linux-kernel - Re: [PATCH] ARM: timer: Shutdown clock event device when stopping local timer

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Date:	Mon, 1 Apr 2013 09:56:50 +0800
From:	Ning Jiang <ning.n.jiang@...il.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	linux@....linux.org.uk, kgene.kim@...sung.com,
	davidb@...eaurora.org, dwalker@...o99.com, bryanh@...eaurora.org,
	john.stultz@...aro.org, tglx@...utronix.de,
	linus.walleij@...aro.org, shawn.guo@...aro.org,
	rob.herring@...xeda.com, arnd@...db.de,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] ARM: timer: Shutdown clock event device when stopping
 local timer

2013/4/1 Daniel Lezcano <daniel.lezcano@...aro.org>:
> On 03/29/2013 10:24 AM, ning.n.jiang@...il.com wrote:
>> From: Ning Jiang <ning.n.jiang@...il.com>
>>
>> Currently there are two problems when we try to stop local timer.
>> First, it calls set_mode function directly so mode state is not
>> updated for the clock event device. Second, it makes the device
>> unused instead of shutdown.
>>
>> A subtle error will happen because of it. When a cpu is plugged out
>> it will stop the local timer. It will call tick_nohz_idle_enter()
>> in idle thread afterwards. It will cancel the sched timer and try
>> to reprogram the next event. This is wrong since the local timer
>> is supposed to be stopped.
>>
>> The right way to stop the local timer is to shutdown it by calling
>> clockevents_set_mode(). Thus when we try to reprogram the clock
>> event device, it will return directly without doing anything since
>> the clock mode is CLOCK_EVT_MODE_SHUTDOWN.
>>
>> Signed-off-by: Ning Jiang <ning.n.jiang@...il.com>
>> ---
>>  arch/arm/kernel/smp_twd.c                |    2 +-
>>  arch/arm/mach-exynos/mct.c               |    2 +-
>>  arch/arm/mach-msm/timer.c                |    2 +-
>>  drivers/clocksource/arm_arch_timer.c     |    2 +-
>>  drivers/clocksource/time-armada-370-xp.c |    2 +-
>>  5 files changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
>> index 3f25650..c1d4ab4 100644
>> --- a/arch/arm/kernel/smp_twd.c
>> +++ b/arch/arm/kernel/smp_twd.c
>> @@ -92,7 +92,7 @@ static int twd_timer_ack(void)
>>
>>  static void twd_timer_stop(struct clock_event_device *clk)
>>  {
>> -     twd_set_mode(CLOCK_EVT_MODE_UNUSED, clk);
>> +     clockevents_set_mode(clk, CLOCK_EVT_MODE_SHUTDOWN);
>>       disable_percpu_irq(clk->irq);
>
> Wouldn't be clockevents_shutdown more adequate here ? The next event
> will be also set.

You're right. clockevents_shutdown seems more appropriate here. I'll
submit a revised patch for it.

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