RE: [RFC 0/5] ARM: dma-mapping: New dma_map_ops to control IOVAmore precisely

[Krishna Reddy]

> > 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



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