linux-kernel - Re: [PATCH v4 1/2] device property: Add scoped fwnode child node iterators

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Message-ID: <aLhAKJBUNQVH1Vmf@kekkonen.localdomain>
Date: Wed, 3 Sep 2025 16:18:32 +0300
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Jean-François Lessard <jefflessard3@...il.com>
Cc: Wolfram Sang <wsa+renesas@...g-engineering.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Daniel Scally <djrscally@...il.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v4 1/2] device property: Add scoped fwnode child node
 iterators

Hi Jean-François,

On Tue, Sep 02, 2025 at 03:04:39PM -0400, Jean-François Lessard wrote:
> Add scoped versions of fwnode child node iterators that automatically
> handle reference counting cleanup using the __free() attribute:
> 
> - fwnode_for_each_child_node_scoped()
> - fwnode_for_each_available_child_node_scoped()
> 
> These macros follow the same pattern as existing scoped iterators in the
> kernel, ensuring fwnode references are automatically released when the
> iterator variable goes out of scope. This prevents resource leaks and
> eliminates the need for manual cleanup in error paths.
> 
> The implementation mirrors the non-scoped variants but uses
> __free(fwnode_handle) for automatic resource management, providing a
> safer and more convenient interface for drivers iterating over firmware
> node children.
> 
> Signed-off-by: Jean-François Lessard <jefflessard3@...il.com>
> ---
> 
> Notes:
>     checkpatch reports false positives that are intentionally ignored:
>     MACRO_ARG_REUSE, MACRO_ARG_PRECEDENCE
>     This is a standard iterator pattern following kernel conventions.
> 
>  include/linux/property.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/include/linux/property.h b/include/linux/property.h
> index 82f0cb3ab..862e20813 100644
> --- a/include/linux/property.h
> +++ b/include/linux/property.h
> @@ -176,6 +176,16 @@ struct fwnode_handle *fwnode_get_next_available_child_node(
>  	for (child = fwnode_get_next_available_child_node(fwnode, NULL); child;\
>  	     child = fwnode_get_next_available_child_node(fwnode, child))
>  
> +#define fwnode_for_each_child_node_scoped(fwnode, child)		\
> +	for (struct fwnode_handle *child __free(fwnode_handle) =	\
> +		fwnode_get_next_child_node(fwnode, NULL);		\
> +	     child; child = fwnode_get_next_child_node(fwnode, child))
> +
> +#define fwnode_for_each_available_child_node_scoped(fwnode, child)	\
> +	for (struct fwnode_handle *child __free(fwnode_handle) =	\
> +		fwnode_get_next_available_child_node(fwnode, NULL);	\
> +	     child; child = fwnode_get_next_available_child_node(fwnode, child))
> +

Do we really need the available variant?

Please see
<URL:https://lore.kernel.org/linux-acpi/Zwj12J5bTNUEnxA0@kekkonen.localdomain/>.

I'll post a patch to remove fwnode_get_next_available_child_node(), too.

>  struct fwnode_handle *device_get_next_child_node(const struct device *dev,
>  						 struct fwnode_handle *child);
>  

-- 
Kind regards,

Sakari Ailus