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

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Message-ID: <80347dcf-419b-489e-9b0e-d901fbacc71a@kernel.org>
Date: Mon, 6 Oct 2025 22:55:04 +0100
From: Srinivas Kandagatla <srini@...nel.org>
To: Bartosz Golaszewski <brgl@...ev.pl>,
 Srinivas Kandagatla <srini@...nel.org>
Cc: 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>,
 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>,
 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 10/6/25 12:55 PM, Bartosz Golaszewski wrote:
> On Sat, Oct 4, 2025 at 3:32 PM Srinivas Kandagatla <srini@...nel.org> wrote:
>> On 9/24/25 3:51 PM, 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.
>>
>> Isn't the main issue here is about not using a correct framework around
>> to the gpios that driver uses. ex: the codec usecase that you are
>> refering in this is using gpio to reset the line, instead of using a
>> proper gpio-reset control. same with some of the gpio-muxes. the problem
>> is fixed once such direct users of gpio are move their correct frameworks.
>>
> 
> If they were called "reset-gpios" then we could (and should) use
> Krzysztof's reset-gpio driver here, but we have many cases where
> that's not the case and the names (and implied functions) are
Yes, these codec drivers are due to be moved to use reset-gpios.

--srini
> arbitrary. In the case addressed in this series, the GPIOs are called
> "powerdown". The second big user of nonexclusive GPIOs are fixed
> regulators where the line isn't called "reset" either. There are also
> various other uses sprinkled all over the kernel for which no good
> abstraction exists or can even be designed in a generic way.
> 
>> Am not sure adding a abstraction with-in gpio framework is right
>> solution, But I do agree that NONEXCLUSIVE flags should disappear and
>> users that are using this should be moved to correct frameworks where
>> they belong.
>>
> 
> I'm open to suggestions but DT maintainers have not been particularly
> fond of creating "virtual" devices to accommodate driver
> implementations.
> 
> Bartosz