I'm using the lastest radeon stack from xorg-edgers which is working well w/KMS. The problem is that I'm pushing a rear projection DLP @ 1080p and getting the usual ~5% overscan. With the catalyst blob the default modelines come up perfectly scanned to the viewable edges of the screen. So figured I'd start by feeding the modelines that fglrx reports to the radeon driver. The modelines are identical for all resolutions with the exception of the h/vsync settings:
"1920x1080" 148.50 1920 2008 2052 2200 1080 1084 1089 1125 -hsync -vsync
"1920x1080" 148.50 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync
These are as detected by EDID. So it's likely that the fglrx is doing some additional scaling to produce the correctly scanned output. The detected DPI and sceen demensions are identical on both drivers.
Using xrandr to add the fglrx modeline to the radeon driver works but switching to "1080_test" does not. The screen flashes and Xrandr reports that it has switched but the output of xvidtune -show indicates that the settings in use are from the originally detected modeline. I should note that I have not disabled EDID yet, but I've never needed to do so to use custom modelines with other drivers/cards.
Any advice on fixing overscan on the oss driver? Any idea as to what ATI may be doing to default to correct viewable area for my screen with identical modeline demensions?