drivers/tty/n_tracerouter.c

   1 /*
   2  *  n_tracerouter.c - Trace data router through tty space
   3  *
   4  *  Copyright (C) Intel 2011
   5  *
   6  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   7  *
   8  *  This program is free software; you can redistribute it and/or modify
   9  *  it under the terms of the GNU General Public License version 2
  10  *  as published by the Free Software Foundation.
  11  *
  12  *  This program is distributed in the hope that it will be useful,
  13  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  *  GNU General Public License for more details.
  16  *
  17  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  18  *
  19  * This trace router uses the Linux line discipline framework to route
  20  * trace data coming from a HW Modem to a PTI (Parallel Trace Module) port.
  21  * The solution is not specific to a HW modem and this line disciple can
  22  * be used to route any stream of data in kernel space.
  23  * This is part of a solution for the P1149.7, compact JTAG, standard.
  24  */
  25
  26 #include <linux/init.h>
  27 #include <linux/kernel.h>
  28 #include <linux/module.h>
  29 #include <linux/types.h>
  30 #include <linux/ioctl.h>
  31 #include <linux/tty.h>
  32 #include <linux/tty_ldisc.h>
  33 #include <linux/errno.h>
  34 #include <linux/string.h>
  35 #include <linux/mutex.h>
  36 #include <linux/slab.h>
  37 #include <asm-generic/bug.h>
  38 #include "n_tracesink.h"
  39
  40 /*
  41  * Other ldisc drivers use 65536 which basically means,
  42  * 'I can always accept 64k' and flow control is off.
  43  * This number is deemed appropriate for this driver.
  44  */
  45 #define RECEIVE_ROOM    65536
  46 #define DRIVERNAME      "n_tracerouter"
  47
  48 /*
  49  * struct to hold private configuration data for this ldisc.
  50  * opencalled is used to hold if this ldisc has been opened.
  51  * kref_tty holds the tty reference the ldisc sits on top of.
  52  */
  53 struct tracerouter_data {
  54         u8 opencalled;
  55         struct tty_struct *kref_tty;
  56 };
  57 static struct tracerouter_data *tr_data;
  58
  59 /* lock for when tty reference is being used */
  60 static DEFINE_MUTEX(routelock);
  61
  62 /**
  63  * n_tracerouter_open() - Called when a tty is opened by a SW entity.
  64  * @tty: terminal device to the ldisc.
  65  *
  66  * Return:
  67  *      0 for success.
  68  *
  69  * Caveats: This should only be opened one time per SW entity.
  70  */
  71 static int n_tracerouter_open(struct tty_struct *tty)
  72 {
  73         int retval = -EEXIST;
  74
  75         mutex_lock(&routelock);
  76         if (tr_data->opencalled == 0) {
  77
  78                 tr_data->kref_tty = tty_kref_get(tty);
  79                 if (tr_data->kref_tty == NULL) {
  80                         retval = -EFAULT;
  81                 } else {
  82                         tr_data->opencalled = 1;
  83                         tty->disc_data      = tr_data;
  84                         tty->receive_room   = RECEIVE_ROOM;
  85                         tty_driver_flush_buffer(tty);
  86                         retval = 0;
  87                 }
  88         }
  89         mutex_unlock(&routelock);
  90         return retval;
  91 }
  92
  93 /**
  94  * n_tracerouter_close() - close connection
  95  * @tty: terminal device to the ldisc.
  96  *
  97  * Called when a software entity wants to close a connection.
  98  */
  99 static void n_tracerouter_close(struct tty_struct *tty)
 100 {
 101         struct tracerouter_data *tptr = tty->disc_data;
 102
 103         mutex_lock(&routelock);
 104         WARN_ON(tptr->kref_tty != tr_data->kref_tty);
 105         tty_driver_flush_buffer(tty);
 106         tty_kref_put(tr_data->kref_tty);
 107         tr_data->kref_tty = NULL;
 108         tr_data->opencalled = 0;
 109         tty->disc_data = NULL;
 110         mutex_unlock(&routelock);
 111 }
 112
 113 /**
 114  * n_tracerouter_read() - read request from user space
 115  * @tty:  terminal device passed into the ldisc.
 116  * @file: pointer to open file object.
 117  * @buf:  pointer to the data buffer that gets eventually returned.
 118  * @nr:   number of bytes of the data buffer that is returned.
 119  *
 120  * function that allows read() functionality in userspace. By default if this
 121  * is not implemented it returns -EIO. This module is functioning like a
 122  * router via n_tracerouter_receivebuf(), and there is no real requirement
 123  * to implement this function. However, an error return value other than
 124  * -EIO should be used just to show that there was an intent not to have
 125  * this function implemented.  Return value based on read() man pages.
