linux-kernel - Re: fwnode_for_each_child_node() and OF backend discrepancy

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Message-ID: <0b8e357d-1d8b-843f-d8b6-72c760bcd6fb@linaro.org>
Date:   Tue, 28 Jun 2022 12:32:12 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Michael Walle <michael@...le.cc>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Saravana Kannan <saravanak@...gle.com>
Subject: Re: fwnode_for_each_child_node() and OF backend discrepancy

On 27/06/2022 15:33, Rafael J. Wysocki wrote:
> On Mon, Jun 27, 2022 at 3:08 PM Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
>>
>> On 27/06/2022 14:49, Michael Walle wrote:
>>> Hi,
>>>
>>> I tired to iterate over all child nodes, regardless if they are
>>> available
>>> or not. Now there is that handy fwnode_for_each_child_node() (and the
>>> fwnode_for_each_available_child_node()). The only thing is the OF
>>> backend
>>> already skips disabled nodes [1], making fwnode_for_each_child_node()
>>> and
>>> fwnode_for_each_available_child_node() behave the same with the OF
>>> backend.
>>>
>>> Doesn't seem to be noticed by anyone for now. I'm not sure how to fix
>>> that
>>> one. fwnode_for_each_child_node() and also fwnode_get_next_child_node()
>>> are
>>> used by a handful of drivers. I've looked at some, but couldn't decide
>>> whether they really want to iterate over all child nodes or just the
>>> enabled
>>> ones.
>>
>> If I get it correctly, this was introduced  by 8a0662d9ed29 ("Driver
>> core: Unified interface for firmware node properties")
>> .
> 
> Originally it was, but then it has been reworked a few times.
> 
> The backend callbacks were introduced by Sakari, in particular.

I see you as an author of 8a0662d9ed29 which adds
device_get_next_child_node() and uses of_get_next_available_child()
instead of of_get_next_child(). Although it was back in 2014, so maybe
it will be tricky to get original intention. :)

Which commit do you mean when you refer to Sakari's work?

> 
>> The question to Rafael - what was your intention when you added
>> device_get_next_child_node() looking only for available nodes?
> 
> That depends on the backend.

We talk about OF backend. In your commit device_get_next_child_node for
OF uses explicitly available node, not any node.

> fwnode_for_each_available_child_node() is more specific and IIRC it
> was introduced for fw_devlink (CC Saravana).
> 
>> My understanding is that this implementation should be consistent with
>> OF implementation, so fwnode_get_next_child_node=get any child.
> 
> IIUC, the OF implementation is not consistent with the
> fwnode_get_next_child_node=get any child thing.
> 
>> However maybe ACPI treats it somehow differently?
> 
> acpi_get_next_subnode() simply returns the next subnode it can find.


Best regards,
Krzysztof