CentOS, radeon driver, dual monitor, fun (NOT)

[m.roth at 5-cent.us]

I've just joined the list in desperation, after days of fighting this.

The ati & radeon drivers in CentOS (== RHEL) 6.4 are what I need to use,
since neither kmod-fglrx nor the proprietary drivers from AMD/ATI have now
dropped all support for "older" cards. My user has an Advanced Micro
Devices [AMD] nee ATI RV620 [FirePro 2260] card, which is among those no
longer supported (and it was in a machine we got in Nov!).

Here's the problem: he's got two monitors. Like the rest of us, and as he
was doing, he wants them side-by-side, like one large screen. I've tried
Xorg --configure, which failed, and I've handcrafted some. The two best
I've gotten give us a choice:
   a) I can enable xinerama, which I gather is xor with randr. In that
case, we
         get what we want... EXCEPT that you can drag things offmonitor.
and if
         go a tad too far, what you wind up where you can move it up and
down,
         off monitor, but the whole thing moves right, and won't come
back. The
         result is an "L" of black; in ascii art,
                  ________   _________
                  |B|     |  |B|      |
                  |B|     |  |B|      |
                  |B|     |  |B|      |
                  |B|     |  |B|      |
                  |BBBBBBB|  |BBBBBBBB|
                  ---------   ---------
   b) I can disable xinerama, in which case we can drag the mouse from
       monitor to monitor, but once logged in, you cannot drag a *window*
       from one to the other, and they seem to almost be like two sessions,
       with slightly different menus (he's using gnome; I installed the
       gconf-editor, and disabled the xrandr plugin for gnome, so what I
       get is all my xorg.conf file.

The latter xorg.conf is as follows:
Section "ServerFlags"
    Option        "AllowMouseOpenFail" "true"
EndSection
<snip> of files, and input device>
Section "Module"
        Load  "glx"
EndSection

Section       "Device"
  Identifier  "mycard0"
  Driver      "radeon"
  BusID       "PCI:2:0:0"
  Screen      0
EndSection

Section       "Device"
  Identifier  "mycard1"
  Driver      "radeon"
  BusID       "PCI:2:0:0"
  Screen      1
EndSection

Section       "Monitor"
  Identifier  "mymon0"
  Option      "Monitor-DisplayPort-0"
  Option      "Rotate" "left"
#   Option      "Position" "0 0"
EndSection
Section       "Monitor"
  Identifier  "mymon1"
  Option      "Monitor-DisplayPort-1"
  Option      "Rotate" "left"
EndSection

Section       "Screen"
  Identifier  "myhead0"
  Device      "mycard0"
  Monitor     "mymon0"
  DefaultDepth  24
  SubSection  "Display"
    Depth     24
    Modes     "1280x1024"
  EndSubSection
EndSection

Section       "Screen"
  Identifier  "myhead1"
  Device      "mycard1"
  Monitor     "mymon1"
  DefaultDepth  24
  SubSection "Display"
    Depth     24
    Modes     "1280x1024"
  EndSubSection
EndSection

Section "ServerLayout"
  Identifier  "layout0"
  InputDevice "keyboard0" "CoreKeyboard"
  InputDevice "mouse0" "CorePointer"
  Screen      0 "myhead0" RightOf "myhead1"
  Screen      1 "myhead1"
  Option      "Xinerama" "0"
EndSection

Any clues for the poor gladly accepted.

         mark