[PATCH V4] PCI: Add support for preserving boot configuration

[Vidya Sagar <vidyas@nvidia.com>]

Add support for preserving the boot configuration done by the
platform firmware per host bridge basis, based on the presence of
'linux,pci-probe-only' property in the respective PCI host bridge
device-tree node. It also unifies the ACPI and DT based boot flows
in this regard.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
V4:
* Addressed Bjorn's review comments

V3:
* Unified ACPI and DT flows as part of addressing Bjorn's review comments

V2:
* Addressed issues reported by kernel test robot <lkp@intel.com>

 drivers/acpi/pci_root.c                  | 12 -------
 drivers/pci/controller/pci-host-common.c |  4 ---
 drivers/pci/of.c                         | 21 +++++++++++
 drivers/pci/probe.c                      | 46 ++++++++++++++++++------
 include/linux/of_pci.h                   |  6 ++++
 5 files changed, 62 insertions(+), 27 deletions(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 84030804a763..ddc2b3e89111 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -1008,7 +1008,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	int node = acpi_get_node(device->handle);
 	struct pci_bus *bus;
 	struct pci_host_bridge *host_bridge;
-	union acpi_object *obj;
 
 	info->root = root;
 	info->bridge = device;
@@ -1050,17 +1049,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	if (!(root->osc_ext_control_set & OSC_CXL_ERROR_REPORTING_CONTROL))
 		host_bridge->native_cxl_error = 0;
 
-	/*
-	 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
-	 * exists and returns 0, we must preserve any PCI resource
-	 * assignments made by firmware for this host bridge.
-	 */
-	obj = acpi_evaluate_dsm(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid, 1,
-				DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
-	if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
-		host_bridge->preserve_config = 1;
-	ACPI_FREE(obj);
-
 	acpi_dev_power_up_children_with_adr(device);
 
 	pci_scan_child_bus(bus);
diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
index 6be3266cd7b5..e2602e38ae45 100644
--- a/drivers/pci/controller/pci-host-common.c
+++ b/drivers/pci/controller/pci-host-common.c
@@ -73,10 +73,6 @@ int pci_host_common_probe(struct platform_device *pdev)
 	if (IS_ERR(cfg))
 		return PTR_ERR(cfg);
 
-	/* Do not reassign resources if probe only */
-	if (!pci_has_flag(PCI_PROBE_ONLY))
-		pci_add_flags(PCI_REASSIGN_ALL_BUS);
-
 	bridge->sysdata = cfg;
 	bridge->ops = (struct pci_ops *)&ops->pci_ops;
 	bridge->msi_domain = true;
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..f0f1156040a5 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -258,6 +258,27 @@ void of_pci_check_probe_only(void)
 }
 EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
 
+/**
+ * of_pci_bridge_preserve_resources - Return true if the boot configuration
+ *                                    needs to be preserved
+ * @node: Device tree node with the domain information.
+ *
+ * This function looks for "linux,pci-probe-only" property for a given
+ * PCI controller's node and returns true if found. Having this property
+ * for a PCI controller ensures that the kernel doesn't reconfigure the
+ * BARs and bridge windows that are already done by the platform firmware.
+ * NOTE: The scope of "linux,pci-probe-only" defined within a PCI bridge device
+ *       is limited to the hierarchy under that particular bridge device. whereas
+ *       the scope of "linux,pci-probe-only" defined within chosen node is
+ *       system wide.
+ *
+ * Return: true if the property exists false otherwise.
+ */
+bool of_pci_bridge_preserve_resources(struct device_node *node)
+{
+	return of_property_read_bool(node, "linux,pci-probe-only");
+}
+
 /**
  * devm_of_pci_get_host_bridge_resources() - Resource-managed parsing of PCI
  *                                           host bridge resources from DT
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 795534589b98..c57648084503 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -15,6 +15,7 @@
 #include <linux/cpumask.h>
 #include <linux/aer.h>
 #include <linux/acpi.h>
+#include <linux/pci-acpi.h>
 #include <linux/hypervisor.h>
 #include <linux/irqdomain.h>
 #include <linux/pm_runtime.h>
@@ -877,6 +878,28 @@ static void pci_set_bus_msi_domain(struct pci_bus *bus)
 	dev_set_msi_domain(&bus->dev, d);
 }
 
