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");