I have two 7950 in my Linux PC.
#:~$ aticonfig --lsa
* 0. 01:00.0 AMD Radeon HD 7900 Series
1. 07:00.0 AMD Radeon HD 7900 Series
If I switch Xinerama on, then OpenCL can only see 1 gpu. Here is what cgminer says:
#:~$ cgminer -n
[2013-06-15 15:35:36] CL Platform 0 vendor: Advanced Micro Devices, Inc.
[2013-06-15 15:35:36] CL Platform 0 name: AMD Accelerated Parallel Processing
[2013-06-15 15:35:36] CL Platform 0 version: OpenCL 1.2 AMD-APP (1113.2)
[2013-06-15 15:35:36] Platform 0 devices: 1
[2013-06-15 15:35:36] 0 Tahiti
[2013-06-15 15:35:36] 1 GPU devices max detected
Switch Xinerama Off, and it can see the two gpu's. The dev for cgminer says it's because Xinerama mode creates one virtual screen, and OpenCL for some reason looks at the "Screen" rather than "Device" configuration.
Has there been any progress on this? This seems like a pretty severe limitation. Xinerama is really the only choice for multiple monitor desktops with the Catalyst drivers since the RandR support is, well, horrific. We use two 7970 cards to drive 6 HD TVs, but this is proving to be non ideal since we now can't use both the cards for OpenCL with Xinerama enabled.
Update: This looks to be fixed in the latest 14.1 beta! Awesome, I can use both GPUs now! Thanks!