Re: [PATCH v3 1/8] Input: synaptics-rmi4: Use of_get_child_by_name() instead of of_find_node_by_name()

From: Andrew Duggan
Date: Mon Jul 18 2016 - 19:13:06 EST

On 07/18/2016 07:48 AM, Benjamin Tissoires wrote:
On Jul 13 2016 or thereabouts, Andrew Duggan wrote:
Calling of_find_node_by_name() assumes that the caller has incremented
the refcount of the of_node being passed in. Currently, the caller is
not incrementing the refcount of the of_node which results in the node
being prematurely freed when of_find_node_by_name() calls of_node_put()
on it. Instead use of_get_child_by_name() which does not call put on the
There are 2 other differences in using of_get_child_by_name() in place
of of_find_node_by_name(). One is that now we are following the OF tree
while the spinlock is not held. I think it's fine in our case. The
other difference is that the returned of_node has not been called
of_node_get() on it. I am not 100% sure, but I think it might be good to
call of_node_get() on the of node here, and in remove call
of_node_put(), just to be sure we don't use the of_node while it has
been freed.

The comment for of_get_child_by_name() says that it returns an of_node with the refcount incremented (drivers/of/base.c:717). Also, that the caller needs to call of_node_put() when finished with it. I take that to mean that the of_node_get() has been done for me by of_get_child_by_name(). Then rmi_unregister_function() calls of_node_put() when unregistered the function device undoing of_get_child_by_name()'s increment of the refcount.

Unless I am missing something I think the current implementation is correct. Hopefully, it is since this patch has already landed in Linus's tree.



Signed-off-by: Andrew Duggan <aduggan@xxxxxxxxxxxxx>
drivers/input/rmi4/rmi_bus.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/input/rmi4/rmi_bus.c b/drivers/input/rmi4/rmi_bus.c
index b368b05..253df96 100644
--- a/drivers/input/rmi4/rmi_bus.c
+++ b/drivers/input/rmi4/rmi_bus.c
@@ -157,11 +157,11 @@ static int rmi_function_match(struct device *dev, struct device_driver *drv)
static void rmi_function_of_probe(struct rmi_function *fn)
char of_name[9];
+ struct device_node *node = fn->rmi_dev->xport->dev->of_node;
snprintf(of_name, sizeof(of_name), "rmi4-f%02x",
- fn->dev.of_node = of_find_node_by_name(
- fn->rmi_dev->xport->dev->of_node, of_name);
+ fn->dev.of_node = of_get_child_by_name(node, of_name);
static inline void rmi_function_of_probe(struct rmi_function *fn)