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

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Date:	Wed, 14 Jan 2009 12:40:06 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jon Masters <jcm@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Stefan Assmann <sassmann@...e.de>, Len Brown <lenb@...nel.org>,
	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, Sven Dietrich <sdietrich@...ell.com>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>
Subject: Re: PCI, ACPI, IRQ, IOAPIC: reroute PCI interrupt to legacy boot
	interrupt equivalent


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

> On Mon, 2009-01-12 at 19:47 -0800, Eric W. Biederman wrote:
> > Ingo Molnar <mingo@...e.hu> writes:
> 
> > > 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.
> > 
> > Yep.  Right now it might be simpler to fix the mainline drivers.
> 
> Taking the easy option now doesn't make the pain go away later :) Just 
> because ACPI doesn't provide a handy description doesn't mean we 
> shouldn't handle "boot interrupts" - the kernel is riddled with quirks 
> already to deal with broken, buggy, or just quirky hardware scenarios.
> 
> > We are outside the descriptions provided by ACPI so it requires 
> > chipset specific knowledge, and a general understanding of how 
> > chipsets work to actually even comprehend the problem.
> 
> But how does that differ from most other chipset code? I'm not being 
> belligerent but I'm not seeing how your argument is uniquely special to 
> this particular situation. Personally, I'm a little biased because I'd 
> eventually like to see RT merged upstream and I /know/ that's going to 
> re-open this whole can of worms once again, even if it's "fixed" now.

it's not just -rt, but it is also needed for the concept of threaded IRQ 
handlers - which was discussed at the Kernel Summit to be desired for 
mainline.

	Ingo
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