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 09:27:51 +0100
From: neil.armstrong@...aro.org
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>, 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
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 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(-)
> 
> diff --git a/drivers/reset/core.c b/drivers/reset/core.c
> index 4d5a78d3c085..60a8a33c4419 100644
> --- a/drivers/reset/core.c
> +++ b/drivers/reset/core.c

<snip>

> +	}
> +
> +	ret = __reset_add_reset_gpio_lookup(id, args->np, args->args[0],
> +					    args->args[1]);

What would happen with gpio controllers using #gpio-cells = <3> (or more) like allwinner,sun4i-a10-pinctrl.yaml ?

On this example the flags are args->args[2] so this would probably fail.

This would also fails badly with #gpio-cells = <1>, args->args[1] value would be undefined.

You should probably limit to args->args_count == 2 for now.

Neil

> +	if (ret < 0)
> +		goto err_kfree;
> +
> +	rgpio_dev->of_args = *args;
> +	/*
> +	 * We keep the device_node reference, but of_args.np is put at the end
> +	 * of __of_reset_control_get(), so get it one more time.
> +	 * Hold reference as long as rgpio_dev memory is valid.
> +	 */
> +	of_node_get(rgpio_dev->of_args.np);
> +	pdev = platform_device_register_data(NULL, "reset-gpio", id,
> +					     &rgpio_dev->of_args,
> +					     sizeof(rgpio_dev->of_args));

<snip>