2 files changed, 45 insertions, 0 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 315fea47e784..aad62af2b4c6 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -297,6 +297,49 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap)
 }
 EXPORT_SYMBOL_GPL(pci_find_ext_capability);
 
+/**
+ * pci_bus_find_ext_capability - find an extended capability
+ * @bus:   the PCI bus to query
+ * @devfn: PCI device to query
+ * @cap:   capability code
+ *
+ * Like pci_find_ext_capability() but works for pci devices that do not have a
+ * pci_dev structure set up yet.
+ *
+ * Returns the address of the requested capability structure within the
+ * device's PCI configuration space or 0 in case the device does not
+ * support it.
+ */
+int pci_bus_find_ext_capability(struct pci_bus *bus, unsigned int devfn,
+                                int cap)
+{
+        u32 header;
+        int ttl;
+        int pos = PCI_CFG_SPACE_SIZE;
+
+        /* minimum 8 bytes per capability */
+        ttl = (PCI_CFG_SPACE_EXP_SIZE - PCI_CFG_SPACE_SIZE) / 8;
+
+        if (!pci_bus_read_config_dword(bus, devfn, pos, &header))
+                return 0;
+        if (header == 0xffffffff || header == 0)
+                return 0;
+
+        while (ttl-- > 0) {
+                if (PCI_EXT_CAP_ID(header) == cap)
+                        return pos;
+
+                pos = PCI_EXT_CAP_NEXT(header);
+                if (pos < PCI_CFG_SPACE_SIZE)
+                        break;
+
+                if (!pci_bus_read_config_dword(bus, devfn, pos, &header))
+                        break;
+        }
+
+        return 0;
+}
+
 static int __pci_find_next_ht_cap(struct pci_dev *dev, int pos, int ht_cap)
 {
         int rc, ttl = PCI_FIND_CAP_TTL;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index c1968f464c38..65f8a8f9d3e5 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -631,6 +631,8 @@ enum pci_lost_interrupt_reason pci_lost_interrupt(struct pci_dev *dev);
 int pci_find_capability(struct pci_dev *dev, int cap);
 int pci_find_next_capability(struct pci_dev *dev, u8 pos, int cap);
 int pci_find_ext_capability(struct pci_dev *dev, int cap);
+int pci_bus_find_ext_capability(struct pci_bus *bus, unsigned int devfn,
+                                int cap);
 int pci_find_ht_capability(struct pci_dev *dev, int ht_cap);
 int pci_find_next_ht_capability(struct pci_dev *dev, int pos, int ht_cap);
 struct pci_bus *pci_find_next_bus(const struct pci_bus *from);