Subject: [PATCH] ARM: OMAP4: Fix the boot regression with CPU_IDLE enabled

From: [email-masked] (Daniel Lezcano)
Date: Wed, 14 May 2014 22:02:01 +0200

On 05/14/2014 09:50 PM, Santosh Shilimkar wrote:
> On Wednesday 14 May 2014 03:44 PM, Daniel Lezcano wrote:
>> On 05/13/2014 04:39 PM, Santosh Shilimkar wrote:
>>> On OMAP4 panda board, there have been several bug reports about boot
>>> hang and lock-ups with CPU_IDLE enabled. The root cause of the issue
>>> is missing interrupts while in idle state. Commit cb7094e8 {cpuidle / omap4 :
>>> use CPUIDLE_FLAG_TIMER_STOP flag} moved the broadcast notifiers to common
>>> code for right reasons but on OMAP4 which suffers from a nasty ROM code
>>> bug with GIC, commit ff999b8a {ARM: OMAP4460: Workaround for ROM bug ..},
>>> we loose interrupts which leads to issues like lock-up, hangs etc.
>>>
>>> Patch reverts commit cb7094 {cpuidle / omap4 : use CPUIDLE_FLAG_TIMER_STOP
>>> flag} to avoid the issue. With this change, OMAP4 panda boards, the mentioned
>>> issues are getting fixed. We no longer loose interrupts which was the cause
>>> of the regression.
>>>
>>> Cc: Roger Quadros <[email-masked]>
>>> Cc: Kevin Hilman <[email-masked]>
>>> Cc: Tony Lindgren <[email-masked]>
>>> Cc: Daniel Lezcano <[email-masked]>
>>> Reported-tested-by: Roger Quadros <[email-masked]>
>>> Reported-tested-by: Kevin Hilman <[email-masked]>
>>> Tested-by: Tony Lindgren <[email-masked]>
>>> Signed-off-by: Santosh Shilimkar <[email-masked]>
>>> ---

[ ... ]

>>>
>>> +    clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu_id);
>>> +
>>>        /*
>>>         * Call idle CPU PM enter notifier chain so that
>>>         * VFP and per CPU interrupt context is saved.
>>> @@ -165,6 +169,8 @@ static int omap_enter_idle_coupled(struct cpuidle_device *dev,
>>>        if (dev->cpu == 0 && mpuss_can_lose_context)
>>>            cpu_cluster_pm_exit();
>>>
>>> +    clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu_id);

[ ... ]

>>
>> Shouldn't the broadcast timer to be setup with CLOCK_EVT_NOTIFY_BROADCAST_ON also ?
>>
> Which is already taken care by __cpuidle_register_driver(). Note that setup code
> is still used from generic code...

Nope, if the flag CPUIDLE_FLAG_TIMER_STOP is not set, the cpuidle 
framework won't setup the timer.

static void __cpuidle_driver_init(struct cpuidle_driver *drv)
{

	...

	for (i = drv->state_count - 1; i >= 0 ; i--) {
		if (drv->states[i].flags & CPUIDLE_FLAG_TIMER_STOP) {
			drv->bctimer = 1;
			break;
		}
	}

	...

}

static int __cpuidle_register_driver(struct cpuidle_driver *drv)
{
	...

	if (drv->bctimer)
		on_each_cpu_mask(drv->cpumask,
		cpuidle_setup_broadcast_timer,
		 (void *)CLOCK_EVT_NOTIFY_BROADCAST_ON, 1);

	...
}

So the broadcast timer does not operate with this revert. Moreover, I am 
not sure reverting this patch is the right solution.

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