Message-ID: <p4fwvwbhwbdpiqvspjq4stjyuxy5pqvdei3wfianw4aeujmgbx@utumnrffangf>
Date: Wed, 7 Jan 2026 14:12:28 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Manivannan Sadhasivam <mani@...nel.org>
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>
Subject: Re: [PATCH v4 00/10] gpio: improve support for shared GPIOs

On Wed, Jan 07, 2026 at 05:17:09PM +0530, Manivannan Sadhasivam wrote:
> 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

CONFIG_GPIO_SHARED_PROXY=y ?

> 
> 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

-- 
With best wishes
Dmitry

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