linux-kernel - Re: [PATCH v5 4/6] reset: Instantiate reset GPIO controller for shared reset-gpios

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Date: Thu, 25 Jan 2024 09:49:51 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: 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 v5 4/6] reset: Instantiate reset GPIO controller for
 shared reset-gpios

On Thu, Jan 25, 2024 at 9:02 AM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> On 24/01/2024 08:45, Krzysztof Kozlowski 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>
> > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> >
> > ---
> >
> > Depends on previous of change.
> > ---
> >  drivers/reset/core.c             | 215 +++++++++++++++++++++++++++++--
> >  include/linux/reset-controller.h |   4 +
> >  2 files changed, 206 insertions(+), 13 deletions(-)
> >
>
> LKP reported issue when building !GPIOLIB:
> https://lore.kernel.org/oe-kbuild-all/202401250958.YksQmnWj-lkp@intel.com/
>
> but I intend to solve it providing the stubs. Therefore this patch will
> not change.
>
> Best regards,
> Krzysztof
>

Ah, so this is why you sent the patches. I don't like stubs in
gpio/driver.h but I get why they're needed here. Maybe we should
consider adding gpio/misc.h for that kind of stuff.

Bart