drivers/usb/serial/safe_serial.c - third_party/linux - Git at Google

 /*
  * Safe Encapsulated USB Serial Driver
  *
  *      Copyright (C) 2010 Johan Hovold <jhovold@gmail.com>
  *      Copyright (C) 2001 Lineo
  *      Copyright (C) 2001 Hewlett-Packard
  *
  *	This program is free software; you can redistribute it and/or modify
  *	it under the terms of the GNU General Public License as published by
  *	the Free Software Foundation; either version 2 of the License, or
  *	(at your option) any later version.
  *
  * By:
  *      Stuart Lynne <sl@lineo.com>, Tom Rushworth <tbr@lineo.com>
  */

 /*
  * The encapsultaion is designed to overcome difficulties with some USB
  * hardware.
  *
  * While the USB protocol has a CRC over the data while in transit, i.e. while
  * being carried over the bus, there is no end to end protection. If the
  * hardware has any problems getting the data into or out of the USB transmit
  * and receive FIFO's then data can be lost.
  *
  * This protocol adds a two byte trailer to each USB packet to specify the
  * number of bytes of valid data and a 10 bit CRC that will allow the receiver
  * to verify that the entire USB packet was received without error.
  *
  * Because in this case the sender and receiver are the class and function
  * drivers there is now end to end protection.
  *
  * There is an additional option that can be used to force all transmitted
  * packets to be padded to the maximum packet size. This provides a work
  * around for some devices which have problems with small USB packets.
  *
  * Assuming a packetsize of N:
  *
  *      0..N-2  data and optional padding
  *
  *      N-2     bits 7-2 - number of bytes of valid data
  *              bits 1-0 top two bits of 10 bit CRC
  *      N-1     bottom 8 bits of 10 bit CRC
  *
  *
  *      | Data Length       | 10 bit CRC                                |
  *      + 7 . 6 . 5 . 4 . 3 . 2 . 1 . 0 | 7 . 6 . 5 . 4 . 3 . 2 . 1 . 0 +
  *
  * The 10 bit CRC is computed across the sent data, followed by the trailer
  * with the length set and the CRC set to zero. The CRC is then OR'd into
  * the trailer.
  *
  * When received a 10 bit CRC is computed over the entire frame including
  * the trailer and should be equal to zero.
  *
  * Two module parameters are used to control the encapsulation, if both are
  * turned of the module works as a simple serial device with NO
  * encapsulation.
  *
  * See linux/drivers/usbd/serial_fd for a device function driver
  * implementation of this.
  *
  */

 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/gfp.h>
 #include <linux/tty.h>
 #include <linux/tty_driver.h>
 #include <linux/tty_flip.h>
 #include <linux/module.h>
 #include <linux/spinlock.h>
 #include <linux/uaccess.h>
 #include <linux/usb.h>
 #include <linux/usb/serial.h>

 static bool safe = true;
 static bool padded = IS_ENABLED(CONFIG_USB_SERIAL_SAFE_PADDED);

 #define DRIVER_AUTHOR "sl@lineo.com, tbr@lineo.com, Johan Hovold <jhovold@gmail.com>"
 #define DRIVER_DESC "USB Safe Encapsulated Serial"

 MODULE_AUTHOR(DRIVER_AUTHOR);
 MODULE_DESCRIPTION(DRIVER_DESC);
 MODULE_LICENSE("GPL");

 module_param(safe, bool, 0);
 MODULE_PARM_DESC(safe, "Turn Safe Encapsulation On/Off");

 module_param(padded, bool, 0);
 MODULE_PARM_DESC(padded, "Pad to full wMaxPacketSize On/Off");

 #define CDC_DEVICE_CLASS                        0x02

 #define CDC_INTERFACE_CLASS                     0x02
 #define CDC_INTERFACE_SUBCLASS                  0x06

