How to tell a radeon chip it is connected to a TV

[Göran Uddeborg]

We're using a F15 MythTV system as a DVB receiver.  It displays via
SCART on an old CRT PAL TV.  So there is no signalling from the TV to
the computer specifying the properties of the display.

We have created an xorg.conf file with a Monitor section with the
appropriate Modeline configuration.  This works fine.  Once X comes up
everything is ok.

But during the boot before X starts, the TV can not display the
signal.  I guess it isn't possible to do anything about that during
the initial BIOS boot.

But isn't it possible to do it when the radeon driver takes control?
It seems it ought to be possible, but we haven't succeeded so far.
We've tried to use various boot options, but can not see any obvious
effect.

Is there a way to do this?

Graphics: Radeon HD 3200
Current kernel option (not working): video=radeon:720x576-32 at 25i
Modeline in xorg.conf (works fine, from http://www.mythtv.org/wiki/RGB_Scart):
    ModeLine     "720x576" 15.125 720 778 834 968 576 579 607 625 -hsync -vsync interlace