linux-kernel - Re: [PATCH] irq: Add a new IRQF_ACK_BEFORE

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Date:	Wed, 12 Mar 2014 11:48:45 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	Hans de Goede <hdegoede@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Carlo Caione <carlo.caione@...il.com>
Subject: Re: [PATCH] irq: Add a new IRQF_ACK_BEFORE_UNMASK irq flag

On Wed, 12 Mar 2014, Russell King - ARM Linux wrote:

> On Wed, Mar 12, 2014 at 11:38:24AM +0100, Thomas Gleixner wrote:
> > If the interrupt chip has this behaviour then handle_level_irq as the
> > flow handler is the wrong thing to start with because it always acks
> > before calling the handler.
> 
> This sounds like the situation with the Dove PMC irqchip too, except
> that it has the additional complication that "acking" any interrupt is
> potentially distructive to other pending interrupts, so should be done
> as infrequently as possible.

Right. I was wondering about that, but then reminded myself that the
"ack" on that chip is total clusterf*ck.
 
> > +void unmask_threaded_irq(struct irq_desc *desc)
> > +{
> > +	struct irq_chip *chip = desc->irq_data.chip;
> > +
> > +	if (chip->flags & IRQCHIP_EOI_THREADED)
> > +		chip->irq_eoi(&desc->irq_data);
> > +
> > +	if (chip->irq_unmask) {
> > +		desc->irq_data.chip->irq_unmask(&desc->irq_data);
> 
> ITYM:
> 		chip->irq_unmask(&desc->irq_data);

True.

Thanks,

	tglx
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