linux-kernel - Re: [PATCH 3/9] software node: allow referencing firmware nodes

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Message-ID: <CAMRc=Me0YyBK5DtyJO4ZZvfvnhdtJx92_ktQA_eVhqFEkh=Bqg@mail.gmail.com>
Date: Tue, 21 Oct 2025 02:06:36 -0700
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
	Linus Walleij <linus.walleij@...aro.org>, 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>, Philipp Zabel <p.zabel@...gutronix.de>, 
	Krzysztof Kozlowski <krzk@...nel.org>, linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-acpi@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>
Subject: Re: [PATCH 3/9] software node: allow referencing firmware nodes

On Tue, 21 Oct 2025 08:54:22 +0200, Sakari Ailus
<sakari.ailus@...ux.intel.com> said:
> Hi Bartosz, Andy,
>
> On Mon, Oct 20, 2025 at 01:26:59PM +0200, Bartosz Golaszewski wrote:
>> On Mon, Oct 20, 2025 at 12:05 PM Andy Shevchenko
>> <andriy.shevchenko@...ux.intel.com> wrote:
>> >
>> > > >
>> > > > Can't we always have an fwnode reference?
>> > >
>> > > Unfortunately no. A const struct software_node is not yet a full
>> > > fwnode, it's just a template that becomes an actual firmware node when
>> > > it's registered with the swnode framework. However in order to allow
>> > > creating a graph of software nodes before we register them, we need a
>> > > way to reference those templates and then look them up internally in
>> > > swnode code.
>> >
>> > Strange that you need this way. The IPU3 bridge driver (that creates a graph of
>> > fwnodes at run-time for being consumed by the respective parts of v4l2
>> > framework) IIRC has no such issue. Why your case is different?
>> >
>>
>> From what I can tell the ipu-bridge driver only references software
>> nodes (as struct software_node) from other software nodes. I need to
>> reference ANY implementation of firmware node from a software node.
>
> Yes, the IPU bridge only references software nodes.
>
> I might use two distinct pointers instead of an union and an integer field
> that tells which type is the right one. I don't expect more such cases
> here; it's either a software node or an fwnode handle (ACPI or OF node).
>

Like:

struct software_node_ref_args {
	const struct software_node *swnode;
	struct fwnode_handle *fwnode;
	unsigned int nargs;
	u64 args[NR_FWNODE_REFERENCE_ARGS];
};

And then if swnode is NULL then assume fwnode must not be?

I'm not sure if it's necessarily better but I don't have a strong opinion on
this either.

Bartosz