powerpc/pseries: Cleanup on pci_dn_reconfig_notifier()

This applies cleanup on pci_dn_reconfig_notifier(), no functional
changes:

   * Rename variable "pci" to "pdn" to indicate its purpose clearly.
   * The parent node can be released at any time. So it should be
     hold with of_get_parent() before accessing it.
   * The device node doesn't have to have parent node in theory.
     More check on this.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/pseries/setup.c

@@ -254,24 +254,26 @@ static void __init pseries_discover_pic(void)
 static int pci_dn_reconfig_notifier(struct notifier_block *nb, unsigned long action, void *data)
 {
 	struct of_reconfig_data *rd = data;
-	struct device_node *np = rd->dn;
-	struct pci_dn *pci = NULL;
+	struct device_node *parent, *np = rd->dn;
+	struct pci_dn *pdn;
 	int err = NOTIFY_OK;
 
 	switch (action) {
 	case OF_RECONFIG_ATTACH_NODE:
-		pci = np->parent->data;
-		if (pci) {
-			update_dn_pci_info(np, pci->phb);
-
-			/* Create EEH device for the OF node */
-			eeh_dev_init(PCI_DN(np), pci->phb);
+		parent = of_get_parent(np);
+		pdn = parent ? PCI_DN(parent) : NULL;
+		if (pdn) {
+			/* Create pdn and EEH device */
+			update_dn_pci_info(np, pdn->phb);
+			eeh_dev_init(PCI_DN(np), pdn->phb);
 		}
+
+		of_node_put(parent);
 		break;
 	case OF_RECONFIG_DETACH_NODE:
-		pci = PCI_DN(np);
-		if (pci)
-			list_del(&pci->list);
+		pdn = PCI_DN(np);
+		if (pdn)
+			list_del(&pdn->list);
 		break;
 	default:
 		err = NOTIFY_DONE;