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Linux/drivers/usb/serial/safe_serial.c

  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 static bool safe = true;
 80 static bool padded = IS_ENABLED(CONFIG_USB_SERIAL_SAFE_PADDED);
 81 
 82 #define DRIVER_AUTHOR "sl@lineo.com, tbr@lineo.com, Johan Hovold <jhovold@gmail.com>"
 83 #define DRIVER_DESC "USB Safe Encapsulated Serial"
 84 
 85 MODULE_AUTHOR(DRIVER_AUTHOR);
 86 MODULE_DESCRIPTION(DRIVER_DESC);
 87 MODULE_LICENSE("GPL");
 88 
 89 module_param(safe, bool, 0);
 90 MODULE_PARM_DESC(safe, "Turn Safe Encapsulation On/Off");
 91 
 92 module_param(padded, bool, 0);
 93 MODULE_PARM_DESC(padded, "Pad to full wMaxPacketSize On/Off");
 94 
 95 #define CDC_DEVICE_CLASS                        0x02
 96 
 97 #define CDC_INTERFACE_CLASS                     0x02
 98 #define CDC_INTERFACE_SUBCLASS                  0x06
 99 
100 #define LINEO_INTERFACE_CLASS                   0xff
101 
102 #define LINEO_INTERFACE_SUBCLASS_SAFENET        0x01
103 #define LINEO_SAFENET_CRC                       0x01
104 #define LINEO_SAFENET_CRC_PADDED                0x02
105 
106 #define LINEO_INTERFACE_SUBCLASS_SAFESERIAL     0x02
107 #define LINEO_SAFESERIAL_CRC                    0x01
108 #define LINEO_SAFESERIAL_CRC_PADDED             0x02
109 
110 
111 #define MY_USB_DEVICE(vend, prod, dc, ic, isc) \
112         .match_flags = USB_DEVICE_ID_MATCH_DEVICE | \
113                        USB_DEVICE_ID_MATCH_DEV_CLASS | \
114                        USB_DEVICE_ID_MATCH_INT_CLASS | \
115                        USB_DEVICE_ID_MATCH_INT_SUBCLASS, \
116         .idVendor = (vend), \
117         .idProduct = (prod),\
118         .bDeviceClass = (dc),\
119         .bInterfaceClass = (ic), \
120         .bInterfaceSubClass = (isc),
121 
122 static const struct usb_device_id id_table[] = {
123         {MY_USB_DEVICE(0x49f, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Itsy */
124         {MY_USB_DEVICE(0x3f0, 0x2101, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Calypso */
125         {MY_USB_DEVICE(0x4dd, 0x8001, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Iris */
126         {MY_USB_DEVICE(0x4dd, 0x8002, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Collie */
127         {MY_USB_DEVICE(0x4dd, 0x8003, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Collie */
128         {MY_USB_DEVICE(0x4dd, 0x8004, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Collie */
129         {MY_USB_DEVICE(0x5f9, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Sharp tmp */
130         {}                      /* terminating entry  */
131 };
132 
133 MODULE_DEVICE_TABLE(usb, id_table);
134 
135 static const __u16 crc10_table[256] = {
