you would have to do
    > >mem=3G as well.
    > >
    > >The reason is that (and you can see that yourself by looking at the
    > >E820), is that 1GB is actually _above_ the 4GB.
    > Just another question on this one:
    > Why can a driver not simply ask for DMA-capable memory, is this not
    > what memory zones are for?

    In many cases the memory gets passed into the driver.

    If it's not already in the right boundaries it would need to copy through
    a bounce buffer. That is what swiotlb does, if there's no IOMMU.


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