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
  80 #ifndef CONFIG_USB_SERIAL_SAFE_PADDED
  81 #define CONFIG_USB_SERIAL_SAFE_PADDED 0
  82 #endif
  83
  84 static bool safe = 1;
  85 static 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
  90 MODULE_AUTHOR(DRIVER_AUTHOR);
  91 MODULE_DESCRIPTION(DRIVER_DESC);
  92 MODULE_LICENSE("GPL");
  93
  94 module_param(safe, bool, 0);
  95 MODULE_PARM_DESC(safe, "Turn Safe Encapsulation On/Off");
  96
  97 module_param(padded, bool, 0);
  98 MODULE_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
 127 static 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
 138 MODULE_DEVICE_TABLE(usb, id_table);
 139
 140 static 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  */
 188 static __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
 194 static 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;
 222 out:
 223         tty_insert_flip_string(&port->port, data, length);
 224         tty_flip_buffer_push(&port->port);
 225 }
 226
 227 static 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
 263 static 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
 289 static 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
 301 static struct usb_serial_driver * const serial_drivers[] = {
 302         &safe_device, NULL
 303 };
 304
 305 module_usb_serial_driver(serial_drivers, id_table);