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 .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