drivers/usb/serial/safe_serial.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  * Safe Encapsulated USB Serial Driver
   4  *
   5  *      Copyright (C) 2010 Johan Hovold <jhovold@gmail.com>
   6  *      Copyright (C) 2001 Lineo
   7  *      Copyright (C) 2001 Hewlett-Packard
   8  *
   9  * By:
  10  *      Stuart Lynne <sl@lineo.com>, Tom Rushworth <tbr@lineo.com>
  11  */
  12
  13 /*
  14  * The encapsultaion is designed to overcome difficulties with some USB
  15  * hardware.
  16  *
  17  * While the USB protocol has a CRC over the data while in transit, i.e. while
  18  * being carried over the bus, there is no end to end protection. If the
  19  * hardware has any problems getting the data into or out of the USB transmit
  20  * and receive FIFO's then data can be lost.
  21  *
  22  * This protocol adds a two byte trailer to each USB packet to specify the
  23  * number of bytes of valid data and a 10 bit CRC that will allow the receiver
  24  * to verify that the entire USB packet was received without error.
  25  *
  26  * Because in this case the sender and receiver are the class and function
  27  * drivers there is now end to end protection.
  28  *
  29  * There is an additional option that can be used to force all transmitted
  30  * packets to be padded to the maximum packet size. This provides a work
  31  * around for some devices which have problems with small USB packets.
  32  *
  33  * Assuming a packetsize of N:
  34  *
  35  *      0..N-2  data and optional padding
  36  *
  37  *      N-2     bits 7-2 - number of bytes of valid data
  38  *              bits 1-0 top two bits of 10 bit CRC
  39  *      N-1     bottom 8 bits of 10 bit CRC
  40  *
  41  *
  42  *      | Data Length       | 10 bit CRC                                |
  43  *      + 7 . 6 . 5 . 4 . 3 . 2 . 1 . 0 | 7 . 6 . 5 . 4 . 3 . 2 . 1 . 0 +
  44  *
  45  * The 10 bit CRC is computed across the sent data, followed by the trailer
  46  * with the length set and the CRC set to zero. The CRC is then OR'd into
  47  * the trailer.
  48  *
  49  * When received a 10 bit CRC is computed over the entire frame including
  50  * the trailer and should be equal to zero.
  51  *
  52  * Two module parameters are used to control the encapsulation, if both are
  53  * turned of the module works as a simple serial device with NO
  54  * encapsulation.
  55  *
  56  * See linux/drivers/usbd/serial_fd for a device function driver
  57  * implementation of this.
  58  *
  59  */
  60
  61 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  62
  63 #include <linux/kernel.h>
  64 #include <linux/errno.h>
  65 #include <linux/gfp.h>
  66 #include <linux/tty.h>
  67 #include <linux/tty_driver.h>
  68 #include <linux/tty_flip.h>
  69 #include <linux/module.h>
  70 #include <linux/spinlock.h>
  71 #include <linux/uaccess.h>
  72 #include <linux/usb.h>
  73 #include <linux/usb/serial.h>
  74
  75 static bool safe = true;
  76 static bool padded = IS_ENABLED(CONFIG_USB_SERIAL_SAFE_PADDED);
  77
  78 #define DRIVER_AUTHOR "sl@lineo.com, tbr@lineo.com, Johan Hovold <jhovold@gmail.com>"
  79 #define DRIVER_DESC "USB Safe Encapsulated Serial"
  80
  81 MODULE_AUTHOR(DRIVER_AUTHOR);
  82 MODULE_DESCRIPTION(DRIVER_DESC);
  83 MODULE_LICENSE("GPL");
  84
  85 module_param(safe, bool, 0);
  86 MODULE_PARM_DESC(safe, "Turn Safe Encapsulation On/Off");
  87
  88 module_param(padded, bool, 0);
  89 MODULE_PARM_DESC(padded, "Pad to full wMaxPacketSize On/Off");
  90
  91 #define CDC_DEVICE_CLASS                        0x02
  92
  93 #define CDC_INTERFACE_CLASS                     0x02
  94 #define CDC_INTERFACE_SUBCLASS                  0x06
  95
  96 #define LINEO_INTERFACE_CLASS                   0xff
  97
  98 #define LINEO_INTERFACE_SUBCLASS_SAFENET        0x01
  99 #define LINEO_SAFENET_CRC                       0x01
 100 #define LINEO_SAFENET_CRC_PADDED                0x02
 101
 102 #define LINEO_INTERFACE_SUBCLASS_SAFESERIAL     0x02
 103 #define LINEO_SAFESERIAL_CRC                    0x01
 104 #define LINEO_SAFESERIAL_CRC_PADDED             0x02
 105
 106
 107 #define MY_USB_DEVICE(vend, prod, dc, ic, isc) \
