drivers/usb/serial/ipaq.h

   1 /*
   2  * USB Compaq iPAQ driver
   3  *
   4  *      Copyright (C) 2001 - 2002
   5  *          Ganesh Varadarajan <ganesh@veritas.com>
   6  *
   7  *      This program is free software; you can redistribute it and/or modify
   8  *      it under the terms of the GNU General Public License as published by
   9  *      the Free Software Foundation; either version 2 of the License, or
  10  *      (at your option) any later version.
  11  *
  12  */
  13
  14 #ifndef __LINUX_USB_SERIAL_IPAQ_H
  15 #define __LINUX_USB_SERIAL_IPAQ_H
  16
  17 /*
  18  * Since we can't queue our bulk write urbs (don't know why - it just
  19  * doesn't work), we can send down only one write urb at a time. The simplistic
  20  * approach taken by the generic usbserial driver will work, but it's not good
  21  * for performance. Therefore, we buffer upto URBDATA_QUEUE_MAX bytes of write
  22  * requests coming from the line discipline. This is done by chaining them
  23  * in lists of struct ipaq_packet, each packet holding a maximum of
  24  * PACKET_SIZE bytes.
  25  *
  26  * ipaq_write() can be called from bottom half context; hence we can't
  27  * allocate memory for packets there. So we initialize a pool of packets at
  28  * the first open and maintain a freelist.
  29  *
  30  * The value of PACKET_SIZE was empirically determined by
  31  * checking the maximum write sizes sent down by the ppp ldisc.
  32  * URBDATA_QUEUE_MAX is set to 64K, which is the maximum TCP window size.
  33  */
  34
  35 struct ipaq_packet {
  36         char                    *data;
  37         size_t                  len;
  38         size_t                  written;
  39         struct list_head        list;
  40 };
  41
  42 struct ipaq_private {
  43         int                     active;
  44         int                     queue_len;
  45         int                     free_len;
  46         struct list_head        queue;
  47         struct list_head        freelist;
  48 };
  49
  50 #define URBDATA_SIZE            4096
  51 #define URBDATA_QUEUE_MAX       (64 * 1024)
  52 #define PACKET_SIZE             256
  53
  54 #endif