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, '0', 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