[PATCH 2/8] PCI: Add pci_find_common_upstream_dev()

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

From: "wdavis@nvidia.com" <wdavis@nvidia.com>

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

Signed-off-by: Will Davis <wdavis@nvidia.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/pci/search.c | 24 ++++++++++++++++++++++++
 include/linux/pci.h  |  2 ++
 2 files changed, 26 insertions(+)

diff --git a/drivers/pci/search.c b/drivers/pci/search.c
index bc1e023f1353..446648f4238b 100644
--- a/drivers/pci/search.c
+++ b/drivers/pci/search.c
@@ -393,3 +393,27 @@ 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
+ * @dev: the PCI device from which the bus hierarchy walk will start
+ * @other: the PCI device whose bus number will be used for the search
+ *
+ * Walks up the bus hierarchy from the @dev device, looking for the first bus
+ * which the @other 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 *dev,
+					     struct pci_dev *other)
+{
+	struct pci_dev *pdev = dev;
+
+	while (pdev != NULL) {
+		if ((other->bus->number >= pdev->bus->busn_res.start) &&
+		    (other->bus->number <= pdev->bus->busn_res.end))
+			return pdev;
+		pdev = pci_upstream_bridge(pdev);
+	}
+
+	return NULL;
+}
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 024a1beda008..0d29f5cdcb04 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -956,6 +956,8 @@ 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);
-- 
2.14.1