[PATCH 4.18 140/235] of: fix phandle cache creation for DTs with no phandles

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rob Herring <robh@xxxxxxxxxx>

commit e54192b48da75f025ae4b277925eaf6aca1d13bd upstream.

With commit 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of
of_find_node_by_phandle()"), a G3 PowerMac fails to boot. The root cause
is the DT for this system has no phandle properties when booted with
BootX. of_populate_phandle_cache() does not handle the case of no
phandles correctly. The problem is roundup_pow_of_two() for 0 is
undefined. The implementation subtracts 1 underflowing and then things
are in the weeds.

Fixes: 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of of_find_node_by_phandle()")
Cc: stable@xxxxxxxxxxxxxxx # 4.17+
Reported-by: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>
Tested-by: Stan Johnson <userm57@xxxxxxxxx>
Reviewed-by: Frank Rowand <frank.rowand@xxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/of/base.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -118,6 +118,9 @@ void of_populate_phandle_cache(void)
 		if (np->phandle && np->phandle != OF_PHANDLE_ILLEGAL)
 			phandles++;
 
+	if (!phandles)
+		goto out;
+
 	cache_entries = roundup_pow_of_two(phandles);
 	phandle_cache_mask = cache_entries - 1;