mach64 EXA bits

[Benjamin Herrenschmidt]

Hi George !

I've seen with interest your various commits to the mach64 driver.
However, I wonder if your EXA implementation has been tested on big
endian at all. ATI chips generally have swappers at the front of the
framebuffer, and thus need tweaking when doing things like memcpy
to/from it (UFS/DFS can be called for different bit depth than the front
buffer) and need proper Prepare/FinishAccess. Also, I don't know for
sure (I don't have docs at hand) how the swappers work on mach64 but if
you don't have surfaces like radeon, you might have to fail multiple
calls to PrepareAccess for pixmaps of different depth (thus possibly
forcing a full migration to memory for some composite fallbacks).

I have access to a mach64 (LT-G) based mac (and maybe some other one
too) so I can have a look after I'm back from travels/vacation.

Cheers,
Ben.