/*
 * Roccat driver for Linux
 *
 * Copyright (c) 2010 Stefan Achatz <erazor_de@users.sourceforge.net>
 */

/*
 * 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.
 */

/*
 * Module roccat is a char device used to report special events of roccat
 * hardware to userland. These events include requests for on-screen-display of
 * profile or dpi settings or requests for execution of macro sequences that are
 * not stored in device. The information in these events depends on hid device
 * implementation and contains data that is not available in a single hid event
 * or else hidraw could have been used.
 * It is inspired by hidraw, but uses only one circular buffer for all readers.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/cdev.h>
#include <linux/poll.h>
#include <linux/sched/signal.h>
#include <linux/hid-roccat.h>
#include <linux/module.h>

#define ROCCAT_FIRST_MINOR 0
#define ROCCAT_MAX_DEVICES 8

/* should be a power of 2 for performance reason */
#define ROCCAT_CBUF_SIZE 16

struct roccat_report {
        uint8_t *value;
};

struct roccat_device {
        unsigned int minor;
        int report_size;
        int open;
        int exist;
        wait_queue_head_t wait;
        struct device *dev;
        struct hid_device *hid;
        struct list_head readers;
        /* protects modifications of readers list */
        struct mutex readers_lock;

        /*
         * circular_buffer has one writer and multiple readers with their own
         * read pointers
         */
        struct roccat_report cbuf[ROCCAT_CBUF_SIZE];
        int cbuf_end;
        struct mutex cbuf_lock;
};

struct roccat_reader {
        struct list_head node;
        struct roccat_device *device;
        int cbuf_start;
};

static int roccat_major;
static struct cdev roccat_cdev;

static struct roccat_device *devices[ROCCAT_MAX_DEVICES];
/* protects modifications of devices array */
static DEFINE_MUTEX(devices_lock);

static ssize_t roccat_read(struct file *file, char __user *buffer,
                size_t count, loff_t *ppos)
{
        struct roccat_reader *reader = file->private_data;
        struct roccat_device *device = reader->device;
        struct roccat_report *report;
        ssize_t retval = 0, len;
        DECLARE_WAITQUEUE(wait, current);

        mutex_lock(&device->cbuf_lock);

        /* no data? */
        if (reader->cbuf_start == device->cbuf_end) {
                add_wait_queue(&device->wait, &wait);
                set_current_state(TASK_INTERRUPTIBLE);

                /* wait for data */
                while (reader->cbuf_start == device->cbuf_end) {
                        if (file->f_flags & O_NONBLOCK) {
                                retval = -EAGAIN;
                                break;
                        }
                        if (signal_pending(current)) {
                                retval = -ERESTARTSYS;
                                break;
                        }
                        if (!device->exist) {
                                retval = -EIO;
                                break;
                        }

                        mutex_unlock(&device->cbuf_lock);
                        schedule();
                        mutex_lock(&device->cbuf_lock);
                        set_current_state(TASK_INTERRUPTIBLE);
                }

                set_current_state(TASK_RUNNING);
                remove_wait_queue(&device->wait, &wait);
        }

        /* here we either have data or a reason to return if retval is set */
        if (retval)
                goto exit_unlock;

        report = &device->cbuf[reader->cbuf_start];
        /*
         * If report is larger than requested amount of data, rest of report
         * is lost!
         */
        len = device->report_size > count ? count : device->report_size;

        if (copy_to_user(buffer, report->value, len)) {
                retval = -EFAULT;
                goto exit_unlock;
        }
        retval += len;
        reader->cbuf_start = (reader->cbuf_start + 1) % ROCCAT_CBUF_SIZE;

exit_unlock:
        mutex_unlock(&device->cbuf_lock);
        return retval;
}

static __poll_t roccat_poll(struct file *file, poll_table *wait)
{
        struct roccat_reader *reader = file->private_data;
        poll_wait(file, &reader->device->wait, wait);
        if (reader->cbuf_start != reader->device->cbuf_end)
                return EPOLLIN | EPOLLRDNORM;
        if (!reader->device->exist)
                return EPOLLERR | EPOLLHUP;
        return 0;
}

static int roccat_open(struct inode *inode, struct file *file)
{
        unsigned int minor = iminor(inode);
        struct roccat_reader *reader;
        struct roccat_device *device;
        int error = 0;

