PCI: Add pcie_get_width_cap() to find max supported link width

Add pcie_get_width_cap() to find the max link width supported by a device.
Change max_link_width_show() to use pcie_get_width_cap().

Signed-off-by: Tal Gilboa <talgi@mellanox.com>
[bhelgaas: return width directly instead of error and *width, don't export
outside drivers/pci]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>

drivers/pci/pci-sysfs.c

@@ -167,15 +167,9 @@ static DEVICE_ATTR_RO(max_link_speed);
 static ssize_t max_link_width_show(struct device *dev,
 				   struct device_attribute *attr, char *buf)
 {
-	struct pci_dev *pci_dev = to_pci_dev(dev);
-	u32 linkcap;
-	int err;
-
-	err = pcie_capability_read_dword(pci_dev, PCI_EXP_LNKCAP, &linkcap);
-	if (err)
-		return -EINVAL;
+	struct pci_dev *pdev = to_pci_dev(dev);
 
-	return sprintf(buf, "%u\n", (linkcap & PCI_EXP_LNKCAP_MLW) >> 4);
+	return sprintf(buf, "%u\n", pcie_get_width_cap(pdev));
 }
 static DEVICE_ATTR_RO(max_link_width);
 

drivers/pci/pci.c

@@ -5190,6 +5190,24 @@ enum pci_bus_speed pcie_get_speed_cap(struct pci_dev *dev)
 	return PCI_SPEED_UNKNOWN;
 }
 
+/**
+ * pcie_get_width_cap - query for the PCI device's link width capability
+ * @dev: PCI device to query
+ *
+ * Query the PCI device width capability.  Return the maximum link width
+ * supported by the device.
+ */
+enum pcie_link_width pcie_get_width_cap(struct pci_dev *dev)
+{
+	u32 lnkcap;
+
+	pcie_capability_read_dword(dev, PCI_EXP_LNKCAP, &lnkcap);
+	if (lnkcap)
+		return (lnkcap & PCI_EXP_LNKCAP_MLW) >> 4;
+
+	return PCIE_LNK_WIDTH_UNKNOWN;
+}
+
 /**
  * pci_select_bars - Make BAR mask from the type of resource
  * @dev: the PCI device for which BAR mask is made

drivers/pci/pci.h

@@ -262,6 +262,7 @@ void pci_disable_bridge_window(struct pci_dev *dev);
 	 "Unknown speed")
 
 enum pci_bus_speed pcie_get_speed_cap(struct pci_dev *dev);
+enum pcie_link_width pcie_get_width_cap(struct pci_dev *dev);
 
 /* Single Root I/O Virtualization */
 struct pci_sriov {