[PATCH] TTY layer buffering revamp

[deliverable/linux.git] / drivers / usb / class / cdc-acm.c

/*
 * cdc-acm.c
 *
 * Copyright (c) 1999 Armin Fuerst      <fuerst@in.tum.de>
 * Copyright (c) 1999 Pavel Machek      <pavel@suse.cz>
 * Copyright (c) 1999 Johannes Erdfelt  <johannes@erdfelt.com>
 * Copyright (c) 2000 Vojtech Pavlik    <vojtech@suse.cz>
 * Copyright (c) 2004 Oliver Neukum     <oliver@neukum.name>
 * Copyright (c) 2005 David Kubicek     <dave@awk.cz>
 *
 * USB Abstract Control Model driver for USB modems and ISDN adapters
 *
 * Sponsored by SuSE
 *
 * ChangeLog:
 *      v0.9  - thorough cleaning, URBification, almost a rewrite
 *      v0.10 - some more cleanups
 *      v0.11 - fixed flow control, read error doesn't stop reads
 *      v0.12 - added TIOCM ioctls, added break handling, made struct acm kmalloced
 *      v0.13 - added termios, added hangup
 *      v0.14 - sized down struct acm
 *      v0.15 - fixed flow control again - characters could be lost
 *      v0.16 - added code for modems with swapped data and control interfaces
 *      v0.17 - added new style probing
 *      v0.18 - fixed new style probing for devices with more configurations
 *      v0.19 - fixed CLOCAL handling (thanks to Richard Shih-Ping Chan)
 *      v0.20 - switched to probing on interface (rather than device) class
 *      v0.21 - revert to probing on device for devices with multiple configs
 *      v0.22 - probe only the control interface. if usbcore doesn't choose the
 *              config we want, sysadmin changes bConfigurationValue in sysfs.
 *      v0.23 - use softirq for rx processing, as needed by tty layer
 *      v0.24 - change probe method to evaluate CDC union descriptor
 *      v0.25 - downstream tasks paralelized to maximize throughput
 */

/*
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#undef DEBUG

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>
#include <linux/module.h>
#include <linux/smp_lock.h>
#include <asm/uaccess.h>
#include <linux/usb.h>
#include <linux/usb_cdc.h>
#include <asm/byteorder.h>
#include <asm/unaligned.h>
#include <linux/list.h>

#include "cdc-acm.h"

/*
 * Version Information
 */
#define DRIVER_VERSION "v0.25"
#define DRIVER_AUTHOR "Armin Fuerst, Pavel Machek, Johannes Erdfelt, Vojtech Pavlik, David Kubicek"
#define DRIVER_DESC "USB Abstract Control Model driver for USB modems and ISDN adapters"

static struct usb_driver acm_driver;
static struct tty_driver *acm_tty_driver;
static struct acm *acm_table[ACM_TTY_MINORS];

static DECLARE_MUTEX(open_sem);

#define ACM_READY(acm)  (acm && acm->dev && acm->used)

/*
 * Functions for ACM control messages.
 */

static int acm_ctrl_msg(struct acm *acm, int request, int value, void *buf, int len)
{
        int retval = usb_control_msg(acm->dev, usb_sndctrlpipe(acm->dev, 0),
                request, USB_RT_ACM, value,
                acm->control->altsetting[0].desc.bInterfaceNumber,
                buf, len, 5000);
        dbg("acm_control_msg: rq: 0x%02x val: %#x len: %#x result: %d", request, value, len, retval);
        return retval < 0 ? retval : 0;
}

/* devices aren't required to support these requests.
 * the cdc acm descriptor tells whether they do...
 */
#define acm_set_control(acm, control) \
        acm_ctrl_msg(acm, USB_CDC_REQ_SET_CONTROL_LINE_STATE, control, NULL, 0)
#define acm_set_line(acm, line) \
        acm_ctrl_msg(acm, USB_CDC_REQ_SET_LINE_CODING, 0, line, sizeof *(line))
#define acm_send_break(acm, ms) \
        acm_ctrl_msg(acm, USB_CDC_REQ_SEND_BREAK, ms, NULL, 0)

/*
 * Write buffer management.
 * All of these assume proper locks taken by the caller.
 */

static int acm_wb_alloc(struct acm *acm)
{
        int i, wbn;
        struct acm_wb *wb;

        wbn = acm->write_current;
        i = 0;
        for (;;) {
                wb = &acm->wb[wbn];
                if (!wb->use) {
                        wb->use = 1;
                        return wbn;
                }
                wbn = (wbn + 1) % ACM_NWB;
                if (++i >= ACM_NWB)
                        return -1;
        }
}

static void acm_wb_free(struct acm *acm, int wbn)
{
        acm->wb[wbn].use = 0;
}

static int acm_wb_is_avail(struct acm *acm)
{
        int i, n;

        n = 0;
        for (i = 0; i < ACM_NWB; i++) {
                if (!acm->wb[i].use)
                        n++;
        }
        return n;
}

static inline int acm_wb_is_used(struct acm *acm, int wbn)
{
        return acm->wb[wbn].use;
}

