Re: [PATCH 8/8] Cell IOMMU fixed mapping support

On Wed, Jan 30, 2008 at 02:13:45AM +1100, Michael Ellerman wrote:

On Tue, 2008-01-29 at 09:15 -0600, Olof Johansson wrote:

quoted

On Wed, Jan 30, 2008 at 01:14:03AM +1100, Michael Ellerman wrote:

quoted

For example a machine with 4GB of memory would end up with the normal
IOMMU window from 0-2GB and the fixed mapping window from 2GB to 6GB. In
this case a 64-bit device wishing to DMA to 1GB would be told to DMA to
3GB, plus any offset required by firmware. The firmware offset is encoded
in the "dma-ranges" property.

Shouldn't the fixed mapping be between 4G and 8G (and the offset for 1G
is at 5G), to account for the MMIO range at 2-4G?

I don't think so, ie. it works setup like that, but I'm not entirely
sure why. Presumably the 2-4GB for MMIO is only for cycles heading out
of the CPU.

Ben denied that being so yesterday. :-)

If that's the case, then you can stick the dynamic range there for >32GB
configs, since it's still addressable with 32 bits.


-Olof