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

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Date: Fri, 16 Feb 2024 11:46:36 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: "Philipp Zabel" <p.zabel@...gutronix.de>, "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

Hello,

On Thu Feb 15, 2024 at 11:19 AM CET, Philipp Zabel wrote:
> 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?

Those resets are shared only across GPIO banks which have no reason to
be unbind-able. I'll add a comment and disable unbind.

> > 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.

Makes sense, will do so for next revision.

Thanks for the review Philipp,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com