1/*
2 * Safe Encapsulated USB Serial Driver
3 *
4 *      Copyright (C) 2010 Johan Hovold <jhovold@gmail.com>
5 *      Copyright (C) 2001 Lineo
6 *      Copyright (C) 2001 Hewlett-Packard
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 as published by
10 *	the Free Software Foundation; either version 2 of the License, or
11 *	(at your option) any later version.
12 *
13 * By:
14 *      Stuart Lynne <sl@lineo.com>, Tom Rushworth <tbr@lineo.com>
15 */
16
17/*
18 * The encapsultaion is designed to overcome difficulties with some USB
19 * hardware.
20 *
21 * While the USB protocol has a CRC over the data while in transit, i.e. while
22 * being carried over the bus, there is no end to end protection. If the
23 * hardware has any problems getting the data into or out of the USB transmit
24 * and receive FIFO's then data can be lost.
25 *
26 * This protocol adds a two byte trailer to each USB packet to specify the
27 * number of bytes of valid data and a 10 bit CRC that will allow the receiver
28 * to verify that the entire USB packet was received without error.
29 *
30 * Because in this case the sender and receiver are the class and function
31 * drivers there is now end to end protection.
32 *
33 * There is an additional option that can be used to force all transmitted
34 * packets to be padded to the maximum packet size. This provides a work
35 * around for some devices which have problems with small USB packets.
36 *
37 * Assuming a packetsize of N:
38 *
39 *      0..N-2  data and optional padding
40 *
41 *      N-2     bits 7-2 - number of bytes of valid data
42 *              bits 1-0 top two bits of 10 bit CRC
43 *      N-1     bottom 8 bits of 10 bit CRC
44 *
45 *
46 *      | Data Length       | 10 bit CRC                                |
47 *      + 7 . 6 . 5 . 4 . 3 . 2 . 1 . 0 | 7 . 6 . 5 . 4 . 3 . 2 . 1 . 0 +
48 *
49 * The 10 bit CRC is computed across the sent data, followed by the trailer
50 * with the length set and the CRC set to zero. The CRC is then OR'd into
51 * the trailer.
52 *
53 * When received a 10 bit CRC is computed over the entire frame including
54 * the trailer and should be equal to zero.
55 *
56 * Two module parameters are used to control the encapsulation, if both are
57 * turned of the module works as a simple serial device with NO
58 * encapsulation.
59 *
60 * See linux/drivers/usbd/serial_fd for a device function driver
61 * implementation of this.
62 *
63 */
64
65#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
66
67#include <linux/kernel.h>
68#include <linux/errno.h>
69#include <linux/gfp.h>
70#include <linux/tty.h>
71#include <linux/tty_driver.h>
72#include <linux/tty_flip.h>
73#include <linux/module.h>
74#include <linux/spinlock.h>
75#include <linux/uaccess.h>
76#include <linux/usb.h>
77#include <linux/usb/serial.h>
78
79
80#ifndef CONFIG_USB_SERIAL_SAFE_PADDED
81#define CONFIG_USB_SERIAL_SAFE_PADDED 0
82#endif
83
84static bool safe = 1;
85static bool padded = CONFIG_USB_SERIAL_SAFE_PADDED;
86
87#define DRIVER_AUTHOR "sl@lineo.com, tbr@lineo.com, Johan Hovold <jhovold@gmail.com>"
88#define DRIVER_DESC "USB Safe Encapsulated Serial"
89
90MODULE_AUTHOR(DRIVER_AUTHOR);
91MODULE_DESCRIPTION(DRIVER_DESC);
92MODULE_LICENSE("GPL");
93
94module_param(safe, bool, 0);
95MODULE_PARM_DESC(safe, "Turn Safe Encapsulation On/Off");
96
97module_param(padded, bool, 0);
98MODULE_PARM_DESC(padded, "Pad to full wMaxPacketSize On/Off");
99
100#define CDC_DEVICE_CLASS                        0x02
101
102#define CDC_INTERFACE_CLASS                     0x02
103#define CDC_INTERFACE_SUBCLASS                  0x06
104
105#define LINEO_INTERFACE_CLASS                   0xff
106
107#define LINEO_INTERFACE_SUBCLASS_SAFENET        0x01
108#define LINEO_SAFENET_CRC                       0x01
109#define LINEO_SAFENET_CRC_PADDED                0x02
