Re: LED subsystem child DT node ref counting

[Jacek Anaszewski <j.anaszewski@samsung.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