Well it seems ATY,Rockhopper2 (not Rockhopper) in the Mac Mini is in fact a Radeon, and the way the radeonfb driver handles the pallete appears to match the cmap_radeon in offb, so perhaps this would work in offb.c
--- a/drivers/video/fbdev/offb.c +++ b/drivers/video/fbdev/offb.c @@ -333,7 +333,7 @@ par->cmap_adr = offb_map_reg(dp, 2, 0, 0x1fff); if (par->cmap_adr) par->cmap_type = cmap_M3B; - } else if (dp && !strncmp(name, "ATY,Rage6", 9)) { + } else if (dp && (!strncmp(name, "ATY,Rage6", 9)) || !strncmp(name, "ATY,Rockhopper2", 15)) { par->cmap_adr = offb_map_reg(dp, 1, 0, 0x1fff); if (par->cmap_adr) par->cmap_type = cmap_radeon; -- Len Sorensen