intel_ring_offset_valid
GEM_BUG_ON(!intel_ring_offset_valid(ring, head));
GEM_BUG_ON(!intel_ring_offset_valid(ring, ring->tail));
GEM_BUG_ON(!intel_ring_offset_valid(ring, tail));
GEM_BUG_ON(!intel_ring_offset_valid(ring, ring->head));
GEM_BUG_ON(!intel_ring_offset_valid(ring, ring->tail));