/*
 * Finish write.
 */
static void acm_write_done(struct acm *acm)
{
        unsigned long flags;
        int wbn;

        spin_lock_irqsave(&acm->write_lock, flags);
        acm->write_ready = 1;
        wbn = acm->write_current;
        acm_wb_free(acm, wbn);
        acm->write_current = (wbn + 1) % ACM_NWB;
        spin_unlock_irqrestore(&acm->write_lock, flags);
}

/*
 * Poke write.
 */
static int acm_write_start(struct acm *acm)
{
        unsigned long flags;
        int wbn;
        struct acm_wb *wb;
        int rc;

        spin_lock_irqsave(&acm->write_lock, flags);
        if (!acm->dev) {
                spin_unlock_irqrestore(&acm->write_lock, flags);
                return -ENODEV;
        }

        if (!acm->write_ready) {
                spin_unlock_irqrestore(&acm->write_lock, flags);
                return 0;       /* A white lie */
        }

        wbn = acm->write_current;
        if (!acm_wb_is_used(acm, wbn)) {
                spin_unlock_irqrestore(&acm->write_lock, flags);
                return 0;
        }
        wb = &acm->wb[wbn];

        acm->write_ready = 0;
        spin_unlock_irqrestore(&acm->write_lock, flags);

        acm->writeurb->transfer_buffer = wb->buf;
        acm->writeurb->transfer_dma = wb->dmah;
        acm->writeurb->transfer_buffer_length = wb->len;
        acm->writeurb->dev = acm->dev;

        if ((rc = usb_submit_urb(acm->writeurb, GFP_ATOMIC)) < 0) {
                dbg("usb_submit_urb(write bulk) failed: %d", rc);
                acm_write_done(acm);
        }
        return rc;
}

/*
 * Interrupt handlers for various ACM device responses
 */

/* control interface reports status changes with "interrupt" transfers */
static void acm_ctrl_irq(struct urb *urb, struct pt_regs *regs)
{
        struct acm *acm = urb->context;
        struct usb_cdc_notification *dr = urb->transfer_buffer;
        unsigned char *data;
        int newctrl;
        int status;

        switch (urb->status) {
        case 0:
                /* success */
                break;
        case -ECONNRESET:
        case -ENOENT:
        case -ESHUTDOWN:
                /* this urb is terminated, clean up */
                dbg("%s - urb shutting down with status: %d", __FUNCTION__, urb->status);
                return;
        default:
                dbg("%s - nonzero urb status received: %d", __FUNCTION__, urb->status);
                goto exit;
        }

        if (!ACM_READY(acm))
                goto exit;

        data = (unsigned char *)(dr + 1);
        switch (dr->bNotificationType) {

                case USB_CDC_NOTIFY_NETWORK_CONNECTION:

                        dbg("%s network", dr->wValue ? "connected to" : "disconnected from");
                        break;

                case USB_CDC_NOTIFY_SERIAL_STATE:

                        newctrl = le16_to_cpu(get_unaligned((__le16 *) data));

                        if (acm->tty && !acm->clocal && (acm->ctrlin & ~newctrl & ACM_CTRL_DCD)) {
                                dbg("calling hangup");
                                tty_hangup(acm->tty);
                        }

                        acm->ctrlin = newctrl;

                        dbg("input control lines: dcd%c dsr%c break%c ring%c framing%c parity%c overrun%c",
                                acm->ctrlin & ACM_CTRL_DCD ? '+' : '-', acm->ctrlin & ACM_CTRL_DSR ? '+' : '-',
                                acm->ctrlin & ACM_CTRL_BRK ? '+' : '-', acm->ctrlin & ACM_CTRL_RI  ? '+' : '-',
                                acm->ctrlin & ACM_CTRL_FRAMING ? '+' : '-',     acm->ctrlin & ACM_CTRL_PARITY ? '+' : '-',
                                acm->ctrlin & ACM_CTRL_OVERRUN ? '+' : '-');

                        break;

                default:
                        dbg("unknown notification %d received: index %d len %d data0 %d data1 %d",
                                dr->bNotificationType, dr->wIndex,
                                dr->wLength, data[0], data[1]);
                        break;
        }
exit:
        status = usb_submit_urb (urb, GFP_ATOMIC);
        if (status)
                err ("%s - usb_submit_urb failed with result %d",
                     __FUNCTION__, status);
}

