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

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Message-ID: <CAJZ5v0jz=ee5TrvYs0_ovWn9sT06bcKDucmmocD8L-d9ZZ5DzQ@mail.gmail.com>
Date:   Mon, 27 Jun 2022 15:33:37 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Michael Walle <michael@...le.cc>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        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 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.

> 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.

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.