From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Duggan Subject: Re: [PATCH v3 1/8] Input: synaptics-rmi4: Use of_get_child_by_name() instead of of_find_node_by_name() Date: Mon, 18 Jul 2016 16:13:00 -0700 Message-ID: <578D627C.3020800@synaptics.com> References: <1468476488-7935-1-git-send-email-aduggan@synaptics.com> <20160718144820.GL4663@mail.corp.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from us-mx1.synaptics.com ([192.147.44.131]:64924 "EHLO us-mx1.synaptics.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751930AbcGRXNC (ORCPT ); Mon, 18 Jul 2016 19:13:02 -0400 In-Reply-To: <20160718144820.GL4663@mail.corp.redhat.com> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Benjamin Tissoires Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, Dmitry Torokhov , Linus Walleij , Jiri Kosina , Vincent Huang , Nick Dyer , Chris Healy 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 >> --- >> 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 >>