From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jacek Anaszewski <j.anaszewski@samsung.com>
Subject: Re: LED subsystem child DT node ref counting
Date: Mon, 27 Apr 2015 11:26:27 +0200
Message-ID: <553E00C3.3060409@samsung.com>
References: <5530E891.20707@samsung.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Return-path: <linux-leds-owner@vger.kernel.org>
Received: from mailout3.w1.samsung.com ([210.118.77.13]:31011 "EHLO
	mailout3.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S932428AbbD0J0b (ORCPT
	<rfc822;linux-leds@vger.kernel.org>); Mon, 27 Apr 2015 05:26:31 -0400
In-reply-to: <5530E891.20707@samsung.com>
Sender: linux-leds-owner@vger.kernel.org
List-Id: linux-leds@vger.kernel.org
To: "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>, Grant Likely <grant.likely@linaro.org>, Rob Herring <robh+dt@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Pawel Moll <pawel.moll@arm.com>, Ian Campbell <ijc+devicetree@hellion.org.uk>, Kumar Gala <galak@codeaurora.org>
Cc: Linux LED Subsystem <linux-leds@vger.kernel.org>, Sakari Ailus <sakari.ailus@iki.fi>, Bryan Wu <cooloney@gmail.com>

Gentle reminder. Can anyone clarify this?

On 04/17/2015 01:03 PM, Jacek Anaszewski wrote:
> Hi,
>
> I'd like to clarify whether LED subsystem drivers behave correctly
> or not, regarding child DT nodes reference counting.
>
> Single LED controller can have connected more then one LED to it.
> The LEDs are represented by child DT nodes of the node representing
> the controller (see Documentation/devicetree/bindings/leds).
>
> LED subsystem drivers parse child DT nodes and use the node name,
> or 'label' property string as the LED class device name.
>
> This is usually accomplished like below:
>
> for_each_child_of_node(np, child) {
>      ...
>      led.name = of_get_property(child, "label", NULL) ? : child->name;
>
>
> The question is whether reference count of the child node shouldn't
> be increased here with of_node_get(child). Whereas intuitively it could
> be thought of as a right thing to do, empirical experiments don't
> necessary confirm that.
>
> When I print the value of child_node->kobj.kref.refcount.counter
> inside for_each loop it is 3 and and after leaving the loop it gets
> decreased to 2. On driver removal the value is also 2. It means that
> label is available all the time, without increasing child node ref
> counter.
>
> I'd like to ask if this is guaranteed to be always true.
>


-- 
Best Regards,
Jacek Anaszewski