 #define LINEO_INTERFACE_CLASS                   0xff

 #define LINEO_INTERFACE_SUBCLASS_SAFENET        0x01
 #define LINEO_SAFENET_CRC                       0x01
 #define LINEO_SAFENET_CRC_PADDED                0x02

 #define LINEO_INTERFACE_SUBCLASS_SAFESERIAL     0x02
 #define LINEO_SAFESERIAL_CRC                    0x01
 #define LINEO_SAFESERIAL_CRC_PADDED             0x02


 #define MY_USB_DEVICE(vend, prod, dc, ic, isc) \
 	.match_flags = USB_DEVICE_ID_MATCH_DEVICE | \
 		       USB_DEVICE_ID_MATCH_DEV_CLASS | \
 		       USB_DEVICE_ID_MATCH_INT_CLASS | \
 		       USB_DEVICE_ID_MATCH_INT_SUBCLASS, \
 	.idVendor = (vend), \
 	.idProduct = (prod),\
 	.bDeviceClass = (dc),\
 	.bInterfaceClass = (ic), \
 	.bInterfaceSubClass = (isc),

 static const struct usb_device_id id_table[] = {
 	{MY_USB_DEVICE(0x49f, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Itsy */
 	{MY_USB_DEVICE(0x3f0, 0x2101, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Calypso */
 	{MY_USB_DEVICE(0x4dd, 0x8001, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Iris */
 	{MY_USB_DEVICE(0x4dd, 0x8002, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Collie */
 	{MY_USB_DEVICE(0x4dd, 0x8003, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Collie */
 	{MY_USB_DEVICE(0x4dd, 0x8004, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Collie */
 	{MY_USB_DEVICE(0x5f9, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},	/* Sharp tmp */
 	{}			/* terminating entry  */
 };

 MODULE_DEVICE_TABLE(usb, id_table);

 static const __u16 crc10_table[256] = {
 	0x000, 0x233, 0x255, 0x066, 0x299, 0x0aa, 0x0cc, 0x2ff,
 	0x301, 0x132, 0x154, 0x367, 0x198, 0x3ab, 0x3cd, 0x1fe,
 	0x031, 0x202, 0x264, 0x057, 0x2a8, 0x09b, 0x0fd, 0x2ce,
 	0x330, 0x103, 0x165, 0x356, 0x1a9, 0x39a, 0x3fc, 0x1cf,
 	0x062, 0x251, 0x237, 0x004, 0x2fb, 0x0c8, 0x0ae, 0x29d,
 	0x363, 0x150, 0x136, 0x305, 0x1fa, 0x3c9, 0x3af, 0x19c,
 	0x053, 0x260, 0x206, 0x035, 0x2ca, 0x0f9, 0x09f, 0x2ac,
 	0x352, 0x161, 0x107, 0x334, 0x1cb, 0x3f8, 0x39e, 0x1ad,
 	0x0c4, 0x2f7, 0x291, 0x0a2, 0x25d, 0x06e, 0x008, 0x23b,
 	0x3c5, 0x1f6, 0x190, 0x3a3, 0x15c, 0x36f, 0x309, 0x13a,
 	0x0f5, 0x2c6, 0x2a0, 0x093, 0x26c, 0x05f, 0x039, 0x20a,
 	0x3f4, 0x1c7, 0x1a1, 0x392, 0x16d, 0x35e, 0x338, 0x10b,
 	0x0a6, 0x295, 0x2f3, 0x0c0, 0x23f, 0x00c, 0x06a, 0x259,
 	0x3a7, 0x194, 0x1f2, 0x3c1, 0x13e, 0x30d, 0x36b, 0x158,
 	0x097, 0x2a4, 0x2c2, 0x0f1, 0x20e, 0x03d, 0x05b, 0x268,
 	0x396, 0x1a5, 0x1c3, 0x3f0, 0x10f, 0x33c, 0x35a, 0x169,
 	0x188, 0x3bb, 0x3dd, 0x1ee, 0x311, 0x122, 0x144, 0x377,
 	0x289, 0x0ba, 0x0dc, 0x2ef, 0x010, 0x223, 0x245, 0x076,
 	0x1b9, 0x38a, 0x3ec, 0x1df, 0x320, 0x113, 0x175, 0x346,
 	0x2b8, 0x08b, 0x0ed, 0x2de, 0x021, 0x212, 0x274, 0x047,
 	0x1ea, 0x3d9, 0x3bf, 0x18c, 0x373, 0x140, 0x126, 0x315,
 	0x2eb, 0x0d8, 0x0be, 0x28d, 0x072, 0x241, 0x227, 0x014,
 	0x1db, 0x3e8, 0x38e, 0x1bd, 0x342, 0x171, 0x117, 0x324,
 	0x2da, 0x0e9, 0x08f, 0x2bc, 0x043, 0x270, 0x216, 0x025,
 	0x14c, 0x37f, 0x319, 0x12a, 0x3d5, 0x1e6, 0x180, 0x3b3,
 	0x24d, 0x07e, 0x018, 0x22b, 0x0d4, 0x2e7, 0x281, 0x0b2,
 	0x17d, 0x34e, 0x328, 0x11b, 0x3e4, 0x1d7, 0x1b1, 0x382,
 	0x27c, 0x04f, 0x029, 0x21a, 0x0e5, 0x2d6, 0x2b0, 0x083,
 	0x12e, 0x31d, 0x37b, 0x148, 0x3b7, 0x184, 0x1e2, 0x3d1,
 	0x22f, 0x01c, 0x07a, 0x249, 0x0b6, 0x285, 0x2e3, 0x0d0,
 	0x11f, 0x32c, 0x34a, 0x179, 0x386, 0x1b5, 0x1d3, 0x3e0,
 	0x21e, 0x02d, 0x04b, 0x278, 0x087, 0x2b4, 0x2d2, 0x0e1,
 };

