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/init.h>
  71 #include <linux/tty.h>
  72 #include <linux/tty_driver.h>
  73 #include <linux/tty_flip.h>
  74 #include <linux/module.h>
  75 #include <linux/spinlock.h>
  76 #include <linux/uaccess.h>
  77 #include <linux/usb.h>
  78 #include <linux/usb/serial.h>
  79
  80
  81 #ifndef CONFIG_USB_SERIAL_SAFE_PADDED
  82 #define CONFIG_USB_SERIAL_SAFE_PADDED 0
  83 #endif
  84
  85 static bool safe = 1;
  86 static bool padded = CONFIG_USB_SERIAL_SAFE_PADDED;
  87
  88 #define DRIVER_AUTHOR "sl@lineo.com, tbr@lineo.com, Johan Hovold <jhovold@gmail.com>"
  89 #define DRIVER_DESC "USB Safe Encapsulated Serial"
  90
  91 MODULE_AUTHOR(DRIVER_AUTHOR);
  92 MODULE_DESCRIPTION(DRIVER_DESC);
  93 MODULE_LICENSE("GPL");
  94
  95 module_param(safe, bool, 0);
  96 MODULE_PARM_DESC(safe, "Turn Safe Encapsulation On/Off");
  97
  98 module_param(padded, bool, 0);
  99 MODULE_PARM_DESC(padded, "Pad to full wMaxPacketSize On/Off");
 100
 101 #define CDC_DEVICE_CLASS                        0x02
 102
 103 #define CDC_INTERFACE_CLASS                     0x02
 104 #define CDC_INTERFACE_SUBCLASS                  0x06
 105
 106 #define LINEO_INTERFACE_CLASS                   0xff
 107
 108 #define LINEO_INTERFACE_SUBCLASS_SAFENET        0x01
 109 #define LINEO_SAFENET_CRC                       0x01
 110 #define LINEO_SAFENET_CRC_PADDED                0x02
 111
 112 #define LINEO_INTERFACE_SUBCLASS_SAFESERIAL     0x02
 113 #define LINEO_SAFESERIAL_CRC                    0x01
 114 #define LINEO_SAFESERIAL_CRC_PADDED             0x02
 115
 116
 117 #define MY_USB_DEVICE(vend, prod, dc, ic, isc) \
 118         .match_flags = USB_DEVICE_ID_MATCH_DEVICE | \
 119                        USB_DEVICE_ID_MATCH_DEV_CLASS | \
 120                        USB_DEVICE_ID_MATCH_INT_CLASS | \
 121                        USB_DEVICE_ID_MATCH_INT_SUBCLASS, \
 122         .idVendor = (vend), \
 123         .idProduct = (prod),\
 124         .bDeviceClass = (dc),\
 125         .bInterfaceClass = (ic), \
 126         .bInterfaceSubClass = (isc),
 127
 128 static struct usb_device_id id_table[] = {
 129         {MY_USB_DEVICE(0x49f, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Itsy */
 130         {MY_USB_DEVICE(0x3f0, 0x2101, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Calypso */
 131         {MY_USB_DEVICE(0x4dd, 0x8001, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Iris */
 132         {MY_USB_DEVICE(0x4dd, 0x8002, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Collie */
 133         {MY_USB_DEVICE(0x4dd, 0x8003, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Collie */
 134         {MY_USB_DEVICE(0x4dd, 0x8004, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Collie */
 135         {MY_USB_DEVICE(0x5f9, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Sharp tmp */