 126  *
 127  * Return:
 128  *       -EINVAL
 129  */
 130 static ssize_t n_tracerouter_read(struct tty_struct *tty, struct file *file,
 131                                   unsigned char __user *buf, size_t nr) {
 132         return -EINVAL;
 133 }
 134
 135 /**
 136  * n_tracerouter_write() - Function that allows write() in userspace.
 137  * @tty:  terminal device passed into the ldisc.
 138  * @file: pointer to open file object.
 139  * @buf:  pointer to the data buffer that gets eventually returned.
 140  * @nr:   number of bytes of the data buffer that is returned.
 141  *
 142  * By default if this is not implemented, it returns -EIO.
 143  * This should not be implemented, ever, because
 144  * 1. this driver is functioning like a router via
 145  *    n_tracerouter_receivebuf()
 146  * 2. No writes to HW will ever go through this line discpline driver.
 147  * However, an error return value other than -EIO should be used
 148  * just to show that there was an intent not to have this function
 149  * implemented.  Return value based on write() man pages.
 150  *
 151  * Return:
 152  *      -EINVAL
 153  */
 154 static ssize_t n_tracerouter_write(struct tty_struct *tty, struct file *file,
 155                                    const unsigned char *buf, size_t nr) {
 156         return -EINVAL;
 157 }
 158
 159 /**
 160  * n_tracerouter_receivebuf() - Routing function for driver.
 161  * @tty: terminal device passed into the ldisc.  It's assumed
 162  *       tty will never be NULL.
 163  * @cp:  buffer, block of characters to be eventually read by
 164  *       someone, somewhere (user read() call or some kernel function).
 165  * @fp:  flag buffer.
 166  * @count: number of characters (aka, bytes) in cp.
 167  *
 168  * This function takes the input buffer, cp, and passes it to
 169  * an external API function for processing.
 170  */
 171 static void n_tracerouter_receivebuf(struct tty_struct *tty,
 172                                         const unsigned char *cp,
 173                                         char *fp, int count)
 174 {
 175         mutex_lock(&routelock);
 176         n_tracesink_datadrain((u8 *) cp, count);
 177         mutex_unlock(&routelock);
 178 }
 179
 180 /*
 181  * Flush buffer is not impelemented as the ldisc has no internal buffering
 182  * so the tty_driver_flush_buffer() is sufficient for this driver's needs.
 183  */
 184
 185 static struct tty_ldisc_ops tty_ptirouter_ldisc = {
 186         .owner          = THIS_MODULE,
 187         .magic          = TTY_LDISC_MAGIC,
 188         .name           = DRIVERNAME,
 189         .open           = n_tracerouter_open,
 190         .close          = n_tracerouter_close,
 191         .read           = n_tracerouter_read,
 192         .write          = n_tracerouter_write,
 193         .receive_buf    = n_tracerouter_receivebuf
 194 };
 195
 196 /**
 197  * n_tracerouter_init - module initialisation
 198  *
 199  * Registers this module as a line discipline driver.
 200  *
 201  * Return:
 202  *      0 for success, any other value error.
 203  */
 204 static int __init n_tracerouter_init(void)
 205 {
 206         int retval;
 207
 208         tr_data = kzalloc(sizeof(struct tracerouter_data), GFP_KERNEL);
 209         if (tr_data == NULL)
 210                 return -ENOMEM;
 211
 212
 213         /* Note N_TRACEROUTER is defined in linux/tty.h */
 214         retval = tty_register_ldisc(N_TRACEROUTER, &tty_ptirouter_ldisc);
 215         if (retval < 0) {
 216                 pr_err("%s: Registration failed: %d\n", __func__, retval);
 217                 kfree(tr_data);
 218         }
 219         return retval;
 220 }
 221
 222 /**
 223  * n_tracerouter_exit - module unload
 224  *
 225  * Removes this module as a line discipline driver.
 226  */
 227 static void __exit n_tracerouter_exit(void)
 228 {
 229         int retval = tty_unregister_ldisc(N_TRACEROUTER);
 230
 231         if (retval < 0)
 232                 pr_err("%s: Unregistration failed: %d\n", __func__,  retval);
 233         else
 234                 kfree(tr_data);
 235 }
 236
 237 module_init(n_tracerouter_init);
 238 module_exit(n_tracerouter_exit);
 239
 240 MODULE_LICENSE("GPL");
 241 MODULE_AUTHOR("Jay Freyensee");
 242 MODULE_ALIAS_LDISC(N_TRACEROUTER);
 243 MODULE_DESCRIPTION("Trace router ldisc driver");