Memory layout transition:

the 2D driver initializes MC_FB_LOCATION and related registers sanely
the DRM deduces the layout from these registers
clients use the new SETPARAM ioctl to tell the DRM where they think the
    framebuffer is located in the card's address space
the DRM uses all this information to check client state and fix it up if
    necessary
This is a prerequisite for things like direct rendering with IGP chips and
    video capturing.