1// SPDX-License-Identifier: GPL-2.0
2/*
3 * n_tracerouter.c - Trace data router through tty space
4 *
5 * Copyright (C) Intel 2011
6 *
7 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
8 *
9 * This trace router uses the Linux line discipline framework to route
10 * trace data coming from a HW Modem to a PTI (Parallel Trace Module) port.
11 * The solution is not specific to a HW modem and this line disciple can
12 * be used to route any stream of data in kernel space.
13 * This is part of a solution for the P1149.7, compact JTAG, standard.
14 */
15
16#include <linux/init.h>
17#include <linux/kernel.h>
18#include <linux/module.h>
19#include <linux/types.h>
20#include <linux/ioctl.h>
21#include <linux/tty.h>
22#include <linux/tty_ldisc.h>
23#include <linux/errno.h>
24#include <linux/string.h>
25#include <linux/mutex.h>
26#include <linux/slab.h>
27#include <linux/bug.h>
28#include "n_tracesink.h"
29
30/*
31 * Other ldisc drivers use 65536 which basically means,
32 * 'I can always accept 64k' and flow control is off.
33 * This number is deemed appropriate for this driver.
34 */
35#define RECEIVE_ROOM 65536
36#define DRIVERNAME "n_tracerouter"
37
38/*
39 * struct to hold private configuration data for this ldisc.
40 * opencalled is used to hold if this ldisc has been opened.
41 * kref_tty holds the tty reference the ldisc sits on top of.
42 */
43struct tracerouter_data {
44 u8 opencalled;
45 struct tty_struct *kref_tty;
46};
47static struct tracerouter_data *tr_data;
48
49/* lock for when tty reference is being used */
50static DEFINE_MUTEX(routelock);
51
52/**
53 * n_tracerouter_open() - Called when a tty is opened by a SW entity.
54 * @tty: terminal device to the ldisc.
55 *
56 * Return:
57 * 0 for success.
58 *
59 * Caveats: This should only be opened one time per SW entity.
60 */
61static int n_tracerouter_open(struct tty_struct *tty)
62{
63 int retval = -EEXIST;
64
65 mutex_lock(&routelock);
66 if (tr_data->opencalled == 0) {
67
68 tr_data->kref_tty = tty_kref_get(tty);
69 if (tr_data->kref_tty == NULL) {
70 retval = -EFAULT;
71 } else {
72 tr_data->opencalled = 1;
73 tty->disc_data = tr_data;
74 tty->receive_room = RECEIVE_ROOM;
75 tty_driver_flush_buffer(tty);
76 retval = 0;
77 }
78 }
79 mutex_unlock(&routelock);
80 return retval;
81}
82
83/**
84 * n_tracerouter_close() - close connection
85 * @tty: terminal device to the ldisc.
86 *
87 * Called when a software entity wants to close a connection.
88 */
89static void n_tracerouter_close(struct tty_struct *tty)
90{
91 struct tracerouter_data *tptr = tty->disc_data;
92
93 mutex_lock(&routelock);
94 WARN_ON(tptr->kref_tty != tr_data->kref_tty);
95 tty_driver_flush_buffer(tty);
96 tty_kref_put(tr_data->kref_tty);
97 tr_data->kref_tty = NULL;
98 tr_data->opencalled = 0;
99 tty->disc_data = NULL;
100 mutex_unlock(&routelock);
101}
102
103/**
104 * n_tracerouter_read() - read request from user space
105 * @tty: terminal device passed into the ldisc.
106 * @file: pointer to open file object.
107 * @buf: pointer to the data buffer that gets eventually returned.
108 * @nr: number of bytes of the data buffer that is returned.
109 *
110 * function that allows read() functionality in userspace. By default if this
111 * is not implemented it returns -EIO. This module is functioning like a
112 * router via n_tracerouter_receivebuf(), and there is no real requirement
113 * to implement this function. However, an error return value other than
114 * -EIO should be used just to show that there was an intent not to have
115 * this function implemented. Return value based on read() man pages.
