VBLANK
vblank_reg = VBLANK(pipe);
I915_WRITE(VBLANK(pipe), (480 - 1) | ((525 - 1) << 16));
error->transcoder[i].vblank = I915_READ(VBLANK(cpu_transcoder));
I915_READ(VBLANK(cpu_transcoder)));
I915_WRITE(VBLANK(cpu_transcoder),
tmp = I915_READ(VBLANK(cpu_transcoder));