[Bug 81476] three monitors on two radeon cards works with some layouts not others

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=81476

Alex Deucher <agd5f at yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |NOTOURBUG

--- Comment #3 from Alex Deucher <agd5f at yahoo.com> ---
(In reply to comment #2)
> (In reply to comment #1)
> > Your desktop is too large for the 3D engine.  The max surface size
> > supported by the r5xx 3D engine is 4096x4096.  1600*3 = 4800 pixels.
> > That's why it only works above and below.
> 
> I don't think that is the problem:
> 
> 1. I'm not asking any one FireMV card to do more than two 1600x1200
> monitors; that's only 3200x1200 pixels per card, well within 4096x4096.
> 

They way the core provider stuff in the xserver works the rendering is done on
one GPU and the respective updated regions are sent to the other displays.  If
you want to use a dedicated GPU per displays, you'll have to use zaphod mode
and set up a static configuration in your xorg.conf.  If you want 3D, you'll
have to use the displays independently.  If you enable xinerama, you won't get
3D.  There have been several proposals to extend the xserver to support
splitting rendering across GPUs, but it it a huge amount of work and so far no
one has finished.  See: http://bz.bzflag.bz/~Ch3ck/ for the latest proposal or
google for "xorg shatter" for more information.

> 2. Three adjacent monitors works fine (no video garbage) if I flip 180 the
> two affected screens.  (But then of course I can't use those screens unless
> I physically turn those two monitors upside-down!)  Here's the relevant
> xrandr output for this working configuration, with the first two screens
> inverted:
> 
> Screen 0: minimum 320 x 200, current 4800 x 1200, maximum 8192 x 8192
> DVI-0 connected primary 1600x1200+0+0 inverted (normal left inverted right x
> axis y axis) 367mm x 275mm
> DVI-1 connected 1600x1200+1600+0 inverted (normal left inverted right x axis
> y axis) 367mm x 275mm
> DVI-1-2 connected 1600x1200+3200+0 367mm x 275mm
> DVI-1-3 disconnected
> 
> 3. The failure is always on the card with the two monitors, even if I
> configure the third monitor to the left of those two.  If I was going
> out-of-bounds, surely moving the screen from one side to the other side
> would affect where the error appeared?

It depends which card is the one doing the rendering and which is the one that
is diplaying only.

> 
> 4. Is the software really so badly written that it can't tell me that I'm
> going out-of-bounds?  I get no error from xrandr for the three-adjacent
> layout.

The OpenGL compositing manager you are running should check for the max limits
of the GL driver before using it for surfaces which may exceed that.  If you
disable the OpenGL compositor, your desktop should work fine.

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