safe_serial.c

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/*
 * Safe Encapsulated USB Serial Driver
 *
 *      Copyright (C) 2010 Johan Hovold <[email protected]>
 *      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 <[email protected]>, Tom Rushworth <[email protected]>
 */

/*
 * 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/init.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>


#ifndef CONFIG_USB_SERIAL_SAFE_PADDED
#define CONFIG_USB_SERIAL_SAFE_PADDED 0
#endif

static bool safe = 1;
static bool padded = CONFIG_USB_SERIAL_SAFE_PADDED;

#define DRIVER_AUTHOR "[email protected], [email protected], Johan Hovold <[email protected]>"
#define DRIVER_DESC "USB Safe Encapsulated Serial"

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

static __u16 vendor;        /* no default */
static __u16 product;       /* no default */
module_param(vendor, ushort, 0);
MODULE_PARM_DESC(vendor, "User specified USB idVendor (required)");
module_param(product, ushort, 0);
MODULE_PARM_DESC(product, "User specified USB idProduct (required)");

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 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 */
    /* extra null entry for module vendor/produc parameters */
    {MY_USB_DEVICE(0, 0, CDC_DEVICE_CLASS, LINEO_INTERFACE_CLASS, LINEO_INTERFACE_SUBCLASS_SAFESERIAL)},
    {}          /* 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))

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;
    struct tty_struct *tty;
    __u16 fcs;

    if (!length)
        return;

    tty = tty_port_tty_get(&port->port);
    if (!tty)
        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);
        goto err;
    }

    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);
        goto err;
    }
    dev_info(&urb->dev->dev, "%s - actual: %d\n", __func__, actual_length);
    length = actual_length;
out:
    tty_insert_flip_string(tty, data, length);
    tty_flip_buffer_push(tty);
err:
    tty_kref_put(tty);
}

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)
{
    switch (serial->interface->cur_altsetting->desc.bInterfaceProtocol) {
    case LINEO_SAFESERIAL_CRC:
        break;
    case LINEO_SAFESERIAL_CRC_PADDED:
        padded = 1;
        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
};

static int __init safe_init(void)
{
    int i;

    /* if we have vendor / product parameters patch them into id list */
    if (vendor || product) {
        pr_info("vendor: %x product: %x\n", vendor, product);

        for (i = 0; i < ARRAY_SIZE(id_table); i++) {
            if (!id_table[i].idVendor && !id_table[i].idProduct) {
                id_table[i].idVendor = vendor;
                id_table[i].idProduct = product;
                break;
            }
        }
    }

    return usb_serial_register_drivers(serial_drivers, KBUILD_MODNAME, id_table);
}

static void __exit safe_exit(void)
{
    usb_serial_deregister_drivers(serial_drivers);
}

module_init(safe_init);
module_exit(safe_exit);