/*
 * cdc-wdm.c
 *
 * This driver supports USB CDC WCM Device Management.
 *
 * Copyright (c) 2007-2009 Oliver Neukum
 *
 * Some code taken from cdc-acm.c
 *
 * Released under the GPLv2.
 *
 * Many thanks to Carl Nordbeck
 */
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
#include <linux/poll.h>
#include <linux/usb.h>
#include <linux/usb/cdc.h>
#include <asm/byteorder.h>
#include <asm/unaligned.h>
#include <linux/usb/cdc-wdm.h>

/*
 * Version Information
 */
#define DRIVER_VERSION "v0.03"
#define DRIVER_AUTHOR "Oliver Neukum"
#define DRIVER_DESC "USB Abstract Control Model driver for USB WCM Device Management"

static const struct usb_device_id wdm_ids[] = {
        {
                .match_flags = USB_DEVICE_ID_MATCH_INT_CLASS |
                                 USB_DEVICE_ID_MATCH_INT_SUBCLASS,
                .bInterfaceClass = USB_CLASS_COMM,
                .bInterfaceSubClass = USB_CDC_SUBCLASS_DMM
        },
        { }
};

MODULE_DEVICE_TABLE (usb, wdm_ids);

#define WDM_MINOR_BASE  176


#define WDM_IN_USE              1
#define WDM_DISCONNECTING       2
#define WDM_RESULT              3
#define WDM_READ                4
#define WDM_INT_STALL           5
#define WDM_POLL_RUNNING        6
#define WDM_RESPONDING          7
#define WDM_SUSPENDING          8
#define WDM_RESETTING           9
#define WDM_OVERFLOW            10

#define WDM_MAX                 16

/* CDC-WMC r1.1 requires wMaxCommand to be "at least 256 decimal (0x100)" */
#define WDM_DEFAULT_BUFSIZE     256

static DEFINE_MUTEX(wdm_mutex);
static DEFINE_SPINLOCK(wdm_device_list_lock);
static LIST_HEAD(wdm_device_list);

/* --- method tables --- */

struct wdm_device {
        u8                      *inbuf; /* buffer for response */
        u8                      *outbuf; /* buffer for command */
        u8                      *sbuf; /* buffer for status */
        u8                      *ubuf; /* buffer for copy to user space */

        struct urb              *command;
        struct urb              *response;
        struct urb              *validity;
        struct usb_interface    *intf;
        struct usb_ctrlrequest  *orq;
        struct usb_ctrlrequest  *irq;
        spinlock_t              iuspin;

        unsigned long           flags;
        u16                     bufsize;
        u16                     wMaxCommand;
        u16                     wMaxPacketSize;
        __le16                  inum;
        int                     reslength;
        int                     length;
        int                     read;
        int                     count;
        dma_addr_t              shandle;
        dma_addr_t              ihandle;
        struct mutex            wlock;
        struct mutex            rlock;
        wait_queue_head_t       wait;
        struct work_struct      rxwork;
        int                     werr;
        int                     rerr;

        struct list_head        device_list;
        int                     (*manage_power)(struct usb_interface *, int);
};

static struct usb_driver wdm_driver;

/* return intfdata if we own the interface, else look up intf in the list */
static struct wdm_device *wdm_find_device(struct usb_interface *intf)
{
        struct wdm_device *desc;

        spin_lock(&wdm_device_list_lock);
        list_for_each_entry(desc, &wdm_device_list, device_list)
                if (desc->intf == intf)
                        goto found;
        desc = NULL;
found:
        spin_unlock(&wdm_device_list_lock);

        return desc;
}

static struct wdm_device *wdm_find_device_by_minor(int minor)
{
        struct wdm_device *desc;

        spin_lock(&wdm_device_list_lock);
        list_for_each_entry(desc, &wdm_device_list, device_list)
                if (desc->intf->minor == minor)
                        goto found;
        desc = NULL;
found:
        spin_unlock(&wdm_device_list_lock);