/* data interface returns incoming bytes, or we got unthrottled */
static void acm_read_bulk(struct urb *urb, struct pt_regs *regs)
{
        struct acm_rb *buf;
        struct acm_ru *rcv = urb->context;
        struct acm *acm = rcv->instance;
        dbg("Entering acm_read_bulk with status %d\n", urb->status);

        if (!ACM_READY(acm))
                return;

        if (urb->status)
                dev_dbg(&acm->data->dev, "bulk rx status %d\n", urb->status);

        buf = rcv->buffer;
        buf->size = urb->actual_length;

        spin_lock(&acm->read_lock);
        list_add_tail(&rcv->list, &acm->spare_read_urbs);
        list_add_tail(&buf->list, &acm->filled_read_bufs);
        spin_unlock(&acm->read_lock);

        tasklet_schedule(&acm->urb_task);
}

static void acm_rx_tasklet(unsigned long _acm)
{
        struct acm *acm = (void *)_acm;
        struct acm_rb *buf;
        struct tty_struct *tty = acm->tty;
        struct acm_ru *rcv;
        //unsigned long flags;
        int i = 0;
        dbg("Entering acm_rx_tasklet");

        if (!ACM_READY(acm) || acm->throttle)
                return;

next_buffer:
        spin_lock(&acm->read_lock);
        if (list_empty(&acm->filled_read_bufs)) {
                spin_unlock(&acm->read_lock);
                goto urbs;
        }
        buf = list_entry(acm->filled_read_bufs.next,
                         struct acm_rb, list);
        list_del(&buf->list);
        spin_unlock(&acm->read_lock);

        dbg("acm_rx_tasklet: procesing buf 0x%p, size = %d\n", buf, buf->size);

        tty_buffer_request_room(tty, buf->size);
        if (!acm->throttle)
                tty_insert_flip_string(tty, buf->base, buf->size);
        tty_flip_buffer_push(tty);

        spin_lock(&acm->throttle_lock);
        if (acm->throttle) {
                dbg("Throtteling noticed");
                memmove(buf->base, buf->base + i, buf->size - i);
                buf->size -= i;
                spin_unlock(&acm->throttle_lock);
                spin_lock(&acm->read_lock);
                list_add(&buf->list, &acm->filled_read_bufs);
                spin_unlock(&acm->read_lock);
                return;
        }
        spin_unlock(&acm->throttle_lock);

        spin_lock(&acm->read_lock);
        list_add(&buf->list, &acm->spare_read_bufs);
        spin_unlock(&acm->read_lock);
        goto next_buffer;

urbs:
        while (!list_empty(&acm->spare_read_bufs)) {
                spin_lock(&acm->read_lock);
                if (list_empty(&acm->spare_read_urbs)) {
                        spin_unlock(&acm->read_lock);
                        return;
                }
                rcv = list_entry(acm->spare_read_urbs.next,
                                 struct acm_ru, list);
                list_del(&rcv->list);
                spin_unlock(&acm->read_lock);

                buf = list_entry(acm->spare_read_bufs.next,
                                 struct acm_rb, list);
                list_del(&buf->list);

                rcv->buffer = buf;

                usb_fill_bulk_urb(rcv->urb, acm->dev,
                                  acm->rx_endpoint,
                                  buf->base,
                                  acm->readsize,
                                  acm_read_bulk, rcv);
                rcv->urb->transfer_dma = buf->dma;
                rcv->urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;

                dbg("acm_rx_tasklet: sending urb 0x%p, rcv 0x%p, buf 0x%p\n", rcv->urb, rcv, buf);

                /* This shouldn't kill the driver as unsuccessful URBs are returned to the
                   free-urbs-pool and resubmited ASAP */
                if (usb_submit_urb(rcv->urb, GFP_ATOMIC) < 0) {
                        list_add(&buf->list, &acm->spare_read_bufs);
                        spin_lock(&acm->read_lock);
                        list_add(&rcv->list, &acm->spare_read_urbs);
                        spin_unlock(&acm->read_lock);
                        return;
                }
        }
}

/* data interface wrote those outgoing bytes */
static void acm_write_bulk(struct urb *urb, struct pt_regs *regs)
{
        struct acm *acm = (struct acm *)urb->context;

        dbg("Entering acm_write_bulk with status %d\n", urb->status);

        acm_write_done(acm);
        acm_write_start(acm);
        if (ACM_READY(acm))
                schedule_work(&acm->work);
}

static void acm_softint(void *private)
{
        struct acm *acm = private;
        dbg("Entering acm_softint.\n");
        
        if (!ACM_READY(acm))
                return;
        tty_wakeup(acm->tty);
}

/*
 * TTY handlers
 */

static int acm_tty_open(struct tty_struct *tty, struct file *filp)
{
        struct acm *acm;
        int rv = -EINVAL;
        int i;
        dbg("Entering acm_tty_open.\n");
        
        down(&open_sem);

        acm = acm_table[tty->index];
        if (!acm || !acm->dev)
                goto err_out;
        else
                rv = 0;

        tty->driver_data = acm;
        acm->tty = tty;

        /* force low_latency on so that our tty_push actually forces the data through,
           otherwise it is scheduled, and with high data rates data can get lost. */
        tty->low_latency = 1;

        if (acm->used++) {
                goto done;
        }

        acm->ctrlurb->dev = acm->dev;
        if (usb_submit_urb(acm->ctrlurb, GFP_KERNEL)) {
                dbg("usb_submit_urb(ctrl irq) failed");
                goto bail_out;
        }

        if (0 > acm_set_control(acm, acm->ctrlout = ACM_CTRL_DTR | ACM_CTRL_RTS))
                goto full_bailout;

