linux-kernel - Re: [PATCH v7 14/24] ACPI: property: Refactor acpi_fwnode_get_reference

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Message-ID: <aGVF8Gqzs2YZf1Os@sunil-laptop>
Date: Wed, 2 Jul 2025 20:15:04 +0530
From: Sunil V L <sunilvl@...tanamicro.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Anup Patel <apatel@...tanamicro.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Jassi Brar <jassisinghbrar@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>,
	Uwe Kleine-König <ukleinek@...nel.org>,
	Palmer Dabbelt <palmer@...belt.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Alexandre Ghiti <alex@...ti.fr>, Len Brown <lenb@...nel.org>,
	Rahul Pathak <rpathak@...tanamicro.com>,
	Leyfoon Tan <leyfoon.tan@...rfivetech.com>,
	Atish Patra <atish.patra@...ux.dev>,
	Andrew Jones <ajones@...tanamicro.com>,
	Samuel Holland <samuel.holland@...ive.com>,
	Anup Patel <anup@...infault.org>, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 14/24] ACPI: property: Refactor
 acpi_fwnode_get_reference_args()

On Wed, Jul 02, 2025 at 12:07:36PM +0200, Rafael J. Wysocki wrote:
> On Wed, Jul 2, 2025 at 7:15 AM Anup Patel <apatel@...tanamicro.com> wrote:
> >
> > From: Sunil V L <sunilvl@...tanamicro.com>
> >
> > Currently acpi_fwnode_get_reference_args() calls the public function
> > __acpi_node_get_property_reference() which ignores the nargs_prop
> > parameter.
> 
> Which I suppose is a problem.  Why is it so?
> 
fwnode_property_get_reference_args() documents as below.

* @nargs_prop: The name of the property telling the number of
 *              arguments in the referred node. NULL if @nargs is known,
 *              otherwise @nargs is ignored. Only relevant on OF.
 * @nargs:      Number of arguments. Ignored if @nargs_prop is non-NULL.

You can see that nargs_prop is not supported with ACPI currently. Since
fwnode_property_get_reference_args() calls
__acpi_node_get_property_reference(), there is no way to determine the
nargs from the nargs_prop currently with ACPI. Since
fwnode_property_get_reference_args() is a common API across DT and ACPI,
it is a problem for users.


> > To fix this, make __acpi_node_get_property_reference() to
> > call the static acpi_fwnode_get_reference() so that callers of
> > fwnode_get_reference_args() can still pass a valid property name to
> > fetch the number of arguments.
> 
> Are the current callers of acpi_fwnode_get_reference_args() going to
> be affected by this change and if so, then how?
> 
Good question!. If some one is currently passing both valid nargs_prop and
nargs with ACPI, now with this change it will start getting the value
from nargs_prop which was simply ignored earlier. However, I see only 2
combinations how fwnode_property_get_reference_args() is being used. 

(nargs_prop = NULL) && (args_count !=0)
or
(nargs_prop != NULL) && (args_count = 0)

So, IMO it should be safe to make this change. But let me know if I am
missing something.

Thanks!
Sunil