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 * This program is free software; you can redistribute it and/or modify 10 * it under the terms of the GNU General Public License as published by 11 * the Free Software Foundation; either version 2 of the License, or 12 * (at your option) any later version. 13 * 14 * By: 15 * Stuart Lynne <sl@lineo.com>, Tom Rushworth <tbr@lineo.com> 16 */ 17 18 /* 19 * The encapsultaion is designed to overcome difficulties with some USB 20 * hardware. 21 * 22 * While the USB protocol has a CRC over the data while in transit, i.e. while 23 * being carried over the bus, there is no end to end protection. If the 24 * hardware has any problems getting the data into or out of the USB transmit 25 * and receive FIFO's then data can be lost. 26 * 27 * This protocol adds a two byte trailer to each USB packet to specify the 28 * number of bytes of valid data and a 10 bit CRC that will allow the receiver 29 * to verify that the entire USB packet was received without error. 30 * 31 * Because in this case the sender and receiver are the class and function 32 * drivers there is now end to end protection. 33 * 34 * There is an additional option that can be used to force all transmitted 35 * packets to be padded to the maximum packet size. This provides a work 36 * around for some devices which have problems with small USB packets. 37 * 38 * Assuming a packetsize of N: 39 * 40 * 0..N-2 data and optional padding 41 * 42 * N-2 bits 7-2 - number of bytes of valid data 43 * bits 1-0 top two bits of 10 bit CRC 44 * N-1 bottom 8 bits of 10 bit CRC 45 * 46 * 47 * | Data Length | 10 bit CRC | 48 * + 7 . 6 . 5 . 4 . 3 . 2 . 1 . 0 | 7 . 6 . 5 . 4 . 3 . 2 . 1 . 0 + 49 * 50 * The 10 bit CRC is computed across the sent data, followed by the trailer 51 * with the length set and the CRC set to zero. The CRC is then OR'd into 52 * the trailer. 53 * 54 * When received a 10 bit CRC is computed over the entire frame including 55 * the trailer and should be equal to zero. 56 * 57 * Two module parameters are used to control the encapsulation, if both are 58 * turned of the module works as a simple serial device with NO 59 * encapsulation. 60 * 61 * See linux/drivers/usbd/serial_fd for a device function driver 62 * implementation of this. 63 * 64 */ 65 66 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 67 68 #include <linux/kernel.h> 69 #include <linux/errno.h> 70 #include <linux/gfp.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 static bool safe = true; 81 static bool padded = IS_ENABLED(CONFIG_USB_SERIAL_SAFE_PADDED); 82 83 #define DRIVER_AUTHOR "sl@lineo.com, tbr@lineo.com, Johan Hovold <jhovold@gmail.com>" 84 #define DRIVER_DESC "USB Safe Encapsulated Serial" 85 86 MODULE_AUTHOR(DRIVER_AUTHOR); 87 MODULE_DESCRIPTION(DRIVER_DESC); 88 MODULE_LICENSE("GPL"); 89 90 module_param(safe, bool, 0); 91 MODULE_PARM_DESC(safe, "Turn Safe Encapsulation On/Off"); 92 93 module_param(padded, bool, 0); 94 MODULE_PARM_DESC(padded, "Pad to full wMaxPacketSize On/Off"); 95 96 #define CDC_DEVICE_CLASS 0x02 97 98 #define CDC_INTERFACE_CLASS 0x02 99 #define CDC_INTERFACE_SUBCLASS 0x06 100 101 #define LINEO_INTERFACE_CLASS 0xff 102 103 #define LINEO_INTERFACE_SUBCLASS_SAFENET 0x01 104 #define LINEO_SAFENET_CRC 0x01 105 #define LINEO_SAFENET_CRC_PADDED 0x02 106 107 #define LINEO_INTERFACE_SUBCLASS_SAFESERIAL 0x02 108 #define LINEO_SAFESERIAL_CRC 0x01 109 #define LINEO_SAFESERIAL_CRC_PADDED 0x02 110 111 112 #define MY_USB_DEVICE(vend, prod, dc, ic, isc) \ 113 .match_flags = USB_DEVICE_ID_MATCH_DEVICE | \ 114 USB_DEVICE_ID_MATCH_DEV_CLASS | \ 115 USB_DEVICE_ID_MATCH_INT_CLASS | \ 116 USB_DEVICE_ID_MATCH_INT_SUBCLASS, \ 117 .idVendor = (vend), \ 118 .idProduct = (prod),\ 119 .bDeviceClass = (dc),\ 120 .bInterfaceClass = (ic), \ 121 .bInterfaceSubClass = (isc), 122 123 static const struct usb_device_id id_table[] = { 