On Tue, Jan 28, 2025 at 05:07:36PM -0500, Frank Li wrote: > Introduce `parent_bus_offset` in `resource_entry` and a new API, > `pci_add_resource_parent_bus_offset()`, to provide necessary information > for PCI controllers with address translation units. > > Typical PCI data flow involves: > CPU (CPU address) -> Bus Fabric (Intermediate address) -> > PCI Controller (PCI bus address) -> PCI Bus. > > While most bus fabrics preserve address consistency, some modify addresses > to intermediate values. s/modify/translate/ Specifically, they *translate* addresses, which means the same offset is added to every address in the range, as opposed to masking or some other transformation. I think we can take advantage of this to simplify the callers of .cpu_addr_fixup() later. Ironically, most of the .cpu_addr_fixup() implementations *do* mask the address, e.g., cdns_plat_cpu_addr_fixup() masks with 0x0fffffff. But I think this is actually incorrect because masking results in a many-to-one mapping, e.g., 0x42000000 & 0x0fffffff == 0x02000000 0x52000000 & 0x0fffffff == 0x02000000 But presumably the addresses we pass to cdns_plat_cpu_addr_fixup() don't cross a 256MB (0x10000000) boundary, so we could accomplish the same by subtracting 0x40000000: 0x42000000 - 0x40000000 == 0x02000000 > +++ b/drivers/pci/of.c > @@ -402,7 +402,17 @@ static int devm_of_pci_get_host_bridge_resources(struct device *dev, > res->flags &= ~IORESOURCE_MEM_64; > } > > - pci_add_resource_offset(resources, res, res->start - range.pci_addr); > + /* > + * IORESOURCE_IO res->start is io space start address. > + * IORESOURCE_MEM res->start is cpu start address, which is the > + * same as range.cpu_addr. > + * > + * Use (range.cpu_addr - range.parent_bus_addr) to align both > + * IO and MEM's parent_bus_offset always offset to cpu address. > + */ > + > + pci_add_resource_parent_bus_offset(resources, res, res->start - range.pci_addr, > + range.cpu_addr - range.parent_bus_addr); Wrap to fit in 80 columns like the rest of the file. Will have to unindent the two lines of arguments to make this work.
