Re: [PATCHv3 4/4] arm: Add generic timer broadcast support

[Mark Rutland]

Hi Stephen,

Sorry about this; I'm to blame for the bug.

On Wed, Feb 06, 2013 at 08:51:43PM +0000, Stephen Warren wrote:
> On 01/14/2013 10:05 AM, Mark Rutland wrote:
> > Implement timer_broadcast for the arm architecture, allowing for the use
> > of clock_event_device_drivers decoupled from the timer tick broadcast
> > mechanism.
> 
> Mark, this patch is now in next-20130206 and causes a crash during boot
> on Tegra. The reason appears to be because of:
> 
> > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> 
> > @@ -524,7 +524,6 @@ static void __cpuinit percpu_timer_setup(void)
> >  	struct clock_event_device *evt = &per_cpu(percpu_clockevent, cpu);
> >  
> >  	evt->cpumask = cpumask_of(cpu);
> > -	evt->broadcast = smp_timer_broadcast;
> 
> After that change, evt->broadcast is never assigned, and hence is NULL.
> Yet elsewhere in kernel/time/tick-broadcast.c it's used unconditionally:
> 
> static void tick_do_broadcast(struct cpumask *mask)
> ...
> 	if (!cpumask_empty(mask)) {
> ...
> 		td = &per_cpu(tick_cpu_device, cpumask_first(mask));
> 		td->evtdev->broadcast(mask);
> 
> Now perhaps the Tegra timer driver simply isn't being set up correctly,
> so the bug is there... But the only other place I can find where
> ->broadcast is assigned is in tick_device_uses_broadcast() which only
> does it for "non-functional" timers, which doesn't apply to Tegra's timer.
> 

The intent of 12ad100046: "clockevents: Add generic timer broadcast function"
was to setup the broadcast function both for non-functional/dummy timers and
those that stop in low-power states (CLOCK_EVT_FEAT_C3STOP). I missed the
CLOCK_EVT_FEAT_C3STOP case.

I believe the patch below will fix this for Tegra and any other platforms where
broadcast is required in low power states.

Stephen, could you test this for Tegra?

Thanks,
Mark.

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