linux-kernel - Re: linux-next: Tree for June 13: IO APIC breakage on HP nx6325

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Date:	Sun, 29 Jun 2008 21:14:35 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	Andi Kleen <andi-suse@...stfloor.org>
Subject: Re: linux-next: Tree for June 13: IO APIC breakage on HP nx6325

On Sun, 29 Jun 2008, Ingo Molnar wrote:

> >  You may argue this is a regression, but this is simply the cost paid 
> > for progress -- the kernel stays within the spec as defined both by 
> > ACPI and MPS, we have just started using a different configuration now 
> > and an interrupt source override provided by the manufacturer 
> > explicitly states INTIN2 is good to use.  In a sense you were simply 
> > lucky previously the kernel was bad enough with the way it configured 
> > the timer through the I/O APIC it failed completely avoiding the bug 
> > in your firmware.  Now the bug has got uncovered.
> 
> well as long as we eliminate the bad effects around via DMI exceptions 
> nobody will feel the need to argue whether it's a regression ;-) [this 
> problem could be argued to be a regression, even if it's caused by prior 
> luck/stupidity of Linux. We have to live with the effects of our 
> mistakes.]

 Of course -- this is the only reason I can be bothered with the issue in
the first place.  Otherwise, I would have said: 'Get the manufacturer to
fix it, use "noapic" or live with a local patch.'

 This is actually how I have kept one of my old MPS SMP systems up for
years now -- it has a broken MP table which prevents interrupts from
working when too many PCI option cards are present, so I have prepared a
patch for patching the table manually.  I proposed it once, which you may
recall, but it was rejected on the grounds of the syntax being too tough
to comprehend to a poor average user being.  I am sure more systems would
benefit as MP table breakages used to be quite common.

 Here the simple workaround was "noapic" too, so everyone else could be
happy and I have been happy to keep the patch and use the capabilities of
the piece of hardware properly despite its broken firmware.

  Maciej
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