2 files changed, 103 insertions, 23 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ab36fb34ed01..4fa4c9ff04ae 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3000,7 +3000,7 @@
                                 or a set of devices (<pci_dev>). These are
                                 specified in one of the following formats:
 
-                                [<domain>:]<bus>:<device>.<func>
+                                [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
                                 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
 
                                 Note: the first format specifies a PCI
@@ -3009,7 +3009,11 @@
                                 firmware changes, or due to changes caused
                                 by other kernel parameters. If the
                                 domain is left unspecified, it is
-                                taken to be zero. The second format
+                                taken to be zero. Optionally, a path
+                                to a device through multiple device/function
+                                addresses can be specified after the base
+                                address (this is more robust against
+                                renumbering issues).  The second format
                                 selects devices using IDs from the
                                 configuration space which may match multiple
                                 devices in the system.
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 1574b2da25e7..a6c38b15ac33 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -192,6 +192,89 @@ EXPORT_SYMBOL_GPL(pci_ioremap_wc_bar);
 #endif
 
 /**
+ * pci_dev_str_match_path - test if a path string matches a device
+ * @dev:    the PCI device to test
+ * @p:      string to match the device against
+ * @endptr: pointer to the string after the match
+ *
+ * Test if a string (typically from a kernel parameter) formatted as a
+ * path of device/function addresses matches a PCI device. The string must
+ * be of the form:
+ *
+ *   [<domain>:]<bus>:<device>.<func>[/<device>.<func>]*
+ *
+ * A path for a device can be obtained using 'lspci -t'.  Using a path
+ * is more robust against bus renumbering than using only a single bus,
+ * device and function address.
+ *
+ * Returns 1 if the string matches the device, 0 if it does not and
+ * a negative error code if it fails to parse the string.
+ */
+static int pci_dev_str_match_path(struct pci_dev *dev, const char *path,
+                                  const char **endptr)
+{
+        int ret;
+        int seg, bus, slot, func;
+        char *wpath, *p;
+        char end;
+
+        *endptr = strchrnul(path, ';');
+
+        wpath = kmemdup_nul(path, *endptr - path, GFP_KERNEL);
+        if (!wpath)
+                return -ENOMEM;
+
+        while (1) {
+                p = strrchr(wpath, '/');
+                if (!p)
+                        break;
+                ret = sscanf(p, "/%x.%x%c", &slot, &func, &end);
+                if (ret != 2) {
+                        ret = -EINVAL;
+                        goto free_and_exit;
+                }
+
+                if (dev->devfn != PCI_DEVFN(slot, func)) {
+                        ret = 0;
+                        goto free_and_exit;
+                }
+
+                /*
+                 * Note: we don't need to get a reference to the upstream
+                 * bridge because we hold a reference to the top level
+                 * device which should hold a reference to the bridge,
+                 * and so on.
+                 */
+                dev = pci_upstream_bridge(dev);
+                if (!dev) {
+                        ret = 0;
+                        goto free_and_exit;
+                }
+
+                *p = 0;
+        }
+
+        ret = sscanf(wpath, "%x:%x:%x.%x%c", &seg, &bus, &slot,
+                     &func, &end);
+        if (ret != 4) {
+                seg = 0;
+                ret = sscanf(wpath, "%x:%x.%x%c", &bus, &slot, &func, &end);
+                if (ret != 3) {
+                        ret = -EINVAL;
+                        goto free_and_exit;
+                }
+        }
+
+        ret = (seg == pci_domain_nr(dev->bus) &&
+               bus == dev->bus->number &&
+               dev->devfn == PCI_DEVFN(slot, func));
+
+free_and_exit:
+        kfree(wpath);
+        return ret;
+}
+
+/**
  * pci_dev_str_match - test if a string matches a device
  * @dev:    the PCI device to test
  * @p:      string to match the device against
@@ -200,13 +283,16 @@ EXPORT_SYMBOL_GPL(pci_ioremap_wc_bar);
  * Test if a string (typically from a kernel parameter) matches a specified
  * PCI device. The string may be of one of the following formats:
  *
- *   [<domain>:]<bus>:<device>.<func>
+ *   [<domain>:]<bus>:<device>.<func>[/<device>.<func>]*
  *   pci:<vendor>:<device>[:<subvendor>:<subdevice>]
  *
  * The first format specifies a PCI bus/device/function address which
  * may change if new hardware is inserted, if motherboard firmware changes,
  * or due to changes caused in kernel parameters. If the domain is
- * left unspecified, it is taken to be 0.
+ * left unspecified, it is taken to be 0.  In order to be robust against
+ * bus renumbering issues, a path of PCI device/function numbers may be used
+ * to address the specific device.  The path for a device can be determined
+ * through the use of 'lspci -t'.
  *
  * The second format matches devices using IDs in the configuration
  * space which may match multiple devices in the system. A value of 0
@@ -222,7 +308,7 @@ static int pci_dev_str_match(struct pci_dev *dev, const char *p,
                              const char **endptr)
 {
         int ret;
-        int seg, bus, slot, func, count;
+        int count;
         unsigned short vendor, device, subsystem_vendor, subsystem_device;
 
         if (strncmp(p, "pci:", 4) == 0) {
@@ -248,25 +334,15 @@ static int pci_dev_str_match(struct pci_dev *dev, const char *p,
                     (!subsystem_device ||
                             subsystem_device == dev->subsystem_device))
                         goto found;
-
         } else {
-                /* PCI Bus, Device, Function IDs are specified */
-                ret = sscanf(p, "%x:%x:%x.%x%n", &seg, &bus, &slot,
-                             &func, &count);
-                if (ret != 4) {
-                        seg = 0;
-                        ret = sscanf(p, "%x:%x.%x%n", &bus, &slot,
-                                     &func, &count);
-                        if (ret != 3)
-                                return -EINVAL;
-                }
-
-                p += count;
-
-                if (seg == pci_domain_nr(dev->bus) &&
-                    bus == dev->bus->number &&
-                    slot == PCI_SLOT(dev->devfn) &&
-                    func == PCI_FUNC(dev->devfn))
+                /*
+                 * PCI Bus, Device, Function IDs are specified
+                 *  (optionally, may include a path of devfns following it)
+                 */
+                ret = pci_dev_str_match_path(dev, p, &p);
+                if (ret < 0)
+                        return ret;
+                else if (ret)
                         goto found;
         }