On Wed, Oct 25, 2017 at 5:46 AM, David Laight <David.Laight@xxxxxxxxxx> wrote: > From: Jim QuinlanPCIE_IPROC_MSI >> Sent: 24 October 2017 19:16 >> The Broadcom STB PCIe host controller is intimately related to the >> memory subsystem. This close relationship adds complexity to how cpu >> system memory is mapped to PCIe memory. Ideally, this mapping is an >> identity mapping, or an identity mapping off by a constant. Not so in >> this case. >> >> Consider the Broadcom reference board BCM97445LCC_4X8 which has 6 GB >> of system memory. Here is how the PCIe controller maps the >> system memory to PCIe memory: >> >> memc0-a@[ 0....3fffffff] <=> pci@[ 0....3fffffff] >> memc0-b@[100000000...13fffffff] <=> pci@[ 40000000....7fffffff] >> memc1-a@[ 40000000....7fffffff] <=> pci@[ 80000000....bfffffff] >> memc1-b@[300000000...33fffffff] <=> pci@[ c0000000....ffffffff] >> memc2-a@[ 80000000....bfffffff] <=> pci@[100000000...13fffffff] >> memc2-b@[c00000000...c3fffffff] <=> pci@[140000000...17fffffff] > > I presume the first column is the 'cpu physical address' > and the second the 'pci' address? > Yes. I probably made this more difficult to read because I ordered the rows by PCI addresses. > ... > > Isn't this just the same as having an iommu that converts 'bus' > addresses into 'physical' ones? Pretty much, but for PCIe devices only. This could be done by somehow overriding the arch specific phys_to_dma() and dma_to_phys() calls. > > A simple table lookup of the high address bits will do the > conversion. True, but this table could be passed something like ARM_MAPPING_ERROR, which may be out the table (the driver is not privy to ARM_MAPPING_ERROR's definition). Thanks, Jim > > David >
