On 09/20/2012 12:40 AM, Krishna Reddy wrote:

quoted

quoted

On Tegra, the following use cases need specific IOVA mapping.
1. Few MMIO blocks need IOVA=PA mapping setup.

In that case, why would we enable the IOMMU for that one device; IOMMU
disabled means VA==PA, right? Perhaps isolation of the device so it can only
access certain PA ranges for security?

The device(H/W controller) need to access few special memory blocks(IOVA==PA)
and DRAM as well.

OK, so only /some/ of the VA space is VA==PA, and some is remapped;
that's a little different that what you originally implied above.

BTW, which HW module is this; AVP/COP or something else. This sounds
like an odd requirement.

There is also a case where frame buffer memory is passed from BootLoader to Kernel and
display H/W  continues to access it with IOMMU enabled. To support this, the one to one
mapping has to be setup before enabling IOMMU.

Yes, that makes sense.