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); 307