linux-kernel - Re: [RFC][PATCH] irq: Rework IRQF_NO

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Date:	Fri, 25 Jul 2014 14:40:37 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	rjw@...ysocki.net, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] irq: Rework IRQF_NO_SUSPENDED

On Fri, Jul 25, 2014 at 11:40:48AM +0200, Thomas Gleixner wrote:
> On Thu, 24 Jul 2014, Peter Zijlstra wrote:
> > @@ -29,14 +29,20 @@ void suspend_device_irqs(void)
> >  	for_each_irq_desc(irq, desc) {
> >  		unsigned long flags;
> >  
> > +		/*
> > +		 * Ideally this would be a global state, but we cannot
> > +		 * for the trainwreck that is IRQD_WAKEUP_STATE.
> > +		 */
> >  		raw_spin_lock_irqsave(&desc->lock, flags);
> > -		__disable_irq(desc, irq, true);
> > +		if (!irqd_has_set(&desc->irq_data, IRQD_WAKEUP_STATE))
> > +			desc->istate |= IRQS_SUSPENDED;
> >  		raw_spin_unlock_irqrestore(&desc->lock, flags);
> >  	}
> >  
> > -	for_each_irq_desc(irq, desc)
> > +	for_each_irq_desc(irq, desc) {
> >  		if (desc->istate & IRQS_SUSPENDED)
> >  			synchronize_irq(irq);
> > +	}
> >  }
> 
> So, instead of disabling the interrupt you just mark it
> suspended. Good luck with level triggered interrupt lines then.
> 
> Assume the interrupt fires after you marked it suspended. Then the
> flow handler will call handle_irq_event() which will do nothing and
> return handled. So the flow handler will reenable the interrupt line,
> which will cause the interrupt to fire immediately again after the
> RETI. Guess how much progress the system is going to make when that
> happens.

Urgh, right. I knew it was too easy. Can we have do_irqhandler() ACK the
interrupt and not call the handler?
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