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Subject: Re: PATCH 2.5.x disable BAR when sizing
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Paul Mackerras <paulus@samba.org>
Cc: Linus Torvalds <torvalds@transmeta.com>,
       "Eric W. Biederman" <ebiederm@xmission.com>, davidm@hpl.hp.com,
       Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
       linux-kernel@vger.kernel.org
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On Sun, 2002-12-22 at 08:15, Paul Mackerras wrote:
> Linus Torvalds writes:
> 
> > Actually, I think it's certainly valid to not allow "printk()" to happen
> > around the BAR probing, at least at bootup when we control all the CPU's
> > tightly anyway.
> 
> I'd like us to disable interrupts too.  On powermacs, the interrupt
> controller is typically inside a combo I/O ASIC which is on the PCI
> bus.  If we take an interrupt while the ASIC's BAR is relocated or
> turned off, we will get a machine check when we try to access the
> interrupt controller and the kernel will die at that point.

Actually, it's even worse, as the current probe code also turn off
address decoders of PCI<->PCI bridges when probing, and in a lot of
case, the combo ASIC containing the interrupt controller _is_ behind a
PCI<->PCI bridge ! Same problem with serial port (so printk is unsafe
for quite a while on serial consoles) etc...

The code has a comment that clearly says that we don't know why address
decoding is turned off and that should be fixed, so I suggest we either
fix it now or replace the comment with an explanation of why we need to
turn it off ;) Eventually, turning it off could be made an exception via
some quirks mecanism.

Ben.


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