[PATCH V1 2/2] PCI: Add support for "preserve-boot-config" property

[Vidya Sagar]

Add support for "preserve-boot-config" property that can be used to
selectively (i.e. per host bridge) instruct the kernel to preserve the
boot time configuration done by the platform firmware.

Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
---
 drivers/pci/controller/pci-host-common.c |  5 ++++-
 drivers/pci/of.c                         | 15 +++++++++++++++
 drivers/pci/probe.c                      |  2 +-
 include/linux/of_pci.h                   |  6 ++++++
 4 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
index 6be3266cd7b5..d3475dc9ec44 100644
--- a/drivers/pci/controller/pci-host-common.c
+++ b/drivers/pci/controller/pci-host-common.c
@@ -68,13 +68,16 @@ int pci_host_common_probe(struct platform_device *pdev)
 
 	of_pci_check_probe_only();
 
+	bridge->preserve_config =
+		of_pci_check_preserve_boot_config(dev->of_node);
+
 	/* Parse and map our Configuration Space windows */
 	cfg = gen_pci_init(dev, bridge, ops);
 	if (IS_ERR(cfg))
 		return PTR_ERR(cfg);
 
 	/* Do not reassign resources if probe only */
-	if (!pci_has_flag(PCI_PROBE_ONLY))
+	if (!(pci_has_flag(PCI_PROBE_ONLY) || bridge->preserve_config))
 		pci_add_flags(PCI_REASSIGN_ALL_BUS);
 
 	bridge->sysdata = cfg;
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..3216d4557212 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -258,6 +258,21 @@ void of_pci_check_probe_only(void)
 }
 EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
 
+/**
+ * of_pci_check_preserve_boot_config - Return true if the boot configuration
+ *                                     needs to be preserved
+ *
+ * This function looks for a property called "preserve-boot-config" for a given
+ * PCIe controller's node and returns true if found. Having this property
+ * for a PCIe controller ensures that the kernel doesn't re-enumerate and
+ * reconfigure the BAR resources that are already done by the platform firmware.
+ */
+bool of_pci_check_preserve_boot_config(struct device_node *node)
+{
+	return of_property_read_bool(node, "preserve-boot-config");
+}
+EXPORT_SYMBOL_GPL(of_pci_check_preserve_boot_config);
+
 /**
  * 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..79d0ac34f567 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -3085,7 +3085,7 @@ int pci_host_probe(struct pci_host_bridge *bridge)
 	 * ioport_resource trees in either pci_bus_claim_resources()
 	 * or pci_bus_assign_resources().
 	 */
-	if (pci_has_flag(PCI_PROBE_ONLY)) {
+	if (pci_has_flag(PCI_PROBE_ONLY) || bridge->preserve_config) {
 		pci_bus_claim_resources(bus);
 	} else {
 		pci_bus_size_bridges(bus);
diff --git a/include/linux/of_pci.h b/include/linux/of_pci.h
index 29658c0ee71f..a408e54128c6 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_check_preserve_boot_config(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 bool of_pci_check_preserve_boot_config(struct device_node *node)
+{
+	return false;
+}
 #endif
 
 #if IS_ENABLED(CONFIG_OF_IRQ)
-- 
2.25.1