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

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Date:	Thu, 27 Sep 2007 11:36:32 -0700
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
CC:	Jesse Barnes <jesse.barnes@...el.com>, Greg KH <greg@...ah.com>,
	linux-pci@...ey.karlin.mff.cuni.cz,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	Robert Hancock <hancockr@...w.ca>,
	Matthew Wilcox <matthew@....cx>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: PCI: Fix boot-time hang on G31/G33 PC

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.

Cheers,

Auke
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