ns2501 DVO - success at last

[Thomas Richter <thor@math.tu-berlin.de>]

Hi Daniel, hi Ville,

some success at last. I couldn't stop myself playing with the NatSemi 
2501 DVO in my Fujitsu S6010 and I believe I finally got a hang on this 
chip. I believe I understand now most of the undocumented registers.

There are also a couple of additional features that are, apparently, not 
used by the video BIOS of the S6010, namely the chip has a ditherer on 
board - quite like the Intel Video Controller hub in the IBM R31.
Unfortunately, to enable the scaler, the bypass must be turned off, and 
hence, parameters for a 1:1 through-mapping of the scaler are required.

After quite some experimenting, I believe I found now the right settings 
to enable the scaler and configure it to pass the 1024x768 input to the 
output.

The chip is really a bit weird. It not only requires the scaling 
factors, but also the input timings, (sync width, front/back porch for 
both horizontal and vertical) and the output timing, and the 
configuration of its PLL to sample the incoming data. Currently, most of 
the data I obtained by "trail and error", at least for the 1024x768 mode 
in which the bios configures the DVO in bypass mode.

It turned out we forgot to configure a couple of registers (and some 
others are pretty much blank).

Thus, my question at this time is whether there is any interface how to 
get the precise timing of the loaded video mode from the i915 module 
directly instead of second-guessing the parameters, i.e. dimensions of 
the frame, porch sizes, size of the sync pulses, pixel clock and so on.

Other than that, I'll try to clean up the code I have to so far in the 
next days and release it.

Greetings,
	Thomas

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