116 *
117 * Return:
118 * -EINVAL
119 */
120static ssize_t n_tracerouter_read(struct tty_struct *tty, struct file *file,
121 unsigned char __user *buf, size_t nr) {
122 return -EINVAL;
123}
124
125/**
126 * n_tracerouter_write() - Function that allows write() in userspace.
127 * @tty: terminal device passed into the ldisc.
128 * @file: pointer to open file object.
129 * @buf: pointer to the data buffer that gets eventually returned.
130 * @nr: number of bytes of the data buffer that is returned.
131 *
132 * By default if this is not implemented, it returns -EIO.
133 * This should not be implemented, ever, because
134 * 1. this driver is functioning like a router via
135 * n_tracerouter_receivebuf()
136 * 2. No writes to HW will ever go through this line discpline driver.
137 * However, an error return value other than -EIO should be used
138 * just to show that there was an intent not to have this function
139 * implemented. Return value based on write() man pages.
140 *
141 * Return:
142 * -EINVAL
143 */
144static ssize_t n_tracerouter_write(struct tty_struct *tty, struct file *file,
145 const unsigned char *buf, size_t nr) {
146 return -EINVAL;
147}
148
149/**
150 * n_tracerouter_receivebuf() - Routing function for driver.
151 * @tty: terminal device passed into the ldisc. It's assumed
152 * tty will never be NULL.
153 * @cp: buffer, block of characters to be eventually read by
154 * someone, somewhere (user read() call or some kernel function).
155 * @fp: flag buffer.
156 * @count: number of characters (aka, bytes) in cp.
157 *
158 * This function takes the input buffer, cp, and passes it to
159 * an external API function for processing.
160 */
161static void n_tracerouter_receivebuf(struct tty_struct *tty,
162 const unsigned char *cp,
163 char *fp, int count)
164{
165 mutex_lock(&routelock);
166 n_tracesink_datadrain((u8 *) cp, count);
167 mutex_unlock(&routelock);
168}
169
170/*
171 * Flush buffer is not impelemented as the ldisc has no internal buffering
172 * so the tty_driver_flush_buffer() is sufficient for this driver's needs.
173 */
174
175static struct tty_ldisc_ops tty_ptirouter_ldisc = {
176 .owner = THIS_MODULE,
177 .magic = TTY_LDISC_MAGIC,
178 .name = DRIVERNAME,
179 .open = n_tracerouter_open,
180 .close = n_tracerouter_close,
181 .read = n_tracerouter_read,
182 .write = n_tracerouter_write,
183 .receive_buf = n_tracerouter_receivebuf
184};
185
186/**
187 * n_tracerouter_init - module initialisation
188 *
189 * Registers this module as a line discipline driver.
190 *
191 * Return:
192 * 0 for success, any other value error.
193 */
194static int __init n_tracerouter_init(void)
195{
196 int retval;
197
198 tr_data = kzalloc(sizeof(struct tracerouter_data), GFP_KERNEL);
199 if (tr_data == NULL)
200 return -ENOMEM;
201
202
203 /* Note N_TRACEROUTER is defined in linux/tty.h */
204 retval = tty_register_ldisc(N_TRACEROUTER, &tty_ptirouter_ldisc);
205 if (retval < 0) {
206 pr_err("%s: Registration failed: %d\n", __func__, retval);
207 kfree(tr_data);
208 }
209 return retval;
210}
211
212/**
213 * n_tracerouter_exit - module unload
214 *
215 * Removes this module as a line discipline driver.
216 */
217static void __exit n_tracerouter_exit(void)
218{
219 int retval = tty_unregister_ldisc(N_TRACEROUTER);
220
221 if (retval < 0)
222 pr_err("%s: Unregistration failed: %d\n", __func__, retval);
223 else
224 kfree(tr_data);
225}
226
227module_init(n_tracerouter_init);
228module_exit(n_tracerouter_exit);
229
230MODULE_LICENSE("GPL");
231MODULE_AUTHOR("Jay Freyensee");
232MODULE_ALIAS_LDISC(N_TRACEROUTER);
233MODULE_DESCRIPTION("Trace router ldisc driver");
234