linux-kernel - Re: [RFC PATCH 2/5] of: Introduce for_each_child_of_node_scoped() to automate of_node

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Date: Wed, 31 Jan 2024 17:51:48 -0600
From: Rob Herring <robh@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Jonathan Cameron <jic23@...nel.org>, linux-iio@...r.kernel.org,
	Frank Rowand <frowand.list@...il.com>, linux-kernel@...r.kernel.org,
	Julia Lawall <Julia.Lawall@...ia.fr>,
	Nicolas Palix <nicolas.palix@...g.fr>,
	Sumera Priyadarsini <sylphrenadin@...il.com>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nuno Sá <nuno.sa@...log.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [RFC PATCH 2/5] of: Introduce for_each_child_of_node_scoped() to
 automate of_node_put() handling

On Sun, Jan 28, 2024 at 03:11:01PM -0600, David Lechner wrote:
> On Sun, Jan 28, 2024 at 10:06 AM Jonathan Cameron <jic23@...nel.org> wrote:
> >
> > From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> >
> > To avoid issues with out of order cleanup, or ambiguity about when the
> > auto freed data is first instantiated, do it within the for loop definition.
> >
> > The disadvantage is that the struct device_node *child variable creation
> > is not immediately obvious where this is used.
> > However, in many cases, if there is another definition of
> > struct device_node *child; the compiler / static analysers will notify us
> > that it is unused, or uninitialized.
> >
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> > ---
> >  include/linux/of.h | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/include/linux/of.h b/include/linux/of.h
> > index 50e882ee91da..f822226eac6d 100644
> > --- a/include/linux/of.h
> > +++ b/include/linux/of.h
> > @@ -1434,6 +1434,12 @@ static inline int of_property_read_s32(const struct device_node *np,
> >         for (child = of_get_next_available_child(parent, NULL); child != NULL; \
> >              child = of_get_next_available_child(parent, child))
> >
> > +#define for_each_child_of_node_scoped(parent, child) \
> > +       for (struct device_node *child __free(device_node) =            \
> > +            of_get_next_child(parent, NULL);                           \
> > +            child != NULL;                                             \
> > +            child = of_get_next_available_child(parent, child))
> 
> Doesn't this need to match the initializer (of_get_next_child)?
> Otherwise it seems like the first node could be a disabled node but no
> other disabled nodes would be included in the iteration.
> 
> It seems like we would want two macros, one for each variation,
> analogous to for_each_child_of_node() and
> for_each_available_child_of_node().

Yes, but really I'd like these the other way around. 'available' should 
be the default as disabled should really be the same as a node not 
present except for a few cases where it is not.

I bring it up only because if we're changing things then it is a 
convenient time to change this. That's really a side issue to sorting 
out how this new way should work.

Rob