PCI: Add pci_scan_root_bus_bridge() interface

The current pci_scan_root_bus() interface is made up of two main code
paths:

- pci_create_root_bus()
- pci_scan_child_bus()

pci_create_root_bus() is a wrapper function that allows to create a struct
pci_host_bridge structure, initialize it with the passed parameters and
register it with the kernel.

As the struct pci_host_bridge require additional struct members,
pci_create_root_bus() parameters list has grown in time, making it unwieldy
to add further parameters to it in case the struct pci_host_bridge gains
more members fields to augment its functionality.

Since PCI core code provides functions to allocate struct pci_host_bridge,
instead of forcing the pci_create_root_bus() interface to add new
parameters to cater for new struct pci_host_bridge functionality, it is
more suitable to add an interface in PCI core code to scan a PCI bus
straight from a struct pci_host_bridge created and customized by each
specific PCI host controller driver.

Add a pci_scan_root_bus_bridge() function to allow PCI host controller
drivers to create and initialize struct pci_host_bridge and scan the
resulting bus.

Signed-off-by: Lorenzo Pieralisi <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>

drivers/pci/probe.c

···
 			res, ret ? "can not be" : "is");
 }
 
+int pci_scan_root_bus_bridge(struct pci_host_bridge *bridge)
+{
+	struct resource_entry *window;
+	bool found = false;
+	struct pci_bus *b;
+	int max, bus, ret;
+
+	if (!bridge)
+		return -EINVAL;
+
+	resource_list_for_each_entry(window, &bridge->windows)
+		if (window->res->flags & IORESOURCE_BUS) {
+			found = true;
+			break;
+		}
+
+	ret = pci_register_host_bridge(bridge);
+	if (ret < 0)
+		return ret;
+
+	b = bridge->bus;
+	bus = bridge->busnr;
+
+	if (!found) {
+		dev_info(&b->dev,
+		 "No busn resource found for root bus, will use [bus %02x-ff]\n",
+			bus);
+		pci_bus_insert_busn_res(b, bus, 255);
+	}
+
+	max = pci_scan_child_bus(b);
+
+	if (!found)
+		pci_bus_update_busn_res_end(b, max);
+
+	return 0;
+}
+EXPORT_SYMBOL(pci_scan_root_bus_bridge);
+
 struct pci_bus *pci_scan_root_bus_msi(struct device *parent, int bus,
 		struct pci_ops *ops, void *sysdata,
 		struct list_head *resources, struct msi_controller *msi)

include/linux/pci.h

···
 struct pci_bus *pci_scan_root_bus(struct device *parent, int bus,
 					     struct pci_ops *ops, void *sysdata,
 					     struct list_head *resources);
+int pci_scan_root_bus_bridge(struct pci_host_bridge *bridge);
 struct pci_bus *pci_add_new_bus(struct pci_bus *parent, struct pci_dev *dev,
 				int busnr);
 void pcie_update_link_speed(struct pci_bus *bus, u16 link_status);