G550 Dual-head questions

[Daniil V. Kolpakov]

Hello developers,

I've bought a Matrox G550 recently, and a second monitor, too. Now I'm having 
some dualhead.

But, uh, dualhead is not fun without DRI, and xv is working on the first head 
only. I've googled alot and I've read pretty anything related to the dualhead 
on Matrox. :) I know I could download a binary driver from Matrox to enable 
MergedFB mode, but that's too scary.

Basically, I've one question, which I would like to adress to the current mga 
driver maintainer and other driver developers:

  What's the problem in implementing MergedFB mode without MGA_HAL?

Currently I have the following setup:
 - Matrox G550 (plain dualhead, not the Dual-DVI one)
 - one CRT monitor (MAG 570FD, 1024x768 FD Trinitron)
 - one analog LCD monitor (Samsung SyncMaster 152x, 1024x768)

My thoughts:

 1) G550 has videomodes like 2048x768;
 2) It's possible to setup the 1024x768 mode with virtual size
    of 2048x768 in the clone mode; DRI&xv works
 3) mga driver can do dual-head, so I guess it could program both heads
    to use the same framebuffer, with different viewports?

I'm not C programmed and I've never tried to hack XFree86 or XOrg before I've 
got this G550, but I'm so curious now that I've downloaded sources (I had to 
use Mandrake SRPMS since the XOrg release doesn't compile with GCC4) and 
started to make stuppid changes here and there; after messing with 
pMga->Restore I've eventially got something like a 1024x384 (actually 
1024x768 interlaced with garbage ;)) on the first monitor, showing the upper 
top of the 2048x768 framebuffer, and a 1024x768 on the second screen showing 
the mouse-controllable viewport, just like in the plain clone/singlehead 
mode. Later I've realised that it was not garbage on the first head 
- it was the wrong virtual size, and the every second line actually was the 
first line prolonged.

So far, I understand very little in the sources, but I would like to hear 
something from the mga driver developers, and maybe from the radeon driver 
developers as well, since radeon driver has MergedFB working.

Thanks for reading,

--Daniil

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