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

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Message-ID: <CAMknhBEL3cv4L0A-W=_1EcDmD3Cj8apheDcpnqjyJjKBZuPYew@mail.gmail.com>
Date: Sun, 28 Jan 2024 15:11:01 -0600
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>
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, 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().


> +
>  #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
>
>