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

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Date:	Wed, 06 Feb 2013 13:51:43 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Mark Rutland <mark.rutland@....com>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	tglx@...utronix.de, nico@...aro.org, Will.Deacon@....com,
	Marc.Zyngier@....com, john.stultz@...aro.org
Subject: Re: [PATCHv3 4/4] arm: Add generic timer broadcast support

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.
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