linux-kernel - Re: PCI: Fix boot-time hang on G31/G33 PC

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Message-ID: <470FA9D3.2050701@intel.com>
Date:	Fri, 12 Oct 2007 10:07:31 -0700
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Vitaliy Gusev <vgusev@...nvz.org>
CC:	Greg KH <greg@...ah.com>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Jesse Barnes <jesse.barnes@...el.com>,
	linux-pci@...ey.karlin.mff.cuni.cz,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	Robert Hancock <hancockr@...w.ca>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: PCI: Fix boot-time hang on G31/G33 PC

Vitaliy Gusev wrote:
> On the 28 September 2007 03:13 Greg KH, wrote:
>> On Thu, Sep 27, 2007 at 11:36:32AM -0700, Kok, Auke wrote:
>>> Ivan Kokshaysky wrote:
>>>> On Wed, Sep 26, 2007 at 03:20:40PM -0700, Jesse Barnes wrote:
>>>>> Ivan, your concern is about disabling things like interrupt
>>>>> controllers and power management chips during probe right?  You're
>>>>> right that doing that could cause problems if we get and interrupt or
>>>>> PMU event at just the wrong time, but that could just as easily happen
>>>>> if decode was still enabled but the BAR had a bogus address programmed
>>>>> (as it would during probing).
>>>> Yes, nobody is arguing that moving the BAR around is unsafe, but
>>>> generally it's the less of two evils.
>>>>
>>>> The major problem here is that with IO and MEM bits cleared in the
>>>> command register you disable *all* address decoders on the device, not
>>>> just ranges that have respective BARs. At least this behaviour is
>>>> required by PCI spec. Examples:
>>>> - legacy VGA IO and memory (no corresponding BARs);
>>>> - base/limit registers of P2P bridge;
>>>> - PMU and SMBus registers (sort of normal BARs, but hidden elsewhere
>>>>   in the config space);
>>>> - IDE legacy mode registers;
>>>> - IO-APIC registers (typically sort of read-only BAR).
>>>>
>>>> For all of these address ranges our current BAR probe is effectively
>>>> a no-op, but disable/re-enable clearly isn't.
>>>>
>>>>> Ultimately, I don't care much one way or another as long as we can get
>>>>> the desktop platforms fixed somehow.  I think disabling decode is the
>>>>> most correct way of doing this, but I'm open to other solutions (this
>>>>> is the only patch I've seen though that's been tested to solve the
>>>>> problem).
>>>> There are two other solutions: one is to disable decode selectively,
>>>> only on devices or systems where it's necessary and known to be safe.
>>>> I've posted a patch which introduces "disable_while_probe" pci_dev
>>>> field for that purpose.
>>>> Another one is to delay mmconfig probe until after the PCI probe is
>>>> done, as Matthew suggested, and Robert confirmed that it's feasible.
>>> for everyone who's using this quirk or has the same boot issue: I just
>>> confirmed that the new dg33tl bios update v0287 (released 9/20) fixes the
>>> boot issue for my systems. I encourage everyone to update their BIOS
>>> image and see if this works.
> 
> No, it still doesn't work even with a latest BIOS verstion. I have a computer 
> with Intel DQ35MP motherboard. I upgraded BIOS to rev. 0696, released 
> Oct 1. But kernel (2.6.22.5) still hangs up. Kernel with this fix patch boots 
> and works fine.

please note that your BIOS is completely different than the one posted above. This
may be a clue.

interestingly enough I can attest (somewhat) to this. After the BIOS upgrade
2.6.22 booted just fine without pci=nommconf, but I've had several boot lockups
with 2.6.23-rc8.

So, the issue is still open and Matthew/Jesse's suggested fix becomes much more
attractive to me now.

Greg, I suggest putting this patch back in the "grey" zone

Auke
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