PCI: dwc: Use devicetree 'reg[config]' to derive CPU -> ATU addr offset

The 'ranges' property of a PCI controller's parent can indicate address
translation information. Most system use 1:1 map between CPU physical and
PCI controller input addresses.

But some hardware, like i.MX8QXP, doesn't use 1:1 map.  See below diagram:

              ┌─────────┐                    ┌────────────┐
   ┌─────┐    │         │ IA: 0x8ff8_0000    │            │
   │ CPU ├───►│   ┌────►├─────────────────┐  │ PCI        │
   └─────┘    │   │     │ IA: 0x8ff0_0000 │  │            │
    CPU Addr  │   │  ┌─►├─────────────┐   │  │ Controller │
  0x7ff8_0000─┼───┘  │  │             │   │  │            │
              │      │  │             │   │  │            │   PCI Addr
  0x7ff0_0000─┼──────┘  │             │   └──► IOSpace   ─┼────────────►
              │         │             │      │            │    0
  0x7000_0000─┼────────►├─────────┐   │      │            │
              └─────────┘         │   └──────► CfgSpace  ─┼────────────►
               Bus Fabric         │          │            │    0
                                  │          │            │
                                  └──────────► MemSpace  ─┼────────────►
                          IA: 0x8000_0000    │            │  0x8000_0000
                                             └────────────┘

  bus@5f000000 {
          compatible = "simple-bus";
          #address-cells = <1>;
          #size-cells = <1>;
          ranges = <0x80000000 0x0 0x70000000 0x10000000>;

          pcie@5f010000 {
                  compatible = "fsl,imx8q-pcie";
                  reg = <0x5f010000 0x10000>, <0x8ff00000 0x80000>;
                  reg-names = "dbi", "config";
                  ...
          };
  };

Intermediate address (IA) here means the PCIe controller input address.
The pcie@5f010000 'reg[config]' address is the parent bus (PCIe controller
input) address of CfgSpace.

The ATU in MemSpace is not explicitly described via devicetree, so we
assume the offset from CPU address to intermediate MemSpace address is the
same as that for CfgSpace.

We could use bus@5f000000 'ranges' for the same purpose.

Set parent_bus_offset using dw_pcie_init_parent_bus_offset().  The
parent_bus_offset is not used yet, so no functional change intended.

Link: https://lore.kernel.org/r/20250315201548.858189-8-helgaas@kernel.org
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

2 files changed, 7 insertions, 0 deletions

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 9ce06b1ee266..9e38ac7d1bcb 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -452,6 +452,12 @@ static int dw_pcie_host_get_resources(struct dw_pcie_rp *pp)
 		pp->io_base = pci_pio_to_address(win->res->start);
 	}
 
+	/*
+	 * visconti_pcie_cpu_addr_fixup() uses pp->io_base, so we have to
+	 * call dw_pcie_parent_bus_offset() after setting pp->io_base.
+	 */
+	pci->parent_bus_offset = dw_pcie_parent_bus_offset(pci, "config",
+							   pp->cfg0_base);
 	return 0;
 }
 
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index f08d2852cfd5..741c46926ce2 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -445,6 +445,7 @@ struct dw_pcie {
 	void __iomem		*atu_base;
 	resource_size_t		atu_phys_addr;
 	size_t			atu_size;
+	resource_size_t		parent_bus_offset;
 	u32			num_ib_windows;
 	u32			num_ob_windows;
 	u32			region_align;