/*
   * USB Skeleton driver - 2.2
   *
   * Copyright (C) 2001-2004 Greg Kroah-Hartman (greg@kroah.com)
   *
   *	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, version 2.
   *
   * This driver is based on the 2.6.3 version of drivers/usb/usb-skeleton.c
   * but has been rewritten to be easier to read and use.
   *
   */
  
  #include <linux/kernel.h>
  #include <linux/errno.h>
  #include <linux/slab.h>
  #include <linux/module.h>
  #include <linux/kref.h>
  #include <linux/uaccess.h>
  #include <linux/usb.h>
  #include <linux/mutex.h>
  
  
  /* Define these values to match your devices */
  #define USB_SKEL_VENDOR_ID	0xfff0
  #define USB_SKEL_PRODUCT_ID	0xfff0
  
  /* table of devices that work with this driver */
  static const struct usb_device_id skel_table[] = {
  	{ USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
  	{ }					/* Terminating entry */
  };
  MODULE_DEVICE_TABLE(usb, skel_table);
  
  
  /* Get a minor range for your devices from the usb maintainer */
  #define USB_SKEL_MINOR_BASE	192
  
  /* our private defines. if this grows any larger, use your own .h file */
  #define MAX_TRANSFER		(PAGE_SIZE - 512)
  /* MAX_TRANSFER is chosen so that the VM is not stressed by
     allocations > PAGE_SIZE and the number of packets in a page
     is an integer 512 is the largest possible packet on EHCI */
  #define WRITES_IN_FLIGHT	8
  /* arbitrarily chosen */
  
  /* Structure to hold all of our device specific stuff */
  struct usb_skel {
  	struct usb_device	*udev;			/* the usb device for this device */
  	struct usb_interface	*interface;		/* the interface for this device */
  	struct semaphore	limit_sem;		/* limiting the number of writes in progress */
  	struct usb_anchor	submitted;		/* in case we need to retract our submissions */
  	struct urb		*bulk_in_urb;		/* the urb to read data with */
  	unsigned char           *bulk_in_buffer;	/* the buffer to receive data */
  	size_t			bulk_in_size;		/* the size of the receive buffer */
  	size_t			bulk_in_filled;		/* number of bytes in the buffer */
  	size_t			bulk_in_copied;		/* already copied to user space */
  	__u8			bulk_in_endpointAddr;	/* the address of the bulk in endpoint */
  	__u8			bulk_out_endpointAddr;	/* the address of the bulk out endpoint */
  	int			errors;			/* the last request tanked */
  	bool			ongoing_read;		/* a read is going on */
  	spinlock_t		err_lock;		/* lock for errors */
  	struct kref		kref;
  	struct mutex		io_mutex;		/* synchronize I/O with disconnect */
  	wait_queue_head_t	bulk_in_wait;		/* to wait for an ongoing read */
  };
  #define to_skel_dev(d) container_of(d, struct usb_skel, kref)
  
  static struct usb_driver skel_driver;
  static void skel_draw_down(struct usb_skel *dev);
  
  static void skel_delete(struct kref *kref)
  {
  	struct usb_skel *dev = to_skel_dev(kref);
  
  	usb_free_urb(dev->bulk_in_urb);
  	usb_put_dev(dev->udev);
  	kfree(dev->bulk_in_buffer);
  	kfree(dev);
  }
  
  static int skel_open(struct inode *inode, struct file *file)
  {
  	struct usb_skel *dev;
  	struct usb_interface *interface;
  	int subminor;
  	int retval = 0;
  
  	subminor = iminor(inode);
  
  	interface = usb_find_interface(&skel_driver, subminor);
  	if (!interface) {
  		pr_err("%s - error, can't find device for minor %d
  ",
  			__func__, subminor);
  		retval = -ENODEV;
  		goto exit;
  	}
  
  	dev = usb_get_intfdata(interface);
  	if (!dev) {
  		retval = -ENODEV;
  		goto exit;
  	}
  
  	retval = usb_autopm_get_interface(interface);
  	if (retval)
  		goto exit;
  
  	/* increment our usage count for the device */
  	kref_get(&dev->kref);
  
  	/* save our object in the file's private structure */
  	file->private_data = dev;
  
  exit:
  	return retval;
  }
  
  static int skel_release(struct inode *inode, struct file *file)
  {
  	struct usb_skel *dev;
  
  	dev = file->private_data;
  	if (dev == NULL)
  		return -ENODEV;
  
