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

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Date: Wed, 24 Jan 2024 08:28:40 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Philipp Zabel <p.zabel@...gutronix.de>,
 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 23/01/2024 16:06, Philipp Zabel wrote:
> 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.

Ack

> 
>> +		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.

Ack

Best regards,
Krzysztof