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Subject: Re: fwnode_for_each_child_node() and OF backend discrepancy
From:   Grant Likely <grant.likely@linaro.org>
In-Reply-To: <CAJZ5v0g1VqJ2_2MtKGv-sHmKVQ12Rmj9r3Lr6D9wjmUYJwtoCw@mail.gmail.com>
Date:   Wed, 29 Jun 2022 14:01:00 +0100
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Michael Walle <michael@walle.cc>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Saravana Kannan <saravanak@google.com>
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Message-Id: <30D246E1-B0C7-404A-B690-A894AA79A524@linaro.org>
References: <4e1d5db9dea68d82c94336a1d6aac404@walle.cc>
 <b8ec04dc-f803-ee2c-29b7-b0311eb8c5fb@linaro.org>
 <CAJZ5v0jz=ee5TrvYs0_ovWn9sT06bcKDucmmocD8L-d9ZZ5DzQ@mail.gmail.com>
 <0b8e357d-1d8b-843f-d8b6-72c760bcd6fb@linaro.org>
 <CAJZ5v0g1VqJ2_2MtKGv-sHmKVQ12Rmj9r3Lr6D9wjmUYJwtoCw@mail.gmail.com>
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Precedence: bulk


> On 29 Jun 2022, at 11:50, Rafael J. Wysocki <rafael@kernel.org> wrote:
>=20
> On Tue, Jun 28, 2022 at 12:32 PM Krzysztof Kozlowski
> <krzysztof.kozlowski@linaro.org> wrote:
>>=20
>> On 27/06/2022 15:33, Rafael J. Wysocki wrote:
>>> On Mon, Jun 27, 2022 at 3:08 PM Krzysztof Kozlowski
>>> <krzysztof.kozlowski@linaro.org> wrote:
>>>>=20
>>>> On 27/06/2022 14:49, Michael Walle wrote:
>>>>> Hi,
>>>>>=20
>>>>> I tired to iterate over all child nodes, regardless if they are
>>>>> available
>>>>> or not. Now there is that handy fwnode_for_each_child_node() (and =
the
>>>>> fwnode_for_each_available_child_node()). The only thing is the OF
>>>>> backend
>>>>> already skips disabled nodes [1], making =
fwnode_for_each_child_node()
>>>>> and
>>>>> fwnode_for_each_available_child_node() behave the same with the OF
>>>>> backend.
>>>>>=20
>>>>> Doesn't seem to be noticed by anyone for now. I'm not sure how to =
fix
>>>>> that
>>>>> one. fwnode_for_each_child_node() and also =
fwnode_get_next_child_node()
>>>>> are
>>>>> used by a handful of drivers. I've looked at some, but couldn't =
decide
>>>>> whether they really want to iterate over all child nodes or just =
the
>>>>> enabled
>>>>> ones.
>>>>=20
>>>> If I get it correctly, this was introduced  by 8a0662d9ed29 =
("Driver
>>>> core: Unified interface for firmware node properties")
>>>> .
>>>=20
>>> Originally it was, but then it has been reworked a few times.
>>>=20
>>> The backend callbacks were introduced by Sakari, in particular.
>>=20
>> I see you as an author of 8a0662d9ed29 which adds
>> device_get_next_child_node() and uses of_get_next_available_child()
>> instead of of_get_next_child(). Although it was back in 2014, so =
maybe
>> it will be tricky to get original intention. :)
>=20
> The OF part of this was based on Grant's suggestions.  My
> understanding at that time was that this was the right thing to do for
> OF and nobody told me otherwise.
>=20
>> Which commit do you mean when you refer to Sakari's work?
>=20
> 3708184afc77 device property: Move FW type specific functionality to
> FW specific files
>=20
> However, it didn't change the "available" vs "any" behavior for OF.

Back in the mists of time indeed. I don=E2=80=99t remember anything =
specific about all/available variants of the fwnode_ helpers. Auditing =
the existing users is probably needed to decide whether or not it can be =
changed.

g.

>=20
>>>=20
>>>> The question to Rafael - what was your intention when you added
>>>> device_get_next_child_node() looking only for available nodes?
>>>=20
>>> That depends on the backend.
>>=20
>> We talk about OF backend. In your commit device_get_next_child_node =
for
>> OF uses explicitly available node, not any node.
>=20
> Yes, it does.
>=20
> If that doesn't match the cases in which it is used, I guess it can be =
adjusted.
>=20
>>> fwnode_for_each_available_child_node() is more specific and IIRC it
>>> was introduced for fw_devlink (CC Saravana).
>>>=20
>>>> My understanding is that this implementation should be consistent =
with
>>>> OF implementation, so fwnode_get_next_child_node=3Dget any child.
>>>=20
>>> IIUC, the OF implementation is not consistent with the
>>> fwnode_get_next_child_node=3Dget any child thing.
>>>=20
>>>> However maybe ACPI treats it somehow differently?
>>>=20
>>> acpi_get_next_subnode() simply returns the next subnode it can find.
>=20
> I guess that the confusion is related to what "available" means for =
ACPI and OF.
>=20
> In the ACPI case it means "this a device object corresponding to a
> device that is present".  In OF it is related to the "status" property
> AFAICS.