linux-kernel - Re: [PATCH RFC 0/9] gpio: improve support for shared GPIOs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <hyzzrjn7jzo3tt3oyg7azijouawe3zopfjzq6zfhoo6e6z2m4t@ssl5vl4g557e>
Date: Wed, 24 Sep 2025 11:25:12 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Kees Cook <kees@...nel.org>, Mika Westerberg <westeri@...nel.org>, 
	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>, 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>, 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 RFC 0/9] gpio: improve support for shared GPIOs

Hi Bartosz,

On Wed, Sep 24, 2025 at 04:51:28PM +0200, Bartosz Golaszewski wrote:
> Here's a functional RFC for improving the handling of shared GPIOs in
> linux.
> 
> 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.

How is this different from the existing gpio-backed regulator/supply?
IMO GPIOs are naturally exclusive-use resources (in cases when you need
to control them, not simply read their state), and when there is a need
to share them there are more appropriate abstractions that are built on
top of GPIOs...

Thanks.

-- 
Dmitry