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 10:43:44 +0100
From: Philipp Zabel <p.zabel@...gutronix.de>
To: 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>, "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
Cc: Bartosz Golaszewski <brgl@...ev.pl>, 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 Mi, 2024-01-24 at 08:45 +0100, 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>

Reviewed-by: Philipp Zabel <p.zabel@...gutronix.de>

regards
Philipp