  	/* allow the device to be autosuspended */
  	mutex_lock(&dev->io_mutex);
  	if (dev->interface)
  		usb_autopm_put_interface(dev->interface);
  	mutex_unlock(&dev->io_mutex);
  
  	/* decrement the count on our device */
  	kref_put(&dev->kref, skel_delete);
  	return 0;
  }
  
  static int skel_flush(struct file *file, fl_owner_t id)
  {
  	struct usb_skel *dev;
  	int res;
  
  	dev = file->private_data;
  	if (dev == NULL)
  		return -ENODEV;
  
  	/* wait for io to stop */
  	mutex_lock(&dev->io_mutex);
  	skel_draw_down(dev);
  
  	/* read out errors, leave subsequent opens a clean slate */
  	spin_lock_irq(&dev->err_lock);
  	res = dev->errors ? (dev->errors == -EPIPE ? -EPIPE : -EIO) : 0;
  	dev->errors = 0;
  	spin_unlock_irq(&dev->err_lock);
  
  	mutex_unlock(&dev->io_mutex);
  
  	return res;
  }
  
  static void skel_read_bulk_callback(struct urb *urb)
  {
  	struct usb_skel *dev;
  
  	dev = urb->context;
  
  	spin_lock(&dev->err_lock);
  	/* sync/async unlink faults aren't errors */
  	if (urb->status) {
  		if (!(urb->status == -ENOENT ||
  		    urb->status == -ECONNRESET ||
  		    urb->status == -ESHUTDOWN))
  			dev_err(&dev->interface->dev,
  				"%s - nonzero write bulk status received: %d
  ",
  				__func__, urb->status);
  
  		dev->errors = urb->status;
  	} else {
  		dev->bulk_in_filled = urb->actual_length;
  	}
  	dev->ongoing_read = 0;
  	spin_unlock(&dev->err_lock);
  
  	wake_up_interruptible(&dev->bulk_in_wait);
  }
  
  static int skel_do_read_io(struct usb_skel *dev, size_t count)
  {
  	int rv;
  
  	/* prepare a read */
  	usb_fill_bulk_urb(dev->bulk_in_urb,
  			dev->udev,
  			usb_rcvbulkpipe(dev->udev,
  				dev->bulk_in_endpointAddr),
  			dev->bulk_in_buffer,
  			min(dev->bulk_in_size, count),
  			skel_read_bulk_callback,
  			dev);
  	/* tell everybody to leave the URB alone */
  	spin_lock_irq(&dev->err_lock);
  	dev->ongoing_read = 1;
  	spin_unlock_irq(&dev->err_lock);
  
  	/* submit bulk in urb, which means no data to deliver */
  	dev->bulk_in_filled = 0;
  	dev->bulk_in_copied = 0;
  
  	/* do it */
  	rv = usb_submit_urb(dev->bulk_in_urb, GFP_KERNEL);
  	if (rv < 0) {
  		dev_err(&dev->interface->dev,
  			"%s - failed submitting read urb, error %d
  ",
  			__func__, rv);
  		rv = (rv == -ENOMEM) ? rv : -EIO;
  		spin_lock_irq(&dev->err_lock);
  		dev->ongoing_read = 0;
  		spin_unlock_irq(&dev->err_lock);
  	}
  
  	return rv;
  }
  
  static ssize_t skel_read(struct file *file, char *buffer, size_t count,
  			 loff_t *ppos)
  {
  	struct usb_skel *dev;
  	int rv;
  	bool ongoing_io;
  
  	dev = file->private_data;
  
  	/* if we cannot read at all, return EOF */
  	if (!dev->bulk_in_urb || !count)
  		return 0;
  
  	/* no concurrent readers */
  	rv = mutex_lock_interruptible(&dev->io_mutex);
  	if (rv < 0)
  		return rv;
  
  	if (!dev->interface) {		/* disconnect() was called */
  		rv = -ENODEV;
  		goto exit;
  	}
  
