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

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Date:	Fri, 16 Jan 2015 11:23:32 +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>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 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.
> 
> 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 920a4da58eb0..baea4e42ae90 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);

This might be dangerous. If the clocksource has no enable/disable
callbacks, but suspend/resume, then you might leave it enabled across
suspend.

Thanks,

	tglx

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