+static void pci_check_config_preserve(struct pci_host_bridge *host_bridge)
+{
+	if (ACPI_HANDLE(&host_bridge->dev)) {
+		union acpi_object *obj;
+
+		/*
+		 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
+		 * exists and returns 0, we must preserve any PCI resource
+		 * assignments made by firmware for this host bridge.
+		 */
+		obj = acpi_evaluate_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
+					DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
+		if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
+			host_bridge->preserve_config = 1;
+		ACPI_FREE(obj);
+	}
+
+	if (host_bridge->dev.parent && host_bridge->dev.parent->of_node)
+		host_bridge->preserve_config =
+			of_pci_bridge_preserve_resources(host_bridge->dev.parent->of_node);
+}
+
 static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 {
 	struct device *parent = bridge->dev.parent;
@@ -971,6 +994,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	if (nr_node_ids > 1 && pcibus_to_node(bus) == NUMA_NO_NODE)
 		dev_warn(&bus->dev, "Unknown NUMA node; performance will be reduced\n");
 
+	/* Check if the boot configuration by FW needs to be preserved */
+	pci_check_config_preserve(bridge);
+
 	/* Coalesce contiguous windows */
 	resource_list_for_each_entry_safe(window, n, &resources) {
 		if (list_is_last(&window->node, &resources))
@@ -3080,20 +3106,18 @@ int pci_host_probe(struct pci_host_bridge *bridge)
 
 	bus = bridge->bus;
 
+	/* If we must preserve the resource configuration, claim now */
+	if (pci_has_flag(PCI_PROBE_ONLY) || bridge->preserve_config)
+		pci_bus_claim_resources(bus);
+
 	/*
-	 * We insert PCI resources into the iomem_resource and
-	 * ioport_resource trees in either pci_bus_claim_resources()
-	 * or pci_bus_assign_resources().
+	 * Assign whatever was left unassigned. If we didn't claim above,
+	 * this will reassign everything.
 	 */
-	if (pci_has_flag(PCI_PROBE_ONLY)) {
-		pci_bus_claim_resources(bus);
-	} else {
-		pci_bus_size_bridges(bus);
-		pci_bus_assign_resources(bus);
+	pci_assign_unassigned_root_bus_resources(bus);
 
-		list_for_each_entry(child, &bus->children, node)
-			pcie_bus_configure_settings(child);
-	}
+	list_for_each_entry(child, &bus->children, node)
+		pcie_bus_configure_settings(child);
 
 	pci_bus_add_devices(bus);
 	return 0;
diff --git a/include/linux/of_pci.h b/include/linux/of_pci.h
index 29658c0ee71f..3f3909a5d55d 100644
--- a/include/linux/of_pci.h
+++ b/include/linux/of_pci.h
@@ -13,6 +13,7 @@ struct device_node *of_pci_find_child_device(struct device_node *parent,
 					     unsigned int devfn);
 int of_pci_get_devfn(struct device_node *np);
 void of_pci_check_probe_only(void);
+bool of_pci_bridge_preserve_resources(struct device_node *node);
 #else
 static inline struct device_node *of_pci_find_child_device(struct device_node *parent,
 					     unsigned int devfn)
@@ -26,6 +27,11 @@ static inline int of_pci_get_devfn(struct device_node *np)
 }
 
 static inline void of_pci_check_probe_only(void) { }
+
+static inline bool of_pci_bridge_preserve_resources(struct device_node *node)
+{
+	return false;
+}
 #endif
 
 #if IS_ENABLED(CONFIG_OF_IRQ)
-- 
2.25.1