linux-kernel - Re: [PATCH v2 0/4] gpio: deprecate and track the removal of GPIO workarounds for regulators

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=MeYcgje7dFq8WDiTB8mTQ1COv3a_6xhAGkTukD_V25Wgw@mail.gmail.com>
Date: Mon, 7 Apr 2025 15:29:09 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Mark Brown <broonie@...nel.org>
Cc: Linus Walleij <linus.walleij@...aro.org>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 0/4] gpio: deprecate and track the removal of GPIO
 workarounds for regulators

On Mon, Apr 7, 2025 at 3:24 PM Mark Brown <broonie@...nel.org> wrote:
>
> On Mon, Apr 07, 2025 at 03:15:13PM +0200, Bartosz Golaszewski wrote:
> > On Wed, Apr 2, 2025 at 4:08 PM Mark Brown <broonie@...nel.org> wrote:
>
> > > > I believe pwrseq could actually be used to hide the enable counting
> > > > for GPIOs behind a faux GPIO chip and the consumer would never see a
> > > > pwrseq handle - they would instead use GPIO consumer interfaces and
> > > > we'd have to agree on what logic would we put behind gpiod_set_value()
> > > > (should it effectively work as gpiod_enable() meaning: value is 1 as
> > > > long as at least one user sets it to 1?) and
> > > > gpiod_direction_input()/output() (same thing: highest priority is
> > > > gpiod_direction_output(HIGH) and as long as at least one user sets it
> > > > as such, we keep it).
>
> > > Like I say that doesn't do the right thing since other users need to be
> > > able to see when something changes on the GPIO.  If that just happens on
> > > normal gpiolib then that complicates usage for the default case since
> > > they now have to worry about things not actually happening when
> > > requested which doesn't seem ideal.
>
> > If I understand correctly, regulator_ena_gpio_ctrl()[1] changes the
> > GPIO value (even if it's shared) and then notifies regulator consumers
> > about a DISABLE event. Now if we'd be implicitly sharing the GPIO with
> > an enable-counter, we could possibly emit an event that's a
> > false-positive?
>
> Yes (or vice versa for enable).  If the device thinks power got pulled
> when it didn't it might get confused about what the hardware is doing.

Sure, that's the example I was going for, maybe my wording isn't clear.

Basically: we may set the GPIO to 1 but it was already enabled and we
tell consumers the regulator was just enabled when it wasn't OR we set
the GPIO to 0 and tell consumers the regulator was disabled when there
are still users of this GPIO so it's not true either.

AFAICT, it's used in a few places to put the regulator consumer in
reset if the power was *actually* disabled.

I'll think about how that could be improved.

Bartosz