PCI: fix ARI code to be compatible with mixed ARI/non-ARI systems

The original ARI support code has a compatibility problem with non-ARI
devices.  If a device doesn't support ARI, turning on ARI forwarding on
its upper level bridge will cause undefined behavior.

This fix turns on ARI forwarding only when the subordinate devices
support it.

Tested-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Yu Zhao <yu.zhao@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/pci.c

@@ -1309,27 +1309,32 @@ void pci_enable_ari(struct pci_dev *dev)
 	int pos;
 	u32 cap;
 	u16 ctrl;
+	struct pci_dev *bridge;
 
-	if (!dev->is_pcie)
+	if (!dev->is_pcie || dev->devfn)
 		return;
 
-	if (dev->pcie_type != PCI_EXP_TYPE_ROOT_PORT &&
-	    dev->pcie_type != PCI_EXP_TYPE_DOWNSTREAM)
+	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ARI);
+	if (!pos)
 		return;
 
-	pos = pci_find_capability(dev, PCI_CAP_ID_EXP);
+	bridge = dev->bus->self;
+	if (!bridge || !bridge->is_pcie)
+		return;
+
+	pos = pci_find_capability(bridge, PCI_CAP_ID_EXP);
 	if (!pos)
 		return;
 
-	pci_read_config_dword(dev, pos + PCI_EXP_DEVCAP2, &cap);
+	pci_read_config_dword(bridge, pos + PCI_EXP_DEVCAP2, &cap);
 	if (!(cap & PCI_EXP_DEVCAP2_ARI))
 		return;
 
-	pci_read_config_word(dev, pos + PCI_EXP_DEVCTL2, &ctrl);
+	pci_read_config_word(bridge, pos + PCI_EXP_DEVCTL2, &ctrl);
 	ctrl |= PCI_EXP_DEVCTL2_ARI;
-	pci_write_config_word(dev, pos + PCI_EXP_DEVCTL2, ctrl);
+	pci_write_config_word(bridge, pos + PCI_EXP_DEVCTL2, ctrl);
 
-	dev->ari_enabled = 1;
+	bridge->ari_enabled = 1;
 }
 
 int