linux-kernel - Re: [PATCH v6 4/6] reset: Instantiate reset GPIO controller for shared reset-gpios

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Message-ID: <CACRpkdbaxqTzwL9L02vCpMMdBYsubNP1VkNuJ8mXB_=4E3Kjaw@mail.gmail.com>
Date: Wed, 31 Jan 2024 14:17:54 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, 
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>, Banajit Goswami <bgoswami@...cinc.com>, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, 
	Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Philipp Zabel <p.zabel@...gutronix.de>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Viresh Kumar <viresh.kumar@...aro.org>, Frank Rowand <frowand.list@...il.com>, 
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org, 
	linux-arm-msm@...r.kernel.org, linux-sound@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org, Chris Packham <chris.packham@...iedtelesis.co.nz>, 
	Sean Anderson <sean.anderson@...o.com>
Subject: Re: [PATCH v6 4/6] reset: Instantiate reset GPIO controller for
 shared reset-gpios

On Wed, Jan 31, 2024 at 10:37 AM Bartosz Golaszewski <brgl@...ev.pl> wrote:

> [Me]
> > reset -> virtual "gpio" -> many physical gpios[0..n]
>
> This is a different problem: it supports many users enabling the same
> GPIO (in Krzysztof's patch it's one but could be more if needed) but -
> unlike the broken NONEXCLUSIVE GPIOs in GPIOLIB - it counts the number
> of users and doesn't disable the GPIO for as long as there's at least
> one.

I don't know if the NONEXCLUSIVE stuff is broken, if you mean reference
counting isn't working on them, then that is by design because they were
invented for regulators and such use cases that do their own reference
counting. It's also used for hacks where people need to look up a desc in
a second spot, (perhaps we can fix those better).

As I say in commit b0ce7b29bfcd090ddba476f45a75ec0a797b048a
"This solution with a special flag is not entirely elegant and should ideally
be replaced by something more careful as this makes it possible for
several consumers to enable/disable the same GPIO line to the left
and right without any consistency."

I think for regulators (which is the vast majority using it) it isn't broken
because the regulator reference counting is working.

So if we solve that problem for reset, we probably should put it in
drivers/gpio/* somewhere so we can reuse the same solution for
regulators and get rid of NONEXCLUSIVE altogether I think?

The NONEXCLUSIVE stuff was prompted by converting regulators to
gpio descriptors, so it was for the greater good one can say. Or the
lesser evil :( my judgement can be questioned here.

Yours,
Linus Walleij