linux-kernel - Re: [PATCH v2 2/6] ASoC: aoa: Use helper function for_each_child_of_node

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Message-ID: <9ec008a8-b569-4ad1-9206-fe241fb1712d@kylinos.cn>
Date: Mon, 26 May 2025 16:20:37 +0800
From: Ai Chao <aichao@...inos.cn>
To: Johannes Berg <johannes@...solutions.net>, perex <perex@...ex.cz>,
 tiwai <tiwai@...e.com>,
 "kuninori.morimoto.gx" <kuninori.morimoto.gx@...esas.com>,
 lgirdwood <lgirdwood@...il.com>, broonie <broonie@...nel.org>,
 jbrunet <jbrunet@...libre.com>, "neil.armstrong"
 <neil.armstrong@...aro.org>, khilman <khilman@...libre.com>,
 "martin.blumenstingl" <martin.blumenstingl@...glemail.com>,
 "shengjiu.wang" <shengjiu.wang@...il.com>, "Xiubo.Lee"
 <Xiubo.Lee@...il.com>, festevam <festevam@...il.com>,
 nicoleotsuka <nicoleotsuka@...il.com>, shawnguo <shawnguo@...nel.org>,
 "s.hauer" <s.hauer@...gutronix.de>,
 "srinivas.kandagatla" <srinivas.kandagatla@...aro.org>
Cc: linux-sound <linux-sound@...r.kernel.org>,
 linux-kernel <linux-kernel@...r.kernel.org>,
 linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
 linux-renesas-soc <linux-renesas-soc@...r.kernel.org>,
 linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
 linux-amlogic <linux-amlogic@...ts.infradead.org>, imx
 <imx@...ts.linux.dev>, kernel <kernel@...gutronix.de>,
 linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] ASoC: aoa: Use helper function
 for_each_child_of_node_scoped()


Hi Johannes:
>> Hi Johannes:
>>
>>>> "simplifies the code" is no need to callof_node_put() .
>>> Fair. Except that's not what you _actually_ changed here. Like I said,
>>> either it's buggy before or after.
>>>
>> In the function i2sbus_probe, it not return a struct device_node, so , I
>> think function for_each_child_of_node_scoped is better than
>> for_each_child_of_node.
> You still haven't explained why it's even correct.
>
> johannes

The for_each_child_of_node() function is used to iterate over all child 
nodes of a device tree node.
During each iteration, it retrieves a pointer to the child node via 
of_get_next_child() and automatically increments the node's reference 
count (of_node_get()).
Each call to of_get_next_child() increases the reference count 
(refcount) of the returned child node, ensuring that the node is not 
freed while in use.
for_each_child_of_node() increments the child node's reference count in 
each iteration but does not decrement it automatically.
If of_node_put() is not called manually, the reference count will never 
reach zero, resulting in a memory leak of the node.

Best regards,
Ai Chao