I developped a simple test code that prints CPU and GPU devices supported on the host platform.
I used same hardware and I compiled/tested the same code on two different OS : Windows 7 64bit and Ubuntu 12.04 LTS with same version APP SDK 2.7
The CPU is recognized the same way on both, but GPU is not OpenCL capable on Ubuntu side ... however I installed the fglrx driver correctly (version 12.6) which shall be supported by APP SDK 2.7
I guess something shall be still wrong with my fglrx installation somewhere .... ???
As it's working on Windows 7, I guess my GPU HW is OpenCL capable (Mobility RADEON HD 4570)
(I attached the sample C code I use....)
Are you connecting remotely to your linux machine?
Is X-server running?
Try logging into X-server console directly and run "clinfo" from an xterm and see if GPU is visible.
After installing 12.8 sdk version and directly using the laptop instead of sshx connection i can now get the GPU device for openCL !!
There are forum thread that have discussed this issue extensively.
(not sure why fonts bloated up.. :-( )
Th basic thing that you need to do is a "xhost +" - to provde remote access control to x-server.
Once you do this, you can get GPU device listed even when you connect remotely.
Usually, we add "xhost +" to the X startup script.
For GDM based desktops, one needs to edit the GDM specific script.
For LightDM, you need to look at LigthDM specifi script.
Here is an excert from the thread above:
$ cat /etc/lightdm/lightdm.conf
$ cat /etc/lightdm/xhost.sh
chmod uog+rw /dev/ati/card*
Make sure that xhost.sh is executable:
sudo chmod a+x /etc/lightdm/xhost.sh