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

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Message-ID: <C883B982-5984-4714-B322-BB8205B47D6E@gmail.com>
Date: Wed, 03 Sep 2025 12:43:56 -0400
From: Jean-François Lessard <jefflessard3@...il.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.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 Sakari,

Le 3 septembre 2025 09 h 18 min 32 s HAE, Sakari Ailus <sakari.ailus@...ux.intel.com> a écrit :
>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.
>

Thanks for the link to the discussion.

I see you're planning to remove fwnode_get_next_available_child_node() 
entirely. In that context, adding a scoped version doesn't make sense.

For my driver use case, I can handle the status checking manually if 
the _available_ variant is being deprecated.

Should I drop the _available_ variant and submit v5 with only 
fwnode_for_each_child_node_scoped()?

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