        return desc;
}

/* --- callbacks --- */
static void wdm_out_callback(struct urb *urb)
{
        struct wdm_device *desc;
        desc = urb->context;
        spin_lock(&desc->iuspin);
        desc->werr = urb->status;
        spin_unlock(&desc->iuspin);
        kfree(desc->outbuf);
        desc->outbuf = NULL;
        clear_bit(WDM_IN_USE, &desc->flags);
        wake_up(&desc->wait);
}

static void wdm_in_callback(struct urb *urb)
{
        struct wdm_device *desc = urb->context;
        int status = urb->status;
        int length = urb->actual_length;

        spin_lock(&desc->iuspin);
        clear_bit(WDM_RESPONDING, &desc->flags);

        if (status) {
                switch (status) {
                case -ENOENT:
                        dev_dbg(&desc->intf->dev,
                                "nonzero urb status received: -ENOENT");
                        goto skip_error;
                case -ECONNRESET:
                        dev_dbg(&desc->intf->dev,
                                "nonzero urb status received: -ECONNRESET");
                        goto skip_error;
                case -ESHUTDOWN:
                        dev_dbg(&desc->intf->dev,
                                "nonzero urb status received: -ESHUTDOWN");
                        goto skip_error;
                case -EPIPE:
                        dev_err(&desc->intf->dev,
                                "nonzero urb status received: -EPIPE\n");
                        break;
                default:
                        dev_err(&desc->intf->dev,
                                "Unexpected error %d\n", status);
                        break;
                }
        }

        desc->rerr = status;
        if (length + desc->length > desc->wMaxCommand) {
                /* The buffer would overflow */
                set_bit(WDM_OVERFLOW, &desc->flags);
        } else {
                /* we may already be in overflow */
                if (!test_bit(WDM_OVERFLOW, &desc->flags)) {
                        memmove(desc->ubuf + desc->length, desc->inbuf, length);
                        desc->length += length;
                        desc->reslength = length;
                }
        }
skip_error:
        wake_up(&desc->wait);

        set_bit(WDM_READ, &desc->flags);
        spin_unlock(&desc->iuspin);
}

static void wdm_int_callback(struct urb *urb)
{
        int rv = 0;
        int status = urb->status;
        struct wdm_device *desc;
        struct usb_cdc_notification *dr;

        desc = urb->context;
        dr = (struct usb_cdc_notification *)desc->sbuf;

        if (status) {
                switch (status) {
                case -ESHUTDOWN:
                case -ENOENT:
                case -ECONNRESET:
                        return; /* unplug */
                case -EPIPE:
                        set_bit(WDM_INT_STALL, &desc->flags);
                        dev_err(&desc->intf->dev, "Stall on int endpoint\n");
                        goto sw; /* halt is cleared in work */
                default:
                        dev_err(&desc->intf->dev,
                                "nonzero urb status received: %d\n", status);
                        break;
                }
        }

        if (urb->actual_length < sizeof(struct usb_cdc_notification)) {
                dev_err(&desc->intf->dev, "wdm_int_callback - %d bytes\n",
                        urb->actual_length);
                goto exit;
        }

        switch (dr->bNotificationType) {
        case USB_CDC_NOTIFY_RESPONSE_AVAILABLE:
                dev_dbg(&desc->intf->dev,
                        "NOTIFY_RESPONSE_AVAILABLE received: index %d len %d",
                        dr->wIndex, dr->wLength);
                break;

        case USB_CDC_NOTIFY_NETWORK_CONNECTION:

                dev_dbg(&desc->intf->dev,
                        "NOTIFY_NETWORK_CONNECTION %s network",
                        dr->wValue ? "connected to" : "disconnected from");
                goto exit;
        default:
                clear_bit(WDM_POLL_RUNNING, &desc->flags);
                dev_err(&desc->intf->dev,
                        "unknown notification %d received: index %d len %d\n",
                        dr->bNotificationType, dr->wIndex, dr->wLength);
                goto exit;
        }

