PCI: introduce pci_pcie_cap()

Introduce pci_pcie_cap() API that returns saved PCIe capability offset
(currently it is saved in 'pcie_cap' field in the struct PCI dev).
Using pci_pcie_cap() instead of pci_find_capability() avoids
unnecessary search in PCI configuration space.
Signed-off-by: NKenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>

include/linux/pci.h

@@ -1301,5 +1301,21 @@ extern void pci_hp_create_module_link(struct pci_slot *pci_slot);
 extern void pci_hp_remove_module_link(struct pci_slot *pci_slot);
 #endif
 
+/**
+ * pci_pcie_cap - get the saved PCIe capability offset
+ * @dev: PCI device
+ *
+ * PCIe capability offset is calculated at PCI device initialization
+ * time and saved in the data structure. This function returns saved
+ * PCIe capability offset. Using this instead of pci_find_capability()
+ * reduces unnecessary search in the PCI configuration space. If you
+ * need to calculate PCIe capability offset from raw device for some
+ * reasons, please use pci_find_capability() instead.
+ */
+static inline int pci_pcie_cap(struct pci_dev *dev)
+{
+	return dev->pcie_cap;
+}
+
 #endif /* __KERNEL__ */
 #endif /* LINUX_PCI_H */