136         0x000, 0x233, 0x255, 0x066, 0x299, 0x0aa, 0x0cc, 0x2ff,
137         0x301, 0x132, 0x154, 0x367, 0x198, 0x3ab, 0x3cd, 0x1fe,
138         0x031, 0x202, 0x264, 0x057, 0x2a8, 0x09b, 0x0fd, 0x2ce,
139         0x330, 0x103, 0x165, 0x356, 0x1a9, 0x39a, 0x3fc, 0x1cf,
140         0x062, 0x251, 0x237, 0x004, 0x2fb, 0x0c8, 0x0ae, 0x29d,
141         0x363, 0x150, 0x136, 0x305, 0x1fa, 0x3c9, 0x3af, 0x19c,
142         0x053, 0x260, 0x206, 0x035, 0x2ca, 0x0f9, 0x09f, 0x2ac,
143         0x352, 0x161, 0x107, 0x334, 0x1cb, 0x3f8, 0x39e, 0x1ad,
144         0x0c4, 0x2f7, 0x291, 0x0a2, 0x25d, 0x06e, 0x008, 0x23b,
145         0x3c5, 0x1f6, 0x190, 0x3a3, 0x15c, 0x36f, 0x309, 0x13a,
146         0x0f5, 0x2c6, 0x2a0, 0x093, 0x26c, 0x05f, 0x039, 0x20a,
147         0x3f4, 0x1c7, 0x1a1, 0x392, 0x16d, 0x35e, 0x338, 0x10b,
148         0x0a6, 0x295, 0x2f3, 0x0c0, 0x23f, 0x00c, 0x06a, 0x259,
149         0x3a7, 0x194, 0x1f2, 0x3c1, 0x13e, 0x30d, 0x36b, 0x158,
150         0x097, 0x2a4, 0x2c2, 0x0f1, 0x20e, 0x03d, 0x05b, 0x268,
151         0x396, 0x1a5, 0x1c3, 0x3f0, 0x10f, 0x33c, 0x35a, 0x169,
152         0x188, 0x3bb, 0x3dd, 0x1ee, 0x311, 0x122, 0x144, 0x377,
153         0x289, 0x0ba, 0x0dc, 0x2ef, 0x010, 0x223, 0x245, 0x076,
154         0x1b9, 0x38a, 0x3ec, 0x1df, 0x320, 0x113, 0x175, 0x346,
155         0x2b8, 0x08b, 0x0ed, 0x2de, 0x021, 0x212, 0x274, 0x047,
156         0x1ea, 0x3d9, 0x3bf, 0x18c, 0x373, 0x140, 0x126, 0x315,
157         0x2eb, 0x0d8, 0x0be, 0x28d, 0x072, 0x241, 0x227, 0x014,
158         0x1db, 0x3e8, 0x38e, 0x1bd, 0x342, 0x171, 0x117, 0x324,
159         0x2da, 0x0e9, 0x08f, 0x2bc, 0x043, 0x270, 0x216, 0x025,
160         0x14c, 0x37f, 0x319, 0x12a, 0x3d5, 0x1e6, 0x180, 0x3b3,
161         0x24d, 0x07e, 0x018, 0x22b, 0x0d4, 0x2e7, 0x281, 0x0b2,
162         0x17d, 0x34e, 0x328, 0x11b, 0x3e4, 0x1d7, 0x1b1, 0x382,
163         0x27c, 0x04f, 0x029, 0x21a, 0x0e5, 0x2d6, 0x2b0, 0x083,
164         0x12e, 0x31d, 0x37b, 0x148, 0x3b7, 0x184, 0x1e2, 0x3d1,
165         0x22f, 0x01c, 0x07a, 0x249, 0x0b6, 0x285, 0x2e3, 0x0d0,
166         0x11f, 0x32c, 0x34a, 0x179, 0x386, 0x1b5, 0x1d3, 0x3e0,
167         0x21e, 0x02d, 0x04b, 0x278, 0x087, 0x2b4, 0x2d2, 0x0e1,
168 };
169 
170 #define CRC10_INITFCS     0x000 /* Initial FCS value */
171 #define CRC10_GOODFCS     0x000 /* Good final FCS value */
172 #define CRC10_FCS(fcs, c) ((((fcs) << 8) & 0x3ff) ^ crc10_table[((fcs) >> 2) & 0xff] ^ (c))
173 
174 /**
175  * fcs_compute10 - memcpy and calculate 10 bit CRC across buffer
176  * @sp: pointer to buffer
177  * @len: number of bytes
178  * @fcs: starting FCS
179  *
180  * Perform a memcpy and calculate fcs using ppp 10bit CRC algorithm. Return
181  * new 10 bit FCS.
