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

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Date:	Fri, 16 Jan 2015 11:35:30 +0100
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Thomas Gleixner <tglx@...utronix.de>
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 16/01/2015 at 11:23:32 +0100, Thomas Gleixner wrote :
> 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.
> 

Isn't that already the case?
Right now, if you call clocksource_suspend, it doesn't matter whether
the clocksource has an enable or not, it will be suspended. Maybe I'm
mistaken but my patch doesn't seem to change that behaviour.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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