 #define CRC10_INITFCS     0x000	/* Initial FCS value */
 #define CRC10_GOODFCS     0x000	/* Good final FCS value */
 #define CRC10_FCS(fcs, c) ((((fcs) << 8) & 0x3ff) ^ crc10_table[((fcs) >> 2) & 0xff] ^ (c))

 /**
  * fcs_compute10 - memcpy and calculate 10 bit CRC across buffer
  * @sp: pointer to buffer
  * @len: number of bytes
  * @fcs: starting FCS
  *
  * Perform a memcpy and calculate fcs using ppp 10bit CRC algorithm. Return
  * new 10 bit FCS.
  */
 static __u16 __inline__ fcs_compute10(unsigned char *sp, int len, __u16 fcs)
 {
 	for (; len-- > 0; fcs = CRC10_FCS(fcs, *sp++));
 	return fcs;
 }

 static void safe_process_read_urb(struct urb *urb)
 {
 	struct usb_serial_port *port = urb->context;
 	unsigned char *data = urb->transfer_buffer;
 	unsigned char length = urb->actual_length;
 	int actual_length;
 	__u16 fcs;

 	if (!length)
 		return;

 	if (!safe)
 		goto out;

 	fcs = fcs_compute10(data, length, CRC10_INITFCS);
 	if (fcs) {
 		dev_err(&port->dev, "%s - bad CRC %x\n", __func__, fcs);
 		return;
 	}

 	actual_length = data[length - 2] >> 2;
 	if (actual_length > (length - 2)) {
 		dev_err(&port->dev, "%s - inconsistent lengths %d:%d\n",
 				__func__, actual_length, length);
 		return;
 	}
 	dev_info(&urb->dev->dev, "%s - actual: %d\n", __func__, actual_length);
 	length = actual_length;
 out:
 	tty_insert_flip_string(&port->port, data, length);
 	tty_flip_buffer_push(&port->port);
 }

 static int safe_prepare_write_buffer(struct usb_serial_port *port,
 						void *dest, size_t size)
 {
 	unsigned char *buf = dest;
 	int count;
 	int trailer_len;
 	int pkt_len;
 	__u16 fcs;

 	trailer_len = safe ? 2 : 0;

 	count = kfifo_out_locked(&port->write_fifo, buf, size - trailer_len,
 								&port->lock);
 	if (!safe)
 		return count;

