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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.

-Andi


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