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Re: [Qemu-devel] Standard vga breakage

From: Anthony Liguori
Subject: Re: [Qemu-devel] Standard vga breakage
Date: Mon, 16 Nov 2009 13:12:48 -0600
User-agent: Thunderbird (X11/20090825)

Stefan Weil 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 <address@hidden> 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
- 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
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.

0xe00... is the VBE mapping. The VGABIOS assumes this mapping exists when using VBE. Cirrus doesn't support VBE so it wouldn't be exposed there.

Does the following help:

diff --git a/hw/vga-pci.c b/hw/vga-pci.c
index 479ffb1..e273b8b 100644
--- a/hw/vga-pci.c
+++ b/hw/vga-pci.c
@@ -107,6 +107,12 @@ static int pci_vga_initfn(PCIDevice *dev)
                         PCI_BASE_ADDRESS_MEM_PREFETCH, vga_map);

+    /* XXX: use optimized standard vga accesses */
+    cpu_register_physical_memory(VBE_DISPI_LFB_PHYSICAL_ADDRESS,
+                                 vga_ram_size, s->vga.vram_offset);
     /* ROM BIOS */
     return 0;


Anthony Liguori

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