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); 306