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

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Message-ID: <rfr5cou6jr7wmtxixfgjxhnda6yywlsxsei7md7ne3qge7r3gk@xv6n5pvcjzrm>
Date: Mon, 6 Oct 2025 15:09:06 -0700
From: Manivannan Sadhasivam <mani@...nel.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
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 06, 2025 at 06:10:59PM +0200, Bartosz Golaszewski wrote:
> 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.
> 

I was referring to the PCIe PERST# line, for which the 'reset-gpios' property
already exist in the schema. Now, you want me to model this simple GPIO as a
fake reset controller and use it the PCIe Bridge nodes through 'resets'
property?

- Mani

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