 108         .match_flags = USB_DEVICE_ID_MATCH_DEVICE | \
 109                        USB_DEVICE_ID_MATCH_DEV_CLASS | \
 110                        USB_DEVICE_ID_MATCH_INT_CLASS | \
 111                        USB_DEVICE_ID_MATCH_INT_SUBCLASS, \
 112         .idVendor = (vend), \
 113         .idProduct = (prod),\
 114         .bDeviceClass = (dc),\
 115         .bInterfaceClass = (ic), \
 116         .bInterfaceSubClass = (isc),
 117
 118 static const struct usb_device_id id_table[] = {
 119         {MY_USB_DEVICE(0x49f, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Itsy */
 120         {MY_USB_DEVICE(0x3f0, 0x2101, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Calypso */
 121         {MY_USB_DEVICE(0x4dd, 0x8001, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Iris */
 122         {MY_USB_DEVICE(0x4dd, 0x8002, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Collie */
 123         {MY_USB_DEVICE(0x4dd, 0x8003, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Collie */
 124         {MY_USB_DEVICE(0x4dd, 0x8004, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Collie */
 125         {MY_USB_DEVICE(0x5f9, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},   /* Sharp tmp */
 126         {}                      /* terminating entry  */
 127 };
 128
 129 MODULE_DEVICE_TABLE(usb, id_table);
 130
 131 static const __u16 crc10_table[256] = {
 132         0x000, 0x233, 0x255, 0x066, 0x299, 0x0aa, 0x0cc, 0x2ff,
 133         0x301, 0x132, 0x154, 0x367, 0x198, 0x3ab, 0x3cd, 0x1fe,
 134         0x031, 0x202, 0x264, 0x057, 0x2a8, 0x09b, 0x0fd, 0x2ce,
 135         0x330, 0x103, 0x165, 0x356, 0x1a9, 0x39a, 0x3fc, 0x1cf,
 136         0x062, 0x251, 0x237, 0x004, 0x2fb, 0x0c8, 0x0ae, 0x29d,
 137         0x363, 0x150, 0x136, 0x305, 0x1fa, 0x3c9, 0x3af, 0x19c,
 138         0x053, 0x260, 0x206, 0x035, 0x2ca, 0x0f9, 0x09f, 0x2ac,
 139         0x352, 0x161, 0x107, 0x334, 0x1cb, 0x3f8, 0x39e, 0x1ad,
 140         0x0c4, 0x2f7, 0x291, 0x0a2, 0x25d, 0x06e, 0x008, 0x23b,
 141         0x3c5, 0x1f6, 0x190, 0x3a3, 0x15c, 0x36f, 0x309, 0x13a,
 142         0x0f5, 0x2c6, 0x2a0, 0x093, 0x26c, 0x05f, 0x039, 0x20a,
 143         0x3f4, 0x1c7, 0x1a1, 0x392, 0x16d, 0x35e, 0x338, 0x10b,
 144         0x0a6, 0x295, 0x2f3, 0x0c0, 0x23f, 0x00c, 0x06a, 0x259,
 145         0x3a7, 0x194, 0x1f2, 0x3c1, 0x13e, 0x30d, 0x36b, 0x158,
 146         0x097, 0x2a4, 0x2c2, 0x0f1, 0x20e, 0x03d, 0x05b, 0x268,
 147         0x396, 0x1a5, 0x1c3, 0x3f0, 0x10f, 0x33c, 0x35a, 0x169,
 148         0x188, 0x3bb, 0x3dd, 0x1ee, 0x311, 0x122, 0x144, 0x377,
 149         0x289, 0x0ba, 0x0dc, 0x2ef, 0x010, 0x223, 0x245, 0x076,
 150         0x1b9, 0x38a, 0x3ec, 0x1df, 0x320, 0x113, 0x175, 0x346,
 151         0x2b8, 0x08b, 0x0ed, 0x2de, 0x021, 0x212, 0x274, 0x047,
 152         0x1ea, 0x3d9, 0x3bf, 0x18c, 0x373, 0x140, 0x126, 0x315,
 153         0x2eb, 0x0d8, 0x0be, 0x28d, 0x072, 0x241, 0x227, 0x014,
 154         0x1db, 0x3e8, 0x38e, 0x1bd, 0x342, 0x171, 0x117, 0x324,
 155         0x2da, 0x0e9, 0x08f, 0x2bc, 0x043, 0x270, 0x216, 0x025,
 156         0x14c, 0x37f, 0x319, 0x12a, 0x3d5, 0x1e6, 0x180, 0x3b3,
 157         0x24d, 0x07e, 0x018, 0x22b, 0x0d4, 0x2e7, 0x281, 0x0b2,
 158         0x17d, 0x34e, 0x328, 0x11b, 0x3e4, 0x1d7, 0x1b1, 0x382,
 159         0x27c, 0x04f, 0x029, 0x21a, 0x0e5, 0x2d6, 0x2b0, 0x083,
 160         0x12e, 0x31d, 0x37b, 0x148, 0x3b7, 0x184, 0x1e2, 0x3d1,
 161         0x22f, 0x01c, 0x07a, 0x249, 0x0b6, 0x285, 0x2e3, 0x0d0,
 162         0x11f, 0x32c, 0x34a, 0x179, 0x386, 0x1b5, 0x1d3, 0x3e0,
 163         0x21e, 0x02d, 0x04b, 0x278, 0x087, 0x2b4, 0x2d2, 0x0e1,
 164 };
 165
 166 #define CRC10_INITFCS     0x000 /* Initial FCS value */
 167 #define CRC10_GOODFCS     0x000 /* Good final FCS value */
 168 #define CRC10_FCS(fcs, c) ((((fcs) << 8) & 0x3ff) ^ crc10_table[((fcs) >> 2) & 0xff] ^ (c))
 169
 170 /**
 171  * fcs_compute10 - memcpy and calculate 10 bit CRC across buffer
 172  * @sp: pointer to buffer
 173  * @len: number of bytes
 174  * @fcs: starting FCS
 175  *
 176  * Perform a memcpy and calculate fcs using ppp 10bit CRC algorithm. Return
 177  * new 10 bit FCS.
