linux-kernel - Re: [PATCH v3 1/2] device property: Add scoped fwnode child node iterators

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Message-ID: <85D46ECF-B4A6-4C78-A4DD-0785FE58B2A3@gmail.com>
Date: Mon, 01 Sep 2025 14:16:35 -0400
From: Jean-François Lessard <jefflessard3@...il.com>
To: Danilo Krummrich <dakr@...nel.org>
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>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, linux-i2c@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v3 1/2] device property: Add scoped fwnode child node iterators

Le 1 septembre 2025 13 h 48 min 14 s HAE, Danilo Krummrich <dakr@...nel.org> a écrit :
>On 9/1/25 6:36 PM, 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>
>
>Thanks for adding a user and splitting it up (Andy was a bit faster than me :).
>

Very welcome! Thanks for reviewing.

>> 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))
>
>IIRC, your first patch mentioned that your driver series would only use
>fwnode_for_each_available_child_node_scoped().

You are correct. Next version of TM16XX driver patch series will use
fwnode_for_each_available_child_node_scoped()

>
>And this series adds a user for fwnode_for_each_child_node_scoped(); do you also have a user for fwnode_for_each_named_child_node_scoped()?

No, I haven't found an existing user that requires the scoped version. The only
usage I found of the non-scoped fwnode_for_each_named_child_node() is in 
drivers/base/property.c in fwnode_get_named_child_node_count(), which doesn't
need to put the fwnode.

I included it for consistency since the header defines all three non-scoped
variants, but I understand the "no dead code" policy concern.

Would you prefer I drop the fwnode_for_each_named_child_node_scoped() 
variant and submit a v4 with only the two variants that have real users?

Regards,

Jean-François Lessard