20 Sep
2012
20 Sep
'12
6:40 a.m.
On Tegra, the following use cases need specific IOVA mapping.
- 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. If IOMMU is disabled, then it has to handle memory fragmentation, which defeats the purpose of IOMMU support. 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.
-KR