  	/* if IO is under way, we must not touch things */
  retry:
  	spin_lock_irq(&dev->err_lock);
  	ongoing_io = dev->ongoing_read;
  	spin_unlock_irq(&dev->err_lock);
  
  	if (ongoing_io) {
  		/* nonblocking IO shall not wait */
  		if (file->f_flags & O_NONBLOCK) {
  			rv = -EAGAIN;
  			goto exit;
  		}
  		/*
  		 * IO may take forever
  		 * hence wait in an interruptible state
  		 */
  		rv = wait_event_interruptible(dev->bulk_in_wait, (!dev->ongoing_read));
  		if (rv < 0)
  			goto exit;
  	}
  
  	/* errors must be reported */
  	rv = dev->errors;
  	if (rv < 0) {
  		/* any error is reported once */
  		dev->errors = 0;
  		/* to preserve notifications about reset */
  		rv = (rv == -EPIPE) ? rv : -EIO;
  		/* report it */
  		goto exit;
  	}
  
  	/*
  	 * if the buffer is filled we may satisfy the read
  	 * else we need to start IO
  	 */
  
  	if (dev->bulk_in_filled) {
  		/* we had read data */
  		size_t available = dev->bulk_in_filled - dev->bulk_in_copied;
  		size_t chunk = min(available, count);
  
  		if (!available) {
  			/*
  			 * all data has been used
  			 * actual IO needs to be done
  			 */
  			rv = skel_do_read_io(dev, count);
  			if (rv < 0)
  				goto exit;
  			else
  				goto retry;
  		}
  		/*
  		 * data is available
  		 * chunk tells us how much shall be copied
  		 */
  
  		if (copy_to_user(buffer,
  				 dev->bulk_in_buffer + dev->bulk_in_copied,
  				 chunk))
  			rv = -EFAULT;
  		else
  			rv = chunk;
  
  		dev->bulk_in_copied += chunk;
  
  		/*
  		 * if we are asked for more than we have,
  		 * we start IO but don't wait
  		 */
  		if (available < count)
  			skel_do_read_io(dev, count - chunk);
  	} else {
  		/* no data in the buffer */
  		rv = skel_do_read_io(dev, count);
  		if (rv < 0)
  			goto exit;
  		else
  			goto retry;
  	}
  exit:
  	mutex_unlock(&dev->io_mutex);
  	return rv;
  }
  
  static void skel_write_bulk_callback(struct urb *urb)
  {
  	struct usb_skel *dev;
  
  	dev = urb->context;
  
  	/* sync/async unlink faults aren't errors */
  	if (urb->status) {
  		if (!(urb->status == -ENOENT ||
  		    urb->status == -ECONNRESET ||
  		    urb->status == -ESHUTDOWN))
  			dev_err(&dev->interface->dev,
  				"%s - nonzero write bulk status received: %d
  ",
  				__func__, urb->status);
  
  		spin_lock(&dev->err_lock);
  		dev->errors = urb->status;
  		spin_unlock(&dev->err_lock);
  	}
  
  	/* free up our allocated buffer */
  	usb_free_coherent(urb->dev, urb->transfer_buffer_length,
  			  urb->transfer_buffer, urb->transfer_dma);
  	up(&dev->limit_sem);
  }
  
  static ssize_t skel_write(struct file *file, const char *user_buffer,
  			  size_t count, loff_t *ppos)
  {
  	struct usb_skel *dev;
  	int retval = 0;
  	struct urb *urb = NULL;
  	char *buf = NULL;
  	size_t writesize = min(count, (size_t)MAX_TRANSFER);
  
  	dev = file->private_data;
  
  	/* verify that we actually have some data to write */
  	if (count == 0)
  		goto exit;
  
  	/*
  	 * limit the number of URBs in flight to stop a user from using up all
  	 * RAM
  	 */
  	if (!(file->f_flags & O_NONBLOCK)) {
  		if (down_interruptible(&dev->limit_sem)) {
  			retval = -ERESTARTSYS;
  			goto exit;
  		}
  	} else {
  		if (down_trylock(&dev->limit_sem)) {
  			retval = -EAGAIN;
  			goto exit;
  		}
  	}
  
  	spin_lock_irq(&dev->err_lock);
  	retval = dev->errors;
  	if (retval < 0) {
  		/* any error is reported once */
  		dev->errors = 0;
  		/* to preserve notifications about reset */
  		retval = (retval == -EPIPE) ? retval : -EIO;
  	}
  	spin_unlock_irq(&dev->err_lock);
  	if (retval < 0)
  		goto error;
  
