linux-kernel - Re: [PATCH v2 2/2] clocksource: don't suspend/resume when unused

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Date:	Tue, 20 Jan 2015 12:13:08 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
cc:	John Stultz <john.stultz@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] clocksource: don't suspend/resume when unused

On Fri, 16 Jan 2015, Alexandre Belloni wrote:

> There is no point in calling suspend/resume for unused
> clocksources.

That's true, but ....
 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> ---
>  kernel/time/clocksource.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> index 03cfc5a08e3b..da65b3b73a86 100644
> --- a/kernel/time/clocksource.c
> +++ b/kernel/time/clocksource.c
> @@ -493,7 +493,7 @@ void clocksource_suspend(void)
>  	struct clocksource *cs;
>  
>  	list_for_each_entry_reverse(cs, &clocksource_list, list)
> -		if (cs->suspend)
> +		if (cs->suspend && (cs->flags & CLOCK_SOURCE_USED))
>  			cs->suspend(cs);
>  }
>  
> @@ -505,7 +505,7 @@ void clocksource_resume(void)
>  	struct clocksource *cs;
>  
>  	list_for_each_entry(cs, &clocksource_list, list)
> -		if (cs->resume)
> +		if (cs->resume && (cs->flags & CLOCK_SOURCE_USED))
>  			cs->resume(cs);

I had a deeper look at the clocksources which have a resume
callback. We have implementations, which rely on the resume callback
being called unconditionally. e.g.: arch/x86/kernel/hpet.c. And there
are a few others which have extra PM code in the suspend/resume path
independent of the fact whether the clocksource is enabled or not.

So we really need to make this opt-in with a per clocksource flag.

Thanks,

	tglx
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