> > 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. 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href