Subject: [PATCH] ARM/ARM64: arch-timer: fix arch_timer_probed logic

From: [email-masked] (Mark Rutland)
Date: Tue, 21 Oct 2014 12:07:28 +0100

Hi Daniel,

On Tue, Oct 21, 2014 at 11:58:29AM +0100, Daniel Lezcano wrote:
> On 10/15/2014 05:06 PM, Marc Zyngier wrote:
> > Commit c387f07e6205 (clocksource: arm_arch_timer: Discard unavailable
> > timers correctly) changed the way the driver makes sure both the memory
> > and system-register timers have been probed before finalizing the probing.
> >
> > There is a interesting flaw in this logic that leads to this final step
> > never to be executed. Things seems to work pretty well until something
> > actually needs the data that is produced during this final stage.
> >
> > For example, KVM explodes on the first run of a guest when executed on
> > a platform that has both memory and sysreg nodes (Juno, for example).
> >
> > Just fix the damned logic, and enjoy booting VMs again.
> >
> > Tested on a Juno system.
> >
> > Cc: Sudeep Holla <[email-masked]>
> > Cc: Stephen Boyd <[email-masked]>
> > Cc: Mark Rutland <[email-masked]>
> > Cc: Daniel Lezcano <[email-masked]>
> > Cc: Christoffer Dall <[email-masked]>
> > Reported-by: Riku Voipio <[email-masked]>
> > Signed-off-by: Marc Zyngier <[email-masked]>
> > ---
> 
> Applied to my tree. Also for -next.

Is this going to hit -rc2? This was a regression introduced in -rc1.

Without this fix we've also lost our high precision sched_clock on arm64
platforms.

Thanks,
Mark.

> 
> Thanks !
> 
>    -- Daniel
> 
> >   drivers/clocksource/arm_arch_timer.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> > index 2133f9d..43005d4 100644
> > --- a/drivers/clocksource/arm_arch_timer.c
> > +++ b/drivers/clocksource/arm_arch_timer.c
> > @@ -660,11 +660,11 @@ static bool __init
> >   arch_timer_probed(int type, const struct of_device_id *matches)
> >   {
> >   	struct device_node *dn;
> > -	bool probed = false;
> > +	bool probed = true;
> >
> >   	dn = of_find_matching_node(NULL, matches);
> > -	if (dn && of_device_is_available(dn) && (arch_timers_present & type))
> > -		probed = true;
> > +	if (dn && of_device_is_available(dn) && !(arch_timers_present & type))
> > +		probed = false;
> >   	of_node_put(dn);
> >
> >   	return probed;
> >
> 
> 
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