Inconsistencies with git log

In project root:
 git log arch/powerpc/platforms/52xx
works as expected

 cd arch/powerpc/platforms/52xx
 git log arch/powerpc/platforms/52xx
fatal: ambiguous argument 'arch/powerpc/platforms/52xx': unknown
revision or path not in the working tree.
Use '--' to separate paths from revisions

still in arch/powerpc/platforms/52xx
git log
get log for the whole project

Shouldn't git log give the the log for the tree under the current directory?

jonsmirl@terra:~/mpc5200b/arch/powerpc/platforms/52xx$ git --version
git version 1.5.3.4.1458.g3e72e

-- 
Jon Smirl
jonsmirl@gmail.com