Subject: Re: 2.6.35-rc3 regression: IBM Maia system is unbootable [ACPI
 related?]
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Len Brown <lenb@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>, linux-pci@vger.kernel.org,
       linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org
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Date: Tue, 29 Jun 2010 11:49:08 -0500
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On Mon, 2010-06-28 at 23:49 -0400, Len Brown wrote:
> From: Len Brown <len.brown@intel.com>
> Subject: [PATCH] ACPI: handle systems which asynchoronously enable ACPI mode
> 
> Folklore suggested that such systems existed
> in the pre-history of ACPI.
> 
> However, we removed the SCI_EN polling loop from
> acpi_hw_set_mode() in b430acbd7c4b919886fa7fd92eeb7a695f1940d3
> because it delayed resume by 3 seconds on boxes
> that refused to set SCI_EN.
> 
> Matthew removed the call to acpi_enable() from
> the suspend resume path.
> 
> James found a modern system that still needs to be polled
> upon boot.
> 
> So here we restore the workaround, except that we
> put it in acpi_enable() rather than the low level
> acpi_hw_set_mode().
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=16271
> 
> Signed-off-by: Len Brown <len.brown@intel.com>
> ---
> 
> James, What does the IBM system see with this patch?

The output is this:

[    0.084088] ACPI: Core revision 20100428
[    0.119451] ACPI Warning: Platform took > 100 usec to enter ACPI mode (20100428/evxfevnt-106)
[    0.128231] Setting APIC routing to physical flat

So it's very fast ... actually it's behaving like there's some caching
issue and it needs two reads to return the correct value

James


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