 	/* pad if necessary */
 	if (padded) {
 		pkt_len = size;
 		memset(buf + count, '0', pkt_len - count - trailer_len);
 	} else {
 		pkt_len = count + trailer_len;
 	}

 	/* set count */
 	buf[pkt_len - 2] = count << 2;
 	buf[pkt_len - 1] = 0;

 	/* compute fcs and insert into trailer */
 	fcs = fcs_compute10(buf, pkt_len, CRC10_INITFCS);
 	buf[pkt_len - 2] |= fcs >> 8;
 	buf[pkt_len - 1] |= fcs & 0xff;

 	return pkt_len;
 }

 static int safe_startup(struct usb_serial *serial)
 {
 	struct usb_interface_descriptor	*desc;

 	if (serial->dev->descriptor.bDeviceClass != CDC_DEVICE_CLASS)
 		return -ENODEV;

 	desc = &serial->interface->cur_altsetting->desc;

 	if (desc->bInterfaceClass != LINEO_INTERFACE_CLASS)
 		return -ENODEV;
 	if (desc->bInterfaceSubClass != LINEO_INTERFACE_SUBCLASS_SAFESERIAL)
 		return -ENODEV;

 	switch (desc->bInterfaceProtocol) {
 	case LINEO_SAFESERIAL_CRC:
 		break;
 	case LINEO_SAFESERIAL_CRC_PADDED:
 		padded = true;
 		break;
 	default:
 		return -EINVAL;
 	}
 	return 0;
 }

 static struct usb_serial_driver safe_device = {
 	.driver = {
 		.owner =	THIS_MODULE,
 		.name =		"safe_serial",
 	},
 	.id_table =		id_table,
 	.num_ports =		1,
 	.process_read_urb =	safe_process_read_urb,
 	.prepare_write_buffer =	safe_prepare_write_buffer,
 	.attach =		safe_startup,
 };

 static struct usb_serial_driver * const serial_drivers[] = {
 	&safe_device, NULL
 };

 module_usb_serial_driver(serial_drivers, id_table);
	/*
	* Safe Encapsulated USB Serial Driver
	*
	* Copyright (C) 2010 Johan Hovold <jhovold@gmail.com>
	* Copyright (C) 2001 Lineo
	* Copyright (C) 2001 Hewlett-Packard
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* By:
	* Stuart Lynne <sl@lineo.com>, Tom Rushworth <tbr@lineo.com>
	*/

	/*
	* The encapsultaion is designed to overcome difficulties with some USB
	* hardware.
	*
	* While the USB protocol has a CRC over the data while in transit, i.e. while
	* being carried over the bus, there is no end to end protection. If the
	* hardware has any problems getting the data into or out of the USB transmit
	* and receive FIFO's then data can be lost.
	*
	* This protocol adds a two byte trailer to each USB packet to specify the
	* number of bytes of valid data and a 10 bit CRC that will allow the receiver
	* to verify that the entire USB packet was received without error.
	*
	* Because in this case the sender and receiver are the class and function
	* drivers there is now end to end protection.
	*
	* There is an additional option that can be used to force all transmitted
	* packets to be padded to the maximum packet size. This provides a work
	* around for some devices which have problems with small USB packets.
	*
	* Assuming a packetsize of N:
	*
	* 0..N-2 data and optional padding
	*
	* N-2 bits 7-2 - number of bytes of valid data
	* bits 1-0 top two bits of 10 bit CRC
	* N-1 bottom 8 bits of 10 bit CRC
	*
	*
	* \| Data Length \| 10 bit CRC \|
	* + 7 . 6 . 5 . 4 . 3 . 2 . 1 . 0 \| 7 . 6 . 5 . 4 . 3 . 2 . 1 . 0 +
	*
	* The 10 bit CRC is computed across the sent data, followed by the trailer
	* with the length set and the CRC set to zero. The CRC is then OR'd into
	* the trailer.
	*
	* When received a 10 bit CRC is computed over the entire frame including
	* the trailer and should be equal to zero.
	*
	* Two module parameters are used to control the encapsulation, if both are
	* turned of the module works as a simple serial device with NO
	* encapsulation.
	*
	* See linux/drivers/usbd/serial_fd for a device function driver
	* implementation of this.
	*
	*/