        INIT_LIST_HEAD(&acm->spare_read_urbs);
        INIT_LIST_HEAD(&acm->spare_read_bufs);
        INIT_LIST_HEAD(&acm->filled_read_bufs);
        for (i = 0; i < ACM_NRU; i++) {
                list_add(&(acm->ru[i].list), &acm->spare_read_urbs);
        }
        for (i = 0; i < ACM_NRB; i++) {
                list_add(&(acm->rb[i].list), &acm->spare_read_bufs);
        }

        tasklet_schedule(&acm->urb_task);

done:
err_out:
        up(&open_sem);
        return rv;

full_bailout:
        usb_kill_urb(acm->ctrlurb);
bail_out:
        acm->used--;
        up(&open_sem);
        return -EIO;
}

static void acm_tty_unregister(struct acm *acm)
{
        int i;

        tty_unregister_device(acm_tty_driver, acm->minor);
        usb_put_intf(acm->control);
        acm_table[acm->minor] = NULL;
        usb_free_urb(acm->ctrlurb);
        usb_free_urb(acm->writeurb);
        for (i = 0; i < ACM_NRU; i++)
                usb_free_urb(acm->ru[i].urb);
        kfree(acm);
}

static void acm_tty_close(struct tty_struct *tty, struct file *filp)
{
        struct acm *acm = tty->driver_data;
        int i;

        if (!acm || !acm->used)
                return;

        down(&open_sem);
        if (!--acm->used) {
                if (acm->dev) {
                        acm_set_control(acm, acm->ctrlout = 0);
                        usb_kill_urb(acm->ctrlurb);
                        usb_kill_urb(acm->writeurb);
                        for (i = 0; i < ACM_NRU; i++)
                                usb_kill_urb(acm->ru[i].urb);
                } else
                        acm_tty_unregister(acm);
        }
        up(&open_sem);
}

static int acm_tty_write(struct tty_struct *tty, const unsigned char *buf, int count)
{
        struct acm *acm = tty->driver_data;
        int stat;
        unsigned long flags;
        int wbn;
        struct acm_wb *wb;

        dbg("Entering acm_tty_write to write %d bytes,\n", count);

        if (!ACM_READY(acm))
                return -EINVAL;
        if (!count)
                return 0;

        spin_lock_irqsave(&acm->write_lock, flags);
        if ((wbn = acm_wb_alloc(acm)) < 0) {
                spin_unlock_irqrestore(&acm->write_lock, flags);
                acm_write_start(acm);
                return 0;
        }
        wb = &acm->wb[wbn];

        count = (count > acm->writesize) ? acm->writesize : count;
        dbg("Get %d bytes...", count);
        memcpy(wb->buf, buf, count);
        wb->len = count;
        spin_unlock_irqrestore(&acm->write_lock, flags);

        if ((stat = acm_write_start(acm)) < 0)
                return stat;
        return count;
}

static int acm_tty_write_room(struct tty_struct *tty)
{
        struct acm *acm = tty->driver_data;
        if (!ACM_READY(acm))
                return -EINVAL;
        /*
         * Do not let the line discipline to know that we have a reserve,
         * or it might get too enthusiastic.
         */
        return (acm->write_ready && acm_wb_is_avail(acm)) ? acm->writesize : 0;
}

static int acm_tty_chars_in_buffer(struct tty_struct *tty)
{
        struct acm *acm = tty->driver_data;
        if (!ACM_READY(acm))
                return -EINVAL;
        /*
         * This is inaccurate (overcounts), but it works.
         */
        return (ACM_NWB - acm_wb_is_avail(acm)) * acm->writesize;
}

static void acm_tty_throttle(struct tty_struct *tty)
{
        struct acm *acm = tty->driver_data;
        if (!ACM_READY(acm))
                return;
        spin_lock_bh(&acm->throttle_lock);
        acm->throttle = 1;
        spin_unlock_bh(&acm->throttle_lock);
}

static void acm_tty_unthrottle(struct tty_struct *tty)
{
        struct acm *acm = tty->driver_data;
        if (!ACM_READY(acm))
                return;
        spin_lock_bh(&acm->throttle_lock);
        acm->throttle = 0;
        spin_unlock_bh(&acm->throttle_lock);
        tasklet_schedule(&acm->urb_task);
}

static void acm_tty_break_ctl(struct tty_struct *tty, int state)
{
        struct acm *acm = tty->driver_data;
        if (!ACM_READY(acm))
                return;
        if (acm_send_break(acm, state ? 0xffff : 0))
                dbg("send break failed");
}

static int acm_tty_tiocmget(struct tty_struct *tty, struct file *file)
{
        struct acm *acm = tty->driver_data;

        if (!ACM_READY(acm))
                return -EINVAL;

        return (acm->ctrlout & ACM_CTRL_DTR ? TIOCM_DTR : 0) |
               (acm->ctrlout & ACM_CTRL_RTS ? TIOCM_RTS : 0) |
               (acm->ctrlin  & ACM_CTRL_DSR ? TIOCM_DSR : 0) |
               (acm->ctrlin  & ACM_CTRL_RI  ? TIOCM_RI  : 0) |
               (acm->ctrlin  & ACM_CTRL_DCD ? TIOCM_CD  : 0) |
               TIOCM_CTS;
}

