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

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Message-ID: <20160718144820.GL4663@mail.corp.redhat.com>
Date:	Mon, 18 Jul 2016 16:48:20 +0200
From:	Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:	Andrew Duggan <aduggan@...aptics.com>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Jiri Kosina <jikos@...nel.org>,
	Vincent Huang <vincent.huang@...synaptics.com>,
	Nick Dyer <nick@...anahar.org>, Chris Healy <cphealy@...il.com>
Subject: Re: [PATCH v3 1/8] Input: synaptics-rmi4: Use of_get_child_by_name()
 instead of of_find_node_by_name()

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.

Cheers,
Benjamin

> 
> Signed-off-by: Andrew Duggan <aduggan@...aptics.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
>