PCI: Add pci_upstream_bridge()

This adds a pci_upstream_bridge() interface to find the PCI-to-PCI bridge
upstream from a device.  This is typically just "dev->bus->self", but in
the case of a VF on a virtual bus, we have to start from the corresponding
PF.  Returns NULL if there is no upstream PCI bridge, i.e., if the device
is on a root bus.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>

include/linux/pci.h

@@ -480,6 +480,15 @@ static inline bool pci_is_root_bus(struct pci_bus *pbus)
 	return !(pbus->parent);
 }
 
+static inline struct pci_dev *pci_upstream_bridge(struct pci_dev *dev)
+{
+	dev = pci_physfn(dev);
+	if (pci_is_root_bus(dev->bus))
+		return NULL;
+
+	return dev->bus->self;
+}
+
 #ifdef CONFIG_PCI_MSI
 static inline bool pci_dev_msi_enabled(struct pci_dev *pci_dev)
 {