        spin_lock(&desc->iuspin);
        clear_bit(WDM_READ, &desc->flags);
        set_bit(WDM_RESPONDING, &desc->flags);
        if (!test_bit(WDM_DISCONNECTING, &desc->flags)
                && !test_bit(WDM_SUSPENDING, &desc->flags)) {
                rv = usb_submit_urb(desc->response, GFP_ATOMIC);
                dev_dbg(&desc->intf->dev, "%s: usb_submit_urb %d",
                        __func__, rv);
        }
        spin_unlock(&desc->iuspin);
        if (rv < 0) {
                clear_bit(WDM_RESPONDING, &desc->flags);
                if (rv == -EPERM)
                        return;
                if (rv == -ENOMEM) {
sw:
                        rv = schedule_work(&desc->rxwork);
                        if (rv)
                                dev_err(&desc->intf->dev,
                                        "Cannot schedule work\n");
                }
        }
exit:
        rv = usb_submit_urb(urb, GFP_ATOMIC);
        if (rv)
                dev_err(&desc->intf->dev,
                        "%s - usb_submit_urb failed with result %d\n",
                        __func__, rv);

}

static void kill_urbs(struct wdm_device *desc)
{
        /* the order here is essential */
        usb_kill_urb(desc->command);
        usb_kill_urb(desc->validity);
        usb_kill_urb(desc->response);
}

static void free_urbs(struct wdm_device *desc)
{
        usb_free_urb(desc->validity);
        usb_free_urb(desc->response);
        usb_free_urb(desc->command);
}

static void cleanup(struct wdm_device *desc)
{
        kfree(desc->sbuf);
        kfree(desc->inbuf);
        kfree(desc->orq);
        kfree(desc->irq);
        kfree(desc->ubuf);
        free_urbs(desc);
        kfree(desc);
}

static ssize_t wdm_write
(struct file *file, const char __user *buffer, size_t count, loff_t *ppos)
{
        u8 *buf;
        int rv = -EMSGSIZE, r, we;
        struct wdm_device *desc = file->private_data;
        struct usb_ctrlrequest *req;

        if (count > desc->wMaxCommand)
                count = desc->wMaxCommand;

        spin_lock_irq(&desc->iuspin);
        we = desc->werr;
        desc->werr = 0;
        spin_unlock_irq(&desc->iuspin);
        if (we < 0)
                return -EIO;

        buf = kmalloc(count, GFP_KERNEL);
        if (!buf) {
                rv = -ENOMEM;
                goto outnl;
        }

        r = copy_from_user(buf, buffer, count);
        if (r > 0) {
                kfree(buf);
                rv = -EFAULT;
                goto outnl;
        }

        /* concurrent writes and disconnect */
        r = mutex_lock_interruptible(&desc->wlock);
        rv = -ERESTARTSYS;
        if (r) {
                kfree(buf);
                goto outnl;
        }

        if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
                kfree(buf);
                rv = -ENODEV;
                goto outnp;
        }

        r = usb_autopm_get_interface(desc->intf);
        if (r < 0) {
                kfree(buf);
                rv = usb_translate_errors(r);
                goto outnp;
        }

        if (!(file->f_flags & O_NONBLOCK))
                r = wait_event_interruptible(desc->wait, !test_bit(WDM_IN_USE,
                                                                &desc->flags));
        else
                if (test_bit(WDM_IN_USE, &desc->flags))
                        r = -EAGAIN;

        if (test_bit(WDM_RESETTING, &desc->flags))
                r = -EIO;

        if (r < 0) {
                kfree(buf);
                rv = r;
                goto out;
        }

        req = desc->orq;
        usb_fill_control_urb(
                desc->command,
                interface_to_usbdev(desc->intf),
                /* using common endpoint 0 */
                usb_sndctrlpipe(interface_to_usbdev(desc->intf), 0),
                (unsigned char *)req,
                buf,
                count,
                wdm_out_callback,
                desc
        );

        req->bRequestType = (USB_DIR_OUT | USB_TYPE_CLASS |
                             USB_RECIP_INTERFACE);
        req->bRequest = USB_CDC_SEND_ENCAPSULATED_COMMAND;
        req->wValue = 0;
        req->wIndex = desc->inum;
        req->wLength = cpu_to_le16(count);
        set_bit(WDM_IN_USE, &desc->flags);
        desc->outbuf = buf;

