Subject: [PATCH] gic : check if there are pending interrupts

From: [email-masked] (Daniel Lezcano)
Date: Mon, 27 Feb 2012 15:49:42 +0100

On 02/24/2012 05:49 PM, Rob Herring wrote:
> On 02/24/2012 07:45 AM, Daniel Lezcano wrote:
>> The following patch checks if there are pending interrupts on the gic.
>>
>> This function is needed for example for the ux500 cpuidle driver.
>> When the A9 cores and the gic are decoupled from the PRCMU, the idle
>> routine has to check if an interrupt is pending on the gic before entering
>> in retention mode.
>
> That sounds racy. Soon as you check an interrupt can assert.

Yes it sounds racy but not for the ux500 where the gic can be decoupled 
and the irq are catched by the PRCMU to wake up the core A9.

>> Signed-off-by: Daniel Lezcano<[email-masked]>
>> ---
>>   arch/arm/common/gic.c               |   37 +++++++++++++++++++++++++++++++++++
>>   arch/arm/include/asm/hardware/gic.h |    2 +-
>>   2 files changed, 38 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/arm/common/gic.c b/arch/arm/common/gic.c
>> index aa52699..2528094 100644
>> --- a/arch/arm/common/gic.c
>> +++ b/arch/arm/common/gic.c
>> @@ -750,6 +750,43 @@ void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
>>   }
>>   #endif
>>
>> +/*
>> + * gic_pending_irq - checks if there are pending interrupts on the gic
>> + *
>> + * Disabling an interrupt only disables the forwarding of the
>> + * interrupt to any CPU interface. It does not prevent the interrupt
>> + * from changing state, for example becoming pending, or active and
>> + * pending if it is already active. For this reason, we have to check
>> + * the interrupt is pending *and* is enabled.
>> + *
>> + * Returns true if there are pending and enabled interrupts, false
>> + * otherwise.
>> + */
>> +bool gic_pending_irq(unsigned int gic_nr)
>
> Seems like this should be solved with a generic interface and not gic
> specific.

> Would we ever need this for a secondary gic (gic_nr != 0)?

I don't think so for this specific routine which will be used by the 
ux500 for the moment.

>> +{
>> +	u32 pr; /* Pending register */
>> +	u32 er; /* Enable register */
>> +	void __iomem *dist_base;
>> +	int gic_irqs;
>> +	int i;
>> +
>> +	BUG_ON(gic_nr>= MAX_GIC_NR);
>> +
>> +	gic_irqs = gic_data[gic_nr].gic_irqs;
>> +	dist_base = gic_data_dist_base(&gic_data[gic_nr]);
>> +
>> +	for (i = 0; i<  DIV_ROUND_UP(gic_irqs, 32); i++) {
>
> Wouldn't you want to skip PPIs if the CPU interface is disabled?
>
>> +
>> +		pr = readl_relaxed(dist_base + GIC_DIST_PENDING_SET + i * 4);
>> +		er = readl_relaxed(dist_base + GIC_DIST_ENABLE_SET + i * 4);
>> +
>
> What if an interrupt is pending, but routed to a core which is not
> getting put into low power state?

Hmm, right. That does not happen with the ux500 because the gic is 
decoupled from the cores. Checking if some irq are pending on the gic 
makes sense only on this case which is very specific to the ux500 SoC.
I am wondering if that would not make sense to move this routine to the 
mfd's prcmu.c file, no ?

   -- Daniel

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