linux-kernel - Re: [PATCH v4 2/4] mfd: Add Samsung Exynos Low Power Audio Subsystem driver

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Message-ID: <20160810111918.GS1581@dell>
Date:	Wed, 10 Aug 2016 12:19:18 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Sylwester Nawrocki <s.nawrocki@...sung.com>
Cc:	broonie@...nel.org, robh@...nel.org, alsa-devel@...a-project.org,
	devicetree@...r.kernel.org, ideal.song@...sung.com,
	inki.dae@...sung.com, b.zolnierkie@...sung.com,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Beomho Seo <beomho.seo@...sung.com>
Subject: Re: [PATCH v4 2/4] mfd: Add Samsung Exynos Low Power Audio Subsystem
 driver

On Wed, 10 Aug 2016, Sylwester Nawrocki wrote:

> On 08/09/2016 10:50 PM, Lee Jones wrote:
> > On Tue, 09 Aug 2016, Sylwester Nawrocki wrote:
> > 
> >> > On 08/09/2016 05:05 PM, Lee Jones wrote:
> >>>> > >> +static SIMPLE_DEV_PM_OPS(lpass_pm_ops, exynos_lpass_suspend,
> >>>>> > >> > +					exynos_lpass_resume);
> >>> > > Put this up by the PM functions.
> >> > 
> >> > Sorry, I don't understand this comment, which PM functions do you
> >> > mean exactly?
> > *_suspend and *_resume.  PM == Power Management.
> > 
> > You also need to place the functions in side some CONFIG_PM_SLEEP
> > guards.  Grep around, you'll see what I mean.
> 
> OK, but couldn't we just leave it with that SIMPLE_DEV_PM_OPS()
> macro?  It saves us an #ifdef ugliness and if I actually grep
> drivers/mfd most of the drivers use either SIMPLE_DEV_PM_OPS() or
> SET_SYSTEM_SLEEP_PM_OPS. Are you asking me to change the above to:
> 
> static const struct dev_pm_ops exynos_lpass_pm_ops = {
> #ifdef CONFIG_PM_SLEEP
> 	.suspend = exynos_lpass_suspend,
> 	.resume = exynos_lpass_resume,
> 	.freeze = exynos_lpass_suspend,
> 	.thaw = exynos_lpass_resume,
> 	.poweroff = exynos_lpass_suspend,
> 	.restore = exynos_lpass_resume,
> #endif
> }
> 
> or perhaps
> 
> static const struct dev_pm_ops exynos_lpass_pm_ops = {
> 	SET_SYSTEM_SLEEP_PM_OPS(exynos_lpass_suspend, exynos_lpass_resume)
> }
> 
> ?

Not like that.  Grep 'drivers/mfd' for "CONFIG_PM_SLEEP" as
suggested.  You will find that the actual *_suspend and *_resume
functions are guarded in order to save space.

> I agree about the CONFIG_PM_SLEEP guards.  There is very little
> chance though the LPASS driver will ever be used with
> CONFIG_PM_SLEEP disabled. How about adding __maybe_unused attribute
> to the *_suspend/*_resume functions then?  I can see this pattern
> used already in drivers/mfd.

It's more common practice to use CONFIG_PM_SLEEP:

$ git grep __maybe_unused -- drivers/mfd/ | wc -l
7
$ git grep CONFIG_PM_SLEEP -- drivers/mfd/ | wc -l
31

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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