problem with i830M interlaced VGA output (915G works fine)

[Thomas Hilber]

On Mon, Oct 06, 2008 at 01:09:55PM -0700, Keith Packard wrote:
> Yup, I read through the hardware docs for i845 and compared them with
> i945 -- all of the places where the i945 says 'for interlaced modes, do
> <foo>' just don't exist in the i845 docs.

thank you very much for reading through the hardware docs! This saved
me a lot of further experimenting.

> Btw, let us know when you're happy with the interlaced mode support and
> we'll stick it into the upstream driver sources. Not that we like to
> encourage people to use interlaced modes, but there are times when it's
> the only option.

I would really appreciate upstream interlaced mode support on VGA/DVI
for several reasons:

- the patch above (originating from Krzysztof Halasa) works fine for 
  at least i810e, 915G, 945G, 965GM chipsets
- adding interlaced mode support won't break existing applications
- for boards like Intel D945GCLF this is the only way to connect a SCART
  TV-device without the need for additional hardware
- signal quality on VGA/RGB is superior to S-VIDEO
- support for variable frame rates allowing to deinterlace by display hardware:

As mentioned here:

http://lists.freedesktop.org/archives/xorg/2008-September/038296.html

I wrote a patch for older ATI-radeon type cards, which synchronizes
VGA/DVI output timing with external signals. This is an essential feature 
for jerkyless playback of live TV. I'm currently porting this to intel
9xx-class hardware hoping it will work there as flawless as on radeons. 

Cheers
  Thomas