  	/* create a urb, and a buffer for it, and copy the data to the urb */
  	urb = usb_alloc_urb(0, GFP_KERNEL);
  	if (!urb) {
  		retval = -ENOMEM;
  		goto error;
  	}
  
  	buf = usb_alloc_coherent(dev->udev, writesize, GFP_KERNEL,
  				 &urb->transfer_dma);
  	if (!buf) {
  		retval = -ENOMEM;
  		goto error;
  	}
  
  	if (copy_from_user(buf, user_buffer, writesize)) {
  		retval = -EFAULT;
  		goto error;
  	}
  
  	/* this lock makes sure we don't submit URBs to gone devices */
  	mutex_lock(&dev->io_mutex);
  	if (!dev->interface) {		/* disconnect() was called */
  		mutex_unlock(&dev->io_mutex);
  		retval = -ENODEV;
  		goto error;
  	}
  
  	/* initialize the urb properly */
  	usb_fill_bulk_urb(urb, dev->udev,
  			  usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
  			  buf, writesize, skel_write_bulk_callback, dev);
  	urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
  	usb_anchor_urb(urb, &dev->submitted);
  
  	/* send the data out the bulk port */
  	retval = usb_submit_urb(urb, GFP_KERNEL);
  	mutex_unlock(&dev->io_mutex);
  	if (retval) {
  		dev_err(&dev->interface->dev,
  			"%s - failed submitting write urb, error %d
  ",
  			__func__, retval);
  		goto error_unanchor;
  	}
  
  	/*
  	 * release our reference to this urb, the USB core will eventually free
  	 * it entirely
  	 */
  	usb_free_urb(urb);
  
  
  	return writesize;
  
  error_unanchor:
  	usb_unanchor_urb(urb);
  error:
  	if (urb) {
  		usb_free_coherent(dev->udev, writesize, buf, urb->transfer_dma);
  		usb_free_urb(urb);
  	}
  	up(&dev->limit_sem);
  
  exit:
  	return retval;
  }
  
  static const struct file_operations skel_fops = {
  	.owner =	THIS_MODULE,
  	.read =		skel_read,
  	.write =	skel_write,
  	.open =		skel_open,
  	.release =	skel_release,
  	.flush =	skel_flush,
  	.llseek =	noop_llseek,
  };
  
  /*
   * usb class driver info in order to get a minor number from the usb core,
   * and to have the device registered with the driver core
   */
  static struct usb_class_driver skel_class = {
  	.name =		"skel%d",
  	.fops =		&skel_fops,
  	.minor_base =	USB_SKEL_MINOR_BASE,
  };
  
  static int skel_probe(struct usb_interface *interface,
  		      const struct usb_device_id *id)
  {
  	struct usb_skel *dev;
  	struct usb_host_interface *iface_desc;
  	struct usb_endpoint_descriptor *endpoint;
  	size_t buffer_size;
  	int i;
  	int retval = -ENOMEM;
  
  	/* allocate memory for our device state and initialize it */
  	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
  	if (!dev) {
  		dev_err(&interface->dev, "Out of memory
  ");
  		goto error;
  	}
  	kref_init(&dev->kref);
  	sema_init(&dev->limit_sem, WRITES_IN_FLIGHT);
  	mutex_init(&dev->io_mutex);
  	spin_lock_init(&dev->err_lock);
  	init_usb_anchor(&dev->submitted);
  	init_waitqueue_head(&dev->bulk_in_wait);
  
  	dev->udev = usb_get_dev(interface_to_usbdev(interface));
  	dev->interface = interface;
  
  	/* set up the endpoint information */
  	/* use only the first bulk-in and bulk-out endpoints */
  	iface_desc = interface->cur_altsetting;
  	for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {
  		endpoint = &iface_desc->endpoint[i].desc;
  
