Re: Question about iommu on x86_64 and radeon driver.

From: Andi Kleen
Date: Wed Jun 01 2011 - 17:51:47 EST

On Wed, Jun 01, 2011 at 05:10:44PM +0100, Daniel Haid wrote:
> >Look in the source code. I somehow assumed it would activate it
> >but maybe it isn't. And the problem you have is related to
> >something else?
> If I have read the code correctly the only way to get
> swiotlb_force=1 in lib/swiotlb.c is to add the "swiotlb=force"
> argument to the kernel parameters.
> Without it on VIA chipsets swiotlb gets activated, but with
> swiotlb_force=0. In this case DMA to addresses below 4GB should be
> direct.
> But since I still get the error the radeon driver must (incorrectly)
> allocate memory above 4GB somewhere, but where?

Someone has to debug it. grep for the error message, read the
surrounding code, add printks, run it, until you figure out which allocation
has the problem.

Adding some radeon driver people to cc. The original problem
is described in,106131,115940


ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at