On 5/13/2014 7:58 AM, Grant Likely wrote:

Make of_find_node_by_path() handle aliases as prefixes. To make this

work the name search is refactored to search by path component instead

of by full string. This should be a more efficient search, and it makes

it possible to start a search at a subnode of a tree.

Signed-off-by: David Daney <david.daney-YGCgFSpz5w/QT0dZR+AlfA@public.gmane.org>

Signed-off-by: Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>

[grant.likely: Rework to not require allocating at runtime]

Acked-by: Rob Herring <redacted>

Signed-off-by: Grant Likely <redacted>

---

 drivers/of/base.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++----

 1 file changed, 56 insertions(+), 4 deletions(-)

Was this patch created against a tree that has modifications to device tree

locking?
  I get a hang due to deadlock when I apply it.  Patch to verify the
cause is below.




From: Frank Rowand <frank.rowand-/MT0OVThwyLZJqsBc5GL+g@public.gmane.org>

Do not apply this patch -- it is not a valid fix.  The point of this patch
is to confirm the cause of a bug.

Problem seen on 3.15-rc1 with dragonboard platform patches added.

The dragonboard hangs on boot the very first time that of_find_node_by_path()
is called:

   of_find_node_by_path()
      raw_spin_lock_irqsave(&devtree_lock, flags)
      np = __of_find_node_by_path(np, path)
         for_each_child_of_node(parent, child) {

            // This is a define:
	    #define for_each_child_of_node(parent, child) \
	       for (child = of_get_next_child(parent, NULL); child != NULL; \

	          // Resulting in a deadlock when of_get_next_child()
		  // attempts to lock the same lock:
	          raw_spin_lock_irqsave(&devtree_lock, flags)

When this patch is applied, the first lock is commented out so the
deadlock does not occur and the boot completes.

Not-signed-off-by: Frank Rowand [off-list ref]
---
 drivers/of/base.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: b/drivers/of/base.c
===================================================================

--- a/drivers/of/base.c
+++ b/drivers/of/base.c

@@ -835,13 +835,17 @@ struct device_node *of_find_node_by_path
 	}
 
 	/* Step down the tree matching path components */
+#if 0
 	raw_spin_lock_irqsave(&devtree_lock, flags);
+#endif
 	while (np && *path == '/') {
 		path++; /* Increment past '/' delimiter */
 		np = __of_find_node_by_path(np, path);
 		path = strchrnul(path, '/');
 	}
+#if 0
 	raw_spin_unlock_irqrestore(&devtree_lock, flags);
+#endif
 	return np;
 }
 EXPORT_SYMBOL(of_find_node_by_path);
--

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