Root/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 */
53struct tracerouter_data {
54    u8 opencalled;
55    struct tty_struct *kref_tty;
56};
57static struct tracerouter_data *tr_data;
58
59/* lock for when tty reference is being used */
60static 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 */
71static 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 */
99static 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 */
130static 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 */
154static 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 */
171static 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
185static 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 */
204static 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 */
227static 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
237module_init(n_tracerouter_init);
238module_exit(n_tracerouter_exit);
239
240MODULE_LICENSE("GPL");
241MODULE_AUTHOR("Jay Freyensee");
242MODULE_ALIAS_LDISC(N_TRACEROUTER);
243MODULE_DESCRIPTION("Trace router ldisc driver");
244

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