 136         {}                      /* terminating entry  */
 137 };
 138
 139 MODULE_DEVICE_TABLE(usb, id_table);
 140
 141 static const __u16 crc10_table[256] = {
 142         0x000, 0x233, 0x255, 0x066, 0x299, 0x0aa, 0x0cc, 0x2ff,
 143         0x301, 0x132, 0x154, 0x367, 0x198, 0x3ab, 0x3cd, 0x1fe,
 144         0x031, 0x202, 0x264, 0x057, 0x2a8, 0x09b, 0x0fd, 0x2ce,
 145         0x330, 0x103, 0x165, 0x356, 0x1a9, 0x39a, 0x3fc, 0x1cf,
 146         0x062, 0x251, 0x237, 0x004, 0x2fb, 0x0c8, 0x0ae, 0x29d,
 147         0x363, 0x150, 0x136, 0x305, 0x1fa, 0x3c9, 0x3af, 0x19c,
 148         0x053, 0x260, 0x206, 0x035, 0x2ca, 0x0f9, 0x09f, 0x2ac,
 149         0x352, 0x161, 0x107, 0x334, 0x1cb, 0x3f8, 0x39e, 0x1ad,
 150         0x0c4, 0x2f7, 0x291, 0x0a2, 0x25d, 0x06e, 0x008, 0x23b,
 151         0x3c5, 0x1f6, 0x190, 0x3a3, 0x15c, 0x36f, 0x309, 0x13a,
 152         0x0f5, 0x2c6, 0x2a0, 0x093, 0x26c, 0x05f, 0x039, 0x20a,
 153         0x3f4, 0x1c7, 0x1a1, 0x392, 0x16d, 0x35e, 0x338, 0x10b,
 154         0x0a6, 0x295, 0x2f3, 0x0c0, 0x23f, 0x00c, 0x06a, 0x259,
 155         0x3a7, 0x194, 0x1f2, 0x3c1, 0x13e, 0x30d, 0x36b, 0x158,
 156         0x097, 0x2a4, 0x2c2, 0x0f1, 0x20e, 0x03d, 0x05b, 0x268,
 157         0x396, 0x1a5, 0x1c3, 0x3f0, 0x10f, 0x33c, 0x35a, 0x169,
 158         0x188, 0x3bb, 0x3dd, 0x1ee, 0x311, 0x122, 0x144, 0x377,
 159         0x289, 0x0ba, 0x0dc, 0x2ef, 0x010, 0x223, 0x245, 0x076,
 160         0x1b9, 0x38a, 0x3ec, 0x1df, 0x320, 0x113, 0x175, 0x346,
 161         0x2b8, 0x08b, 0x0ed, 0x2de, 0x021, 0x212, 0x274, 0x047,
 162         0x1ea, 0x3d9, 0x3bf, 0x18c, 0x373, 0x140, 0x126, 0x315,
 163         0x2eb, 0x0d8, 0x0be, 0x28d, 0x072, 0x241, 0x227, 0x014,
 164         0x1db, 0x3e8, 0x38e, 0x1bd, 0x342, 0x171, 0x117, 0x324,
 165         0x2da, 0x0e9, 0x08f, 0x2bc, 0x043, 0x270, 0x216, 0x025,
 166         0x14c, 0x37f, 0x319, 0x12a, 0x3d5, 0x1e6, 0x180, 0x3b3,
 167         0x24d, 0x07e, 0x018, 0x22b, 0x0d4, 0x2e7, 0x281, 0x0b2,
 168         0x17d, 0x34e, 0x328, 0x11b, 0x3e4, 0x1d7, 0x1b1, 0x382,
 169         0x27c, 0x04f, 0x029, 0x21a, 0x0e5, 0x2d6, 0x2b0, 0x083,
 170         0x12e, 0x31d, 0x37b, 0x148, 0x3b7, 0x184, 0x1e2, 0x3d1,
 171         0x22f, 0x01c, 0x07a, 0x249, 0x0b6, 0x285, 0x2e3, 0x0d0,
 172         0x11f, 0x32c, 0x34a, 0x179, 0x386, 0x1b5, 0x1d3, 0x3e0,
 173         0x21e, 0x02d, 0x04b, 0x278, 0x087, 0x2b4, 0x2d2, 0x0e1,
 174 };
 175
 176 #define CRC10_INITFCS     0x000 /* Initial FCS value */
 177 #define CRC10_GOODFCS     0x000 /* Good final FCS value */
 178 #define CRC10_FCS(fcs, c) ((((fcs) << 8) & 0x3ff) ^ crc10_table[((fcs) >> 2) & 0xff] ^ (c))
 179
 180 /**
 181  * fcs_compute10 - memcpy and calculate 10 bit CRC across buffer
 182  * @sp: pointer to buffer
 183  * @len: number of bytes
 184  * @fcs: starting FCS
 185  *
 186  * Perform a memcpy and calculate fcs using ppp 10bit CRC algorithm. Return
 187  * new 10 bit FCS.