        rv = usb_submit_urb(desc->command, GFP_KERNEL);
        if (rv < 0) {
                kfree(buf);
                desc->outbuf = NULL;
                clear_bit(WDM_IN_USE, &desc->flags);
                dev_err(&desc->intf->dev, "Tx URB error: %d\n", rv);
                rv = usb_translate_errors(rv);
        } else {
                dev_dbg(&desc->intf->dev, "Tx URB has been submitted index=%d",
                        req->wIndex);
        }
out:
        usb_autopm_put_interface(desc->intf);
outnp:
        mutex_unlock(&desc->wlock);
outnl:
        return rv < 0 ? rv : count;
}

static ssize_t wdm_read
(struct file *file, char __user *buffer, size_t count, loff_t *ppos)
{
        int rv, cntr;
        int i = 0;
        struct wdm_device *desc = file->private_data;


        rv = mutex_lock_interruptible(&desc->rlock); /*concurrent reads */
        if (rv < 0)
                return -ERESTARTSYS;

        cntr = ACCESS_ONCE(desc->length);
        if (cntr == 0) {
                desc->read = 0;
retry:
                if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
                        rv = -ENODEV;
                        goto err;
                }
                if (test_bit(WDM_OVERFLOW, &desc->flags)) {
                        clear_bit(WDM_OVERFLOW, &desc->flags);
                        rv = -ENOBUFS;
                        goto err;
                }
                i++;
                if (file->f_flags & O_NONBLOCK) {
                        if (!test_bit(WDM_READ, &desc->flags)) {
                                rv = cntr ? cntr : -EAGAIN;
                                goto err;
                        }
                        rv = 0;
                } else {
                        rv = wait_event_interruptible(desc->wait,
                                test_bit(WDM_READ, &desc->flags));
                }

                /* may have happened while we slept */
                if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
                        rv = -ENODEV;
                        goto err;
                }
                if (test_bit(WDM_RESETTING, &desc->flags)) {
                        rv = -EIO;
                        goto err;
                }
                usb_mark_last_busy(interface_to_usbdev(desc->intf));
                if (rv < 0) {
                        rv = -ERESTARTSYS;
                        goto err;
                }

                spin_lock_irq(&desc->iuspin);

                if (desc->rerr) { /* read completed, error happened */
                        desc->rerr = 0;
                        spin_unlock_irq(&desc->iuspin);
                        rv = -EIO;
                        goto err;
                }
                /*
                 * recheck whether we've lost the race
                 * against the completion handler
                 */
                if (!test_bit(WDM_READ, &desc->flags)) { /* lost race */
                        spin_unlock_irq(&desc->iuspin);
                        goto retry;
                }

                if (!desc->reslength) { /* zero length read */
                        dev_dbg(&desc->intf->dev, "%s: zero length - clearing WDM_READ\n", __func__);
                        clear_bit(WDM_READ, &desc->flags);
                        spin_unlock_irq(&desc->iuspin);
                        goto retry;
                }
                cntr = desc->length;
                spin_unlock_irq(&desc->iuspin);
        }

        if (cntr > count)
                cntr = count;
        rv = copy_to_user(buffer, desc->ubuf, cntr);
        if (rv > 0) {
                rv = -EFAULT;
                goto err;
        }

        spin_lock_irq(&desc->iuspin);

        for (i = 0; i < desc->length - cntr; i++)
                desc->ubuf[i] = desc->ubuf[i + cntr];

        desc->length -= cntr;
        /* in case we had outstanding data */
        if (!desc->length)
                clear_bit(WDM_READ, &desc->flags);

        spin_unlock_irq(&desc->iuspin);

        rv = cntr;

err:
        mutex_unlock(&desc->rlock);
        return rv;
}

static int wdm_flush(struct file *file, fl_owner_t id)
{
        struct wdm_device *desc = file->private_data;

        wait_event(desc->wait, !test_bit(WDM_IN_USE, &desc->flags));

