linux-kernel - Re: [PATCH 1/3] irqchip: sun4i: Don't mask + unmask for the non oneshot case

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Date:	Fri, 14 Mar 2014 19:42:00 +0100
From:	Hans de Goede <hdegoede@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org,
	devicetree <devicetree@...r.kernel.org>,
	linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH 1/3] irqchip: sun4i: Don't mask + unmask for the non oneshot
 case

Hi,

On 03/14/2014 12:35 PM, Thomas Gleixner wrote:
> On Thu, 13 Mar 2014, Hans de Goede wrote:
> 
>> Since sun4i and sun5i are single core SOCs there is no need to mask non
>> oneshot IRQs, to achieve this we use handle_fasteoi_irq with a dummy eoi.
> 
> This is slightly wrong :)
> 
> Even on a SMP system there is no need to mask the interrupt when the
> controller works like that sunxi one. If the controller is not broken
> beyond repair then it does not deliver the same interrupt to a
> different cpu. Such a thing would always deliver it to all cores and
> those would race to grab the spinlock and mask it. I've seen such
> horror, but don't ask how that performs.
> 
> The reason why you can spare the mask/unmask dance is that the
> controller does not require any action and clears the interrupt when
> the level goes back to inactive. That happens when the device handler
> acks it at the device level.
> 
> Now there might be the case when the device reactivates the interrupt
> before the RETI. But that does not matter as we run the primary
> interrupt handlers with interrupts disabled.

Ok, I'm going to wait a bit to see if Maxime has anything to say
to this second series, and then I'll do a v2 with the commit msg
fixed.

Regards,

Hans


> 
> Thanks,
> 
> 	tglx
>  
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>> ---
>>  drivers/irqchip/irq-sun4i.c | 11 ++++++++++-
>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/irqchip/irq-sun4i.c b/drivers/irqchip/irq-sun4i.c
>> index a0ed1ea..0a71990 100644
>> --- a/drivers/irqchip/irq-sun4i.c
>> +++ b/drivers/irqchip/irq-sun4i.c
>> @@ -74,8 +74,17 @@ static void sun4i_irq_unmask(struct irq_data *irqd)
>>  	       sun4i_irq_base + SUN4I_IRQ_ENABLE_REG(reg));
>>  }
>>  
>> +/*
>> + * Since sun4i and sun5i are single core SOCs there is no need to mask non
>> + * oneshot IRQs, to achieve this we use handle_fasteoi_irq with a dummy eoi.
>> + */
>> +static void sun4i_irq_dummy_eoi(struct irq_data *irqd)
>> +{
>> +}
>> +
>>  static struct irq_chip sun4i_irq_chip = {
>>  	.name		= "sun4i_irq",
>> +	.irq_eoi	= sun4i_irq_dummy_eoi,
>>  	.irq_mask	= sun4i_irq_mask,
>>  	.irq_unmask	= sun4i_irq_unmask,
>>  };
>> @@ -97,7 +106,7 @@ static int sun4i_irq_map(struct irq_domain *d, unsigned int virq,
>>  					 handle_fasteoi_irq);
>>  	else
>>  		irq_set_chip_and_handler(virq, &sun4i_irq_chip,
>> -					 handle_level_irq);
>> +					 handle_fasteoi_irq);
>>  
>>  	set_irq_flags(virq, IRQF_VALID | IRQF_PROBE);
>>  
>> -- 
>> 1.9.0
>>
>>
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