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

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Date: Sun, 4 Feb 2024 19:56:11 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: linux-iio@...r.kernel.org, Rob Herring <robh@...nel.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, 28 Jan 2024 15:11:01 -0600
David Lechner <dlechner@...libre.com> 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.

FwIW that was was entirely unintentional.  Not sure how it happened :(
Anyhow, now will be for_each_available_child_of_node_scoped() with the
right first call.

> 
> 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().
> 
> 
> > +
> >  #define for_each_of_cpu_node(cpu) \
> >         for (cpu = of_get_next_cpu_node(NULL); cpu != NULL; \
> >              cpu = of_get_next_cpu_node(cpu))
> > --
> > 2.43.0
> >
> >