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 <linux/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 */ n_tracerouter_open(struct tty_struct * tty)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 */ n_tracerouter_close(struct tty_struct * tty)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 */ n_tracerouter_read(struct tty_struct * tty,struct file * file,unsigned char __user * buf,size_t nr)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 */ n_tracerouter_write(struct tty_struct * tty,struct file * file,const unsigned char * buf,size_t nr)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 */ n_tracerouter_receivebuf(struct tty_struct * tty,const unsigned char * cp,char * fp,int count)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 */ n_tracerouter_init(void)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 */ n_tracerouter_exit(void)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"); 244