P50_MBOX_REG_CMD
val = p50_read_mbox_reg(p50, P50_MBOX_REG_CMD);
ret = p50_write_mbox_reg(p50, P50_MBOX_REG_CMD, cmd);
ret = p50_write_mbox_reg(p50, P50_MBOX_REG_CMD, P50_MBOX_CMD_CLEAR);