        /* cannot dereference desc->intf if WDM_DISCONNECTING */
        if (desc->werr < 0 && !test_bit(WDM_DISCONNECTING, &desc->flags))
                dev_err(&desc->intf->dev, "Error in flush path: %d\n",
                        desc->werr);

        return usb_translate_errors(desc->werr);
}

static unsigned int wdm_poll(struct file *file, struct poll_table_struct *wait)
{
        struct wdm_device *desc = file->private_data;
        unsigned long flags;
        unsigned int mask = 0;

        spin_lock_irqsave(&desc->iuspin, flags);
        if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
                mask = POLLHUP | POLLERR;
                spin_unlock_irqrestore(&desc->iuspin, flags);
                goto desc_out;
        }
        if (test_bit(WDM_READ, &desc->flags))
                mask = POLLIN | POLLRDNORM;
        if (desc->rerr || desc->werr)
                mask |= POLLERR;
        if (!test_bit(WDM_IN_USE, &desc->flags))
                mask |= POLLOUT | POLLWRNORM;
        spin_unlock_irqrestore(&desc->iuspin, flags);

        poll_wait(file, &desc->wait, wait);

desc_out:
        return mask;
}

static int wdm_open(struct inode *inode, struct file *file)
{
        int minor = iminor(inode);
        int rv = -ENODEV;
        struct usb_interface *intf;
        struct wdm_device *desc;

        mutex_lock(&wdm_mutex);
        desc = wdm_find_device_by_minor(minor);
        if (!desc)
                goto out;

        intf = desc->intf;
        if (test_bit(WDM_DISCONNECTING, &desc->flags))
                goto out;
        file->private_data = desc;

        rv = usb_autopm_get_interface(desc->intf);
        if (rv < 0) {
                dev_err(&desc->intf->dev, "Error autopm - %d\n", rv);
                goto out;
        }

        /* using write lock to protect desc->count */
        mutex_lock(&desc->wlock);
        if (!desc->count++) {
                desc->werr = 0;
                desc->rerr = 0;
                rv = usb_submit_urb(desc->validity, GFP_KERNEL);
                if (rv < 0) {
                        desc->count--;
                        dev_err(&desc->intf->dev,
                                "Error submitting int urb - %d\n", rv);
                        rv = usb_translate_errors(rv);
                }
        } else {
                rv = 0;
        }
        mutex_unlock(&desc->wlock);
        if (desc->count == 1)
                desc->manage_power(intf, 1);
        usb_autopm_put_interface(desc->intf);
out:
        mutex_unlock(&wdm_mutex);
        return rv;
}

static int wdm_release(struct inode *inode, struct file *file)
{
        struct wdm_device *desc = file->private_data;

        mutex_lock(&wdm_mutex);

        /* using write lock to protect desc->count */
        mutex_lock(&desc->wlock);
        desc->count--;
        mutex_unlock(&desc->wlock);

        if (!desc->count) {
                if (!test_bit(WDM_DISCONNECTING, &desc->flags)) {
                        dev_dbg(&desc->intf->dev, "wdm_release: cleanup");
                        kill_urbs(desc);
                        desc->manage_power(desc->intf, 0);
                } else {
                        /* must avoid dev_printk here as desc->intf is invalid */
                        pr_debug(KBUILD_MODNAME " %s: device gone - cleaning up\n", __func__);
                        cleanup(desc);
                }
        }
        mutex_unlock(&wdm_mutex);
        return 0;
}

static const struct file_operations wdm_fops = {
        .owner =        THIS_MODULE,
        .read =         wdm_read,
        .write =        wdm_write,
        .open =         wdm_open,
        .flush =        wdm_flush,
        .release =      wdm_release,
        .poll =         wdm_poll,
        .llseek =       noop_llseek,
};

static struct usb_class_driver wdm_class = {
        .name =         "cdc-wdm%d",
        .fops =         &wdm_fops,
        .minor_base =   WDM_MINOR_BASE,
};

/* --- error handling --- */
static void wdm_rxwork(struct work_struct *work)
{
        struct wdm_device *desc = container_of(work, struct wdm_device, rxwork);
        unsigned long flags;
        int rv;

        spin_lock_irqsave(&desc->iuspin, flags);
        if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
                spin_unlock_irqrestore(&desc->iuspin, flags);
        } else {
                spin_unlock_irqrestore(&desc->iuspin, flags);
                rv = usb_submit_urb(desc->response, GFP_KERNEL);
                if (rv < 0 && rv != -EPERM) {
                        spin_lock_irqsave(&desc->iuspin, flags);
                        if (!test_bit(WDM_DISCONNECTING, &desc->flags))
                                schedule_work(&desc->rxwork);
                        spin_unlock_irqrestore(&desc->iuspin, flags);
                }
        }
}