static int acm_tty_tiocmset(struct tty_struct *tty, struct file *file,
                            unsigned int set, unsigned int clear)
{
        struct acm *acm = tty->driver_data;
        unsigned int newctrl;

        if (!ACM_READY(acm))
                return -EINVAL;

        newctrl = acm->ctrlout;
        set = (set & TIOCM_DTR ? ACM_CTRL_DTR : 0) | (set & TIOCM_RTS ? ACM_CTRL_RTS : 0);
        clear = (clear & TIOCM_DTR ? ACM_CTRL_DTR : 0) | (clear & TIOCM_RTS ? ACM_CTRL_RTS : 0);

        newctrl = (newctrl & ~clear) | set;

        if (acm->ctrlout == newctrl)
                return 0;
        return acm_set_control(acm, acm->ctrlout = newctrl);
}

static int acm_tty_ioctl(struct tty_struct *tty, struct file *file, unsigned int cmd, unsigned long arg)
{
        struct acm *acm = tty->driver_data;

        if (!ACM_READY(acm))
                return -EINVAL;

        return -ENOIOCTLCMD;
}

static const __u32 acm_tty_speed[] = {
        0, 50, 75, 110, 134, 150, 200, 300, 600,
        1200, 1800, 2400, 4800, 9600, 19200, 38400,
        57600, 115200, 230400, 460800, 500000, 576000,
        921600, 1000000, 1152000, 1500000, 2000000,
        2500000, 3000000, 3500000, 4000000
};

static const __u8 acm_tty_size[] = {
        5, 6, 7, 8
};

static void acm_tty_set_termios(struct tty_struct *tty, struct termios *termios_old)
{
        struct acm *acm = tty->driver_data;
        struct termios *termios = tty->termios;
        struct usb_cdc_line_coding newline;
        int newctrl = acm->ctrlout;

        if (!ACM_READY(acm))
                return;

        newline.dwDTERate = cpu_to_le32p(acm_tty_speed +
                (termios->c_cflag & CBAUD & ~CBAUDEX) + (termios->c_cflag & CBAUDEX ? 15 : 0));
        newline.bCharFormat = termios->c_cflag & CSTOPB ? 2 : 0;
        newline.bParityType = termios->c_cflag & PARENB ?
                (termios->c_cflag & PARODD ? 1 : 2) + (termios->c_cflag & CMSPAR ? 2 : 0) : 0;
        newline.bDataBits = acm_tty_size[(termios->c_cflag & CSIZE) >> 4];

        acm->clocal = ((termios->c_cflag & CLOCAL) != 0);

        if (!newline.dwDTERate) {
                newline.dwDTERate = acm->line.dwDTERate;
                newctrl &= ~ACM_CTRL_DTR;
        } else  newctrl |=  ACM_CTRL_DTR;

        if (newctrl != acm->ctrlout)
                acm_set_control(acm, acm->ctrlout = newctrl);

        if (memcmp(&acm->line, &newline, sizeof newline)) {
                memcpy(&acm->line, &newline, sizeof newline);
                dbg("set line: %d %d %d %d", le32_to_cpu(newline.dwDTERate),
                        newline.bCharFormat, newline.bParityType,
                        newline.bDataBits);
                acm_set_line(acm, &acm->line);
        }
}

/*
 * USB probe and disconnect routines.
 */

/* Little helper: write buffers free */
static void acm_write_buffers_free(struct acm *acm)
{
        int i;
        struct acm_wb *wb;

        for (wb = &acm->wb[0], i = 0; i < ACM_NWB; i++, wb++) {
                usb_buffer_free(acm->dev, acm->writesize, wb->buf, wb->dmah);
        }
}

/* Little helper: write buffers allocate */
static int acm_write_buffers_alloc(struct acm *acm)
{
        int i;
        struct acm_wb *wb;

        for (wb = &acm->wb[0], i = 0; i < ACM_NWB; i++, wb++) {
                wb->buf = usb_buffer_alloc(acm->dev, acm->writesize, GFP_KERNEL,
                    &wb->dmah);
                if (!wb->buf) {
                        while (i != 0) {
                                --i;
                                --wb;
                                usb_buffer_free(acm->dev, acm->writesize,
                                    wb->buf, wb->dmah);
                        }
                        return -ENOMEM;
                }
        }
        return 0;
}

static int acm_probe (struct usb_interface *intf,
                      const struct usb_device_id *id)
{
        struct usb_cdc_union_desc *union_header = NULL;
        char *buffer = intf->altsetting->extra;
        int buflen = intf->altsetting->extralen;
        struct usb_interface *control_interface;
        struct usb_interface *data_interface;
        struct usb_endpoint_descriptor *epctrl;
        struct usb_endpoint_descriptor *epread;
        struct usb_endpoint_descriptor *epwrite;
        struct usb_device *usb_dev = interface_to_usbdev(intf);
        struct acm *acm;
        int minor;
        int ctrlsize,readsize;
        u8 *buf;
        u8 ac_management_function = 0;
        u8 call_management_function = 0;
        int call_interface_num = -1;
        int data_interface_num;
        unsigned long quirks;
        int i;

