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

From: [email-masked] (Daniel Lezcano)
Date: Fri, 16 Jan 2015 11:39:16 +0100

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 <[email-masked]>
>>> ---
>>>   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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