linux-kernel - Re: [PATCH 19/23] gpio: nomadik: grab optional reset control and deassert it at probe

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Date: Thu, 15 Feb 2024 11:19:14 +0100
From: Philipp Zabel <p.zabel@...gutronix.de>
To: Théo Lebrun <theo.lebrun@...tlin.com>, Linus Walleij
 <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>, Rob
 Herring <robh+dt@...nel.org>, Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@...aro.org>,  Conor Dooley <conor+dt@...nel.org>,
 Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: linux-gpio@...r.kernel.org, devicetree@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 linux-mips@...r.kernel.org, Gregory CLEMENT <gregory.clement@...tlin.com>, 
 Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, Tawfik Bayouk <tawfik.bayouk@...ileye.com>
Subject: Re: [PATCH 19/23] gpio: nomadik: grab optional reset control and
 deassert it at probe

On Mi, 2024-02-14 at 17:24 +0100, Théo Lebrun wrote:
> Fetch a reference to the optional shared reset control and deassert it
> if it exists.
> 
> Optional because not all platforms that use this driver have a reset
> attached to the reset block. Shared because some platforms that use the
> reset (at least Mobileye EyeQ5) share the reset across banks.
> 
> Do not keep a reference to the reset control as it is not needed
> afterwards; the driver does not handle suspend, does not use runtime PM
> and does not register a remove callback.

I suppose you don't care that the reset is only ever deasserted once
and never asserted again on this hardware, but for shared reset
controls the expectation is that deassert/assert calls are balanced:

https://docs.kernel.org/driver-api/reset.html?highlight=balanced#assertion-and-deassertion

So maybe this warrants a comment in the code. Or do you mean to
suppress unbind via suppress_bind_attrs to explain away any missing
cleanup?

> The operation is done in nmk_gpio_populate_chip(). This function is
> called by either gpio-nomadik or pinctrl-nomadik, whoever comes first.
> This is here for historic reasons and could probably be removed now; it
> seems gpio-ranges enforces the ordering to be pinctrl-first. It is not
> the topic of the present patch however.
> 
> Signed-off-by: Théo Lebrun <theo.lebrun@...tlin.com>
> ---
>  drivers/gpio/gpio-nomadik.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/gpio/gpio-nomadik.c b/drivers/gpio/gpio-nomadik.c
> index 21bb6d6363fc..b623c093b54d 100644
> --- a/drivers/gpio/gpio-nomadik.c
> +++ b/drivers/gpio/gpio-nomadik.c
> @@ -513,12 +513,14 @@ struct nmk_gpio_chip *nmk_gpio_populate_chip(struct device_node *np,
>  {
>  	struct nmk_gpio_chip *nmk_chip;
>  	struct platform_device *gpio_pdev;
> +	struct reset_control *reset;
>  	struct gpio_chip *chip;
>  	struct resource *res;
>  	struct clk *clk;
>  	void __iomem *base;
>  	uintptr_t flags;
>  	u32 id, ngpio;
> +	int ret;
>  
>  	gpio_pdev = of_find_device_by_node(np);
>  	if (!gpio_pdev) {
> @@ -576,6 +578,19 @@ struct nmk_gpio_chip *nmk_gpio_populate_chip(struct device_node *np,
>  	clk_prepare(clk);
>  	nmk_chip->clk = clk;
>  
> +	reset = devm_reset_control_get_optional_shared(&gpio_pdev->dev, NULL);
> +	if (IS_ERR(reset)) {
> +		dev_err(&pdev->dev, "failed getting reset control: %ld\n",
> +			PTR_ERR(reset));
> +		return ERR_CAST(reset);

Consider using dev_err_probe() here.

regards
Philipp