        reader = kzalloc(sizeof(struct roccat_reader), GFP_KERNEL);
        if (!reader)
                return -ENOMEM;

        mutex_lock(&devices_lock);

        device = devices[minor];

        if (!device) {
                pr_emerg("roccat device with minor %d doesn't exist\n", minor);
                error = -ENODEV;
                goto exit_err_devices;
        }

        mutex_lock(&device->readers_lock);

        if (!device->open++) {
                /* power on device on adding first reader */
                error = hid_hw_power(device->hid, PM_HINT_FULLON);
                if (error < 0) {
                        --device->open;
                        goto exit_err_readers;
                }

                error = hid_hw_open(device->hid);
                if (error < 0) {
                        hid_hw_power(device->hid, PM_HINT_NORMAL);
                        --device->open;
                        goto exit_err_readers;
                }
        }

        reader->device = device;
        /* new reader doesn't get old events */
        reader->cbuf_start = device->cbuf_end;

        list_add_tail(&reader->node, &device->readers);
        file->private_data = reader;

exit_err_readers:
        mutex_unlock(&device->readers_lock);
exit_err_devices:
        mutex_unlock(&devices_lock);
        if (error)
                kfree(reader);
        return error;
}

static int roccat_release(struct inode *inode, struct file *file)
{
        unsigned int minor = iminor(inode);
        struct roccat_reader *reader = file->private_data;
        struct roccat_device *device;

        mutex_lock(&devices_lock);

        device = devices[minor];
        if (!device) {
                mutex_unlock(&devices_lock);
                pr_emerg("roccat device with minor %d doesn't exist\n", minor);
                return -ENODEV;
        }

        mutex_lock(&device->readers_lock);
        list_del(&reader->node);
        mutex_unlock(&device->readers_lock);
        kfree(reader);

        if (!--device->open) {
                /* removing last reader */
                if (device->exist) {
                        hid_hw_power(device->hid, PM_HINT_NORMAL);
                        hid_hw_close(device->hid);
                } else {
                        kfree(device);
                }
        }

        mutex_unlock(&devices_lock);

        return 0;
}

/*
 * roccat_report_event() - output data to readers
 * @minor: minor device number returned by roccat_connect()
 * @data: pointer to data
 *
 * Return value is zero on success, a negative error code on failure.
 *
 * This is called from interrupt handler.
 */
int roccat_report_event(int minor, u8 const *data)
{
        struct roccat_device *device;
        struct roccat_reader *reader;
        struct roccat_report *report;
        uint8_t *new_value;

        device = devices[minor];

        new_value = kmemdup(data, device->report_size, GFP_ATOMIC);
        if (!new_value)
                return -ENOMEM;

        report = &device->cbuf[device->cbuf_end];

        /* passing NULL is safe */
        kfree(report->value);

        report->value = new_value;
        device->cbuf_end = (device->cbuf_end + 1) % ROCCAT_CBUF_SIZE;

        list_for_each_entry(reader, &device->readers, node) {
                /*
                 * As we already inserted one element, the buffer can't be
                 * empty. If start and end are equal, buffer is full and we
                 * increase start, so that slow reader misses one event, but
                 * gets the newer ones in the right order.
                 */
                if (reader->cbuf_start == device->cbuf_end)
                        reader->cbuf_start = (reader->cbuf_start + 1) % ROCCAT_CBUF_SIZE;
        }

        wake_up_interruptible(&device->wait);
        return 0;
}
EXPORT_SYMBOL_GPL(roccat_report_event);