124 {MY_USB_DEVICE(0x49f, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Itsy */ 125 {MY_USB_DEVICE(0x3f0, 0x2101, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Calypso */ 126 {MY_USB_DEVICE(0x4dd, 0x8001, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Iris */ 127 {MY_USB_DEVICE(0x4dd, 0x8002, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Collie */ 128 {MY_USB_DEVICE(0x4dd, 0x8003, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Collie */ 129 {MY_USB_DEVICE(0x4dd, 0x8004, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Collie */ 130 {MY_USB_DEVICE(0x5f9, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Sharp tmp */ 131 {} /* terminating entry */ 132 }; 133 134 MODULE_DEVICE_TABLE(usb, id_table); 135 136 static const __u16 crc10_table[256] = { 137 0x000, 0x233, 0x255, 0x066, 0x299, 0x0aa, 0x0cc, 0x2ff, 138 0x301, 0x132, 0x154, 0x367, 0x198, 0x3ab, 0x3cd, 0x1fe, 139 0x031, 0x202, 0x264, 0x057, 0x2a8, 0x09b, 0x0fd, 0x2ce, 140 0x330, 0x103, 0x165, 0x356, 0x1a9, 0x39a, 0x3fc, 0x1cf, 141 0x062, 0x251, 0x237, 0x004, 0x2fb, 0x0c8, 0x0ae, 0x29d, 142 0x363, 0x150, 0x136, 0x305, 0x1fa, 0x3c9, 0x3af, 0x19c, 143 0x053, 0x260, 0x206, 0x035, 0x2ca, 0x0f9, 0x09f, 0x2ac, 144 0x352, 0x161, 0x107, 0x334, 0x1cb, 0x3f8, 0x39e, 0x1ad, 145 0x0c4, 0x2f7, 0x291, 0x0a2, 0x25d, 0x06e, 0x008, 0x23b, 146 0x3c5, 0x1f6, 0x190, 0x3a3, 0x15c, 0x36f, 0x309, 0x13a, 147 0x0f5, 0x2c6, 0x2a0, 0x093, 0x26c, 0x05f, 0x039, 0x20a, 148 0x3f4, 0x1c7, 0x1a1, 0x392, 0x16d, 0x35e, 0x338, 0x10b, 149 0x0a6, 0x295, 0x2f3, 0x0c0, 0x23f, 0x00c, 0x06a, 0x259, 150 0x3a7, 0x194, 0x1f2, 0x3c1, 0x13e, 0x30d, 0x36b, 0x158, 151 0x097, 0x2a4, 0x2c2, 0x0f1, 0x20e, 0x03d, 0x05b, 0x268, 152 0x396, 0x1a5, 0x1c3, 0x3f0, 0x10f, 0x33c, 0x35a, 0x169, 153 0x188, 0x3bb, 0x3dd, 0x1ee, 0x311, 0x122, 0x144, 0x377, 154 0x289, 0x0ba, 0x0dc, 0x2ef, 0x010, 0x223, 0x245, 0x076, 155 0x1b9, 0x38a, 0x3ec, 0x1df, 0x320, 0x113, 0x175, 0x346, 156 0x2b8, 0x08b, 0x0ed, 0x2de, 0x021, 0x212, 0x274, 0x047, 157 0x1ea, 0x3d9, 0x3bf, 0x18c, 0x373, 0x140, 0x126, 0x315, 158 0x2eb, 0x0d8, 0x0be, 0x28d, 0x072, 0x241, 0x227, 0x014, 159 0x1db, 0x3e8, 0x38e, 0x1bd, 0x342, 0x171, 0x117, 0x324, 160 0x2da, 0x0e9, 0x08f, 0x2bc, 0x043, 0x270, 0x216, 0x025, 161 0x14c, 0x37f, 0x319, 0x12a, 0x3d5, 0x1e6, 0x180, 0x3b3, 162 0x24d, 0x07e, 0x018, 0x22b, 0x0d4, 0x2e7, 0x281, 0x0b2, 163 0x17d, 0x34e, 0x328, 0x11b, 0x3e4, 0x1d7, 0x1b1, 0x382, 164 0x27c, 0x04f, 0x029, 0x21a, 0x0e5, 0x2d6, 0x2b0, 0x083, 165 0x12e, 0x31d, 0x37b, 0x148, 0x3b7, 0x184, 0x1e2, 0x3d1, 166 0x22f, 0x01c, 0x07a, 0x249, 0x0b6, 0x285, 0x2e3, 0x0d0, 167 0x11f, 0x32c, 0x34a, 0x179, 0x386, 0x1b5, 0x1d3, 0x3e0, 168 0x21e, 0x02d, 0x04b, 0x278, 0x087, 0x2b4, 0x2d2, 0x0e1, 169 }; 170 171 #define CRC10_INITFCS 0x000 /* Initial FCS value */ 172 #define CRC10_GOODFCS 0x000 /* Good final FCS value */ 173 #define CRC10_FCS(fcs, c) ((((fcs) << 8) & 0x3ff) ^ crc10_table[((fcs) >> 2) & 0xff] ^ (c)) 174 175 /** 176 * fcs_compute10 - memcpy and calculate 10 bit CRC across buffer 177 * @sp: pointer to buffer 178 * @len: number of bytes 179 * @fcs: starting FCS 180 * 181 * Perform a memcpy and calculate fcs using ppp 10bit CRC algorithm. Return 182 * new 10 bit FCS. 183 */ 184 static inline __u16 fcs_compute10(unsigned char *sp, int len, __u16 fcs) 185 { 186 for (; len-- > 0; fcs = CRC10_FCS(fcs, *sp++)); 187 return fcs; 188 } 189 190 static void safe_process_read_urb(struct urb *urb) 191 { 192 struct usb_serial_port *port = urb->context; 193 unsigned char *data = urb->transfer_buffer; 194 unsigned char length = urb->actual_length; 195 int actual_length; 196 __u16 fcs; 197 198 if (!length) 199 return; 200 201 if (!safe) 202 goto out; 203 204 if (length < 2) { 205 dev_err(&port->dev, "malformed packet\n"); 206 return; 207 } 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 = true; 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