Why does Xorg choose this resolution?

[Chris G]

I have been trying to understand why Xorg chooses an odd resolution
(1152x864) on my system rather than the monitor's native 1600x1200.

Well I can see *where* it does it, here is the relevant section of my
Xorg.0.log file:-

    (II) intel(0): Printing DDC gathered Modelines:
    (II) intel(0): Modeline "1600x1200"x0.0  162.00  1600 1664 1856 2160 1200 1201 1204 1250 +hsync +vsync (75.0 kHz)
    (II) intel(0): Modeline "800x600"x0.0   40.00  800 840 968 1056  600 601 605 628 +hsync +vsync (37.9 kHz)
    (II) intel(0): Modeline "640x480"x0.0   31.50  640 656 720 840  480 481 484 500 -hsync -vsync (37.5 kHz)
    (II) intel(0): Modeline "640x480"x0.0   25.20  640 656 752 800  480 490 492 525 -hsync -vsync (31.5 kHz)
    (II) intel(0): Modeline "720x400"x0.0   28.32  720 738 846 900  400 412 414 449 -hsync +vsync (31.5 kHz)
    (II) intel(0): Modeline "1280x1024"x0.0  135.00  1280 1296 1440 1688 1024 1025 1028 1066 +hsync +vsync (80.0 kHz)
    (II) intel(0): Modeline "1024x768"x0.0   78.80  1024 1040 1136 1312 768 769 772 800 +hsync +vsync (60.1 kHz)
    (II) intel(0): Modeline "1024x768"x0.0   65.00  1024 1048 1184 1344 768 771 777 806 -hsync -vsync (48.4 kHz)
    (II) intel(0): Modeline "800x600"x0.0   49.50  800 816 896 1056  600 601 604 625 +hsync +vsync (46.9 kHz)
    (II) intel(0): Modeline "1280x1024"x60.0  108.88  1280 1360 1496 1712 1024 1025 1028 1060 -hsync +vsync (63.6 kHz)
    (II) intel(0): Modeline "1600x1200"x60.0  160.96  1600 1704 1880 2160 1200 1201 1204 1242 -hsync +vsync (74.5 kHz)
    (II) intel(0): Modeline "1152x864"x75.0  104.99  1152 1224 1352 1552 864 865 868 902 -hsync +vsync (67.7 kHz)
    (II) intel(0): EDID vendor "DEL", prod id 40967
    (II) intel(0): I2C device "HDMIDDC_C:ddc2" registered at address 0xA0.
    (II) intel(0): I2C device "HDMIDDC_C:ddc2" removed.
    (II) intel(0): Output VGA connected
    (II) intel(0): Output HDMI-1 disconnected
    (II) intel(0): Output HDMI-2 connected
    (II) intel(0): Using fuzzy aspect match for initial modes
    (II) intel(0): Output VGA using initial mode 1152x864
    (II) intel(0): Output HDMI-2 using initial mode 1152x864
    (II) intel(0): detected 512 kB GTT.
    (II) intel(0): detected 131072 kB stolen memory.

It simply seems to use the last resolution reported by ddcprobe, not
the best (or native) resolution.  It seems to me that this is simply
*wrong* as 1152x864 looks horrible on my monitor because of the
scaling it has to do.

I can manually set the resolution to 1600x1200 but this isn't really a
satisfactory solution because if I change window manager it reverts to
1152x864 and the gdm login screen is still at 1152x864.

How do I tell the system to default to 1600x1200?

-- 
Chris Green