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Date: Mon, 16 Nov 2009 19:21:27 +0100
From: Stefan Weil <weil@mail.berlios.de>
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Subject: Re: [Qemu-devel] Standard vga breakage
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To: malc <av1474@comtv.ru>
Cc: Blue Swirl <blauwirbel@gmail.com>, qemu-devel <qemu-devel@nongnu.org>, Gleb Natapov <gleb@redhat.com>

malc schrieb:
> On Sun, 15 Nov 2009, Stefan Weil wrote:
>
>   
>> malc schrieb:
>>     
>>> On Sun, 15 Nov 2009, Gleb Natapov wrote:
>>>       
>
> [..snip..]
>
>   
>> Here is a summary of my analysis of this problem:
>>
>> Graphics mode memory (ram 0xe0000000 ...) is not mapped
>> in QEMU address space (which results in unassigned
>> memory writes) for standard pci vga (-vga std), so users
>> don't get vga display output with grub (in graphical mode),
>> debian installer (in graphical mode) or similar boot software.
>>
>> This happens for PC system emulation using SeaBIOS.
>> It won't happen when using Bochs BIOS.
>>
>> Other system emulations which can run standard pci vga
>> seem to suffer from the same problem: when I run mips
>> malta using -vga std, it won't display anything on the vga
>> screen (it works with cirrus pci vga).
>>
>> Malta has no vga bios, so the error might be in QEMU's
>> vga code (hw/vga-pci.c). Maybe wrong initial PCI mappings?
>> Maybe this has always be wrong (which would explain why
>> git bisect does not work).
>>     
>
> git bisect doesn't work because most of the time:
>
> a. Compilation fails
> b. Compilation succeeds but qemu segfaults before even trying to
>    execute any guest code
>   

I did git bisect: even very early versions (from 2006) of std vga had
the same kind of problem (no access to frame buffer at 0xe0000000)
when booted with SeaBIOS). It was not really a bisection, because
I never reached status "good".