of/irq: of_irq_find_parent: check for parent equal to child

An interrupt controller may often implicitly inherit itself from a parent
node when in fact the controller is the interrupt root controller. Guard
against the case of child == parent and return NULL in this case.

This can also be fixed by adding an explicit "interrupt-parent;" to a root
interrupt controller node.

Based on code from Grant Likely.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Grant Likely <grant.likely@secretlab.ca>

1 files changed, 7 insertions, 7 deletions

diff --git a/drivers/of/irq.c b/drivers/of/irq.c
index 9f689f1da0fc..6a5b5e777dd2 100644
--- a/drivers/of/irq.c
+++ b/drivers/of/irq.c
@@ -58,27 +58,27 @@ EXPORT_SYMBOL_GPL(irq_of_parse_and_map);
  */
 struct device_node *of_irq_find_parent(struct device_node *child)
 {
-        struct device_node *p;
+        struct device_node *p, *c = child;
         const __be32 *parp;
 
-        if (!of_node_get(child))
+        if (!of_node_get(c))
                 return NULL;
 
         do {
-                parp = of_get_property(child, "interrupt-parent", NULL);
+                parp = of_get_property(c, "interrupt-parent", NULL);
                 if (parp == NULL)
-                        p = of_get_parent(child);
+                        p = of_get_parent(c);
                 else {
                         if (of_irq_workarounds & OF_IMAP_NO_PHANDLE)
                                 p = of_node_get(of_irq_dflt_pic);
                         else
                                 p = of_find_node_by_phandle(be32_to_cpup(parp));
                 }
-                of_node_put(child);
-                child = p;
+                of_node_put(c);
+                c = p;
         } while (p && of_get_property(p, "#interrupt-cells", NULL) == NULL);
 
-        return p;
+        return (p == child) ? NULL : p;
 }
 
 /**