linux-kernel - Re: [PATCH] gpio: of: make it possible to reference gpios probed in acpi in device tree

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Message-ID: <9ce6b851fa87c6295450c0b0aef7b302ed057f69.camel@posteo.de>
Date: Fri, 03 Oct 2025 13:04:24 +0000
From: Markus Probst <markus.probst@...teo.de>
To: Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, Bartosz Golaszewski
	 <brgl@...ev.pl>, Mika Westerberg <westeri@...nel.org>, Andy Shevchenko
	 <andriy.shevchenko@...ux.intel.com>, linux-gpio@...r.kernel.org, 
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpio: of: make it possible to reference gpios probed in
 acpi in device tree

On Fri, 2025-10-03 at 11:05 +0200, Mika Westerberg wrote:
> On Fri, Oct 03, 2025 at 08:44:12AM +0000, Markus Probst wrote:
> > On Fri, 2025-10-03 at 06:54 +0200, Mika Westerberg wrote:
> > > Hi,
> > > 
> > > On Thu, Oct 02, 2025 at 09:58:05PM +0000, Markus Probst wrote:
> > > > sometimes it is necessary to use both acpi and device tree to
> > > > declare
> > > > devices. Not every gpio device driver which has an
> > > > acpi_match_table
> > > > has
> > > > an of_match table (e.g. amd-pinctrl). Furthermore gpio is an
> > > > device
> > > > which
> > > > can't be easily disabled in acpi and then redeclared in device
> > > > tree, as
> > > > it often gets used by other devices declared in acpi (e.g. via
> > > > GpioInt or
> > > > GpioIo). Thus a disable of acpi and migration to device tree is
> > > > not
> > > > always
> > > > possible or very time consuming, while acpi by itself is very
> > > > limited and
> > > > not always sufficient. This won't affect most configurations,
> > > > as
> > > > most of
> > > > the time either CONFIG_ACPI or CONFIG_OF gets enabled, not
> > > > both.
> > > 
> > > Can you provide a real example where this kind of mixup can
> > > happen?
> > In my specific usecase for the Synology DS923+, there are gpios for
> > powering the usb vbus on (powered down by default), also for
> > powering
> > on sata disks. (defining a fixed-regulator for the usb vbus for
> > example)
> 
> Okay regulators are Power Resources in ACPI.
I did look into it and using a ssdt overlay sounds like a better idea
than using a devicetree, but there is another problem with it. I cannot
define a PowerResource that uses a gpio to control it (or at least
haven't found any docs on it). The gpio controller uses AMDI0030 and is
handled by the linux kernel driver (not acpi). An ACPI method can't
talk to the driver to set it.

Maybe there is a way to expose a kernel function to acpi instead?

- Markus Probst
> 
> > > The
> > > ACPI ID PRP0001 specifically was added to allow using DT bindings
> > > in
> > > ACPI
> > > based systems.
> > Hmm, would requiring patching of the acpi tables. Not sure if it
> > would
> > work with the fixed-regulator though, as it uses dev->of_node
> > instead
> > of dev->fwnode. I will try to see if I can make it work this way.
> 
> I think you can do this by using SSDT overlays instead of patching
> the
> tables:
> 
> https://docs.kernel.org/admin-guide/acpi/ssdt-overlays.html
> 
> There is configfs interface too.