/* --- hotplug --- */

static int wdm_create(struct usb_interface *intf, struct usb_endpoint_descriptor *ep,
                u16 bufsize, int (*manage_power)(struct usb_interface *, int))
{
        int rv = -ENOMEM;
        struct wdm_device *desc;

        desc = kzalloc(sizeof(struct wdm_device), GFP_KERNEL);
        if (!desc)
                goto out;
        INIT_LIST_HEAD(&desc->device_list);
        mutex_init(&desc->rlock);
        mutex_init(&desc->wlock);
        spin_lock_init(&desc->iuspin);
        init_waitqueue_head(&desc->wait);
        desc->wMaxCommand = bufsize;
        /* this will be expanded and needed in hardware endianness */
        desc->inum = cpu_to_le16((u16)intf->cur_altsetting->desc.bInterfaceNumber);
        desc->intf = intf;
        INIT_WORK(&desc->rxwork, wdm_rxwork);

        rv = -EINVAL;
        if (!usb_endpoint_is_int_in(ep))
                goto err;

        desc->wMaxPacketSize = usb_endpoint_maxp(ep);

        desc->orq = kmalloc(sizeof(struct usb_ctrlrequest), GFP_KERNEL);
        if (!desc->orq)
                goto err;
        desc->irq = kmalloc(sizeof(struct usb_ctrlrequest), GFP_KERNEL);
        if (!desc->irq)
                goto err;

        desc->validity = usb_alloc_urb(0, GFP_KERNEL);
        if (!desc->validity)
                goto err;

        desc->response = usb_alloc_urb(0, GFP_KERNEL);
        if (!desc->response)
                goto err;

        desc->command = usb_alloc_urb(0, GFP_KERNEL);
        if (!desc->command)
                goto err;

        desc->ubuf = kmalloc(desc->wMaxCommand, GFP_KERNEL);
        if (!desc->ubuf)
                goto err;

        desc->sbuf = kmalloc(desc->wMaxPacketSize, GFP_KERNEL);
        if (!desc->sbuf)
                goto err;

        desc->inbuf = kmalloc(desc->wMaxCommand, GFP_KERNEL);
        if (!desc->inbuf)
                goto err;

        usb_fill_int_urb(
                desc->validity,
                interface_to_usbdev(intf),
                usb_rcvintpipe(interface_to_usbdev(intf), ep->bEndpointAddress),
                desc->sbuf,
                desc->wMaxPacketSize,
                wdm_int_callback,
                desc,
                ep->bInterval
        );

        desc->irq->bRequestType = (USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE);
        desc->irq->bRequest = USB_CDC_GET_ENCAPSULATED_RESPONSE;
        desc->irq->wValue = 0;
        desc->irq->wIndex = desc->inum;
        desc->irq->wLength = cpu_to_le16(desc->wMaxCommand);

        usb_fill_control_urb(
                desc->response,
                interface_to_usbdev(intf),
                /* using common endpoint 0 */
                usb_rcvctrlpipe(interface_to_usbdev(desc->intf), 0),
                (unsigned char *)desc->irq,
                desc->inbuf,
                desc->wMaxCommand,
                wdm_in_callback,
                desc
        );

        desc->manage_power = manage_power;

        spin_lock(&wdm_device_list_lock);
        list_add(&desc->device_list, &wdm_device_list);
        spin_unlock(&wdm_device_list_lock);

        rv = usb_register_dev(intf, &wdm_class);
        if (rv < 0)
                goto err;
        else
                dev_info(&intf->dev, "%s: USB WDM device\n", dev_name(intf->usb_dev));
out:
        return rv;
err:
        spin_lock(&wdm_device_list_lock);
        list_del(&desc->device_list);
        spin_unlock(&wdm_device_list_lock);
        cleanup(desc);
        return rv;
}

static int wdm_manage_power(struct usb_interface *intf, int on)
{
        /* need autopm_get/put here to ensure the usbcore sees the new value */
        int rv = usb_autopm_get_interface(intf);
        if (rv < 0)
                goto err;