/*
 * roccat_connect() - create a char device for special event output
 * @class: the class thats used to create the device. Meant to hold device
 * specific sysfs attributes.
 * @hid: the hid device the char device should be connected to.
 * @report_size: size of reports
 *
 * Return value is minor device number in Range [0, ROCCAT_MAX_DEVICES] on
 * success, a negative error code on failure.
 */
int roccat_connect(struct class *klass, struct hid_device *hid, int report_size)
{
        unsigned int minor;
        struct roccat_device *device;
        int temp;

        device = kzalloc(sizeof(struct roccat_device), GFP_KERNEL);
        if (!device)
                return -ENOMEM;

        mutex_lock(&devices_lock);

        for (minor = 0; minor < ROCCAT_MAX_DEVICES; ++minor) {
                if (devices[minor])
                        continue;
                break;
        }

        if (minor < ROCCAT_MAX_DEVICES) {
                devices[minor] = device;
        } else {
                mutex_unlock(&devices_lock);
                kfree(device);
                return -EINVAL;
        }

        device->dev = device_create(klass, &hid->dev,
                        MKDEV(roccat_major, minor), NULL,
                        "%s%s%d", "roccat", hid->driver->name, minor);

        if (IS_ERR(device->dev)) {
                devices[minor] = NULL;
                mutex_unlock(&devices_lock);
                temp = PTR_ERR(device->dev);
                kfree(device);
                return temp;
        }

        mutex_unlock(&devices_lock);

        init_waitqueue_head(&device->wait);
        INIT_LIST_HEAD(&device->readers);
        mutex_init(&device->readers_lock);
        mutex_init(&device->cbuf_lock);
        device->minor = minor;
        device->hid = hid;
        device->exist = 1;
        device->cbuf_end = 0;
        device->report_size = report_size;

        return minor;
}
EXPORT_SYMBOL_GPL(roccat_connect);

/* roccat_disconnect() - remove char device from hid device
 * @minor: the minor device number returned by roccat_connect()
 */
void roccat_disconnect(int minor)
{
        struct roccat_device *device;

        mutex_lock(&devices_lock);
        device = devices[minor];
        mutex_unlock(&devices_lock);

        device->exist = 0; /* TODO exist maybe not needed */

        device_destroy(device->dev->class, MKDEV(roccat_major, minor));

        mutex_lock(&devices_lock);
        devices[minor] = NULL;
        mutex_unlock(&devices_lock);

        if (device->open) {
                hid_hw_close(device->hid);
                wake_up_interruptible(&device->wait);
        } else {
                kfree(device);
        }
}
EXPORT_SYMBOL_GPL(roccat_disconnect);

static long roccat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct inode *inode = file_inode(file);
        struct roccat_device *device;
        unsigned int minor = iminor(inode);
        long retval = 0;

        mutex_lock(&devices_lock);

        device = devices[minor];
        if (!device) {
                retval = -ENODEV;
                goto out;
        }

        switch (cmd) {
        case ROCCATIOCGREPSIZE:
                if (put_user(device->report_size, (int __user *)arg))
                        retval = -EFAULT;
                break;
        default:
                retval = -ENOTTY;
        }
out:
        mutex_unlock(&devices_lock);
        return retval;
}

static const struct file_operations roccat_ops = {
        .owner = THIS_MODULE,
        .read = roccat_read,
        .poll = roccat_poll,
        .open = roccat_open,
        .release = roccat_release,
        .llseek = noop_llseek,
        .unlocked_ioctl = roccat_ioctl,
};

static int __init roccat_init(void)
{
        int retval;
        dev_t dev_id;

        retval = alloc_chrdev_region(&dev_id, ROCCAT_FIRST_MINOR,
                        ROCCAT_MAX_DEVICES, "roccat");
        if (retval < 0) {
                pr_warn("can't get major number\n");
                goto error;
        }

        roccat_major = MAJOR(dev_id);

        cdev_init(&roccat_cdev, &roccat_ops);
        retval = cdev_add(&roccat_cdev, dev_id, ROCCAT_MAX_DEVICES);

        if (retval < 0) {
                pr_warn("cannot add cdev\n");
                goto cleanup_alloc_chrdev_region;
        }
        return 0;


 cleanup_alloc_chrdev_region:
        unregister_chrdev_region(dev_id, ROCCAT_MAX_DEVICES);
 error:
        return retval;
}

static void __exit roccat_exit(void)
{
        dev_t dev_id = MKDEV(roccat_major, 0);

        cdev_del(&roccat_cdev);
        unregister_chrdev_region(dev_id, ROCCAT_MAX_DEVICES);
}

module_init(roccat_init);
module_exit(roccat_exit);

MODULE_AUTHOR("Stefan Achatz");
MODULE_DESCRIPTION("USB Roccat char device");
MODULE_LICENSE("GPL v2");