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

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Message-ID: <CAMRc=MfOoHn+mLRpQBEsC3g5sM=VZBgVffsm68CAXJBHffPxdA@mail.gmail.com>
Date: Mon, 20 Oct 2025 10:06:43 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, 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>, 
	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>
Subject: Re: [PATCH 3/9] software node: allow referencing firmware nodes

On Sat, Oct 18, 2025 at 7:34 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Mon, Oct 06, 2025 at 03:00:18PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > At the moment software nodes can only reference other software nodes.
> > This is a limitation for devices created, for instance, on the auxiliary
> > bus with a dynamic software node attached which cannot reference devices
> > the firmware node of which is "real" (as an OF node or otherwise).
> >
> > Make it possible for a software node to reference all firmware nodes in
> > addition to static software nodes. To that end: use a union of different
> > pointers in struct software_node_ref_args and add an enum indicating
> > what kind of reference given instance of it is. Rework the helper macros
> > and deprecate the existing ones whose names don't indicate the reference
> > type.
> >
> > Software node graphs remain the same, as in: the remote endpoints still
> > have to be software nodes.
>
> ...
>
> > +enum software_node_ref_type {
> > +     /* References a software node. */
> > +     SOFTWARE_NODE_REF_SWNODE = 0,
>
>
> I don't see why we need an explicit value here.
>

It was to make it clear, this is the default value and it's the one
used in older code with the legacy macros. I can drop it, it's no big
deal.

> > +     /* References a firmware node. */
> > +     SOFTWARE_NODE_REF_FWNODE,
> > +};
>
> ...
>
> >  /**
> >   * struct software_node_ref_args - Reference property with additional arguments
> > - * @node: Reference to a software node
> > + * @swnode: Reference to a software node
> > + * @fwnode: Alternative reference to a firmware node handle
> >   * @nargs: Number of elements in @args array
> >   * @args: Integer arguments
> >   */
> >  struct software_node_ref_args {
> > -     const struct software_node *node;
> > +     enum software_node_ref_type type;
> > +     union {
> > +             const struct software_node *swnode;
> > +             struct fwnode_handle *fwnode;
> > +     };
>
> 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.

Bart

> >       unsigned int nargs;
> >       u64 args[NR_FWNODE_REFERENCE_ARGS];
> >  };
>
> --
> With Best Regards,
> Andy Shevchenko
>
>
>