1/*
2 * userio kernel serio device emulation module
3 * Copyright (C) 2015 Red Hat
4 * Copyright (C) 2015 Stephen Chandler Paul <thatslyude@gmail.com>
5 *
6 * This program is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU Lesser General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or (at
9 * your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful, but
12 * WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
14 * General Public License for more details.
15 */
16
17#include <linux/circ_buf.h>
18#include <linux/mutex.h>
19#include <linux/module.h>
20#include <linux/init.h>
21#include <linux/kernel.h>
22#include <linux/serio.h>
23#include <linux/slab.h>
24#include <linux/fs.h>
25#include <linux/miscdevice.h>
26#include <linux/sched.h>
27#include <linux/poll.h>
28#include <uapi/linux/userio.h>
29
30#define USERIO_NAME		"userio"
31#define USERIO_BUFSIZE		16
32
33static struct miscdevice userio_misc;
34
35struct userio_device {
36	struct serio *serio;
37	struct mutex mutex;
38
39	bool running;
40
41	u8 head;
42	u8 tail;
43
44	spinlock_t buf_lock;
45	unsigned char buf[USERIO_BUFSIZE];
46
47	wait_queue_head_t waitq;
48};
49
50/**
51 * userio_device_write - Write data from serio to a userio device in userspace
52 * @id: The serio port for the userio device
53 * @val: The data to write to the device
54 */
55static int userio_device_write(struct serio *id, unsigned char val)
56{
57	struct userio_device *userio = id->port_data;
58	unsigned long flags;
59
60	spin_lock_irqsave(&userio->buf_lock, flags);
61
62	userio->buf[userio->head] = val;
63	userio->head = (userio->head + 1) % USERIO_BUFSIZE;
64
65	if (userio->head == userio->tail)
66		dev_warn(userio_misc.this_device,
67			 "Buffer overflowed, userio client isn't keeping up");
68
69	spin_unlock_irqrestore(&userio->buf_lock, flags);
70
71	wake_up_interruptible(&userio->waitq);
72
73	return 0;
74}
75
76static int userio_char_open(struct inode *inode, struct file *file)
77{
78	struct userio_device *userio;
79
80	userio = kzalloc(sizeof(struct userio_device), GFP_KERNEL);
81	if (!userio)
82		return -ENOMEM;
83
84	mutex_init(&userio->mutex);
85	spin_lock_init(&userio->buf_lock);
86	init_waitqueue_head(&userio->waitq);
87
88	userio->serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
89	if (!userio->serio) {
90		kfree(userio);
91		return -ENOMEM;
92	}
93
94	userio->serio->write = userio_device_write;
95	userio->serio->port_data = userio;
96
97	file->private_data = userio;
98
99	return 0;
100}
101
102static int userio_char_release(struct inode *inode, struct file *file)
103{
104	struct userio_device *userio = file->private_data;
105
106	if (userio->running) {
107		/*
108		 * Don't free the serio port here, serio_unregister_port()
109		 * does it for us.
110		 */
111		serio_unregister_port(userio->serio);
112	} else {
113		kfree(userio->serio);
114	}
115
116	kfree(userio);
117
118	return 0;
119}
120
121static ssize_t userio_char_read(struct file *file, char __user *user_buffer,
122				size_t count, loff_t *ppos)
123{
124	struct userio_device *userio = file->private_data;
125	int error;
126	size_t nonwrap_len, copylen;
127	unsigned char buf[USERIO_BUFSIZE];
128	unsigned long flags;
129
130	/*
131	 * By the time we get here, the data that was waiting might have
132	 * been taken by another thread. Grab the buffer lock and check if
133	 * there's still any data waiting, otherwise repeat this process
134	 * until we have data (unless the file descriptor is non-blocking
135	 * of course).
