On Thursday, August 11, 2016 3:00:42 PM CEST Phil Edworthy wrote: > 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. It's a bit tricky: the dma-ranges properties are walked recursively, and a PCI bus may be behind a few other bridges that each have a nontrivial mapping, and the IOMMU may not be on the address space that the PCI host sees. In the past, we have said that the dma-ranges property should reflect the address space that is used when programming the bridge registers in the PCI host bridge itself. I think we have also made the assumption that a PCI host bridge with an IOMMU uses a flat 32-bit DMA address space that goes through the IOMMU (possibly a separate address space per PCI function, depending on the type of IOMMU). One corner case that doesn't really fit in that model is a PCI host bridge that requires the bridge register to be programmed in a special way for the IOMMU to work (e.g. away from the RAM to the address that is routed to the IOMMU). Another tricky case is a PCI host that uses the IOMMU only for 32-bit DMA masters but that does have a dma-ranges property that can be used for direct mapping of all RAM through a nonzero offset that gets set up according to dma-ranges. Can you be more specific which of those cases you actually have here? Arnd -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
