Comment 18 for bug 1010794

So one of the sources seem to be nouveau_exa_prepare_access performing operations directly on the bo, which works but screws up due to tiling. The fix would be to do similar to nouveau_exa_download_from_screen and nouveau_exa_upload_to_screen with a scratch bo to fix up tiling. In this case it would be possible without the extra memcpy since the scratch bo could be operated on directly.