Question about dma-ranges property for PCI host controllers

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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
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