remote branches

hi.

I have troubles (probably due to my misunderstanding) with git remote tracking branches. It seems to me that reality and documentation are different:

- i clone the linux git repo:

$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git linux-2.6.git

- then i add a remote tracking branch:

$ git remote add --tags drm-intel git://git.kernel.org/pub/scm/linux/kernel/git/ickle/drm-intel.git

- Then i do git fetch or git fetch drm-intel, but nothing happens, and 
git branch -r still only show me origin/HEAD and origin/master, no 
drm-intel branches, though these branches do exist since i can see them 
with git remote -v show drm-intel

what am i doing wrong here, any idea? cheers,