vesa driver reports many modes, but only allows a few

Ross Boylan ross at
Sun Feb 28 23:28:56 PST 2010

Could anyone explain to me what the attached log means?

X 7.5 detects a rich array of BIOS modes, but then runs through a list
of modes and says "no mode of this name".  Should it be using something
like "104" or  "104 (1024x768)" instead of, e.g., "1024x768"?  Then X
tries a less strict probe, and rejects all but a couple of
low-resolution modes with "hsync out of range".  I have no xorg.conf

X is running inside a VM, to which I'm connected via vnc.  The VM is
running Debian squeeze (testing).  When it starts up, the boot screen
appears to be 640x480.  If I launch an X session, I get 800x600.  I
would like higher resolutions in both terminal and X mode.

The host runs qemu-kvm-0.12.2, compiled from source on Debian lenny
(stable), amd64 architecture (Xeon).  The VM is also amd64, with
multiple CPU's.

I don't need to do anything special to get the tablet device recognized,
which is nice improvement over X 7.3 on Debian Lenny.  But something is
going wrong with the video.  Other bugs on the net suggest that the
virtual display adapter is not advertising its modes properly.
Consistent with that, the DDC does not seem to work; there is a message
"VESA VBE DDC not supported".  However, the log lists many video modes;
it appears X is getting the information it needs.

I have tried various xorg.conf's, but have gotten nowhere--apparently if I
define one section I need to define all the others.  The logs don't seem
to have any modelines, ruling out the simple solution given in the FAQ.

I launch with 
sudo vdeq bin/qemu-system-x86_64 -net
nic,vlan=1,macaddr=52:54:a0:16:01:01 \
    -net vde,vlan=1,sock=/var/run/vde2/tap0.ctl \
    -boot c \
    -vga std -vnc localhost:7 -usbdevice tablet \
    -name Squeeze00 \
    -hda /dev/turtle/Squeeze00 \
    -soundhw es1370 -m 1G -smp 4

Of course, I'd also welcome help with the virtual machine, but I only
came to this list for help on the X part.  Why are video modes being
detected but not used?  Is there an xorg.conf I can specify that will
work around the problem?

Ross Boylan
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