136	 */
137	for (;;) {
138		spin_lock_irqsave(&userio->buf_lock, flags);
139
140		nonwrap_len = CIRC_CNT_TO_END(userio->head,
141					      userio->tail,
142					      USERIO_BUFSIZE);
143		copylen = min(nonwrap_len, count);
144		if (copylen) {
145			memcpy(buf, &userio->buf[userio->tail], copylen);
146			userio->tail = (userio->tail + copylen) %
147							USERIO_BUFSIZE;
148		}
149
150		spin_unlock_irqrestore(&userio->buf_lock, flags);
151
152		if (nonwrap_len)
153			break;
154
155		/* buffer was/is empty */
156		if (file->f_flags & O_NONBLOCK)
157			return -EAGAIN;
158
159		/*
160		 * count == 0 is special - no IO is done but we check
161		 * for error conditions (see above).
162		 */
163		if (count == 0)
164			return 0;
165
166		error = wait_event_interruptible(userio->waitq,
167						 userio->head != userio->tail);
168		if (error)
169			return error;
170	}
171
172	if (copylen)
173		if (copy_to_user(user_buffer, buf, copylen))
174			return -EFAULT;
175
176	return copylen;
177}
178
179static ssize_t userio_char_write(struct file *file, const char __user *buffer,
180				 size_t count, loff_t *ppos)
181{
182	struct userio_device *userio = file->private_data;
183	struct userio_cmd cmd;
184	int error;
185
186	if (count != sizeof(cmd)) {
187		dev_warn(userio_misc.this_device, "Invalid payload size\n");
188		return -EINVAL;
189	}
190
191	if (copy_from_user(&cmd, buffer, sizeof(cmd)))
192		return -EFAULT;
193
194	error = mutex_lock_interruptible(&userio->mutex);
195	if (error)
196		return error;
197
198	switch (cmd.type) {
199	case USERIO_CMD_REGISTER:
200		if (!userio->serio->id.type) {
201			dev_warn(userio_misc.this_device,
202				 "No port type given on /dev/userio\n");
203
204			error = -EINVAL;
205			goto out;
206		}
207
208		if (userio->running) {
209			dev_warn(userio_misc.this_device,
210				 "Begin command sent, but we're already running\n");
211			error = -EBUSY;
212			goto out;
213		}
214
215		userio->running = true;
216		serio_register_port(userio->serio);
217		break;
218
219	case USERIO_CMD_SET_PORT_TYPE:
220		if (userio->running) {
221			dev_warn(userio_misc.this_device,
222				 "Can't change port type on an already running userio instance\n");
223			error = -EBUSY;
224			goto out;
225		}
226
227		userio->serio->id.type = cmd.data;
228		break;
229
230	case USERIO_CMD_SEND_INTERRUPT:
231		if (!userio->running) {
232			dev_warn(userio_misc.this_device,
233				 "The device must be registered before sending interrupts\n");
234			error = -ENODEV;
235			goto out;
236		}
237
238		serio_interrupt(userio->serio, cmd.data, 0);
239		break;
240
241	default:
242		error = -EOPNOTSUPP;
243		goto out;
244	}
245
246out:
247	mutex_unlock(&userio->mutex);
248	return error ?: count;
249}
250
251static unsigned int userio_char_poll(struct file *file, poll_table *wait)
252{
253	struct userio_device *userio = file->private_data;
254
255	poll_wait(file, &userio->waitq, wait);
256
257	if (userio->head != userio->tail)
258		return POLLIN | POLLRDNORM;
259
260	return 0;
261}
262
263static const struct file_operations userio_fops = {
264	.owner		= THIS_MODULE,
265	.open		= userio_char_open,
266	.release	= userio_char_release,
267	.read		= userio_char_read,
268	.write		= userio_char_write,
269	.poll		= userio_char_poll,
270	.llseek		= no_llseek,
271};
272
273static struct miscdevice userio_misc = {
274	.fops	= &userio_fops,
275	.minor	= USERIO_MINOR,
276	.name	= USERIO_NAME,
277};
278module_driver(userio_misc, misc_register, misc_deregister);
279
280MODULE_ALIAS_MISCDEV(USERIO_MINOR);
281MODULE_ALIAS("devname:" USERIO_NAME);
282
283MODULE_AUTHOR("Stephen Chandler Paul <thatslyude@gmail.com>");
284MODULE_DESCRIPTION("Virtual Serio Device Support");
285MODULE_LICENSE("GPL");
286