        /* handle quirks deadly to normal probing*/
        quirks = (unsigned long)id->driver_info;
        if (quirks == NO_UNION_NORMAL) {
                data_interface = usb_ifnum_to_if(usb_dev, 1);
                control_interface = usb_ifnum_to_if(usb_dev, 0);
                goto skip_normal_probe;
        }
        
        /* normal probing*/
        if (!buffer) {
                err("Wierd descriptor references\n");
                return -EINVAL;
        }

        if (!buflen) {
                if (intf->cur_altsetting->endpoint->extralen && intf->cur_altsetting->endpoint->extra) {
                        dev_dbg(&intf->dev,"Seeking extra descriptors on endpoint\n");
                        buflen = intf->cur_altsetting->endpoint->extralen;
                        buffer = intf->cur_altsetting->endpoint->extra;
                } else {
                        err("Zero length descriptor references\n");
                        return -EINVAL;
                }
        }

        while (buflen > 0) {
                if (buffer [1] != USB_DT_CS_INTERFACE) {
                        err("skipping garbage\n");
                        goto next_desc;
                }

                switch (buffer [2]) {
                        case USB_CDC_UNION_TYPE: /* we've found it */
                                if (union_header) {
                                        err("More than one union descriptor, skipping ...");
                                        goto next_desc;
                                }
                                union_header = (struct usb_cdc_union_desc *)
                                                        buffer;
                                break;
                        case USB_CDC_COUNTRY_TYPE: /* maybe somehow export */
                                break; /* for now we ignore it */
                        case USB_CDC_HEADER_TYPE: /* maybe check version */ 
                                break; /* for now we ignore it */ 
                        case USB_CDC_ACM_TYPE:
                                ac_management_function = buffer[3];
                                break;
                        case USB_CDC_CALL_MANAGEMENT_TYPE:
                                call_management_function = buffer[3];
                                call_interface_num = buffer[4];
                                if ((call_management_function & 3) != 3)
                                        err("This device cannot do calls on its own. It is no modem.");
                                break;
                                
                        default:
                                err("Ignoring extra header, type %d, length %d", buffer[2], buffer[0]);
                                break;
                        }
next_desc:
                buflen -= buffer[0];
                buffer += buffer[0];
        }

        if (!union_header) {
                if (call_interface_num > 0) {
                        dev_dbg(&intf->dev,"No union descriptor, using call management descriptor\n");
                        data_interface = usb_ifnum_to_if(usb_dev, (data_interface_num = call_interface_num));
                        control_interface = intf;
                } else {
                        dev_dbg(&intf->dev,"No union descriptor, giving up\n");
                        return -ENODEV;
                }
        } else {
                control_interface = usb_ifnum_to_if(usb_dev, union_header->bMasterInterface0);
                data_interface = usb_ifnum_to_if(usb_dev, (data_interface_num = union_header->bSlaveInterface0));
                if (!control_interface || !data_interface) {
                        dev_dbg(&intf->dev,"no interfaces\n");
                        return -ENODEV;
                }
        }
        
        if (data_interface_num != call_interface_num)
                dev_dbg(&intf->dev,"Seperate call control interface. That is not fully supported.\n");

skip_normal_probe:

        /*workaround for switched interfaces */
        if (data_interface->cur_altsetting->desc.bInterfaceClass != CDC_DATA_INTERFACE_TYPE) {
                if (control_interface->cur_altsetting->desc.bInterfaceClass == CDC_DATA_INTERFACE_TYPE) {
                        struct usb_interface *t;
                        dev_dbg(&intf->dev,"Your device has switched interfaces.\n");

                        t = control_interface;
                        control_interface = data_interface;
                        data_interface = t;
                } else {
                        return -EINVAL;
                }
        }
        
        if (usb_interface_claimed(data_interface)) { /* valid in this context */
                dev_dbg(&intf->dev,"The data interface isn't available\n");
                return -EBUSY;
        }


        if (data_interface->cur_altsetting->desc.bNumEndpoints < 2)
                return -EINVAL;

        epctrl = &control_interface->cur_altsetting->endpoint[0].desc;
        epread = &data_interface->cur_altsetting->endpoint[0].desc;
        epwrite = &data_interface->cur_altsetting->endpoint[1].desc;


