PCI/ACPI: Reserve firmware-allocated resources for hot-added root buses

Firmware may have assigned PCI BARs for hot-added devices, so reserve
those resources before trying to allocate more.

[bhelgaas: move empty weak definition here]
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 7928d4d..dcbe966 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -650,8 +650,10 @@
 	struct acpi_pci_root *root = acpi_driver_data(device);
 	struct acpi_pci_driver *driver;
 
-	if (system_state != SYSTEM_BOOTING)
+	if (system_state != SYSTEM_BOOTING) {
+		pcibios_resource_survey_bus(root->bus);
 		pci_assign_unassigned_bus_resources(root->bus);
+	}
 
 	mutex_lock(&acpi_pci_root_lock);
 	list_for_each_entry(driver, &acpi_pci_drivers, node)
diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index ad6a8b6..847f3ca 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -158,6 +158,8 @@
 	return ret;
 }
 
+void __weak pcibios_resource_survey_bus(struct pci_bus *bus) { }
+
 /**
  * pci_bus_add_device - add a single device
  * @dev: device to add
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 15472d6..907b455 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -674,6 +674,7 @@
 /* Some device drivers need know if pci is initiated */
 extern int no_pci_devices(void);
 
+void pcibios_resource_survey_bus(struct pci_bus *bus);
 void pcibios_fixup_bus(struct pci_bus *);
 int __must_check pcibios_enable_device(struct pci_dev *, int mask);
 /* Architecture specific versions may override this (weak) */