110
111#define LINEO_INTERFACE_SUBCLASS_SAFESERIAL     0x02
112#define LINEO_SAFESERIAL_CRC                    0x01
113#define LINEO_SAFESERIAL_CRC_PADDED             0x02
114
115
116#define MY_USB_DEVICE(vend, prod, dc, ic, isc) \
117	.match_flags = USB_DEVICE_ID_MATCH_DEVICE | \
118		       USB_DEVICE_ID_MATCH_DEV_CLASS | \
119		       USB_DEVICE_ID_MATCH_INT_CLASS | \
120		       USB_DEVICE_ID_MATCH_INT_SUBCLASS, \
121	.idVendor = (vend), \
122	.idProduct = (prod),\
123	.bDeviceClass = (dc),\
124	.bInterfaceClass = (ic), \
125	.bInterfaceSubClass = (isc),
126
127static const struct usb_device_id id_table[] = {
128	{MY_USB_DEVICE(0x49f, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Itsy */
129	{MY_USB_DEVICE(0x3f0, 0x2101, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Calypso */
130	{MY_USB_DEVICE(0x4dd, 0x8001, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Iris */
131	{MY_USB_DEVICE(0x4dd, 0x8002, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Collie */
132	{MY_USB_DEVICE(0x4dd, 0x8003, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Collie */
133	{MY_USB_DEVICE(0x4dd, 0x8004, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Collie */
134	{MY_USB_DEVICE(0x5f9, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Sharp tmp */
135	{}			/* terminating entry  */
136};
137
138MODULE_DEVICE_TABLE(usb, id_table);
139
140static const __u16 crc10_table[256] = {
141	0x000, 0x233, 0x255, 0x066, 0x299, 0x0aa, 0x0cc, 0x2ff,
142	0x301, 0x132, 0x154, 0x367, 0x198, 0x3ab, 0x3cd, 0x1fe,
143	0x031, 0x202, 0x264, 0x057, 0x2a8, 0x09b, 0x0fd, 0x2ce,
144	0x330, 0x103, 0x165, 0x356, 0x1a9, 0x39a, 0x3fc, 0x1cf,
145	0x062, 0x251, 0x237, 0x004, 0x2fb, 0x0c8, 0x0ae, 0x29d,
146	0x363, 0x150, 0x136, 0x305, 0x1fa, 0x3c9, 0x3af, 0x19c,
147	0x053, 0x260, 0x206, 0x035, 0x2ca, 0x0f9, 0x09f, 0x2ac,
148	0x352, 0x161, 0x107, 0x334, 0x1cb, 0x3f8, 0x39e, 0x1ad,
149	0x0c4, 0x2f7, 0x291, 0x0a2, 0x25d, 0x06e, 0x008, 0x23b,
150	0x3c5, 0x1f6, 0x190, 0x3a3, 0x15c, 0x36f, 0x309, 0x13a,
151	0x0f5, 0x2c6, 0x2a0, 0x093, 0x26c, 0x05f, 0x039, 0x20a,
152	0x3f4, 0x1c7, 0x1a1, 0x392, 0x16d, 0x35e, 0x338, 0x10b,
153	0x0a6, 0x295, 0x2f3, 0x0c0, 0x23f, 0x00c, 0x06a, 0x259,
154	0x3a7, 0x194, 0x1f2, 0x3c1, 0x13e, 0x30d, 0x36b, 0x158,
155	0x097, 0x2a4, 0x2c2, 0x0f1, 0x20e, 0x03d, 0x05b, 0x268,
156	0x396, 0x1a5, 0x1c3, 0x3f0, 0x10f, 0x33c, 0x35a, 0x169,
157	0x188, 0x3bb, 0x3dd, 0x1ee, 0x311, 0x122, 0x144, 0x377,
158	0x289, 0x0ba, 0x0dc, 0x2ef, 0x010, 0x223, 0x245, 0x076,
159	0x1b9, 0x38a, 0x3ec, 0x1df, 0x320, 0x113, 0x175, 0x346,
160	0x2b8, 0x08b, 0x0ed, 0x2de, 0x021, 0x212, 0x274, 0x047,
161	0x1ea, 0x3d9, 0x3bf, 0x18c, 0x373, 0x140, 0x126, 0x315,
162	0x2eb, 0x0d8, 0x0be, 0x28d, 0x072, 0x241, 0x227, 0x014,
163	0x1db, 0x3e8, 0x38e, 0x1bd, 0x342, 0x171, 0x117, 0x324,
164	0x2da, 0x0e9, 0x08f, 0x2bc, 0x043, 0x270, 0x216, 0x025,
165	0x14c, 0x37f, 0x319, 0x12a, 0x3d5, 0x1e6, 0x180, 0x3b3,
166	0x24d, 0x07e, 0x018, 0x22b, 0x0d4, 0x2e7, 0x281, 0x0b2,
167	0x17d, 0x34e, 0x328, 0x11b, 0x3e4, 0x1d7, 0x1b1, 0x382,
168	0x27c, 0x04f, 0x029, 0x21a, 0x0e5, 0x2d6, 0x2b0, 0x083,
169	0x12e, 0x31d, 0x37b, 0x148, 0x3b7, 0x184, 0x1e2, 0x3d1,
170	0x22f, 0x01c, 0x07a, 0x249, 0x0b6, 0x285, 0x2e3, 0x0d0,
171	0x11f, 0x32c, 0x34a, 0x179, 0x386, 0x1b5, 0x1d3, 0x3e0,
172	0x21e, 0x02d, 0x04b, 0x278, 0x087, 0x2b4, 0x2d2, 0x0e1,
173};
174
175#define CRC10_INITFCS     0x000	/* Initial FCS value */
176#define CRC10_GOODFCS     0x000	/* Good final FCS value */
177#define CRC10_FCS(fcs, c) ((((fcs) << 8) & 0x3ff) ^ crc10_table[((fcs) >> 2) & 0xff] ^ (c))
178
179/**
180 * fcs_compute10 - memcpy and calculate 10 bit CRC across buffer
181 * @sp: pointer to buffer
182 * @len: number of bytes
183 * @fcs: starting FCS
184 *
185 * Perform a memcpy and calculate fcs using ppp 10bit CRC algorithm. Return
186 * new 10 bit FCS.