        /* workaround for switched endpoints */
        if ((epread->bEndpointAddress & USB_DIR_IN) != USB_DIR_IN) {
                /* descriptors are swapped */
                struct usb_endpoint_descriptor *t;
                dev_dbg(&intf->dev,"The data interface has switched endpoints\n");
                
                t = epread;
                epread = epwrite;
                epwrite = t;
        }
        dbg("interfaces are valid");
        for (minor = 0; minor < ACM_TTY_MINORS && acm_table[minor]; minor++);

        if (minor == ACM_TTY_MINORS) {
                err("no more free acm devices");
                return -ENODEV;
        }

        if (!(acm = kzalloc(sizeof(struct acm), GFP_KERNEL))) {
                dev_dbg(&intf->dev, "out of memory (acm kzalloc)\n");
                goto alloc_fail;
        }

        ctrlsize = le16_to_cpu(epctrl->wMaxPacketSize);
        readsize = le16_to_cpu(epread->wMaxPacketSize)*2;
        acm->writesize = le16_to_cpu(epwrite->wMaxPacketSize);
        acm->control = control_interface;
        acm->data = data_interface;
        acm->minor = minor;
        acm->dev = usb_dev;
        acm->ctrl_caps = ac_management_function;
        acm->ctrlsize = ctrlsize;
        acm->readsize = readsize;
        acm->urb_task.func = acm_rx_tasklet;
        acm->urb_task.data = (unsigned long) acm;
        INIT_WORK(&acm->work, acm_softint, acm);
        spin_lock_init(&acm->throttle_lock);
        spin_lock_init(&acm->write_lock);
        spin_lock_init(&acm->read_lock);
        acm->write_ready = 1;
        acm->rx_endpoint = usb_rcvbulkpipe(usb_dev, epread->bEndpointAddress);

        buf = usb_buffer_alloc(usb_dev, ctrlsize, GFP_KERNEL, &acm->ctrl_dma);
        if (!buf) {
                dev_dbg(&intf->dev, "out of memory (ctrl buffer alloc)\n");
                goto alloc_fail2;
        }
        acm->ctrl_buffer = buf;

        if (acm_write_buffers_alloc(acm) < 0) {
                dev_dbg(&intf->dev, "out of memory (write buffer alloc)\n");
                goto alloc_fail4;
        }

        acm->ctrlurb = usb_alloc_urb(0, GFP_KERNEL);
        if (!acm->ctrlurb) {
                dev_dbg(&intf->dev, "out of memory (ctrlurb kmalloc)\n");
                goto alloc_fail5;
        }
        for (i = 0; i < ACM_NRU; i++) {
                struct acm_ru *rcv = &(acm->ru[i]);

                if (!(rcv->urb = usb_alloc_urb(0, GFP_KERNEL))) {
                        dev_dbg(&intf->dev, "out of memory (read urbs usb_alloc_urb)\n");
                        goto alloc_fail7;
                }

                rcv->urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
                rcv->instance = acm;
        }
        for (i = 0; i < ACM_NRB; i++) {
                struct acm_rb *buf = &(acm->rb[i]);

                // Using usb_buffer_alloc instead of kmalloc as Oliver suggested
                if (!(buf->base = usb_buffer_alloc(acm->dev, readsize, GFP_KERNEL, &buf->dma))) {
                        dev_dbg(&intf->dev, "out of memory (read bufs usb_buffer_alloc)\n");
                        goto alloc_fail7;
                }
        }
        acm->writeurb = usb_alloc_urb(0, GFP_KERNEL);
        if (!acm->writeurb) {
                dev_dbg(&intf->dev, "out of memory (writeurb kmalloc)\n");
                goto alloc_fail7;
        }

        usb_fill_int_urb(acm->ctrlurb, usb_dev, usb_rcvintpipe(usb_dev, epctrl->bEndpointAddress),
                         acm->ctrl_buffer, ctrlsize, acm_ctrl_irq, acm, epctrl->bInterval);
        acm->ctrlurb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
        acm->ctrlurb->transfer_dma = acm->ctrl_dma;

        usb_fill_bulk_urb(acm->writeurb, usb_dev, usb_sndbulkpipe(usb_dev, epwrite->bEndpointAddress),
                          NULL, acm->writesize, acm_write_bulk, acm);
        acm->writeurb->transfer_flags |= URB_NO_FSBR | URB_NO_TRANSFER_DMA_MAP;

        dev_info(&intf->dev, "ttyACM%d: USB ACM device\n", minor);

        acm_set_control(acm, acm->ctrlout);

        acm->line.dwDTERate = cpu_to_le32(9600);
        acm->line.bDataBits = 8;
        acm_set_line(acm, &acm->line);

        usb_driver_claim_interface(&acm_driver, data_interface, acm);

        usb_get_intf(control_interface);
        tty_register_device(acm_tty_driver, minor, &control_interface->dev);

        acm_table[minor] = acm;
        usb_set_intfdata (intf, acm);
        return 0;

alloc_fail7:
        for (i = 0; i < ACM_NRB; i++)
                usb_buffer_free(usb_dev, acm->readsize, acm->rb[i].base, acm->rb[i].dma);
        for (i = 0; i < ACM_NRU; i++)
                usb_free_urb(acm->ru[i].urb);
        usb_free_urb(acm->ctrlurb);
alloc_fail5:
        acm_write_buffers_free(acm);
alloc_fail4:
        usb_buffer_free(usb_dev, ctrlsize, acm->ctrl_buffer, acm->ctrl_dma);
alloc_fail2:
        kfree(acm);
alloc_fail:
        return -ENOMEM;
}

static void acm_disconnect(struct usb_interface *intf)
{
        struct acm *acm = usb_get_intfdata (intf);
        struct usb_device *usb_dev = interface_to_usbdev(intf);
        int i;

        if (!acm || !acm->dev) {
                dbg("disconnect on nonexisting interface");
                return;
        }

        down(&open_sem);
        acm->dev = NULL;
        usb_set_intfdata (intf, NULL);

        tasklet_disable(&acm->urb_task);

        usb_kill_urb(acm->ctrlurb);
        usb_kill_urb(acm->writeurb);
        for (i = 0; i < ACM_NRU; i++)
                usb_kill_urb(acm->ru[i].urb);

