linux-kernel - Re: [PATCH 1/2] GPIO: Add driver for Zynq GPIO controller

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Date:	Thu, 10 Apr 2014 19:54:57 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Harini Katakam <harinik@...inx.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexandre Courbot <gnurou@...il.com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Michal Simek <michal.simek@...inx.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>, michals@...inx.com,
	Rob Landley <rob@...dley.net>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] GPIO: Add driver for Zynq GPIO controller

On Mon, Apr 7, 2014 at 9:00 PM, Sören Brinkmann
<soren.brinkmann@...inx.com> wrote:
> On Mon, 2014-03-31 at 11:23AM +0200, Ulf Hansson wrote:
>> On 27 March 2014 16:25, Harini Katakam <harinik@...inx.com> wrote:
> [...]
>> > +static int __maybe_unused zynq_gpio_runtime_suspend(struct device *dev)
>> > +{
>> > +       struct platform_device *pdev = to_platform_device(dev);
>> > +       struct zynq_gpio *gpio = platform_get_drvdata(pdev);
>> > +
>> > +       clk_disable(gpio->clk);
>>
>> You should be able can use clk_disable_unprepare() here.
>>
>> > +
>> > +       return 0;
>> > +}
>> > +
>> > +static int __maybe_unused zynq_gpio_runtime_resume(struct device *dev)
>> > +{
>> > +       struct platform_device *pdev = to_platform_device(dev);
>> > +       struct zynq_gpio *gpio = platform_get_drvdata(pdev);
>> > +
>> > +       return clk_enable(gpio->clk);
>>
>> You should be able can use clk_prepare_enable() here.
>
> Is there some common practice regarding this? As I understand it, we
> want to ensure the clock to be gated during suspend, which should happen
> with clk_disable(). Why would we also unprepare the clock? We are highly
> likely to use it again once we resume.

enable() is fastpath (e.g. in IRQs disabled context) whereas
prepare() is slowpath() in normal, threaded context.

As [runtime]_suspend/resume happens in normal context you
want to make sure clocks are both disabled/unprepared
and prepared/enabled to make sure any clocks that can only
be accessed in slowpath are also turned off/on.

Yours,
Linus Walleij
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