        intf->needs_remote_wakeup = on;
        usb_autopm_put_interface(intf);
err:
        return rv;
}

static int wdm_probe(struct usb_interface *intf, const struct usb_device_id *id)
{
        int rv = -EINVAL;
        struct usb_host_interface *iface;
        struct usb_endpoint_descriptor *ep;
        struct usb_cdc_dmm_desc *dmhd;
        u8 *buffer = intf->altsetting->extra;
        int buflen = intf->altsetting->extralen;
        u16 maxcom = WDM_DEFAULT_BUFSIZE;

        if (!buffer)
                goto err;
        while (buflen > 2) {
                if (buffer[1] != USB_DT_CS_INTERFACE) {
                        dev_err(&intf->dev, "skipping garbage\n");
                        goto next_desc;
                }

                switch (buffer[2]) {
                case USB_CDC_HEADER_TYPE:
                        break;
                case USB_CDC_DMM_TYPE:
                        dmhd = (struct usb_cdc_dmm_desc *)buffer;
                        maxcom = le16_to_cpu(dmhd->wMaxCommand);
                        dev_dbg(&intf->dev,
                                "Finding maximum buffer length: %d", maxcom);
                        break;
                default:
                        dev_err(&intf->dev,
                                "Ignoring extra header, type %d, length %d\n",
                                buffer[2], buffer[0]);
                        break;
                }
next_desc:
                buflen -= buffer[0];
                buffer += buffer[0];
        }

        iface = intf->cur_altsetting;
        if (iface->desc.bNumEndpoints != 1)
                goto err;
        ep = &iface->endpoint[0].desc;

        rv = wdm_create(intf, ep, maxcom, &wdm_manage_power);

err:
        return rv;
}

/**
 * usb_cdc_wdm_register - register a WDM subdriver
 * @intf: usb interface the subdriver will associate with
 * @ep: interrupt endpoint to monitor for notifications
 * @bufsize: maximum message size to support for read/write
 *
 * Create WDM usb class character device and associate it with intf
 * without binding, allowing another driver to manage the interface.
 *
 * The subdriver will manage the given interrupt endpoint exclusively
 * and will issue control requests referring to the given intf. It
 * will otherwise avoid interferring, and in particular not do
 * usb_set_intfdata/usb_get_intfdata on intf.
 *
 * The return value is a pointer to the subdriver's struct usb_driver.
 * The registering driver is responsible for calling this subdriver's
 * disconnect, suspend, resume, pre_reset and post_reset methods from
 * its own.
 */
struct usb_driver *usb_cdc_wdm_register(struct usb_interface *intf,
                                        struct usb_endpoint_descriptor *ep,
                                        int bufsize,
                                        int (*manage_power)(struct usb_interface *, int))
{
        int rv = -EINVAL;

        rv = wdm_create(intf, ep, bufsize, manage_power);
        if (rv < 0)
                goto err;

        return &wdm_driver;
err:
        return ERR_PTR(rv);
}
EXPORT_SYMBOL(usb_cdc_wdm_register);

static void wdm_disconnect(struct usb_interface *intf)
{
        struct wdm_device *desc;
        unsigned long flags;

        usb_deregister_dev(intf, &wdm_class);
        desc = wdm_find_device(intf);
        mutex_lock(&wdm_mutex);

        /* the spinlock makes sure no new urbs are generated in the callbacks */
        spin_lock_irqsave(&desc->iuspin, flags);
        set_bit(WDM_DISCONNECTING, &desc->flags);
        set_bit(WDM_READ, &desc->flags);
        /* to terminate pending flushes */
        clear_bit(WDM_IN_USE, &desc->flags);
        spin_unlock_irqrestore(&desc->iuspin, flags);
        wake_up_all(&desc->wait);
        mutex_lock(&desc->rlock);
        mutex_lock(&desc->wlock);
        kill_urbs(desc);
        cancel_work_sync(&desc->rxwork);
        mutex_unlock(&desc->wlock);
        mutex_unlock(&desc->rlock);

