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

[Daniel Lezcano]

On 01/16/2015 11:35 AM, Alexandre Belloni wrote:
> 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@xxxxxxxxxxxxxxxxxx>
> > > ---
> > >   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.

Actually, if there is no enable/disable callback, then CLOCK_SOURCE_USED 
will be never set, hence the condition will always fail and the suspend 
callback won't be called.


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