  		if (!dev->bulk_in_endpointAddr &&
  		    usb_endpoint_is_bulk_in(endpoint)) {
  			/* we found a bulk in endpoint */
  			buffer_size = usb_endpoint_maxp(endpoint);
  			dev->bulk_in_size = buffer_size;
  			dev->bulk_in_endpointAddr = endpoint->bEndpointAddress;
  			dev->bulk_in_buffer = kmalloc(buffer_size, GFP_KERNEL);
  			if (!dev->bulk_in_buffer) {
  				dev_err(&interface->dev,
  					"Could not allocate bulk_in_buffer
  ");
  				goto error;
  			}
  			dev->bulk_in_urb = usb_alloc_urb(0, GFP_KERNEL);
  			if (!dev->bulk_in_urb) {
  				dev_err(&interface->dev,
  					"Could not allocate bulk_in_urb
  ");
  				goto error;
  			}
  		}
  
  		if (!dev->bulk_out_endpointAddr &&
  		    usb_endpoint_is_bulk_out(endpoint)) {
  			/* we found a bulk out endpoint */
  			dev->bulk_out_endpointAddr = endpoint->bEndpointAddress;
  		}
  	}
  	if (!(dev->bulk_in_endpointAddr && dev->bulk_out_endpointAddr)) {
  		dev_err(&interface->dev,
  			"Could not find both bulk-in and bulk-out endpoints
  ");
  		goto error;
  	}
  
  	/* save our data pointer in this interface device */
  	usb_set_intfdata(interface, dev);
  
  	/* we can register the device now, as it is ready */
  	retval = usb_register_dev(interface, &skel_class);
  	if (retval) {
  		/* something prevented us from registering this driver */
  		dev_err(&interface->dev,
  			"Not able to get a minor for this device.
  ");
  		usb_set_intfdata(interface, NULL);
  		goto error;
  	}
  
  	/* let the user know what node this device is now attached to */
  	dev_info(&interface->dev,
  		 "USB Skeleton device now attached to USBSkel-%d",
  		 interface->minor);
  	return 0;
  
  error:
  	if (dev)
  		/* this frees allocated memory */
  		kref_put(&dev->kref, skel_delete);
  	return retval;
  }
  
  static void skel_disconnect(struct usb_interface *interface)
  {
  	struct usb_skel *dev;
  	int minor = interface->minor;
  
  	dev = usb_get_intfdata(interface);
  	usb_set_intfdata(interface, NULL);
  
  	/* give back our minor */
  	usb_deregister_dev(interface, &skel_class);
  
  	/* prevent more I/O from starting */
  	mutex_lock(&dev->io_mutex);
  	dev->interface = NULL;
  	mutex_unlock(&dev->io_mutex);
  
  	usb_kill_anchored_urbs(&dev->submitted);
  
  	/* decrement our usage count */
  	kref_put(&dev->kref, skel_delete);
  
  	dev_info(&interface->dev, "USB Skeleton #%d now disconnected", minor);
  }
  
  static void skel_draw_down(struct usb_skel *dev)
  {
  	int time;
  
  	time = usb_wait_anchor_empty_timeout(&dev->submitted, 1000);
  	if (!time)
  		usb_kill_anchored_urbs(&dev->submitted);
  	usb_kill_urb(dev->bulk_in_urb);
  }
  
  static int skel_suspend(struct usb_interface *intf, pm_message_t message)
  {
  	struct usb_skel *dev = usb_get_intfdata(intf);
  
  	if (!dev)
  		return 0;
  	skel_draw_down(dev);
  	return 0;
  }
  
  static int skel_resume(struct usb_interface *intf)
  {
  	return 0;
  }
  
  static int skel_pre_reset(struct usb_interface *intf)
  {
  	struct usb_skel *dev = usb_get_intfdata(intf);
  
  	mutex_lock(&dev->io_mutex);
  	skel_draw_down(dev);
  
  	return 0;
  }
  
  static int skel_post_reset(struct usb_interface *intf)
  {
  	struct usb_skel *dev = usb_get_intfdata(intf);
  
  	/* we are sure no URBs are active - no locking needed */
  	dev->errors = -EPIPE;
  	mutex_unlock(&dev->io_mutex);
  
  	return 0;
  }
  
  static struct usb_driver skel_driver = {
  	.name =		"skeleton",
  	.probe =	skel_probe,
  	.disconnect =	skel_disconnect,
  	.suspend =	skel_suspend,
  	.resume =	skel_resume,
  	.pre_reset =	skel_pre_reset,
  	.post_reset =	skel_post_reset,
  	.id_table =	skel_table,
  	.supports_autosuspend = 1,
  };
  
  module_usb_driver(skel_driver);
  
  MODULE_LICENSE("GPL");