linux-kernel - Re: [PATCH v2 4/4] irqchip: sun4i: Use handle_fasteoi_late

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Date:	Thu, 13 Mar 2014 16:13:22 +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 v2 4/4] irqchip: sun4i: Use handle_fasteoi_late_irq for
 the ENMI (irq 0)

Hi,

On 03/13/2014 03:46 PM, Thomas Gleixner wrote:
> On Wed, 12 Mar 2014, Hans de Goede wrote:
> 
>> The ENMI needs to have the ack done *after* clearing the interrupt source,
>> otherwise we will get a spurious interrupt for each real interrupt. Switch
>> to the new handle_fasteoi_late_irq handler which gives us the desired behavior.
>>
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>> ---
>>  drivers/irqchip/irq-sun4i.c | 11 +++++++++--
>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-sun4i.c b/drivers/irqchip/irq-sun4i.c
>> index 8a2fbee..4b1c874 100644
>> --- a/drivers/irqchip/irq-sun4i.c
>> +++ b/drivers/irqchip/irq-sun4i.c
>> @@ -77,15 +77,22 @@ static void sun4i_irq_unmask(struct irq_data *irqd)
>>  static struct irq_chip sun4i_irq_chip = {
>>  	.name		= "sun4i_irq",
>>  	.irq_ack	= sun4i_irq_ack,
>> +	.irq_eoi	= sun4i_irq_ack, /* For the ENMI */
>>  	.irq_mask	= sun4i_irq_mask,
>>  	.irq_unmask	= sun4i_irq_unmask,
>> +	.flags		= IRQCHIP_EOI_THREADED, /* Only affects the ENMI */
> 
> That's not really true. The flags affect all interrupts which share
> that chip.

Yep, I figured out as much myself too while thinking a bit more about this
this morning.

So what I'm going to do in my next version of this patch is use 2
irqchip structures for the sun4i irqchip, one to describe the special
IRQ 0 and for all the others.

> 
>>  };
>>  
>>  static int sun4i_irq_map(struct irq_domain *d, unsigned int virq,
>>  			 irq_hw_number_t hw)
>>  {
>> -	irq_set_chip_and_handler(virq, &sun4i_irq_chip,
>> -				 handle_level_irq);
>> +	if (hw == 0) /* IRQ 0, the ENMI needs special handling */
>> +		irq_set_chip_and_handler(virq, &sun4i_irq_chip,
>> +					 handle_fasteoi_late_irq);
>> +	else
>> +		irq_set_chip_and_handler(virq, &sun4i_irq_chip,
>> +					 handle_level_irq);
> 
> I wonder what happens when you use the fasteoi handler for all of
> them.

As mentioned in my previous mail doing an ack (or an eio) seems to
be unnecessary for all but IRQ 0.

I do wonder if handle_level_irq is the right handle*irq function
to use in this case, since this is strictly used in the non smp
case I think that the mask / unmask done by handle_level_irq is
not necessary for non threaded handlers. So what would be the
correct handle*irq function to use in this case ?

Note the irqs are level irqs. IOW they may stay asserted while
the handler runs because of the handler and a new irq raising.

Regards,

Hans
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