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

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Apr 7, 2014 at 9:00 PM, Sören Brinkmann
<soren.brinkmann@xxxxxxxxxx> wrote:
> On Mon, 2014-03-31 at 11:23AM +0200, Ulf Hansson wrote:
>> On 27 March 2014 16:25, Harini Katakam <harinik@xxxxxxxxxx> 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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