linux-kernel - Re: [PATCH v3 00/10] gpio: improve support for shared GPIOs

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Message-ID: <CAMRc=Md4X-GWpeRgun6zv6dddKFqqrjUSveq3fNOe5AboLAcXg@mail.gmail.com>
Date: Mon, 10 Nov 2025 10:45:53 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Kees Cook <kees@...nel.org>, Mika Westerberg <westeri@...nel.org>, 
	Dmitry Torokhov <dmitry.torokhov@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Linus Walleij <linus.walleij@...aro.org>, Manivannan Sadhasivam <mani@...nel.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Andy Shevchenko <andy@...nel.org>, Bartosz Golaszewski <brgl@...ev.pl>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Srinivas Kandagatla <srini@...nel.org>, Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, 
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, 
	Alexey Klimov <alexey.klimov@...aro.org>
Cc: linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-gpio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-sound@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3 00/10] gpio: improve support for shared GPIOs

On Wed, Oct 29, 2025 at 12:20 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> Problem statement: GPIOs are implemented as a strictly exclusive
> resource in the kernel but there are lots of platforms on which single
> pin is shared by multiple devices which don't communicate so need some
> way of properly sharing access to a GPIO. What we have now is the
> GPIOD_FLAGS_BIT_NONEXCLUSIVE flag which was introduced as a hack and
> doesn't do any locking or arbitration of access - it literally just hand
> the same GPIO descriptor to all interested users.
>
> The proposed solution is composed of three major parts: the high-level,
> shared GPIO proxy driver that arbitrates access to the shared pin and
> exposes a regular GPIO chip interface to consumers, a low-level shared
> GPIOLIB module that scans firmware nodes and creates auxiliary devices
> that attach to the proxy driver and finally a set of core GPIOLIB
> changes that plug the former into the GPIO lookup path.
>
> The changes are implemented in a way that allows to seamlessly compile
> out any code related to sharing GPIOs for systems that don't need it.
>
> The practical use-case for this are the powerdown GPIOs shared by
> speakers on Qualcomm db845c platform, however I have also extensively
> tested it using gpio-virtuser on arm64 qemu with various DT
> configurations.
>
> I'm Cc'ing some people that may help with reviewing/be interested in
> this: OF maintainers (because the main target are OF systems initially),
> Mark Brown because most users of GPIOD_FLAGS_BIT_NONEXCLUSIVE live
> in audio or regulator drivers and one of the goals of this series is
> dropping the hand-crafted GPIO enable counting via struct
> regulator_enable_gpio in regulator core), Andy and Mika because I'd like
> to also cover ACPI (even though I don't know about any ACPI platform that
> would need this at the moment, I think it makes sense to make the
> solution complete), Dmitry (same thing but for software nodes), Mani
> (because you have a somewhat related use-case for the PERST# signal and
> I'd like to hear your input on whether this is something you can use or
> maybe it needs a separate, implicit gpio-perst driver similar to what
> Krzysztof did for reset-gpios) and Greg (because I mentioned this to you
> last week in person and I also use the auxiliary bus for the proxy
> devices).
>
> Merging strategy: patches 1-6 should go through the GPIO tree and then
> ARM-SoC, ASoC and regulator trees can pull these changes from an
> immutable branch and apply the remaining patches.
>

Can I get some Reviewed-bys under the GPIO patches if there are no
other open issues? I would like for this to start making its way
upstream if there are no strong objections to the concept. After a
release or two, I'd like to start enabling it on more platforms.

Bart