linux-kernel - Re: [PATCH v2] media: i2c: thp7312: use fwnode_for_each_child

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Message-ID: <a02fca0e-bb67-4fe6-9ba4-24c82a4bbcc1@gmail.com>
Date: Tue, 8 Apr 2025 14:40:05 +0300
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
 Paul Elder <paul.elder@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] media: i2c: thp7312: use fwnode_for_each_child_node()

On 08/04/2025 14:16, Laurent Pinchart wrote:
> On Tue, Apr 08, 2025 at 11:08:10AM +0000, Sakari Ailus wrote:
>> Moi,
>>
>> On Tue, Apr 08, 2025 at 01:42:12PM +0300, Matti Vaittinen wrote:
>>> On 08/04/2025 13:36, Sakari Ailus wrote:
>>>> Hei Laurent, Matti,
>>>>
>>>> On Tue, Apr 08, 2025 at 01:26:42PM +0300, Matti Vaittinen wrote:
>>>>> On 08/04/2025 13:12, Laurent Pinchart wrote:
>>>>>> Hi Sakari,
>>>>>>
>>>>>> On Tue, Apr 08, 2025 at 08:48:45AM +0000, Sakari Ailus wrote:
>>>>>>> On Fri, Mar 21, 2025 at 12:41:00PM +0200, Laurent Pinchart wrote:
>>>>>>>> On Fri, Mar 21, 2025 at 10:58:27AM +0200, Matti Vaittinen wrote:
>>>>>>>>> When fwnode_for_each_available_child_node() is used on the device-tree
>>>>>>>>> backed systems, it renders to same operation as the
>>>>>>>>> fwnode_for_each_child_node(), because the fwnode_for_each_child_node()
>>>>>>>>> does only iterate through those device-tree nodes which are available.
>>>>>>>>
>>>>>>>> This makes me wonder why the OF backend implements
>>>>>>>> fwnode_for_each_child_node() as fwnode_for_each_available_child_node().
>>>>>>>> Is that on purpose, or is it a bug ?
>>>>>>>
>>>>>>> I discussed this with Rafael and he didn't recall why the original
>>>>>>> implementation was like that. The general direction later on has been not
>>>>>>> to present unavailable nodes over the fwnode interface.
>>>>>>>
>>>>>>> So I'd say:
>>>>>>>
>>>>>>> Reviewed-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
>>>>>>>
>>>>>>> We should also change the documentation of the fwnode API accordingly.
>>>>>>
>>>>>> Does that also mean that the fwnode_for_each_available_child_node()
>>>>>> function will be dropped ? It's used by few drivers (5 in addition to
>>>>>> the thp7312 driver, plus 3 call sites in drivers/base/core.c), so a
>>>>>> patch series to drop it should be easy.
>>>>>>
>>>>>
>>>>> I assume the fwnode_for_each_available_child_node() still makes sense for
>>>>> ACPI backed users, no?
>>>>
>>>> Not really (see my earlier explanation in
>>>> <Z9mQPJwnKAkPHriT@...konen.localdomain>).
>>>
>>> I capture that the _named_ available nodes don't have value as ACPI names
>>> aren't really what is expected by the _named_ callers. What I didn't pick is
>>> that the fwnode_for_each_available_child_node() - which should iterate all
>>> available child nodes ignoring the name - wouldn't be useful.
>>
>> Fair enough. I don't think we need to support enumerating unavailable ACPI
>> device nodes in this API. I'd indeed change the behaviour so that only
>> available nodes are enumerated. I can post a patch for that.
> 
> Unless there's a specific reason against it that I wouldn't be aware of,
> I would also very much favour merging the fwnode_for_each_child_node()
> and fwnode_for_each_available_child_node() functions into a single one
> that only enumerates available nodes, with a consistent behaviour across
> all backend. Having fwnode_for_each_child_node() return unavailable ACPI
> nodes but not unavailable DT nodes would be really confusing.

Absolutely no objections.

Yours,
	-- Matti