linux-kernel - Re: [PATCH v4 4/6] reset: Instantiate reset GPIO controller for shared reset-gpios

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Date: Tue, 23 Jan 2024 16:06:47 +0100
From: Philipp Zabel <p.zabel@...gutronix.de>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, Bjorn Andersson
 <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, Srinivas
 Kandagatla <srinivas.kandagatla@...aro.org>, Banajit Goswami
 <bgoswami@...cinc.com>, 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>,
 linux-arm-msm@...r.kernel.org,  alsa-devel@...a-project.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 v4 4/6] reset: Instantiate reset GPIO controller for
 shared reset-gpios

On Di, 2024-01-23 at 15:13 +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>

I'm nearly out of complaints, two tiny cosmetic issues remaining:

[...]
> diff --git a/drivers/reset/core.c b/drivers/reset/core.c
> index 4d5a78d3c085..6e81b8d35055 100644
> --- a/drivers/reset/core.c
> +++ b/drivers/reset/core.c
[...]
> @@ -813,12 +838,161 @@ static void __reset_control_put_internal(struct reset_control *rstc)
>  	kref_put(&rstc->refcnt, __reset_control_release);
>  }
>  
> +static int __reset_add_reset_gpio_lookup(int id, struct device_node *np,
> +					 unsigned int gpio,
> +					 unsigned int of_flags)
> +{
> +	unsigned int lookup_flags;
> +	const char *label_tmp;
> +
> +	/*
> +	 * Later we map GPIO flags between OF and Linux, however not all
> +	 * constants from include/dt-bindings/gpio/gpio.h and
> +	 * include/linux/gpio/machine.h match each other.
> +	 */
> +	if (of_flags > GPIO_ACTIVE_LOW) {
> +		pr_err("reset-gpio code does not support GPIO flags %u for GPIO %u\n",
> +			of_flags, gpio);

Alignment to parenthesis is slightly off.

> +		return -EINVAL;
> +	}
> +
> +	struct gpio_device *gdev __free(gpio_device_put) = gpio_device_find_by_fwnode(of_fwnode_handle(np));

Adding a local fwnode variable would make this fit in the 100 character
limit again.

regards
Philipp