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Date: Wed, 31 Oct 2007 15:17:04 +0200
From: Avi Kivity <avi@qumranet.com>
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Subject: Re: [Qemu-devel] [PATCH] Update i440FX/PIIX3 emulation
References: <20071024224222.GB9226@hansmi.ch>
	<20071031002554.GB20915@hansmi.ch>
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To: qemu-devel@nongnu.org
Cc: igor.lvovsky@qumranet.com

Michael Hanselmann wrote:
>
>> This does not yet remove the workaround introduced by Igor Lvovsky's
>> patch. However, I'm working on that since it, despite my earlier mail,
>> seems to help with my ACPI shutdown problem.
>>     
>
> So, I found the bug causing this behaviour. It turned out to be a
> wrongly named variable in the ACPI DSDT from Bochs. See the patch for
> Bochs below. I already sent it to the bochs-developers list[1].
> qemu/pc-bios/bios.bin needs to be rebuilt from Bochs' code,
> qemu/pc-bios/bios.diff and my patch.
>
> The second patch below reverts the changes made by Igor Lvovsky. After
> applying the patch to the BIOS, ACPI IRQs finally reach the system.
>
> Finding this bug took me about the free time of four weeks. However, I
> learned a lot about the internals of a PC. :-)
>
> Thanks,
> Michael
>
> [1] http://sourceforge.net/mailarchive/forum.php?thread_name=20071031000835.GA20915%40hansmi.ch&forum_name=bochs-developers
>
> ---
> Index: bios/acpi-dsdt.dsl
> ===================================================================
> RCS file: /cvsroot/bochs/bochs/bios/acpi-dsdt.dsl,v
> retrieving revision 1.1
> diff -u -p -u -p -r1.1 acpi-dsdt.dsl
> --- bios/acpi-dsdt.dsl	28 Sep 2006 18:56:20 -0000	1.1
> +++ bios/acpi-dsdt.dsl	30 Oct 2007 23:52:22 -0000
> @@ -369,7 +369,7 @@ DefinitionBlock (
>                  Method (_STA, 0, NotSerialized)
>                  {
>                      Store (0x0B, Local0)
> -                    If (And (0x80, PRQ0, Local1))
> +                    If (And (0x80, PRQ0, Local0))
>                      {
>                           Store (0x09, Local0)
>                      }
>   

Can you explain this?

The original code seems to return either 0xb (present, enabled, 
functional) or 0x9 (present, functional).  The new code seems to return 
either 0x9 (present, functional) or 0 (if PRQ0 had its seventh bit clear).

Am I reading the code incorrectly?

-- 
Any sufficiently difficult bug is indistinguishable from a feature.