Ext. VGA problem with Toshiba Portege R100 (TRIDENT, cyberbladeXP4)

[Markus Kuhn]

My Toshiba Portege R100 laptop uses a Trident XP4m32 graphics
controller and an Intel 852GM chipset.

The X.Org 6.8.2 server (driver: TRIDENT, cyberbladeXP4) that comes with
SuSE Linux 9.3 runs nicely with the built-in display.

However, as soon as I activate the VGA output (for use with a video
projector) by pressing Fn+F5, the following strange effect happens:

The left half of the displayed image remains intact, but the right half
gets replaced by two repetitions of half the left half of the image. In
other words, if the image area is split horizontally into four
rectangles, the second quarter gets repeated where the 3rd and 4th
should appear, as in:

Expected image:

  +---+---+---+---+
  |   |   |   |   |
  | 1 | 2 | 3 | 4 |
  |   |   |   |   |
  |   |   |   |   |
  +---+---+---+---+

Actually visible image (on both the LCD and the VGA output):

  +---+---+---+---+
  |   |   |   |   |
  | 1 | 2 | 2 | 2 |
  |   |   |   |   |
  |   |   |   |   |
  +---+---+---+---+

This effect cannot be reversed by further uses of the Fn+F5 hot key to
deactivate the external VGA. (I also cannot get out of it via xrandr.)

I suspect that the Fn+F5 hot key activates a BIOS system-management
interrupt routine that reprograms the graphics controller completely,
and that this reprogramming is incompatioble with the way the X.Org
server drives this chip.

Detailed X server startup log:

  http://www.cl.cam.ac.uk/~mgk25/Xorg.log-Toshiba-R100.txt

Any ideas or suggestions?

Markus

-- 
Markus Kuhn, Computer Laboratory, University of Cambridge
http://www.cl.cam.ac.uk/~mgk25/ || CB3 0FD, Great Britain