MGA: implementing support for G550 dual-dvi

[Tilman Sauerbeck]

Hi,
I'm trying to implement support for G550's dual dvi feature in the MGA
driver. It seems I got it figured out mostly:
The G450 DH code that is in the driver now (mga_dh.c) works for dual-dvi
in general. Differences are that the 2nd TMDS uses the video PLL
(VID_PLL) for timing. Our driver miscalculates the PLL parameters for
that one, but once you fix them up and power on the 2nd TMDS, you get a
picture on the 2nd head.

The issue that remains is that when I enable CRTC2, the image on the
second head is always misaligned.
Say the expected picture is this:

-----
|123|
|456|
|789|
-----

It's off by zero pixels horizontally and zero pixels vertically.

Now when I enable CRTC2, I get a random offset both horizontally and
vertically. So I might get this eg:

-----      -----
|456|      |321|
|789| or   |654|   or ...
|123|      |987|
-----      -----

The framebuffer is set up correctly, there's no distortions or any
other weirdness in the displayed image except this one.

This is also reproducable with Matrox' official drivers. When I try to
disable and re-enable CRTC2 with my code, I get the same misalignments.
Which means it's not some register that just isn't initialized at all.

Does that look familiar to anyone? Any ideas what this could be related
to?

Regards,
Tilman

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