PCI: dwc: Use custom pci_ops for root bus DBI vs ECAM config access

When the vendor configuration space is 256MB aligned, the DesignWare PCIe
host driver enables ECAM access and sets the DBI base to the start of the
config space. This causes vendor drivers to incorrectly program iATU
regions, as they rely on the DBI address for internal accesses.

To fix this, avoid overwriting the DBI base when ECAM is enabled.  Instead,
introduce a custom pci_ops that accesses the DBI region directly for the
root bus and uses ECAM for other buses.

Fixes: f6fd357 ("PCI: dwc: Prepare the driver for enabling ECAM mechanism using iATU 'CFG Shift Feature'")
Reported-by: Ron Economos <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Suggested-by: Manivannan Sadhasivam <[email protected]>
Signed-off-by: Krishna Chaitanya Chundru <[email protected]>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <[email protected]>
Tested-by: Ron Economos <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: krishnachaitanya-linux

drivers/pci/controller/dwc/pcie-designware-host.c

@@ -23,6 +23,7 @@
 #include "pcie-designware.h"
 
 static struct pci_ops dw_pcie_ops;
+static struct pci_ops dw_pcie_ecam_ops;
 static struct pci_ops dw_child_pcie_ops;
 
 #define DW_PCIE_MSI_FLAGS_REQUIRED (MSI_FLAG_USE_DEF_DOM_OPS		| \
@@ -471,9 +472,6 @@ static int dw_pcie_create_ecam_window(struct dw_pcie_rp *pp, struct resource *re
 	if (IS_ERR(pp->cfg))
 		return PTR_ERR(pp->cfg);
 
-	pci->dbi_base = pp->cfg->win;
-	pci->dbi_phys_addr = res->start;
-
 	return 0;
 }
 
@@ -529,7 +527,7 @@ static int dw_pcie_host_get_resources(struct dw_pcie_rp *pp)
 		if (ret)
 			return ret;
 
-		pp->bridge->ops = (struct pci_ops *)&pci_generic_ecam_ops.pci_ops;
+		pp->bridge->ops = &dw_pcie_ecam_ops;
 		pp->bridge->sysdata = pp->cfg;
 		pp->cfg->priv = pp;
 	} else {
@@ -842,12 +840,34 @@ void __iomem *dw_pcie_own_conf_map_bus(struct pci_bus *bus, unsigned int devfn,
 }
 EXPORT_SYMBOL_GPL(dw_pcie_own_conf_map_bus);
 
+static void __iomem *dw_pcie_ecam_conf_map_bus(struct pci_bus *bus, unsigned int devfn, int where)
+{
+	struct pci_config_window *cfg = bus->sysdata;
+	struct dw_pcie_rp *pp = cfg->priv;
+	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
+	unsigned int busn = bus->number;
+
+	if (busn > 0)
+		return pci_ecam_map_bus(bus, devfn, where);
+
+	if (PCI_SLOT(devfn) > 0)
+		return NULL;
+
+	return pci->dbi_base + where;
+}
+
 static struct pci_ops dw_pcie_ops = {
 	.map_bus = dw_pcie_own_conf_map_bus,
 	.read = pci_generic_config_read,
 	.write = pci_generic_config_write,
 };
 
+static struct pci_ops dw_pcie_ecam_ops = {
+	.map_bus = dw_pcie_ecam_conf_map_bus,
+	.read = pci_generic_config_read,
+	.write = pci_generic_config_write,
+};
+
 static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
 {
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);