Hi, A few PCI host controllers use the "dma-ranges" property to specify the mapping from PCI bus addresses to physical addresses.
In the case of R-Car PCIe Host controllers, the intention was to set this property as a 1 to 1 mapping for all DDR that could be addressed by the device. However, there are some limitations for the R-Car controller which meant that we could only map a subset of the DDR range - this limitation has prompted us to work on enabling the IOMMU behind the PCI controller. When there is an IOMMU behind the PCI controller, the "dma-ranges" property specifies the mapping from PCI bus addresses to an IOVA address. So should the property map all address space? Note that this is not actually possible with the R-Car hardware, but I found that the IOVA address space is outside of the DDR address space that we were using so had change it. Thanks Phil
