Message-ID: <uc7utm7tbtmkk6osaoydibd5evtpm246sjrpkx3lpclpk4srea@a4g65oduswau>
Date: Wed, 7 Jan 2026 17:17:09 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Bartosz Golaszewski <brgl@...ev.pl>, 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>, 
	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>, 
	Alexey Klimov <alexey.klimov@...aro.org>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konradybcio@...nel.org>, 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>, Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Subject: Re: [PATCH v4 00/10] gpio: improve support for shared GPIOs

On Wed, Nov 26, 2025 at 06:27:13PM +0200, Dmitry Baryshkov wrote:
> On Wed, Nov 12, 2025 at 02:55:29PM +0100, Bartosz Golaszewski wrote:
> > Bjorn, Konrad: I should have Cc'ed you on v1 but I just went with what
> > came out of b4 --auto-to-cc. It only gave me arm-msm. :( Patch 7 from
> > this series however impacts Qualcomm platforms. It's a runtime dependency
> > of patches 8 and 9. Would you mind Acking it so that I can take it into
> > an immutable branch that I'll make available to Mark Brown for him to
> > take patches 8-10 through the ASoC and regulator trees for v6.19?
> > 
> > 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).
> 
> Hi,
> 
> I'm sorry if this was already reported and fixed. On Qualcomm RB5
> platform with this patchset in place I'm getting the following backtrace
> (and then a lockup):
> 

On Rb3Gen2 this breaks UFS:

	ufshcd-qcom 1d84000.ufshc: cannot find GPIO chip gpiolib_shared.proxy.4, deferring

But MMC acquired the GPIO successfully,

	sdhci_msm 8804000.mmc: Got CD GPIO

But I can see gpiochips registered as well:

(initramfs) ls /dev/gpio*
crw------- 1 0 0 254,0 /dev/gpiochip0
crw------- 1 0 0 254,1 /dev/gpiochip1
crw------- 1 0 0 254,2 /dev/gpiochip2
crw------- 1 0 0 254,3 /dev/gpiochip3
crw------- 1 0 0 254,4 /dev/gpiochip4

Let me know if you need more info.

- Mani

-- 
மணிவண்ணன் சதாசிவம்

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