linux-kernel - Re: [RFC trollpatch 1/1] genirq: Remove the fits all and nothing __do

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Date:	Mon, 27 Sep 2010 20:01:26 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Tony Luck <tony.luck@...el.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	linux-alpha@...r.kernel.org, linux-cris-kernel@...s.com,
	Haavard Skinnemoen <hskinnemoen@...el.com>,
	linux-ia64@...r.kernel.org,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Hirokazu Takata <takata@...ux-m32r.org>,
	Greg Ungerer <gerg@...inux.org>, Jeff Dike <jdike@...toit.com>,
	linux-parisc@...r.kernel.org, Chris Zankel <chris@...kel.net>,
	linux-arch@...r.kernel.org
Subject: Re: [RFC trollpatch 1/1] genirq: Remove the fits all and nothing
 __do_IRQ() code



On Mon, 27 Sep 2010, Tony Luck wrote:

> On Wed, Sep 8, 2010 at 11:14 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >  The following architectures are still using __do_IRQ():
> >
> >  alpha, cris, ia64, h8300, m32r, m68knommu, parisc, um
> 
> Thomas,
> 
> I (belatedly) took a look at fixing ia64 ... but I've run into a small snag.
> The __do_IRQ() routine makes a call to:
> 
>  desc->chip->end(irq);
> 
> while neither of the "handle_level_irq()" nor "handle_edge_irq()"
> functions do this.
> 
> On ia64 iosapic_end_level_irq() call iosapic_eoi() for me. Without it
> my system hangs during boot (with some driver timeout complaining
> about dropped interrupts).
> 
> Is the omission of desc->chip->end(irq); deliberate? In which case
> I need to find another place to call iosapic_eoi(). Or is it accidental?

No, it's deliberate. The solution is to use the correct flow handler
for your device. We have currently several flow handlers implemented:

    handle_level_irq
	{
		if (chip->mask_ack)
			chip->mask_ack()
		else {
		     chip->mask();
		     if (chip->ack)
		     	chip->ack();
		}

		....

		chip->unmask();
	}

    handle_edge_irq
	{
		chip->ack()

		...
	}

    handle_simple_irq
	{
		...
	}

    handle_fasteoi_irq
	{
		...
		chip->eoi();
	}

    handle_percpu_irq
	{	
		if (chip->ack)
		     	chip->ack();
		
		if (chip->eoi)
		     	chip->eoi();
	}

Note, that handle_percpu_irq does not take the irq_desc->lock.

So the trick is to select the matching handler and have separate irq
chip implementations if necessary.

Hope that helps.

Thanks,

	tglx