/*
 * chaoskey - driver for ChaosKey device from Altus Metrum.
 *
 * This device provides true random numbers using a noise source based
 * on a reverse-biased p-n junction in avalanche breakdown. More
 * details can be found at http://chaoskey.org
 *
 * The driver connects to the kernel hardware RNG interface to provide
 * entropy for /dev/random and other kernel activities. It also offers
 * a separate /dev/ entry to allow for direct access to the random
 * bit stream.
 *
 * Copyright © 2015 Keith Packard <keithp@keithp.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 of the License.
 *
 * 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.
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/usb.h>
#include <linux/wait.h>
#include <linux/hw_random.h>
#include <linux/mutex.h>
#include <linux/uaccess.h>

static struct usb_driver chaoskey_driver;
static struct usb_class_driver chaoskey_class;
static int chaoskey_rng_read(struct hwrng *rng, void *data,
			     size_t max, bool wait);

#define usb_dbg(usb_if, format, arg...) \
	dev_dbg(&(usb_if)->dev, format, ## arg)

#define usb_err(usb_if, format, arg...) \
	dev_err(&(usb_if)->dev, format, ## arg)

/* Version Information */
#define DRIVER_VERSION	"v0.1"
#define DRIVER_AUTHOR	"Keith Packard, keithp@keithp.com"
#define DRIVER_DESC	"Altus Metrum ChaosKey driver"
#define DRIVER_SHORT	"chaoskey"

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

#define CHAOSKEY_VENDOR_ID	0x1d50	/* OpenMoko */
#define CHAOSKEY_PRODUCT_ID	0x60c6	/* ChaosKey */

#define CHAOSKEY_BUF_LEN	64	/* max size of USB full speed packet */

#define NAK_TIMEOUT (HZ)		/* stall/wait timeout for device */

#ifdef CONFIG_USB_DYNAMIC_MINORS
#define USB_CHAOSKEY_MINOR_BASE 0
#else

/* IOWARRIOR_MINOR_BASE + 16, not official yet */
#define USB_CHAOSKEY_MINOR_BASE 224
#endif

static const struct usb_device_id chaoskey_table[] = {
	{ USB_DEVICE(CHAOSKEY_VENDOR_ID, CHAOSKEY_PRODUCT_ID) },
	{ },
};
MODULE_DEVICE_TABLE(usb, chaoskey_table);

/* Driver-local specific stuff */
struct chaoskey {
	struct usb_interface *interface;
	char in_ep;
	struct mutex lock;
	struct mutex rng_lock;
	int open;			/* open count */
	int present;			/* device not disconnected */
	int size;			/* size of buf */
	int valid;			/* bytes of buf read */
	int used;			/* bytes of buf consumed */
	char *name;			/* product + serial */
	struct hwrng hwrng;		/* Embedded struct for hwrng */
	int hwrng_registered;		/* registered with hwrng API */
	wait_queue_head_t wait_q;	/* for timeouts */
	char *buf;
};

static void chaoskey_free(struct chaoskey *dev)
{
	usb_dbg(dev->interface, "free");
	kfree(dev->name);
	kfree(dev->buf);
	kfree(dev);
}

static int chaoskey_probe(struct usb_interface *interface,
			  const struct usb_device_id *id)
{
	struct usb_device *udev = interface_to_usbdev(interface);
	struct usb_host_interface *altsetting = interface->cur_altsetting;
	int i;
	int in_ep = -1;
	struct chaoskey *dev;
	int result;
	int size;

	usb_dbg(interface, "probe %s-%s", udev->product, udev->serial);

	/* Find the first bulk IN endpoint and its packet size */
	for (i = 0; i < altsetting->desc.bNumEndpoints; i++) {
		if (usb_endpoint_is_bulk_in(&altsetting->endpoint[i].desc)) {
			in_ep = usb_endpoint_num(&altsetting->endpoint[i].desc);
			size = usb_endpoint_maxp(&altsetting->endpoint[i].desc);
			break;
		}
	}

	/* Validate endpoint and size */
	if (in_ep == -1) {
		usb_dbg(interface, "no IN endpoint found");
		return -ENODEV;
	}
	if (size <= 0) {
		usb_dbg(interface, "invalid size (%d)", size);
		return -ENODEV;
	}

	if (size > CHAOSKEY_BUF_LEN) {
		usb_dbg(interface, "size reduced from %d to %d\n",
			size, CHAOSKEY_BUF_LEN);
		size = CHAOSKEY_BUF_LEN;
	}

