[PATCH v4 10/12] pci: add pci_find_common_upstream_dev()

[Will Davis <wdavis@nvidia.com>]

Adds an interface to find the first device which is upstream of both
devices.

Signed-off-by: Will Davis <wdavis@nvidia.com>
---
 drivers/pci/search.c | 25 +++++++++++++++++++++++++
 include/linux/pci.h  |  2 ++
 2 files changed, 27 insertions(+)

diff --git a/drivers/pci/search.c b/drivers/pci/search.c
index a20ce7d..cbd8163 100644
--- a/drivers/pci/search.c
+++ b/drivers/pci/search.c
@@ -384,3 +384,28 @@ int pci_dev_present(const struct pci_device_id *ids)
 	return 0;
 }
 EXPORT_SYMBOL(pci_dev_present);
+
+/**
+ * pci_find_common_upstream_dev - Returns the first common upstream device
+ * @from: the PCI device to search for a common upstream device from
+ * @to: the PCI device to search for a common upstream device to
+ *
+ * Walks up the bus hierarchy from the @from device, looking for the first bus
+ * which the @to device is downstream of. Returns %NULL if the devices do not
+ * share any upstream devices.
+ */
+struct pci_dev *pci_find_common_upstream_dev(struct pci_dev *from,
+					     struct pci_dev *to)
+{
+	struct pci_dev *pdev = from;
+
+	while (pdev != NULL) {
+		if ((to->bus->number >= pdev->bus->busn_res.start) &&
+		    (to->bus->number <= pdev->bus->busn_res.end))
+			return pdev;
+		pdev = pdev->bus->self;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL(pci_find_common_upstream_dev);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index d58063e..8262b9e 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -860,6 +860,8 @@ static inline struct pci_dev *pci_get_bus_and_slot(unsigned int bus,
 }
 struct pci_dev *pci_get_class(unsigned int class, struct pci_dev *from);
 int pci_dev_present(const struct pci_device_id *ids);
+struct pci_dev *pci_find_common_upstream_dev(struct pci_dev *from,
+					     struct pci_dev *to);
 
 int pci_bus_read_config_byte(struct pci_bus *bus, unsigned int devfn,
 			     int where, u8 *val);
-- 
2.4.6