Thanks for the link. My system config is: 18.104.22.168-0.fc15.x86_64 and A3850
As per the link, I disconnected the monitor-cable from Llano-mother board and 'cliinfo' reports only cpu from ssh shell from different computer.
Then I tried by loading fglrx module manually, still clinfo reports CPU only.
Finally I have run X server from ssh terminal, now clinfo reports two opencl-devices.
So shoud it understood that headless operation means, we need to run X-server (without any real monitor connected)?