        INIT_LIST_HEAD(&acm->filled_read_bufs);
        INIT_LIST_HEAD(&acm->spare_read_bufs);

        tasklet_enable(&acm->urb_task);

        flush_scheduled_work(); /* wait for acm_softint */

        acm_write_buffers_free(acm);
        usb_buffer_free(usb_dev, acm->ctrlsize, acm->ctrl_buffer, acm->ctrl_dma);
        for (i = 0; i < ACM_NRB; i++)
                usb_buffer_free(usb_dev, acm->readsize, acm->rb[i].base, acm->rb[i].dma);

        usb_driver_release_interface(&acm_driver, acm->data);

        if (!acm->used) {
                acm_tty_unregister(acm);
                up(&open_sem);
                return;
        }

        up(&open_sem);

        if (acm->tty)
                tty_hangup(acm->tty);
}

/*
 * USB driver structure.
 */

static struct usb_device_id acm_ids[] = {
        /* quirky and broken devices */
        { USB_DEVICE(0x0870, 0x0001), /* Metricom GS Modem */
        .driver_info = NO_UNION_NORMAL, /* has no union descriptor */
        },
        { USB_DEVICE(0x0482, 0x0203), /* KYOCERA AH-K3001V */
        .driver_info = NO_UNION_NORMAL, /* has no union descriptor */
        },
        /* control interfaces with various AT-command sets */
        { USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
                USB_CDC_ACM_PROTO_AT_V25TER) },
        { USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
                USB_CDC_ACM_PROTO_AT_PCCA101) },
        { USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
                USB_CDC_ACM_PROTO_AT_PCCA101_WAKE) },
        { USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
                USB_CDC_ACM_PROTO_AT_GSM) },
        { USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
                USB_CDC_ACM_PROTO_AT_3G ) },
        { USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
                USB_CDC_ACM_PROTO_AT_CDMA) },

        /* NOTE:  COMM/ACM/0xff is likely MSFT RNDIS ... NOT a modem!! */
        { }
};

MODULE_DEVICE_TABLE (usb, acm_ids);

static struct usb_driver acm_driver = {
        .name =         "cdc_acm",
        .probe =        acm_probe,
        .disconnect =   acm_disconnect,
        .id_table =     acm_ids,
};

/*
 * TTY driver structures.
 */

static struct tty_operations acm_ops = {
        .open =                 acm_tty_open,
        .close =                acm_tty_close,
        .write =                acm_tty_write,
        .write_room =           acm_tty_write_room,
        .ioctl =                acm_tty_ioctl,
        .throttle =             acm_tty_throttle,
        .unthrottle =           acm_tty_unthrottle,
        .chars_in_buffer =      acm_tty_chars_in_buffer,
        .break_ctl =            acm_tty_break_ctl,
        .set_termios =          acm_tty_set_termios,
        .tiocmget =             acm_tty_tiocmget,
        .tiocmset =             acm_tty_tiocmset,
};

/*
 * Init / exit.
 */

static int __init acm_init(void)
{
        int retval;
        acm_tty_driver = alloc_tty_driver(ACM_TTY_MINORS);
        if (!acm_tty_driver)
                return -ENOMEM;
        acm_tty_driver->owner = THIS_MODULE,
        acm_tty_driver->driver_name = "acm",
        acm_tty_driver->name = "ttyACM",
        acm_tty_driver->devfs_name = "usb/acm/",
        acm_tty_driver->major = ACM_TTY_MAJOR,
        acm_tty_driver->minor_start = 0,
        acm_tty_driver->type = TTY_DRIVER_TYPE_SERIAL,
        acm_tty_driver->subtype = SERIAL_TYPE_NORMAL,
        acm_tty_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_NO_DEVFS,
        acm_tty_driver->init_termios = tty_std_termios;
        acm_tty_driver->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
        tty_set_operations(acm_tty_driver, &acm_ops);

        retval = tty_register_driver(acm_tty_driver);
        if (retval) {
                put_tty_driver(acm_tty_driver);
                return retval;
        }

        retval = usb_register(&acm_driver);
        if (retval) {
                tty_unregister_driver(acm_tty_driver);
                put_tty_driver(acm_tty_driver);
                return retval;
        }

        info(DRIVER_VERSION ":" DRIVER_DESC);

        return 0;
}

static void __exit acm_exit(void)
{
        usb_deregister(&acm_driver);
        tty_unregister_driver(acm_tty_driver);
        put_tty_driver(acm_tty_driver);
}

module_init(acm_init);
module_exit(acm_exit);

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