vesa driver reports many modes, but only allows a few

Adam Jackson ajax at
Mon Mar 1 11:40:23 PST 2010

On Sun, 2010-02-28 at 23:28 -0800, Ross Boylan wrote:
> 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
> file.

The vesa driver attempts to find the intersection of the list of modes
in the BIOS with the list of modes from EDID.  You don't have an EDID,
so this (unsurprisingly) gives you no modes.

If we get to this point, we attempt to validate the BIOS mode list
against the sync ranges configured for the monitor in xorg.conf, or from
the defaults if there's no explicit configuration.  That's what the
"trying less strict filter" bit means.  The default sync ranges for your
server appear to be just big enough for 800x600.

If you want bigger modes, configure a bigger sync range:

# big enough for 1600x1200 @ 60Hz
Section "Monitor"
    Identifier "Monitor0"
    HorizSync 31.5 - 75.0
    VertRefresh 56.0 - 61.0

Use the gtf(1) utility to calculate the upper bounds for sync ranges for
the resolution you want:

% gtf 1600 1200 60

  # 1600x1200 @ 60.00 Hz (GTF) hsync: 74.52 kHz; pclk: 160.96 MHz
  Modeline "1600x1200_60.00"  160.96  1600 1704 1880 2160  1200 1201 1204 1242  -HSync +Vsync

- ajax
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