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

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Message-ID: <2025082919-nebulizer-suitable-6b2c@gregkh>
Date: Fri, 29 Aug 2025 13:39:41 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Jean-François Lessard <jefflessard3@...il.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Daniel Scally <djrscally@...il.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] device property: Add scoped fwnode child node iterators

On Fri, Aug 29, 2025 at 07:34:17AM -0400, Jean-François Lessard wrote:
> Le 29 août 2025 00 h 23 min 22 s HAE, Greg Kroah-Hartman <gregkh@...uxfoundation.org> a écrit :
> >On Thu, Aug 28, 2025 at 10:17:59PM -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_named_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:
> >>     COMPLEX_MACRO, MACRO_ARG_REUSE, MACRO_ARG_PRECEDENCE
> >>     This is a standard iterator pattern following kernel conventions.
> >> 
> >>  include/linux/property.h | 14 ++++++++++++++
> >>  1 file changed, 14 insertions(+)
> >> 
> >> diff --git a/include/linux/property.h b/include/linux/property.h
> >> index 82f0cb3ab..279c244db 100644
> >> --- a/include/linux/property.h
> >> +++ b/include/linux/property.h
> >> @@ -176,6 +176,20 @@ 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_named_child_node_scoped(fwnode, child, name)	\
> >> +	fwnode_for_each_child_node_scoped(fwnode, child)		\
> >> +		for_each_if(fwnode_name_eq(child, name))
> >> +
> >> +#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))
> >> +
> >>  struct fwnode_handle *device_get_next_child_node(const struct device *dev,
> >>  						 struct fwnode_handle *child);
> >>  
> >
> >We need a real user of this before we can add them, so please do that as
> >part of a patch series.
> >
> 
> I understand the "no dead code" policy, but I found existing manual
> implementations of this exact pattern in the current kernel.
> 
> For example, drivers/i2c/i2c-core-slave.c already does:
> 
> 		struct fwnode_handle *child __free(fwnode_handle) = NULL;
> ...
> 		fwnode_for_each_child_node(fwnode, child) {
> ...
> 		}
> 
> This suggests developers are already wanting this functionality but
> implementing it manually.

Great, then add it here and fix up drivers/i2c/i2c-core-slave.c to use
it!

thanks,

greg k-h