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From: Blue Swirl <blauwirbel@gmail.com>
Date: Sun, 15 Nov 2009 22:37:11 +0200
Message-ID: <f43fc5580911151237m5299e5edp61d12de112d4a728@mail.gmail.com>
Subject: Re: [Qemu-devel] Standard vga breakage
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To: Stefan Weil <weil@mail.berlios.de>
Cc: qemu-devel <qemu-devel@nongnu.org>, Gleb Natapov <gleb@redhat.com>

On Sun, Nov 15, 2009 at 10:16 PM, Stefan Weil <weil@mail.berlios.de> wrote:
> malc schrieb:
>> On Sun, 15 Nov 2009, Gleb Natapov wrote:
>>
>>> On Sun, Nov 15, 2009 at 06:22:40PM +0300, malc wrote:
>>>> On Sun, 15 Nov 2009, Blue Swirl wrote:
>>>>
>>>>> On Sun, Nov 15, 2009 at 3:25 AM, malc <av1474@comtv.ru> wrote:
>>>>>> debian-503-i386-netinst.iso when booted on a machine with `-vga
>>>>>> std' just
>>>>>> shows black screen (after bios' setup screen)
>>>>> Just some observations:
>>>>> - if you press enter, installer starts and Linux is able to fix the
>>>>> display
>>>>> - the screen is fine with -bios pcbios.bin, so the issue is related
>>>>> to SeaBIOS
>>>> Yes i forgot to mention that -bios works, also worth noting is that
>>>> before
>>>> the commit that fixed cirrus -bios hack also made it work.
>
>
> 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).
>
> pci_vga_init() is called by sun4u, ppc_prep, ppc_oldworld,
> ppc_newworld, pc and mips, so all these emulations
> share the same potential problem.

At least sun4u, ppc_oldworld and ppc_newworld are fine with -vga std.
There is no VGA BIOS.