	/* Looks good, allocate and initialize */

	dev = kzalloc(sizeof(struct chaoskey), GFP_KERNEL);

	if (dev == NULL)
		return -ENOMEM;

	dev->buf = kmalloc(size, GFP_KERNEL);

	if (dev->buf == NULL) {
		kfree(dev);
		return -ENOMEM;
	}

	/* Construct a name using the product and serial values. Each
	 * device needs a unique name for the hwrng code
	 */

	if (udev->product && udev->serial) {
		dev->name = kmalloc(strlen(udev->product) + 1 +
				    strlen(udev->serial) + 1, GFP_KERNEL);
		if (dev->name == NULL) {
			kfree(dev->buf);
			kfree(dev);
			return -ENOMEM;
		}

		strcpy(dev->name, udev->product);
		strcat(dev->name, "-");
		strcat(dev->name, udev->serial);
	}

	dev->interface = interface;

	dev->in_ep = in_ep;

	dev->size = size;
	dev->present = 1;

	init_waitqueue_head(&dev->wait_q);

	mutex_init(&dev->lock);
	mutex_init(&dev->rng_lock);

	usb_set_intfdata(interface, dev);

	result = usb_register_dev(interface, &chaoskey_class);
	if (result) {
		usb_err(interface, "Unable to allocate minor number.");
		usb_set_intfdata(interface, NULL);
		chaoskey_free(dev);
		return result;
	}

	dev->hwrng.name = dev->name ? dev->name : chaoskey_driver.name;
	dev->hwrng.read = chaoskey_rng_read;

	/* Set the 'quality' metric.  Quality is measured in units of
	 * 1/1024's of a bit ("mills"). This should be set to 1024,
	 * but there is a bug in the hwrng core which masks it with
	 * 1023.
	 *
	 * The patch that has been merged to the crypto development
	 * tree for that bug limits the value to 1024 at most, so by
	 * setting this to 1024 + 1023, we get 1023 before the fix is
	 * merged and 1024 afterwards. We'll patch this driver once
	 * both bits of code are in the same tree.
	 */
	dev->hwrng.quality = 1024 + 1023;

	dev->hwrng_registered = (hwrng_register(&dev->hwrng) == 0);
	if (!dev->hwrng_registered)
		usb_err(interface, "Unable to register with hwrng");

	usb_enable_autosuspend(udev);

	usb_dbg(interface, "chaoskey probe success, size %d", dev->size);
	return 0;
}

static void chaoskey_disconnect(struct usb_interface *interface)
{
	struct chaoskey	*dev;

	usb_dbg(interface, "disconnect");
	dev = usb_get_intfdata(interface);
	if (!dev) {
		usb_dbg(interface, "disconnect failed - no dev");
		return;
	}

	if (dev->hwrng_registered)
		hwrng_unregister(&dev->hwrng);

	usb_deregister_dev(interface, &chaoskey_class);

	usb_set_intfdata(interface, NULL);
	mutex_lock(&dev->lock);

	dev->present = 0;

	if (!dev->open) {
		mutex_unlock(&dev->lock);
		chaoskey_free(dev);
	} else
		mutex_unlock(&dev->lock);

	usb_dbg(interface, "disconnect done");
}

static int chaoskey_open(struct inode *inode, struct file *file)
{
	struct chaoskey *dev;
	struct usb_interface *interface;

	/* get the interface from minor number and driver information */
	interface = usb_find_interface(&chaoskey_driver, iminor(inode));
	if (!interface)
		return -ENODEV;

	usb_dbg(interface, "open");

	dev = usb_get_intfdata(interface);
	if (!dev) {
		usb_dbg(interface, "open (dev)");
		return -ENODEV;
	}

	file->private_data = dev;
	mutex_lock(&dev->lock);
	++dev->open;
	mutex_unlock(&dev->lock);

	usb_dbg(interface, "open success");
	return 0;
}

static int chaoskey_release(struct inode *inode, struct file *file)
{
	struct chaoskey *dev = file->private_data;
	struct usb_interface *interface;

	if (dev == NULL)
		return -ENODEV;

	interface = dev->interface;

	usb_dbg(interface, "release");

	mutex_lock(&dev->lock);

	usb_dbg(interface, "open count at release is %d", dev->open);

	if (dev->open <= 0) {
		usb_dbg(interface, "invalid open count (%d)", dev->open);
		mutex_unlock(&dev->lock);
		return -ENODEV;
	}

	--dev->open;

	if (!dev->present) {
		if (dev->open == 0) {
			mutex_unlock(&dev->lock);
			chaoskey_free(dev);
		} else
			mutex_unlock(&dev->lock);
	} else
		mutex_unlock(&dev->lock);

	usb_dbg(interface, "release success");
	return 0;
}

/* Fill the buffer. Called with dev->lock held
 */
static int _chaoskey_fill(struct chaoskey *dev)
{
	DEFINE_WAIT(wait);
	int result;
	int this_read;
	struct usb_device *udev = interface_to_usbdev(dev->interface);

	usb_dbg(dev->interface, "fill");

	/* Return immediately if someone called before the buffer was
	 * empty */
	if (dev->valid != dev->used) {
		usb_dbg(dev->interface, "not empty yet (valid %d used %d)",
			dev->valid, dev->used);
		return 0;
	}

	/* Bail if the device has been removed */
	if (!dev->present) {
		usb_dbg(dev->interface, "device not present");
		return -ENODEV;
	}