 188  */
 189 static __u16 __inline__ fcs_compute10(unsigned char *sp, int len, __u16 fcs)
 190 {
 191         for (; len-- > 0; fcs = CRC10_FCS(fcs, *sp++));
 192         return fcs;
 193 }
 194
 195 static void safe_process_read_urb(struct urb *urb)
 196 {
 197         struct usb_serial_port *port = urb->context;
 198         unsigned char *data = urb->transfer_buffer;
 199         unsigned char length = urb->actual_length;
 200         int actual_length;
 201         __u16 fcs;
 202
 203         if (!length)
 204                 return;
 205
 206         if (!safe)
 207                 goto out;
 208
 209         fcs = fcs_compute10(data, length, CRC10_INITFCS);
 210         if (fcs) {
 211                 dev_err(&port->dev, "%s - bad CRC %x\n", __func__, fcs);
 212                 return;
 213         }
 214
 215         actual_length = data[length - 2] >> 2;
 216         if (actual_length > (length - 2)) {
 217                 dev_err(&port->dev, "%s - inconsistent lengths %d:%d\n",
 218                                 __func__, actual_length, length);
 219                 return;
 220         }
 221         dev_info(&urb->dev->dev, "%s - actual: %d\n", __func__, actual_length);
 222         length = actual_length;
 223 out:
 224         tty_insert_flip_string(&port->port, data, length);
 225         tty_flip_buffer_push(&port->port);
 226 }
 227
 228 static int safe_prepare_write_buffer(struct usb_serial_port *port,
 229                                                 void *dest, size_t size)
 230 {
 231         unsigned char *buf = dest;
 232         int count;
 233         int trailer_len;
 234         int pkt_len;
 235         __u16 fcs;
 236
 237         trailer_len = safe ? 2 : 0;
 238
 239         count = kfifo_out_locked(&port->write_fifo, buf, size - trailer_len,
 240                                                                 &port->lock);
 241         if (!safe)
 242                 return count;
 243
 244         /* pad if necessary */
 245         if (padded) {
 246                 pkt_len = size;
 247                 memset(buf + count, '0', pkt_len - count - trailer_len);
 248         } else {
 249                 pkt_len = count + trailer_len;
 250         }
 251
 252         /* set count */
 253         buf[pkt_len - 2] = count << 2;
 254         buf[pkt_len - 1] = 0;
 255
 256         /* compute fcs and insert into trailer */
 257         fcs = fcs_compute10(buf, pkt_len, CRC10_INITFCS);
 258         buf[pkt_len - 2] |= fcs >> 8;
 259         buf[pkt_len - 1] |= fcs & 0xff;
 260
 261         return pkt_len;
 262 }
 263
 264 static int safe_startup(struct usb_serial *serial)
 265 {
 266         struct usb_interface_descriptor *desc;
 267
 268         if (serial->dev->descriptor.bDeviceClass != CDC_DEVICE_CLASS)
 269                 return -ENODEV;
 270
 271         desc = &serial->interface->cur_altsetting->desc;
 272
 273         if (desc->bInterfaceClass != LINEO_INTERFACE_CLASS)
 274                 return -ENODEV;
 275         if (desc->bInterfaceSubClass != LINEO_INTERFACE_SUBCLASS_SAFESERIAL)
 276                 return -ENODEV;
 277
 278         switch (desc->bInterfaceProtocol) {
 279         case LINEO_SAFESERIAL_CRC:
 280                 break;
 281         case LINEO_SAFESERIAL_CRC_PADDED:
 282                 padded = 1;
 283                 break;
 284         default:
 285                 return -EINVAL;
 286         }
 287         return 0;
 288 }
 289
 290 static struct usb_serial_driver safe_device = {
 291         .driver = {
 292                 .owner =        THIS_MODULE,
 293                 .name =         "safe_serial",
 294         },
 295         .id_table =             id_table,
 296         .num_ports =            1,
 297         .process_read_urb =     safe_process_read_urb,
 298         .prepare_write_buffer = safe_prepare_write_buffer,
 299         .attach =               safe_startup,
 300 };
 301
 302 static struct usb_serial_driver * const serial_drivers[] = {
 303         &safe_device, NULL
 304 };
 305
 306 module_usb_serial_driver(serial_drivers, id_table);