ATI fglrx driver and large displays

[cmcgrath5035]

I have seen several posts about unreadable desktops when ATI fglrx drivers connect to large screen displays, such as HDTVs.
I have found that the following solution works for me; it may not be the "best" way, please comment if you have a better work around.

When the fglrx driver is installed and an initial configuration established with

aticonfig --initial

several entries are made in /etc/X11/xorg.conf, including this:

Section "Monitor"
        Identifier   "aticonfig-Monitor[0]-0"

        Option      "VendorName" "ATI Proprietary Driver"
        Option      "ModelName" "Generic Autodetecting Monitor"
        Option      "DPMS" "true"
EndSection

It seems by default that the connected monitor characteristics are re-read each time X starts up and a configuration is dynamically set up. With very large displays (e.g. my 1600 mm x 900mm DLP), this yields a calculated DPI around 20,20 or so and the fonts are unreadible on the display. When running cloned mode with a "normal" monitor, this usually affects both displays; it becomes impossible to read anything that is font based.

My solution is to modify xorg.conf to read

Section "Monitor"
        Identifier   "aticonfig-Monitor[0]-0"
#added to force reasonable sized fonts 
        DisplaySize  400        225
#
        Option      "VendorName" "ATI Proprietary Driver"
        Option      "ModelName" "Generic Autodetecting Monitor"
        Option      "DPMS" "true"
EndSection

This overrides what EDID reports to X on startup.
You can see the result in /var/log/Xorg.0.log

.....
......
(WW) fglrx(0): Probed monitor is 1600x900 mm, using Displaysize 400x225 mm
(**) fglrx(0): DPI set to (121, 121)
(--) fglrx(0): Virtual size is 1920x1080 (pitch 1920)
.....
.....

There may be unexpected side effects, but I have not hit them as yet.

If the is a more correct way to do this, please comment.

[deano_ferrari]

Thats a reasonable (and common) technique. If the monitor comes with a setup CD, this can be used to adjust the monitor configuration via the sax2 utility.