	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/kernel.h>
	#include <linux/errno.h>
	#include <linux/gfp.h>
	#include <linux/tty.h>
	#include <linux/tty_driver.h>
	#include <linux/tty_flip.h>
	#include <linux/module.h>
	#include <linux/spinlock.h>
	#include <linux/uaccess.h>
	#include <linux/usb.h>
	#include <linux/usb/serial.h>

	static bool safe = true;
	static bool padded = IS_ENABLED(CONFIG_USB_SERIAL_SAFE_PADDED);

	#define DRIVER_AUTHOR "sl@lineo.com, tbr@lineo.com, Johan Hovold <jhovold@gmail.com>"
	#define DRIVER_DESC "USB Safe Encapsulated Serial"

	MODULE_AUTHOR(DRIVER_AUTHOR);
	MODULE_DESCRIPTION(DRIVER_DESC);
	MODULE_LICENSE("GPL");

	module_param(safe, bool, 0);
	MODULE_PARM_DESC(safe, "Turn Safe Encapsulation On/Off");

	module_param(padded, bool, 0);
	MODULE_PARM_DESC(padded, "Pad to full wMaxPacketSize On/Off");

	#define CDC_DEVICE_CLASS 0x02

	#define CDC_INTERFACE_CLASS 0x02
	#define CDC_INTERFACE_SUBCLASS 0x06

	#define LINEO_INTERFACE_CLASS 0xff

	#define LINEO_INTERFACE_SUBCLASS_SAFENET 0x01
	#define LINEO_SAFENET_CRC 0x01
	#define LINEO_SAFENET_CRC_PADDED 0x02

	#define LINEO_INTERFACE_SUBCLASS_SAFESERIAL 0x02
	#define LINEO_SAFESERIAL_CRC 0x01
	#define LINEO_SAFESERIAL_CRC_PADDED 0x02


	#define MY_USB_DEVICE(vend, prod, dc, ic, isc) \
	.match_flags = USB_DEVICE_ID_MATCH_DEVICE \| \
	USB_DEVICE_ID_MATCH_DEV_CLASS \| \
	USB_DEVICE_ID_MATCH_INT_CLASS \| \
	USB_DEVICE_ID_MATCH_INT_SUBCLASS, \
	.idVendor = (vend), \
	.idProduct = (prod),\
	.bDeviceClass = (dc),\
	.bInterfaceClass = (ic), \
	.bInterfaceSubClass = (isc),

	static const struct usb_device_id id_table[] = {
	{MY_USB_DEVICE(0x49f, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Itsy */
	{MY_USB_DEVICE(0x3f0, 0x2101, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Calypso */
	{MY_USB_DEVICE(0x4dd, 0x8001, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Iris */
	{MY_USB_DEVICE(0x4dd, 0x8002, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Collie */
	{MY_USB_DEVICE(0x4dd, 0x8003, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Collie */
	{MY_USB_DEVICE(0x4dd, 0x8004, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Collie */
	{MY_USB_DEVICE(0x5f9, 0xffff, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)}, /* Sharp tmp */
	{} /* terminating entry */
	};

