Using two dual-head Radeon cards with X on a single PC with 3 monitors

Alex Deucher alexdeucher at
Mon Aug 22 09:31:35 PDT 2011

On Mon, Aug 22, 2011 at 12:16 PM, Mark Cave-Ayland
<mark.cave-ayland at> wrote:
> On 22/08/11 14:09, Jan Kasprzak wrote:
>>        Shouldn't the -isolateDevice be used in order to avoid
>> the X servers disabling the other card? Also you may want to make
>> them share a common VT (although I am not sure if this is necessary
>> in dual-head setup as opposed to dual-seat). In my dual-seat desktop,
>> I use the following command lines:
>> X :0 -layout Primary -isolateDevice PCI:1:0:0 vt7
>> X :1 -layout Secondary -isolateDevice PCI:5:0:0 -sharevts vt7
>> (the -layout option is analogous to your -config, but allows you to share
>> a single xorg.conf file for both X servers).
>>        However, I had problems with my multi-seat desktop with 2.6.39
>> and newer kernels, so you can also try to downgrade the kernel. 2.6.38
>> works for me. FWIW, the Fedora bug report I have filled is here:
> Hi Yenya,
> Thanks for the reference. I'd already tried with the -isolateDevice
> parameter but it didn't seem to make any difference :(
> However, I found out that the PC I'm using has an internal built-in Intel
> graphics card, so I enabled it in the BIOS and tried using that instead. And
> with one server running the radeon driver and another running the intel
> driver it works just fine.
> It seems there is a bug when you have multiple instances of the radeon
> driver instantiated within different X servers (maybe DRI related but I
> really don't know enough at the moment?). I'd like to try and get this fixed
> if possible - what would be the best thing to do, start a thread on the
> xorg-driver-ati mailing list or create a bug report directly in
>'s bugzilla?

File a bug on and attach your xorg
log(s), config(s), and dmesg output.  Note that not many people use
multiple independent X servers on separate cards so the amount of
testing these scenarios get is pretty light.


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