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

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Message-ID: <CAMRc=MeEPvhB1nTwBT5fG7p0G4L2J5FjJfM0GMusQuDnnEN35g@mail.gmail.com>
Date: Mon, 12 Feb 2024 22:32:56 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Linus Walleij <linus.walleij@...aro.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, 
	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 Mon, Feb 12, 2024 at 9:48 PM Linus Walleij <linus.walleij@...aroorg> wrote:
>
> On Mon, Jan 29, 2024 at 12:53 PM Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
>
> > Devices sharing a reset GPIO could use the reset framework for
> > coordinated handling of that shared GPIO line.  We have several cases of
> > such needs, at least for Devicetree-based platforms.
> >
> > If Devicetree-based device requests a reset line, while "resets"
> > Devicetree property is missing but there is a "reset-gpios" one,
> > instantiate a new "reset-gpio" platform device which will handle such
> > reset line.  This allows seamless handling of such shared reset-gpios
> > without need of changing Devicetree binding [1].
> >
> > To avoid creating multiple "reset-gpio" platform devices, store the
> > Devicetree "reset-gpios" GPIO specifiers used for new devices on a
> > linked list.  Later such Devicetree GPIO specifier (phandle to GPIO
> > controller, GPIO number and GPIO flags) is used to check if reset
> > controller for given GPIO was already registered.
> >
> > If two devices have conflicting "reset-gpios" property, e.g. with
> > different ACTIVE_xxx flags, this would allow to spawn two separate
> > "reset-gpio" devices, where the second would fail probing on busy GPIO
> > request.
> >
> > Link: https://lore.kernel.org/all/YXi5CUCEi7YmNxXM@robh.at.kernel.org/ [1]
> > Cc: Bartosz Golaszewski <brgl@...ev.pl>
> > Cc: Chris Packham <chris.packham@...iedtelesis.co.nz>
> > Cc: Sean Anderson <sean.anderson@...o.com>
> > Reviewed-by: Philipp Zabel <p.zabel@...gutronix.de>
> > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>
> Acked-by: Linus Walleij <linus.walleij@...aro.org>
>
> I can't think of anything better, that is reasonable to ask for.
>
> I feel slightly icky about the way the code reaches into gpiolib, and I think

As long as it doesn't include gpiolib.h, I'm fine with it.

> regulators should be able to reuse the code, but unfortunately only the day
> they have no board files left :/
>
> I do feel the core code handling "reset-gpios" could as well have been
> used to handle "enable-gpios" in regulators, just that the regulator code
> has more requirements, and would be really hard to rewrite, and deals
> with descriptors passed in from drivers instead of centralizing it.
>
> Like regulators, reset grows core support for handling GPIO for resets
> which is *long due*, given how common it must be. We really need
> something like this, and this is certainly elegant enough to do the job.
>
> Yours,
> Linus Walleij

Agreed.

Acked-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

I will pick up the stub patches tomorrow and send a tag for Philipp to pull.

Bartosz