I can confirm that the driver fails with no error here as well, on an
e5500-based ppc64 system. Everything works (with acceleration) when depth is
set to 16 bits. I know a handful of other people who have had the same problem
on 32-bit ppc hardware (modern, non-macppc), so we can be reasonably confident
that this is a broad ppc-specific issue (possibly be/byte-swapping related?)