linux-kernel - Re: [PATCH 11/15] x86: move enabling of io_apic to prepare

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Date:	Tue, 10 Jun 2008 14:30:47 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Glauber Costa <gcosta@...hat.com>
cc:	Yinghai Lu <yhlu.kernel@...il.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, tglx@...utronix.de, mingo@...e.hu,
	hugh@...itas.com
Subject: Re: [PATCH 11/15] x86: move enabling of io_apic to prepare_cpus

On Tue, 10 Jun 2008, Glauber Costa wrote:

> >>  Then again -- what if X86_LOCAL_APIC is set, but X86_IO_APIC is not?
> > 
> > config X86_LOCAL_APIC
> >         def_bool y
> >         depends on X86_64 || (X86_32 && (X86_UP_APIC || ((X86_VISWS ||
> > SMP) && !X86_VOYAGER) || X86_GENERICARCH))
> > 
> > config X86_IO_APIC
> >         def_bool y
> >         depends on X86_64 || (X86_32 && (X86_UP_IOAPIC || (SMP &&
> > !(X86_VISWS || X86_VOYAGER)) || X86_GENERICARCH))
> > 
> > for 64bit, those are all set.
> > 
> > for 32bit, may need to null stub if X86_IO_APIC is not set
> > 
> > YH
> Fair Enough.

 That does not answer the question what to do with a 32-bit kernel run on
a system that requires the fixup in the 64-bit mode.  Papering over such
firmware bugs in the kernel encourages hardware vendors to maintain the
breakage.

 Note that the I/O APIC comes out of reset with all the redirection
entries masked out, so if any error conditions are triggered before Linux
configures the chip, they are a result of a deliberate misprogramming done
to the chip by the firmware.

 Does anyone have a reference to the original problem report which lead to
this workaround having been put in place?

  Maciej
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