linux-kernel - Re: [PATCH v3 03/10] software node: allow referencing firmware nodes

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Message-ID: <CAMRc=MdP58d=o7ZL4bAdsaYwzrs6nJo3bhS7Jf1UkDNwPOnAsg@mail.gmail.com>
Date: Thu, 30 Oct 2025 04:17:48 -0700
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Bartosz Golaszewski <brgl@...ev.pl>, 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 v3 03/10] software node: allow referencing firmware nodes

On Thu, 30 Oct 2025 10:41:39 +0100, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> said:
> On Wed, Oct 29, 2025 at 01:28:37PM +0100, Bartosz Golaszewski wrote:
>>
>> 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: add a second pointer to
>> struct software_node_ref_args of type struct fwnode_handle. The core
>> swnode code will first check the swnode pointer and if it's NULL, it
>> will assume the fwnode pointer should be set. 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.
>
> ...
>
>> -#define SOFTWARE_NODE_REFERENCE(_ref_, ...)			\
>> +#define __SOFTWARE_NODE_REF(_ref, _node, ...)			\
>>  (const struct software_node_ref_args) {				\
>> -	.node = _ref_,						\
>> +	._node = _ref,						\
>>  	.nargs = COUNT_ARGS(__VA_ARGS__),			\
>>  	.args = { __VA_ARGS__ },				\
>>  }
>
> Okay, looking at this again I think we don't need a new parameter.
> We may check the type of _ref_
> (actually why are the macro parameters got renamed here and elsewhere?)
> and assign the correct one accordingly. I think this is what _Generic()
> is good for.
>

Oh, that's neat, I would love to use _Generic() here but I honest to god have
no idea how to make it work. I tried something like:

#define __SOFTWARE_NODE_REF(_ref, ...)                          \
_Generic(_ref,                                                  \
        const struct software_node *:                           \
                (const struct software_node_ref_args) {         \
                        .swnode = _ref,                         \
                        .nargs = COUNT_ARGS(__VA_ARGS__),       \
                        .args = { __VA_ARGS__ },                \
                },                                              \
        struct fwnode_handle *:                                 \
                (const struct software_node_ref_args) {         \
                        .fwnode = _ref,                         \
                        .nargs = COUNT_ARGS(__VA_ARGS__),       \
                        .args = { __VA_ARGS__ },                \
                }                                               \
        )


But this fails like this:

In file included from ./include/linux/acpi.h:16,
                 from drivers/reset/core.c:8:
drivers/reset/core.c: In function ‘__reset_add_reset_gpio_device’:
drivers/reset/core.c:958:52: error: initialization of ‘const struct
software_node *’ from incompatible pointer type ‘struct fwnode_handle
*’ [-Wincompatible-pointer-types]
  958 |                                                    parent->fwnode,
      |                                                    ^~~~~~
./include/linux/property.h:374:35: note: in definition of macro
‘__SOFTWARE_NODE_REF’
  374 |                         .swnode = _ref,                         \

So the right branch is not selected. How exactly would you use it here?

Bart