linux-kernel - [PATCH 1/2] PCI: dwc: Fix ECAM enablement when used with vendor drivers

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Message-Id: <20251017-ecam_fix-v1-1-f6faa3d0edf3@oss.qualcomm.com>
Date: Fri, 17 Oct 2025 17:10:53 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Jingoo Han <jingoohan1@...il.com>, Manivannan Sadhasivam <mani@...nel.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
        Ron Economos <re@...z.net>
Subject: [PATCH 1/2] PCI: dwc: Fix ECAM enablement when used with vendor
 drivers

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 ECAM PCI ops implementation that accesses
the DBI region directly for bus 0 and uses ECAM for other buses.

Fixes: f6fd357f7afb ("PCI: dwc: Prepare the driver for enabling ECAM mechanism using iATU 'CFG Shift Feature'")
Reported-by: Ron Economos <re@...z.net>
Closes: https://lore.kernel.org/all/eac81c57-1164-4d74-a1b4-6f353c577731@w6rz.net/
Suggested-by: Manivannan Sadhasivam <mani@...nel.org>
Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
---
 drivers/pci/controller/dwc/pcie-designware-host.c | 28 +++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 20c9333bcb1c4812e2fd96047a49944574df1e6f..e92513c5bda51bde3a7157033ddbd73afa370d78 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/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);

-- 
2.34.1