XRandR failing to expose two monitors on single RV280 as separate heads (was: dual-DPU XRandR almost working, DVI-0 stays blank)

[martin f krafft]

also sprach Alex Deucher <alexdeucher at gmail.com> [2010.02.23.0920 +0100]:
> > This is curious, because when I connect my laptop (Intel GPU) to
> > an external display, and I place LVDS --right-of VGA-1, then the
> > window manager sees two heads, not one spread across both
> > displays.
> 
> You are mistaken.  When you use xrandr to create a dualhead
> layout, it's still only one X screen.  The size of the desktop
> just changes.

How then is the window manager (awesome) able to treat the two heads
separately? It really does.

> > It seems to me that I need to tell the radeon driver that it should
> > present the two displays as separate heads. Apparently, this is not
> > needed for the intel driver.
> 
> The two drivers behave the same way in a single card, multiple
> output setup.  The radeon driver will behave the same way if you
> run it on one card with all the zaphod stuff removed.

This is true, I verified that.

> If you enable the zaphod stuff, you can't use xrandr to configure
> things across screens.

Well, I know that if I use Zaphod to combine screens, I cannot use
xrandr to manipulate *across* them. However, that is not what I am
trying.

I am trying to manipulate the two displays attached to a single
Zaphod screen with xrandr, thus use xrandr *within* Zaphod. I can
use --same-as and --left-of as expected, but the result is a single,
combined head (enlarged desktop).

So it seems like I *can* use xrandr to manipulate displays *within*
a single Zaphod screen. However, there seems to be a bug or an
incompatibility that prevents xrandr from exposing the two displays
as separate heads.

Courtesy to my ASCII-art skills, this is what I currently see:
Zaphod combining two Screens, and the second screen split across two
displays with XRandR. Unfortunately, head 1 spreads across both
displays 1&2.

 ← Display 0      → ← Display 1     →  ← Display 2      →
 ← ScreenLeft     → ← ScreenMiddleRight using XRandR    →
 ←            Zaphod-style combining                    →
  ________________   ________________   ________________
 |  ____________  | |  ______________|_|______________  |
 | |            | | | |              | |              | |
 | | head 0     | | | |             head 1            | |
 | |____________| | | |______________|_|______________| |
 |________________| |________________| |________________|

And this is what I want to see: three separate heads:

 ← Display 0      → ← Display 1     →  ← Display 2      →
 ← ScreenLeft     → ← ScreenMiddleRight using XRandR    →
 ←            Zaphod-style combining                    →
  ________________   ________________   ________________
 |  ____________  | |  ____________  | |  ____________  |
 | |            | | | |            | | | |            | |
 | | head 0     | | | | head 1     | | | | head 2     | |
 | |____________| | | |____________| | | |____________| |
 |________________| |________________| |________________|

If the combination of Zaphod and XRandR doesn't work as intended
(although I am very very close, see above), then I guess I will use
pure Zaphod. Now the problem is that I cannot swap the order of
heads 1&2 (see
http://lists.freedesktop.org/archives/xorg/2010-February/049355.html).

Status quo, notice the order of heads 1&2

 ← Display 0      → ← Display 1     →  ← Display 2      →
 ← ScreenLeft     → ← ScreenMiddle  →  ← ScreenRight    →
 ←                Zaphod-style combining                →
  ________________   ________________   ________________
 |  ____________  | |  ____________  | |  ____________  |
 | |            | | | |            | | | |            | |
 | | head 0     | | | | head *2*   | | | | head *1*   | |
 | |____________| | | |____________| | | |____________| |
 |________________| |________________| |________________|

And this is what I want:

 ← Display 0      → ← Display 1     →  ← Display 2      →
 ← ScreenLeft     → ← ScreenMiddle  →  ← ScreenRight    →
 ←                Zaphod-style combining                →
  ________________   ________________   ________________
 |  ____________  | |  ____________  | |  ____________  |
 | |            | | | |            | | | |            | |
 | | head 0     | | | | head *1*   | | | | head *2*   | |
 | |____________| | | |____________| | | |____________| |
 |________________| |________________| |________________|


Is this now a bit clearer?

-- 
martin | http://madduck.net/ | http://two.sentenc.es/
 
"my father, a good man, told me:
'never lose your ignorance; you cannot replace it.'"
                                               -- erich maria remarque
 
spamtraps: madduck.bogus at madduck.net
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