	MODULE_DEVICE_TABLE(usb, id_table);

	static const __u16 crc10_table[256] = {
	0x000, 0x233, 0x255, 0x066, 0x299, 0x0aa, 0x0cc, 0x2ff,
	0x301, 0x132, 0x154, 0x367, 0x198, 0x3ab, 0x3cd, 0x1fe,
	0x031, 0x202, 0x264, 0x057, 0x2a8, 0x09b, 0x0fd, 0x2ce,
	0x330, 0x103, 0x165, 0x356, 0x1a9, 0x39a, 0x3fc, 0x1cf,
	0x062, 0x251, 0x237, 0x004, 0x2fb, 0x0c8, 0x0ae, 0x29d,
	0x363, 0x150, 0x136, 0x305, 0x1fa, 0x3c9, 0x3af, 0x19c,
	0x053, 0x260, 0x206, 0x035, 0x2ca, 0x0f9, 0x09f, 0x2ac,
	0x352, 0x161, 0x107, 0x334, 0x1cb, 0x3f8, 0x39e, 0x1ad,
	0x0c4, 0x2f7, 0x291, 0x0a2, 0x25d, 0x06e, 0x008, 0x23b,
	0x3c5, 0x1f6, 0x190, 0x3a3, 0x15c, 0x36f, 0x309, 0x13a,
	0x0f5, 0x2c6, 0x2a0, 0x093, 0x26c, 0x05f, 0x039, 0x20a,
	0x3f4, 0x1c7, 0x1a1, 0x392, 0x16d, 0x35e, 0x338, 0x10b,
	0x0a6, 0x295, 0x2f3, 0x0c0, 0x23f, 0x00c, 0x06a, 0x259,
	0x3a7, 0x194, 0x1f2, 0x3c1, 0x13e, 0x30d, 0x36b, 0x158,
	0x097, 0x2a4, 0x2c2, 0x0f1, 0x20e, 0x03d, 0x05b, 0x268,
	0x396, 0x1a5, 0x1c3, 0x3f0, 0x10f, 0x33c, 0x35a, 0x169,
	0x188, 0x3bb, 0x3dd, 0x1ee, 0x311, 0x122, 0x144, 0x377,
	0x289, 0x0ba, 0x0dc, 0x2ef, 0x010, 0x223, 0x245, 0x076,
	0x1b9, 0x38a, 0x3ec, 0x1df, 0x320, 0x113, 0x175, 0x346,
	0x2b8, 0x08b, 0x0ed, 0x2de, 0x021, 0x212, 0x274, 0x047,
	0x1ea, 0x3d9, 0x3bf, 0x18c, 0x373, 0x140, 0x126, 0x315,
	0x2eb, 0x0d8, 0x0be, 0x28d, 0x072, 0x241, 0x227, 0x014,
	0x1db, 0x3e8, 0x38e, 0x1bd, 0x342, 0x171, 0x117, 0x324,
	0x2da, 0x0e9, 0x08f, 0x2bc, 0x043, 0x270, 0x216, 0x025,
	0x14c, 0x37f, 0x319, 0x12a, 0x3d5, 0x1e6, 0x180, 0x3b3,
	0x24d, 0x07e, 0x018, 0x22b, 0x0d4, 0x2e7, 0x281, 0x0b2,
	0x17d, 0x34e, 0x328, 0x11b, 0x3e4, 0x1d7, 0x1b1, 0x382,
	0x27c, 0x04f, 0x029, 0x21a, 0x0e5, 0x2d6, 0x2b0, 0x083,
	0x12e, 0x31d, 0x37b, 0x148, 0x3b7, 0x184, 0x1e2, 0x3d1,
	0x22f, 0x01c, 0x07a, 0x249, 0x0b6, 0x285, 0x2e3, 0x0d0,
	0x11f, 0x32c, 0x34a, 0x179, 0x386, 0x1b5, 0x1d3, 0x3e0,
	0x21e, 0x02d, 0x04b, 0x278, 0x087, 0x2b4, 0x2d2, 0x0e1,
	};

	#define CRC10_INITFCS 0x000 /* Initial FCS value */
	#define CRC10_GOODFCS 0x000 /* Good final FCS value */
	#define CRC10_FCS(fcs, c) ((((fcs) << 8) & 0x3ff) ^ crc10_table[((fcs) >> 2) & 0xff] ^ (c))

