Registering port

 /* Registering port */
  port = check_region(0x378, 1);    //0x378 是 Parallel port 的位置
 if (port) {
 printk("parlelport: cannot reserve 0x378\n");
 result = port;
 goto fail;
 }
 request_region(0x378, 1, "parlelport");

那 COM ports 在 PC-compatible are typically 定義是:
COM1: I/O port 0x3F8, IRQ 4
COM2: I/O port 0x2F8, IRQ 3
COM3: I/O port 0x3E8, IRQ 4
COM4: I/O port 0x2E8, IRQ 3