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>

diff --git a/drivers/of/irq.c b/drivers/of/irq.c
index 9f689f1da0fc05f051bbabc8f29a7fecd6faafc9..6a5b5e777dd21a6ebf7a112d9efae1ef211e4d9e 100644 (file)
--- 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;
 }
 
 /**