Messages in this thread | | | Subject | 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, 18 Jul 2016 16:13:00 -0700 |
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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 >> of_node. > 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.
Andrew
> > Cheers, > Benjamin > >> Signed-off-by: Andrew Duggan <aduggan@synaptics.com> >> --- >> 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->fd.function_number); >> - 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); >> } >> #else >> static inline void rmi_function_of_probe(struct rmi_function *fn) >> -- >> 2.5.0 >>
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