EeePC don't have 640x400x256 mode in vga bios :~

svgalib's vgatest

EeePC:
Using VESA driver, 7872KB. VBE3
svgalib 1.4.3
svgalib: Failed to initialize mouse.
Choose one of the following video modes: 
    1: 320x200, 16 colors (4 bitplanes)
    2: 640x200, 16 colors (4 bitplanes)
    3: 640x350, 16 colors (4 bitplanes)
    4: 640x480, 16 colors (4 bitplanes)
    5: 320x200, 256 colors (packed-pixel)
    6: 320x240, 256 colors (Mode X)
    7: 320x400, 256 colors (Mode X)
    8: 360x480, 256 colors (Mode X)
    9: 640x480, 2 colors (1 bitplane, monochrome)
   10: 640x480, 256 colors (packed-pixel, banked)
   18: 640x480, 64K colors (5-6-5 RGB, blue at LSB, banked)
   32: 720x348, 2 colors (1 bitplane, monochrome)
   34: 640x480, 16M colors (8-8-8 XRGB, 32-bit pixels, 
                blue byte first, banked)
Enter mode number (1-34): 34

Width: 640  Height: 480  Colors: 16777216
DisplayStartRange: 7affffh  Maxpixels: 2015232  Blit: NO

===
EeePC VGA Driver:

Using VGA driver.
svgalib 1.4.3
svgalib: Failed to initialize mouse.
Choose one of the following video modes: 
    1: 320x200, 16 colors (4 bitplanes)
    2: 640x200, 16 colors (4 bitplanes)
    3: 640x350, 16 colors (4 bitplanes)
    4: 640x480, 16 colors (4 bitplanes)
    5: 320x200, 256 colors (packed-pixel)
    6: 320x240, 256 colors (Mode X)
    7: 320x400, 256 colors (Mode X)
    8: 360x480, 256 colors (Mode X)
    9: 640x480, 2 colors (1 bitplane, monochrome)
   32: 720x348, 2 colors (1 bitplane, monochrome)
Enter mode number (1-32):  32
Width: 720  Height: 348  Colors: 2
DisplayStartRange: 3ffffh  Maxpixels: 262144  Blit: NO

===
PC

Using VESA driver, 65536KB. VBE3
svgalib 1.4.3
svgalib: Failed to initialize mouse.
Choose one of the following video modes: 
    1: 320x200, 16 colors (4 bitplanes)
    2: 640x200, 16 colors (4 bitplanes)
    3: 640x350, 16 colors (4 bitplanes)
    4: 640x480, 16 colors (4 bitplanes)
    5: 320x200, 256 colors (packed-pixel)
    6: 320x240, 256 colors (Mode X)
    7: 320x400, 256 colors (Mode X)
    8: 360x480, 256 colors (Mode X)
    9: 640x480, 2 colors (1 bitplane, monochrome)
   10: 640x480, 256 colors (packed-pixel, banked)
   11: 800x600, 256 colors (packed-pixel, banked)
   12: 1024x768, 256 colors (packed-pixel, banked)
   15: 320x200, 64K colors (5-6-5 RGB, blue at LSB, banked)
   18: 640x480, 64K colors (5-6-5 RGB, blue at LSB, banked)
   21: 800x600, 64K colors (5-6-5 RGB, blue at LSB, banked)
   24: 1024x768, 64K colors (5-6-5 RGB, blue at LSB, banked)
   29: 800x600, 16 colors (4 bitplanes)
   30: 1024x768, 16 colors (4 bitplanes)
   32: 720x348, 2 colors (1 bitplane, monochrome)
   33: 320x200, 16M colors (8-8-8 XRGB, 32-bit pixels, 
                blue byte first, banked)
   34: 640x480, 16M colors (8-8-8 XRGB, 32-bit pixels, 
                blue byte first, banked)
   35: 800x600, 16M colors (8-8-8 XRGB, 32-bit pixels, 
                blue byte first, banked)
   36: 1024x768, 16M colors (8-8-8 XRGB, 32-bit pixels, 
                blue byte first, banked)
   52: 320x240, 64K colors (5-6-5 RGB, blue at LSB, banked)
   54: 320x240, 16M colors (8-8-8 XRGB, 32-bit pixels, 
                blue byte first, banked)
   77: 320x400, 64K colors (5-6-5 RGB, blue at LSB, banked)
   79: 320x400, 16M colors (8-8-8 XRGB, 32-bit pixels, 
                blue byte first, banked)
   80: 640x400, 256 colors (packed-pixel, banked)
   82: 640x400, 64K colors (5-6-5 RGB, blue at LSB, banked)
   84: 640x400, 16M colors (8-8-8 XRGB, 32-bit pixels, 
                blue byte first, banked)
Enter mode number (1-84): 34
Width: 640  Height: 480  Colors: 16777216
DisplayStartRange: 3ffffffh  Maxpixels: 16777216  Blit: NO
===

eeepc-1:/var/log/Xorg.0.log
(II) intel(0): Not using default mode 
"2048x1536" (width too large for virtual size)
(II) intel(0): Printing probed modes for output LVDS
(II) intel(0): Modeline "800x480"x57.6   
   30.72  800 840 968 1056  480 481 484 505 (29.1 kHz)
(II) intel(0): Modeline "640x480"x85.0
   36.00  640 696 752 832  480 481 484 509 -hsync -vsync (43.3 kHz)
(II) intel(0): Modeline "640x480"x72.8
   31.50  640 664 704 832  480 489 492 520 -hsync -vsync (37.9 kHz)
(II) intel(0): Modeline "640x480"x75.0
   31.50  640 656 720 840  480 481 484 500 -hsync -vsync (37.5 kHz)
(II) intel(0): Modeline "640x480"x59.9
   25.18  640 656 752 800  480 490 492 525 -hsync -vsync (31.5 kHz)
(II) intel(0): Modeline "720x400"x85.0
   35.50  720 756 828 936  400 401 404 446 -hsync +vsync (37.9 kHz)
(II) intel(0): Modeline "640x400"x85.1
   31.50  640 672 736 832  400 401 404 445 -hsync +vsync (37.9 kHz)
(II) intel(0): Modeline "640x350"x85.1
   31.50  640 672 736 832  350 382 385 445 +hsync -vsync (37.9 kHz)
(II) intel(0): Output TV disconnected
(II) intel(0): EDID for output TV
(II) intel(0): Output VGA disconnected
(II) intel(0): Output LVDS connected
(II) intel(0): Output TV disconnected
(II) intel(0): Output LVDS using initial mode 800x480
(II) intel(0): Monitoring connected displays enabled
(II) intel(0): detected 256 kB GTT.
(II) intel(0): detected 7932 kB stolen memory.
(==) intel(0): video overlay key set to 0x101fe

===
(II) intel(0): Output VGA using monitor section Monitor1
(II) intel(0): I2C bus "CRTDDC_A" initialized.
(II) intel(0): Output LVDS has no monitor section
(II) intel(0): I2C bus "LVDSDDC_C" initialized.
(II) intel(0): I2C device "LVDSDDC_C:ddc2" registered at address 0xA0.
(II) intel(0): I2C device "LVDSDDC_C:ddc2" removed.
(II) intel(0): EDID for output LVDS

==
xrandr -q
LVDS connected (normal left inverted right)
        BACKLIGHT: 250 (0x00000000) range:  (0,250)
   800x480        60.0 +
   640x480        85.0     72.8     75.0     59.9
   720x400        85.0
   640x400        85.1
   640x350        85.1