Hi Clive,
Thought I should create a specific thread with your issue.
I just tested a spare GeForce 6600 I had laying around and the dual
head display behaviour is definitely not working.
Whereas with the Quadro FX4500 it works fine (xrandr and D.H.).
So it is an issue specifically affecting the GeForce 6600 (maybe
others as well).
As you described with the 6600, it seems to detect the second display
head, (i.e. it reads the EDID correctly) but there is no digital
output when connecting a second display via the DVI-I interface (digital).
I don't have a spare DVI-A to VGA adapter, but just curious if it may
work better with a VGA display on the second head?
I have been able to force a digital output on the second head by
appending the following to the kernel command line:
append="video=DVI-I-2:D"
However it then seems to think the second head is a DFP (LVDS) LCD
panel (i.e. a laptop).
Unfortunately, also using the mentioned appended kernel command, the
second head display is quite bad, (wrong colours, incorrect geometry
and graphical corruption). But the output does get enabled.
So in other words, I don't think it is an xrandr issue at all.
Perhaps the issue is is either the nouveau driver doesn't configure
the second head correctly for this particular GPU family (GeForce 6600
or NV43) or the Apple OEM FCODE rom used in the GeForce 6600 is has
incorrect parameters configured in the DCB?
Link below to understand what the DCB is:
ftp://download.nvidia.com/open-gpu-doc/DCB/1/DCB-4.0-Specification.html
I know that others may say "but it works fine in OSX"...
However Apple has written their own drivers so they may have their own
workaround implemented directly in their own driver.
This is a bit of a shame as this particular GPU is the most common one
supplied with the Powermac G5 11.2 (DC) machines...
If the issue is the DCB in the FCODE rom, there may be a magical
appended kernel command to workaround the problem.
Otherwise, perhaps we can try to patch a GeForce 6600 GPU VGA BIOS and
load it from a file so nouveau uses this patched VGA BIOS instead of
extracting it from the original FCODE rom from the OF device tree.
Of course, this is on the assumption that the D.H. issue is indeed
because of the incorrect DCB parameters in the GeForce 6600 Apple OEM
FCODE rom and not nouveau specifically with NV43.
Any takers?