	/* Make sure the device is awake */
	result = usb_autopm_get_interface(dev->interface);
	if (result) {
		usb_dbg(dev->interface, "wakeup failed (result %d)", result);
		return result;
	}

	result = usb_bulk_msg(udev,
			      usb_rcvbulkpipe(udev, dev->in_ep),
			      dev->buf, dev->size, &this_read,
			      NAK_TIMEOUT);

	/* Let the device go back to sleep eventually */
	usb_autopm_put_interface(dev->interface);

	if (result == 0) {
		dev->valid = this_read;
		dev->used = 0;
	}

	usb_dbg(dev->interface, "bulk_msg result %d this_read %d",
		result, this_read);

	return result;
}

static ssize_t chaoskey_read(struct file *file,
			     char __user *buffer,
			     size_t count,
			     loff_t *ppos)
{
	struct chaoskey *dev;
	ssize_t read_count = 0;
	int this_time;
	int result = 0;
	unsigned long remain;

	dev = file->private_data;

	if (dev == NULL || !dev->present)
		return -ENODEV;

	usb_dbg(dev->interface, "read %zu", count);

	while (count > 0) {

		/* Grab the rng_lock briefly to ensure that the hwrng interface
		 * gets priority over other user access
		 */
		result = mutex_lock_interruptible(&dev->rng_lock);
		if (result)
			goto bail;
		mutex_unlock(&dev->rng_lock);

		result = mutex_lock_interruptible(&dev->lock);
		if (result)
			goto bail;
		if (dev->valid == dev->used) {
			result = _chaoskey_fill(dev);
			if (result) {
				mutex_unlock(&dev->lock);
				goto bail;
			}

			/* Read returned zero bytes */
			if (dev->used == dev->valid) {
				mutex_unlock(&dev->lock);
				goto bail;
			}
		}

		this_time = dev->valid - dev->used;
		if (this_time > count)
			this_time = count;

		remain = copy_to_user(buffer, dev->buf + dev->used, this_time);
		if (remain) {
			result = -EFAULT;

			/* Consume the bytes that were copied so we don't leak
			 * data to user space
			 */
			dev->used += this_time - remain;
			mutex_unlock(&dev->lock);
			goto bail;
		}

		count -= this_time;
		read_count += this_time;
		buffer += this_time;
		dev->used += this_time;
		mutex_unlock(&dev->lock);
	}
bail:
	if (read_count) {
		usb_dbg(dev->interface, "read %zu bytes", read_count);
		return read_count;
	}
	usb_dbg(dev->interface, "empty read, result %d", result);
	return result;
}

static int chaoskey_rng_read(struct hwrng *rng, void *data,
			     size_t max, bool wait)
{
	struct chaoskey *dev = container_of(rng, struct chaoskey, hwrng);
	int this_time;

	usb_dbg(dev->interface, "rng_read max %zu wait %d", max, wait);

	if (!dev->present) {
		usb_dbg(dev->interface, "device not present");
		return 0;
	}

	/* Hold the rng_lock until we acquire the device lock so that
	 * this operation gets priority over other user access to the
	 * device
	 */
	mutex_lock(&dev->rng_lock);

	mutex_lock(&dev->lock);

	mutex_unlock(&dev->rng_lock);

	/* Try to fill the buffer if empty. It doesn't actually matter
	 * if _chaoskey_fill works; we'll just return zero bytes as
	 * the buffer will still be empty
	 */
	if (dev->valid == dev->used)
		(void) _chaoskey_fill(dev);

	this_time = dev->valid - dev->used;
	if (this_time > max)
		this_time = max;

	memcpy(data, dev->buf + dev->used, this_time);

	dev->used += this_time;

	mutex_unlock(&dev->lock);

	usb_dbg(dev->interface, "rng_read this_time %d\n", this_time);
	return this_time;
}

#ifdef CONFIG_PM
static int chaoskey_suspend(struct usb_interface *interface,
			    pm_message_t message)
{
	usb_dbg(interface, "suspend");
	return 0;
}

static int chaoskey_resume(struct usb_interface *interface)
{
	usb_dbg(interface, "resume");
	return 0;
}
#else
#define chaoskey_suspend NULL
#define chaoskey_resume NULL
#endif

/* file operation pointers */
static const struct file_operations chaoskey_fops = {
	.owner = THIS_MODULE,
	.read = chaoskey_read,
	.open = chaoskey_open,
	.release = chaoskey_release,
	.llseek = default_llseek,
};

/* class driver information */
static struct usb_class_driver chaoskey_class = {
	.name = "chaoskey%d",
	.fops = &chaoskey_fops,
	.minor_base = USB_CHAOSKEY_MINOR_BASE,
};

/* usb specific object needed to register this driver with the usb subsystem */
static struct usb_driver chaoskey_driver = {
	.name = DRIVER_SHORT,
	.probe = chaoskey_probe,
	.disconnect = chaoskey_disconnect,
	.suspend = chaoskey_suspend,
	.resume = chaoskey_resume,
	.reset_resume = chaoskey_resume,
	.id_table = chaoskey_table,
	.supports_autosuspend = 1,
};

module_usb_driver(chaoskey_driver);