Messages in this thread |  | | | Date | Thu, 26 May 2011 01:05:44 +0200 | | From | Andi Kleen <> | | Subject | Re: Question about iommu on x86_64 and radeon driver. |
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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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