linux-kernel - Re: PCI, ACPI, IRQ, IOAPIC: reroute PCI interrupt to legacy boot interrupt equivalent

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Message-ID: <20090114155529.GP25512@suse.de>
Date:	Wed, 14 Jan 2009 16:55:29 +0100
From:	Olaf Dabrunz <od@...e.de>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
Cc:	Stefan Assmann <sassmann@...e.de>,
	Shaohua Li <shaohua.li@...el.com>, Len Brown <lenb@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Olaf Dabrunz <od@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Sven Dietrich <sdietrich@...ell.com>
Subject: Re: PCI, ACPI, IRQ, IOAPIC: reroute PCI interrupt to legacy boot
	interrupt equivalent

On 14-Jan-09, Bjorn Helgaas wrote:
> On Wednesday 14 January 2009 02:57:22 am Stefan Assmann wrote:
> > Shaohua Li wrote:
> > > So a device can generate interrupt from two irqs. And we can get the irq
> > > number for the routing table. Can we extend the irq mechanism and
> > > automatically register the interrupt handler for the two irqs?
> > 
> > This would not solve the problem of asserting 2 different interrupt
> > lines, in the masked interrupt handling case, for 1 interrupt request.
> > The result would be that the ISR is called twice and at the second call
> > you can't be sure that the device hasn't already been serviced.
> 
> Calling the ISR twice isn't a problem, is it?  We're talking about
> PCI interrupts, which are shareable, so ISRs have to handle being
> called extra times.
> 
> There's still the problem that the core will disable an IRQ if we
> take it too many times without any ISR that cares about it.  But that's
> a core issue, not an ISR issue.

It is not solvable in the core. How do you find out that the "nobody
cared" spurious IRQ is benign?

Regards,

-- 
Olaf Dabrunz (od/odabrunz), SUSE Linux Products GmbH, Nürnberg

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