 178  */
 179 static inline __u16 fcs_compute10(unsigned char *sp, int len, __u16 fcs)
 180 {
 181         for (; len-- > 0; fcs = CRC10_FCS(fcs, *sp++));
 182         return fcs;
 183 }
 184
 185 static void safe_process_read_urb(struct urb *urb)
 186 {
 187         struct usb_serial_port *port = urb->context;
 188         unsigned char *data = urb->transfer_buffer;
 189         unsigned char length = urb->actual_length;
 190         int actual_length;
 191         __u16 fcs;
 192
 193         if (!length)
 194                 return;
 195
 196         if (!safe)
 197                 goto out;
 198
 199         if (length < 2) {
 200                 dev_err(&port->dev, "malformed packet\n");
 201                 return;
 202         }
 203
 204         fcs = fcs_compute10(data, length, CRC10_INITFCS);
 205         if (fcs) {
 206                 dev_err(&port->dev, "%s - bad CRC %x\n", __func__, fcs);
 207                 return;
 208         }
 209
 210         actual_length = data[length - 2] >> 2;
 211         if (actual_length > (length - 2)) {
 212                 dev_err(&port->dev, "%s - inconsistent lengths %d:%d\n",
 213                                 __func__, actual_length, length);
 214                 return;
 215         }
 216         dev_info(&urb->dev->dev, "%s - actual: %d\n", __func__, actual_length);
 217         length = actual_length;
 218 out:
 219         tty_insert_flip_string(&port->port, data, length);
 220         tty_flip_buffer_push(&port->port);
 221 }
 222
 223 static int safe_prepare_write_buffer(struct usb_serial_port *port,
 224                                                 void *dest, size_t size)
 225 {
 226         unsigned char *buf = dest;
 227         int count;
 228         int trailer_len;
 229         int pkt_len;
 230         __u16 fcs;
 231
 232         trailer_len = safe ? 2 : 0;
 233
 234         count = kfifo_out_locked(&port->write_fifo, buf, size - trailer_len,
 235                                                                 &port->lock);
 236         if (!safe)
 237                 return count;
 238
 239         /* pad if necessary */
 240         if (padded) {
 241                 pkt_len = size;
 242                 memset(buf + count, '0', pkt_len - count - trailer_len);
 243         } else {
 244                 pkt_len = count + trailer_len;
 245         }
 246
 247         /* set count */
 248         buf[pkt_len - 2] = count << 2;
 249         buf[pkt_len - 1] = 0;
 250
 251         /* compute fcs and insert into trailer */
 252         fcs = fcs_compute10(buf, pkt_len, CRC10_INITFCS);
 253         buf[pkt_len - 2] |= fcs >> 8;
 254         buf[pkt_len - 1] |= fcs & 0xff;
 255
 256         return pkt_len;
 257 }
 258
 259 static int safe_startup(struct usb_serial *serial)
 260 {
 261         struct usb_interface_descriptor *desc;
 262
 263         if (serial->dev->descriptor.bDeviceClass != CDC_DEVICE_CLASS)
 264                 return -ENODEV;
 265
 266         desc = &serial->interface->cur_altsetting->desc;
 267
 268         if (desc->bInterfaceClass != LINEO_INTERFACE_CLASS)
 269                 return -ENODEV;
 270         if (desc->bInterfaceSubClass != LINEO_INTERFACE_SUBCLASS_SAFESERIAL)
 271                 return -ENODEV;
 272
 273         switch (desc->bInterfaceProtocol) {
 274         case LINEO_SAFESERIAL_CRC:
 275                 break;
 276         case LINEO_SAFESERIAL_CRC_PADDED:
 277                 padded = true;
 278                 break;
 279         default:
 280                 return -EINVAL;
 281         }
 282         return 0;
 283 }
 284
 285 static struct usb_serial_driver safe_device = {
 286         .driver = {
 287                 .owner =        THIS_MODULE,
 288                 .name =         "safe_serial",
 289         },
 290         .id_table =             id_table,
 291         .num_ports =            1,
 292         .process_read_urb =     safe_process_read_urb,
 293         .prepare_write_buffer = safe_prepare_write_buffer,
 294         .attach =               safe_startup,
 295 };
 296
 297 static struct usb_serial_driver * const serial_drivers[] = {
 298         &safe_device, NULL
 299 };
 300
 301 module_usb_serial_driver(serial_drivers, id_table);