182  */
183 static __u16 __inline__ fcs_compute10(unsigned char *sp, int len, __u16 fcs)
184 {
185         for (; len-- > 0; fcs = CRC10_FCS(fcs, *sp++));
186         return fcs;
187 }
188 
189 static void safe_process_read_urb(struct urb *urb)
190 {
191         struct usb_serial_port *port = urb->context;
192         unsigned char *data = urb->transfer_buffer;
193         unsigned char length = urb->actual_length;
194         int actual_length;
195         __u16 fcs;
196 
197         if (!length)
198                 return;
199 
200         if (!safe)
201                 goto out;
202 
203         fcs = fcs_compute10(data, length, CRC10_INITFCS);
204         if (fcs) {
205                 dev_err(&port->dev, "%s - bad CRC %x\n", __func__, fcs);
206                 return;
207         }
208 
209         actual_length = data[length - 2] >> 2;
210         if (actual_length > (length - 2)) {
211                 dev_err(&port->dev, "%s - inconsistent lengths %d:%d\n",
212                                 __func__, actual_length, length);
213                 return;
214         }
215         dev_info(&urb->dev->dev, "%s - actual: %d\n", __func__, actual_length);
216         length = actual_length;
217 out:
218         tty_insert_flip_string(&port->port, data, length);
219         tty_flip_buffer_push(&port->port);
220 }
221 
222 static int safe_prepare_write_buffer(struct usb_serial_port *port,
223                                                 void *dest, size_t size)
224 {
225         unsigned char *buf = dest;
226         int count;
227         int trailer_len;
228         int pkt_len;
229         __u16 fcs;
230 
231         trailer_len = safe ? 2 : 0;
232 
233         count = kfifo_out_locked(&port->write_fifo, buf, size - trailer_len,
234                                                                 &port->lock);
235         if (!safe)
236                 return count;
237 
238         /* pad if necessary */
239         if (padded) {
240                 pkt_len = size;
241                 memset(buf + count, '', pkt_len - count - trailer_len);
242         } else {
243                 pkt_len = count + trailer_len;
244         }
245 
246         /* set count */
247         buf[pkt_len - 2] = count << 2;
248         buf[pkt_len - 1] = 0;
249 
250         /* compute fcs and insert into trailer */
251         fcs = fcs_compute10(buf, pkt_len, CRC10_INITFCS);
252         buf[pkt_len - 2] |= fcs >> 8;
253         buf[pkt_len - 1] |= fcs & 0xff;
254 
255         return pkt_len;
256 }
257 
258 static int safe_startup(struct usb_serial *serial)
259 {
260         struct usb_interface_descriptor *desc;
261 
262         if (serial->dev->descriptor.bDeviceClass != CDC_DEVICE_CLASS)
263                 return -ENODEV;
264 
265         desc = &serial->interface->cur_altsetting->desc;
266 
267         if (desc->bInterfaceClass != LINEO_INTERFACE_CLASS)
268                 return -ENODEV;
269         if (desc->bInterfaceSubClass != LINEO_INTERFACE_SUBCLASS_SAFESERIAL)
270                 return -ENODEV;
271 
272         switch (desc->bInterfaceProtocol) {
273         case LINEO_SAFESERIAL_CRC:
274                 break;
275         case LINEO_SAFESERIAL_CRC_PADDED:
276                 padded = true;
277                 break;
278         default:
279                 return -EINVAL;
280         }
281         return 0;
282 }
283 
284 static struct usb_serial_driver safe_device = {
285         .driver = {
286                 .owner =        THIS_MODULE,
287                 .name =         "safe_serial",
288         },
289         .id_table =             id_table,
290         .num_ports =            1,
291         .process_read_urb =     safe_process_read_urb,
292         .prepare_write_buffer = safe_prepare_write_buffer,
293         .attach =               safe_startup,
294 };
295 
296 static struct usb_serial_driver * const serial_drivers[] = {
297         &safe_device, NULL
298 };
299 
300 module_usb_serial_driver(serial_drivers, id_table);
301 

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