PCI: Add function to obtain minimum link width and speed

[~andy/linux] / drivers / pci / pci.c

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e37fea6e178d2dab00d3334848d231117d525013..c71e78c46705e5f202bda5bd56f39bbfaaa8c46c 100644 (file)
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3578,6 +3578,49 @@ int pcie_set_mps(struct pci_dev *dev, int mps)
                                                  PCI_EXP_DEVCTL_PAYLOAD, v);
 }
 
+/**
+ * pcie_get_minimum_link - determine minimum link settings of a PCI device
+ * @dev: PCI device to query
+ * @speed: storage for minimum speed
+ * @width: storage for minimum width
+ *
+ * This function will walk up the PCI device chain and determine the minimum
+ * link width and speed of the device.
+ */
+int pcie_get_minimum_link(struct pci_dev *dev, enum pci_bus_speed *speed,
+                         enum pcie_link_width *width)
+{
+       int ret;
+
+       *speed = PCI_SPEED_UNKNOWN;
+       *width = PCIE_LNK_WIDTH_UNKNOWN;
+
+       while (dev) {
+               u16 lnksta;
+               enum pci_bus_speed next_speed;
+               enum pcie_link_width next_width;
+
+               ret = pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
+               if (ret)
+                       return ret;
+
+               next_speed = pcie_link_speed[lnksta & PCI_EXP_LNKSTA_CLS];
+               next_width = (lnksta & PCI_EXP_LNKSTA_NLW) >>
+                       PCI_EXP_LNKSTA_NLW_SHIFT;
+
+               if (next_speed < *speed)
+                       *speed = next_speed;
+
+               if (next_width < *width)
+                       *width = next_width;
+
+               dev = dev->bus->self;
+       }
+
+       return 0;
+}
+EXPORT_SYMBOL(pcie_get_minimum_link);
+
 /**
  * pci_select_bars - Make BAR mask from the type of resource
  * @dev: the PCI device for which BAR mask is made