From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: PCI, ACPI, IRQ, IOAPIC: reroute PCI interrupt to legacy boot
	interrupt equivalent
Date: Tue, 13 Jan 2009 02:47:23 +0100
Message-ID: <20090113014723.GA11366@elte.hu>
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To: Jon Masters <jcm@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>, Bjorn Helgaas <bjorn.helgaas@hp.com>, Stefan Assmann <sassmann@suse.de>, Len Brown <lenb@kernel.org>, Jesse Barnes <jbarnes@virtuousgeek.org>, Olaf Dabrunz <od@suse.de>, Thomas Gleixner <tglx@linutronix.de>, Steven Rostedt <rostedt@goodmis.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-acpi@vger.kernel.org, Sven Dietrich <sdietrich@novell.com>, "Maciej W. Rozycki" <macro@linux-mips.org>


* Jon Masters <jcm@redhat.com> wrote:

> On Mon, 2009-01-12 at 15:36 -0800, Eric W. Biederman wrote:
> 
> > This hardware behavior is not specific to boot interrupts or Intel.
> 
> It's not specific to Intel, but it is a specific compatibility behavior.
> 
> > Is this case really so interesting and compelling that we want to 
> > fight through and figure what we need to do to make this work reliably 
> > on every x86 chipset?
> 
> How else do you propose implementing IRQ handling in e.g. the RT kernel? 
> We get a hardware interrupt, we can't FastEOI, we can't process 
> synchronously, we can't do all of those things you might expect. 
> Implementing RT requires that we delay handling of the IRQ until 
> arbitrarily later in the future when we get around to it.

a number of mainline drivers also mask/unmask irqs from within the IRQ 
handler. It's not particularly smart in a native driver, but can happen - 
and if we get an active line after that point (and this can happen because 
the driver is active), we are in trouble.

	Ingo