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

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Message-ID: <CAMRc=MdWmO4wvX6zpzN0-LZF1pF5Y2=sS8fBwr=CKMGWHg+shA@mail.gmail.com>
Date: Mon, 6 Oct 2025 18:10:59 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>, Kees Cook <kees@...nel.org>, 
	Mika Westerberg <westeri@...nel.org>, 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>, 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

On Mon, Oct 6, 2025 at 5:43 PM Manivannan Sadhasivam <mani@...nel.org> wrote:
>
> On Wed, Sep 24, 2025 at 11:25:12AM -0700, Dmitry Torokhov wrote:
> > Hi Bartosz,
> >
> > >
> > > 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...
> >
>
> Not always... For something like shared reset line, consumers request the line
> as GPIO and expect gpiolib to do resource manangement.
>

They could use the reset API and it would implicitly create a virtual
device that requests the reset GPIO and controls its enable count.
Except that some devices also do a specific reset sequence with delays
etc. That would require some additional logic in reset-gpio.

Bart