In 2007 Alex Deucher added preliminary TV-Out-support based on the gatos-code to the randr12-branch of the ati-driver. The branch has now been merged to the git HEAD of xf86-video-ati.
Starting from the 6.7.191 pre-release the X.org ati driver supports TV-Out on selected cards. That means stable version 6.8.0 and newer have the support. A new enough driver is also included starting in eg. Fedora 8 and Ubuntu 7.10.
See RadeonTVbuildHowto.
You can enable TV-Out either dynamically (by issuing commands to the running X server) or statically (through the xorg.config file, before starting the X server). For testing, the dynamic method is probably easier.
Newer R600 / R700 series cards (Radeon HD X2000 - X4870) need this option in xorg.conf:
Option "ATOMTvOut" "TRUE"
The same Option can be applied to R5xx cards too (or at least some of that series). It has been checked to work on x1650 (RV530LE) - this line really needed to detect S-Video tv-out.TV-out may be enabled by using a recent driver and xrandr utility:
Several options need to be specified. See the radeon(4) manpage for a description. In particular, you must set "TVStandard" to match your flavour of video.
This recipe is not definitive, but it has worked.
In the "Device" section:
Driver "radeon"
Option "TVDACLoadDetect" "TRUE"
Option "TVStandard" "ntsc"
Option "monitor-S-video" "TV-monitor"
In the "Monitor" Section:
Option "PreferredMode" "800x600"
In the "Screen" section:
DefaultDepth 24
SubSection "Display"
Depth 24
Modes "800x600"
EndSubSection
There was a very old effort by the gatos-project to support TV Out on ATI Radeons. It was GPL-licensed in the past, but in 2007 all authors agreed with relicensing under MIT-license, so that it was brought to a xf86-video-ati's branch and later on merged to the main driver.
randr-1.2 branch of xf86-video-ati
Update to below patch by Wei-Tsun Sun
Patch up to xorg 7.0 by Rune Petersen
All others agreed to the relicensing
On some older cards the tv out can be enabled with atitvout, which is not developed anymore: