Re: [PATCH v9 3/7] PCI: Add parent_bus_offset to resource_entry
From: Bjorn Helgaas <helgaas@kernel.org>
Date: 2025-02-27 00:08:19
Also in:
imx, linux-devicetree, linux-pci, lkml
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
quoted hunk ↗ jump to hunk
+++ 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.