Re: Question about iommu on x86_64 and radeon driver.

[Andi Kleen]

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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/