	/**
	* fcs_compute10 - memcpy and calculate 10 bit CRC across buffer
	* @sp: pointer to buffer
	* @len: number of bytes
	* @fcs: starting FCS
	*
	* Perform a memcpy and calculate fcs using ppp 10bit CRC algorithm. Return
	* new 10 bit FCS.
	*/
	static __u16 __inline__ fcs_compute10(unsigned char *sp, int len, __u16 fcs)
	{
	for (; len-- > 0; fcs = CRC10_FCS(fcs, *sp++));
	return fcs;
	}

	static void safe_process_read_urb(struct urb *urb)
	{
	struct usb_serial_port *port = urb->context;
	unsigned char *data = urb->transfer_buffer;
	unsigned char length = urb->actual_length;
	int actual_length;
	__u16 fcs;

	if (!length)
	return;

	if (!safe)
	goto out;

	fcs = fcs_compute10(data, length, CRC10_INITFCS);
	if (fcs) {
	dev_err(&port->dev, "%s - bad CRC %x\n", __func__, fcs);
	return;
	}

	actual_length = data[length - 2] >> 2;
	if (actual_length > (length - 2)) {
	dev_err(&port->dev, "%s - inconsistent lengths %d:%d\n",
	__func__, actual_length, length);
	return;
	}
	dev_info(&urb->dev->dev, "%s - actual: %d\n", __func__, actual_length);
	length = actual_length;
	out:
	tty_insert_flip_string(&port->port, data, length);
	tty_flip_buffer_push(&port->port);
	}

	static int safe_prepare_write_buffer(struct usb_serial_port *port,
	void *dest, size_t size)
	{
	unsigned char *buf = dest;
	int count;
	int trailer_len;
	int pkt_len;
	__u16 fcs;

	trailer_len = safe ? 2 : 0;

	count = kfifo_out_locked(&port->write_fifo, buf, size - trailer_len,
	&port->lock);
	if (!safe)
	return count;

	/* pad if necessary */
	if (padded) {
	pkt_len = size;
	memset(buf + count, '0', pkt_len - count - trailer_len);
	} else {
	pkt_len = count + trailer_len;
	}

	/* set count */
	buf[pkt_len - 2] = count << 2;
	buf[pkt_len - 1] = 0;

	/* compute fcs and insert into trailer */
	fcs = fcs_compute10(buf, pkt_len, CRC10_INITFCS);
	buf[pkt_len - 2] \|= fcs >> 8;
	buf[pkt_len - 1] \|= fcs & 0xff;

	return pkt_len;
	}

	static int safe_startup(struct usb_serial *serial)
	{
	struct usb_interface_descriptor *desc;

	if (serial->dev->descriptor.bDeviceClass != CDC_DEVICE_CLASS)
	return -ENODEV;

	desc = &serial->interface->cur_altsetting->desc;

	if (desc->bInterfaceClass != LINEO_INTERFACE_CLASS)
	return -ENODEV;
	if (desc->bInterfaceSubClass != LINEO_INTERFACE_SUBCLASS_SAFESERIAL)
	return -ENODEV;

	switch (desc->bInterfaceProtocol) {
	case LINEO_SAFESERIAL_CRC:
	break;
	case LINEO_SAFESERIAL_CRC_PADDED:
	padded = true;
	break;
	default:
	return -EINVAL;
	}
	return 0;
	}

	static struct usb_serial_driver safe_device = {
	.driver = {
	.owner = THIS_MODULE,
	.name = "safe_serial",
	},
	.id_table = id_table,
	.num_ports = 1,
	.process_read_urb = safe_process_read_urb,
	.prepare_write_buffer = safe_prepare_write_buffer,
	.attach = safe_startup,
	};

	static struct usb_serial_driver * const serial_drivers[] = {
	&safe_device, NULL
	};

	module_usb_serial_driver(serial_drivers, id_table);