187 */
188static __u16 __inline__ fcs_compute10(unsigned char *sp, int len, __u16 fcs)
189{
190	for (; len-- > 0; fcs = CRC10_FCS(fcs, *sp++));
191	return fcs;
192}
193
194static void safe_process_read_urb(struct urb *urb)
195{
196	struct usb_serial_port *port = urb->context;
197	unsigned char *data = urb->transfer_buffer;
198	unsigned char length = urb->actual_length;
199	int actual_length;
200	__u16 fcs;
201
202	if (!length)
203		return;
204
205	if (!safe)
206		goto out;
207
208	fcs = fcs_compute10(data, length, CRC10_INITFCS);
209	if (fcs) {
210		dev_err(&port->dev, "%s - bad CRC %x\n", __func__, fcs);
211		return;
212	}
213
214	actual_length = data[length - 2] >> 2;
215	if (actual_length > (length - 2)) {
216		dev_err(&port->dev, "%s - inconsistent lengths %d:%d\n",
217				__func__, actual_length, length);
218		return;
219	}
220	dev_info(&urb->dev->dev, "%s - actual: %d\n", __func__, actual_length);
221	length = actual_length;
222out:
223	tty_insert_flip_string(&port->port, data, length);
224	tty_flip_buffer_push(&port->port);
225}
226
227static int safe_prepare_write_buffer(struct usb_serial_port *port,
228						void *dest, size_t size)
229{
230	unsigned char *buf = dest;
231	int count;
232	int trailer_len;
233	int pkt_len;
234	__u16 fcs;
235
236	trailer_len = safe ? 2 : 0;
237
238	count = kfifo_out_locked(&port->write_fifo, buf, size - trailer_len,
239								&port->lock);
240	if (!safe)
241		return count;
242
243	/* pad if necessary */
244	if (padded) {
245		pkt_len = size;
246		memset(buf + count, '0', pkt_len - count - trailer_len);
247	} else {
248		pkt_len = count + trailer_len;
249	}
250
251	/* set count */
252	buf[pkt_len - 2] = count << 2;
253	buf[pkt_len - 1] = 0;
254
255	/* compute fcs and insert into trailer */
256	fcs = fcs_compute10(buf, pkt_len, CRC10_INITFCS);
257	buf[pkt_len - 2] |= fcs >> 8;
258	buf[pkt_len - 1] |= fcs & 0xff;
259
260	return pkt_len;
261}
262
263static int safe_startup(struct usb_serial *serial)
264{
265	struct usb_interface_descriptor	*desc;
266
267	if (serial->dev->descriptor.bDeviceClass != CDC_DEVICE_CLASS)
268		return -ENODEV;
269
270	desc = &serial->interface->cur_altsetting->desc;
271
272	if (desc->bInterfaceClass != LINEO_INTERFACE_CLASS)
273		return -ENODEV;
274	if (desc->bInterfaceSubClass != LINEO_INTERFACE_SUBCLASS_SAFESERIAL)
275		return -ENODEV;
276
277	switch (desc->bInterfaceProtocol) {
278	case LINEO_SAFESERIAL_CRC:
279		break;
280	case LINEO_SAFESERIAL_CRC_PADDED:
281		padded = 1;
282		break;
283	default:
284		return -EINVAL;
285	}
286	return 0;
287}
288
289static struct usb_serial_driver safe_device = {
290	.driver = {
291		.owner =	THIS_MODULE,
292		.name =		"safe_serial",
293	},
294	.id_table =		id_table,
295	.num_ports =		1,
296	.process_read_urb =	safe_process_read_urb,
297	.prepare_write_buffer =	safe_prepare_write_buffer,
298	.attach =		safe_startup,
299};
300
301static struct usb_serial_driver * const serial_drivers[] = {
302	&safe_device, NULL
303};
304
305module_usb_serial_driver(serial_drivers, id_table);
306