RING_ACTHD
acthd = ENGINE_READ64(engine, RING_ACTHD, RING_ACTHD_UDW);
acthd = ENGINE_READ(engine, RING_ACTHD);
{ RING_ACTHD(0), 0, 0, "ACTHD_LDW" }, \
MMIO_RING_DFH(RING_ACTHD, D_ALL, 0, mmio_read_from_hw, NULL);
reg = RING_ACTHD(engine->mmio_base);
MMIO_RING_D(RING_ACTHD);
{ RING_ACTHD(0), REG_64BIT_LOW_DW, 0, 0, 0, NULL}, \