Re: [PATCH] iommu/arm-smmu: use a threaded handler for context interrupts

[Mitchel Humpherys <mitchelh-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On Fri, Jan 23 2015 at 03:24:15 AM, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> wrote:
> Hi Mitch,
>
> On Thu, Jan 22, 2015 at 11:48:02PM +0000, Mitchel Humpherys wrote:
>> Context interrupts can call domain-specific handlers which might sleep.
>> Currently we register our handler with request_irq, so our handler is
>> called in atomic context, so domain handlers that sleep result in an
>> invalid context BUG.  Fix this by using request_threaded_irq.
>> 
>> This also prepares the way for doing things like enabling clocks within
>> our interrupt handler.
>> 
>> Signed-off-by: Mitchel Humpherys <mitchelh-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
>> ---
>>  drivers/iommu/arm-smmu.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index 6cd47b75286f..81f6b54d94b1 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -973,8 +973,9 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>>  	spin_unlock_irqrestore(&smmu_domain->lock, flags);
>>  
>>  	irq = smmu->irqs[smmu->num_global_irqs + cfg->irptndx];
>> -	ret = request_irq(irq, arm_smmu_context_fault, IRQF_SHARED,
>> -			  "arm-smmu-context-fault", domain);
>> +	ret = request_threaded_irq(irq, NULL, arm_smmu_context_fault,
>> +				IRQF_ONESHOT | IRQF_SHARED,
>> +				"arm-smmu-context-fault", domain);
>>  	if (IS_ERR_VALUE(ret)) {
>>  		dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
>>  			cfg->irptndx, irq);
>
> I think I'd rather keep a simple atomic handler, then have a threaded
> handler for actually issuing the report_iommu_fault. i.e. we only wake
> the thread when it looks like there's some work to do. That also works
> much better for shared interrupts.

Are you still against adding clock support to the driver?  If not, we'll
need to move to a threaded handler when clocks come in anyways...

Can you elaborate what you mean regarding shared interrupts?  Even
without clocks it seems like the code clarity / performance tradeoff
would favor a threaded handler, given that performance isn't important
here.


-Mitch

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