PCI: Add pci_find_next_ext_capability()

Some extended capabilities, e.g., the vendor-specific capability, can
occur several times.  The existing pci_find_ext_capability() only finds
the first occurrence.  This adds pci_find_next_ext_capability(), which
can iterate through all of them.
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

drivers/pci/pci.c

@@ -286,20 +286,17 @@ static int pci_pcie_cap2(struct pci_dev *dev)
 }
 
 /**
- * pci_find_ext_capability - Find an extended capability
+ * pci_find_next_ext_capability - Find an extended capability
  * @dev: PCI device to query
+ * @start: address at which to start looking (0 to start at beginning of list)
  * @cap: capability code
  *
- * Returns the address of the requested extended capability structure
+ * Returns the address of the next matching extended capability structure
  * within the device's PCI configuration space or 0 if the device does
- * not support it.  Possible values for @cap:
- *
- *  %PCI_EXT_CAP_ID_ERR		Advanced Error Reporting
- *  %PCI_EXT_CAP_ID_VC		Virtual Channel
- *  %PCI_EXT_CAP_ID_DSN		Device Serial Number
- *  %PCI_EXT_CAP_ID_PWR		Power Budgeting
+ * not support it.  Some capabilities can occur several times, e.g., the
+ * vendor-specific capability, and this provides a way to find them all.
  */
-int pci_find_ext_capability(struct pci_dev *dev, int cap)
+int pci_find_next_ext_capability(struct pci_dev *dev, int start, int cap)
 {
 	u32 header;
 	int ttl;
@@ -311,6 +308,9 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap)
 	if (dev->cfg_size <= PCI_CFG_SPACE_SIZE)
 		return 0;
 
+	if (start)
+		pos = start;
+
 	if (pci_read_config_dword(dev, pos, &header) != PCIBIOS_SUCCESSFUL)
 		return 0;
 
@@ -322,7 +322,7 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap)
 		return 0;
 
 	while (ttl-- > 0) {
-		if (PCI_EXT_CAP_ID(header) == cap)
+		if (PCI_EXT_CAP_ID(header) == cap && pos != start)
 			return pos;
 
 		pos = PCI_EXT_CAP_NEXT(header);
@@ -335,6 +335,26 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap)
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(pci_find_next_ext_capability);
+
+/**
+ * pci_find_ext_capability - Find an extended capability
+ * @dev: PCI device to query
+ * @cap: capability code
+ *
+ * Returns the address of the requested extended capability structure
+ * within the device's PCI configuration space or 0 if the device does
+ * not support it.  Possible values for @cap:
+ *
+ *  %PCI_EXT_CAP_ID_ERR		Advanced Error Reporting
+ *  %PCI_EXT_CAP_ID_VC		Virtual Channel
+ *  %PCI_EXT_CAP_ID_DSN		Device Serial Number
+ *  %PCI_EXT_CAP_ID_PWR		Power Budgeting
+ */
+int pci_find_ext_capability(struct pci_dev *dev, int cap)
+{
+	return pci_find_next_ext_capability(dev, 0, cap);
+}
 EXPORT_SYMBOL_GPL(pci_find_ext_capability);
 
 static int __pci_find_next_ht_cap(struct pci_dev *dev, int pos, int ht_cap)

include/linux/pci.h

@@ -755,6 +755,7 @@ 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_find_next_ext_capability(struct pci_dev *dev, int pos, 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);