siliconmotion CSync output ?

Hi,

A little background: I have a single board PC with a SMI712 (lynxEM+) 
graphic chipset. X works like a charm.

I now need to hook up an LCD panel that has an RGB interface, but only 
takes composite sync (CSync) input (not H and V sync).

The SMI chipset can generate composite sync, I see in the SMI spec that 
setting the register CCR65, bit 0 to 0, outputs Hsync for the CRT. Setting 
to 1 outputs composite sync on the same pin.

So what I want to know, is how can I make sure this is supported ?

I see in the Xconfig.conf man page that I can specify 'composite' on the 
modeline to generate composite sync on hardware that supports it. Where is 
that handled ? How can I make sure this setting is passed down to the 
siliconmotion driver and it sets the register appropriately ? I looked 
through the sources of siliconmotion_drv but I can not find anything about 
setting that register.

Reason for investigating this is that obviously the lcd panel is not 
working so I want to make sure the graphic chip actually outputs the right 
stuff...


thank you for all advice !

Bruno