        /* the desc->intf pointer used as list key is now invalid */
        spin_lock(&wdm_device_list_lock);
        list_del(&desc->device_list);
        spin_unlock(&wdm_device_list_lock);

        if (!desc->count)
                cleanup(desc);
        else
                dev_dbg(&intf->dev, "%s: %d open files - postponing cleanup\n", __func__, desc->count);
        mutex_unlock(&wdm_mutex);
}

#ifdef CONFIG_PM
static int wdm_suspend(struct usb_interface *intf, pm_message_t message)
{
        struct wdm_device *desc = wdm_find_device(intf);
        int rv = 0;

        dev_dbg(&desc->intf->dev, "wdm%d_suspend\n", intf->minor);

        /* if this is an autosuspend the caller does the locking */
        if (!PMSG_IS_AUTO(message)) {
                mutex_lock(&desc->rlock);
                mutex_lock(&desc->wlock);
        }
        spin_lock_irq(&desc->iuspin);

        if (PMSG_IS_AUTO(message) &&
                        (test_bit(WDM_IN_USE, &desc->flags)
                        || test_bit(WDM_RESPONDING, &desc->flags))) {
                spin_unlock_irq(&desc->iuspin);
                rv = -EBUSY;
        } else {

                set_bit(WDM_SUSPENDING, &desc->flags);
                spin_unlock_irq(&desc->iuspin);
                /* callback submits work - order is essential */
                kill_urbs(desc);
                cancel_work_sync(&desc->rxwork);
        }
        if (!PMSG_IS_AUTO(message)) {
                mutex_unlock(&desc->wlock);
                mutex_unlock(&desc->rlock);
        }

        return rv;
}
#endif

static int recover_from_urb_loss(struct wdm_device *desc)
{
        int rv = 0;

        if (desc->count) {
                rv = usb_submit_urb(desc->validity, GFP_NOIO);
                if (rv < 0)
                        dev_err(&desc->intf->dev,
                                "Error resume submitting int urb - %d\n", rv);
        }
        return rv;
}

#ifdef CONFIG_PM
static int wdm_resume(struct usb_interface *intf)
{
        struct wdm_device *desc = wdm_find_device(intf);
        int rv;

        dev_dbg(&desc->intf->dev, "wdm%d_resume\n", intf->minor);

        clear_bit(WDM_SUSPENDING, &desc->flags);
        rv = recover_from_urb_loss(desc);

        return rv;
}
#endif

static int wdm_pre_reset(struct usb_interface *intf)
{
        struct wdm_device *desc = wdm_find_device(intf);

        /*
         * we notify everybody using poll of
         * an exceptional situation

         * must be done before recovery lest a spontaneous
         * message from the device is lost
         */
        spin_lock_irq(&desc->iuspin);
        set_bit(WDM_RESETTING, &desc->flags);   /* inform read/write */
        set_bit(WDM_READ, &desc->flags);        /* unblock read */
        clear_bit(WDM_IN_USE, &desc->flags);    /* unblock write */
        desc->rerr = -EINTR;
        spin_unlock_irq(&desc->iuspin);
        wake_up_all(&desc->wait);
        mutex_lock(&desc->rlock);
        mutex_lock(&desc->wlock);
        kill_urbs(desc);
        cancel_work_sync(&desc->rxwork);
        return 0;
}

static int wdm_post_reset(struct usb_interface *intf)
{
        struct wdm_device *desc = wdm_find_device(intf);
        int rv;

        clear_bit(WDM_OVERFLOW, &desc->flags);
        clear_bit(WDM_RESETTING, &desc->flags);
        rv = recover_from_urb_loss(desc);
        mutex_unlock(&desc->wlock);
        mutex_unlock(&desc->rlock);
        return 0;
}

static struct usb_driver wdm_driver = {
        .name =         "cdc_wdm",
        .probe =        wdm_probe,
        .disconnect =   wdm_disconnect,
#ifdef CONFIG_PM
        .suspend =      wdm_suspend,
        .resume =       wdm_resume,
        .reset_resume = wdm_resume,
#endif
        .pre_reset =    wdm_pre_reset,
        .post_reset =   wdm_post_reset,
        .id_table =     wdm_ids,
        .supports_autosuspend = 1,
        .disable_hub_initiated_lpm = 1,
};

module_usb_driver(wdm_driver);

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