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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMRc=Me9Td5G9qZV8A98XkGROKw1D2UeQHpFzt8uApF8995MZw@mail.gmail.com>
Date: Tue, 7 Oct 2025 14:29:01 +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 Tue, Oct 7, 2025 at 12:09 AM Manivannan Sadhasivam <mani@...nel.org> wrote:
>
> > >
> > > 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?
>

No, not at all. It's just that a shared `reset-gpios` property is
pretty common and Krzysztof implemented the reset-gpio driver[1] to
address it. Drivers that request a reset control via the OF interface
will notice that there's no `resets` property but if there's a
`reset-gpios`, the reset core will create a virtual device binding to
the reset-gpio driver which requests the GPIO in question (once!) and
registers with the reset subsystem providing shared reset control to
users. Basically the abstraction Srini mentioned minus any reset
sequence.

That only happens if the driver uses the reset API. If you go with the
GPIOLIB then none of this matters. I definitely don't want to change
the existing DT sources either but I want to find out if the code in
this series is suitable (with some modifications) for supporting the
PERST# line or if the logic behind it is more complex and possibly
requires separate, more fine-grained handling.

Bartosz

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/reset/reset-gpio.c