/*
 * cdev.c - Application interfacing module for character devices
 *
 * Copyright (C) 2013-2015 Microchip Technology Germany II GmbH & Co. KG
 *
 * 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.
 *
 * This file is licensed under GPLv2.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/device.h>
#include <linux/cdev.h>
#include <linux/poll.h>
#include <linux/kfifo.h>
#include <linux/uaccess.h>
#include <linux/idr.h>
#include "mostcore.h"

static dev_t aim_devno;
static struct class *aim_class;
static struct ida minor_id;
static unsigned int major;
static struct most_aim cdev_aim;

struct aim_channel {
        wait_queue_head_t wq;
        struct cdev cdev;
        struct device *dev;
        struct mutex io_mutex;
        struct most_interface *iface;
        struct most_channel_config *cfg;
        unsigned int channel_id;
        dev_t devno;
        bool keep_mbo;
        unsigned int mbo_offs;
        struct mbo *stacked_mbo;
        DECLARE_KFIFO_PTR(fifo, typeof(struct mbo *));
        atomic_t access_ref;
        struct list_head list;
};

#define to_channel(d) container_of(d, struct aim_channel, cdev)
static struct list_head channel_list;
static spinlock_t ch_list_lock;

static struct aim_channel *get_channel(struct most_interface *iface, int id)
{
        struct aim_channel *channel, *tmp;
        unsigned long flags;
        int found_channel = 0;

        spin_lock_irqsave(&ch_list_lock, flags);
        list_for_each_entry_safe(channel, tmp, &channel_list, list) {
                if ((channel->iface == iface) && (channel->channel_id == id)) {
                        found_channel = 1;
                        break;
                }
        }
        spin_unlock_irqrestore(&ch_list_lock, flags);
        if (!found_channel)
                return NULL;
        return channel;
}

/**
 * aim_open - implements the syscall to open the device
 * @inode: inode pointer
 * @filp: file pointer
 *
 * This stores the channel pointer in the private data field of
 * the file structure and activates the channel within the core.
 */
static int aim_open(struct inode *inode, struct file *filp)
{
        struct aim_channel *channel;
        int ret;

        channel = to_channel(inode->i_cdev);
        filp->private_data = channel;

        if (((channel->cfg->direction == MOST_CH_RX) &&
             ((filp->f_flags & O_ACCMODE) != O_RDONLY)) ||
             ((channel->cfg->direction == MOST_CH_TX) &&
                ((filp->f_flags & O_ACCMODE) != O_WRONLY))) {
                pr_info("WARN: Access flags mismatch\n");
                return -EACCES;
        }
        if (!atomic_inc_and_test(&channel->access_ref)) {
                pr_info("WARN: Device is busy\n");
                atomic_dec(&channel->access_ref);
                return -EBUSY;
        }

        ret = most_start_channel(channel->iface, channel->channel_id,
                                 &cdev_aim);
        if (ret)
                atomic_dec(&channel->access_ref);
        return ret;
}

/**
 * aim_close - implements the syscall to close the device
 * @inode: inode pointer
 * @filp: file pointer
 *
 * This stops the channel within the core.
 */
static int aim_close(struct inode *inode, struct file *filp)
{
        int ret;
        struct mbo *mbo;
        struct aim_channel *channel = to_channel(inode->i_cdev);

        mutex_lock(&channel->io_mutex);
        if (!channel->dev) {
                mutex_unlock(&channel->io_mutex);
                atomic_dec(&channel->access_ref);
                device_destroy(aim_class, channel->devno);
                cdev_del(&channel->cdev);
                kfifo_free(&channel->fifo);
                list_del(&channel->list);
                ida_simple_remove(&minor_id, MINOR(channel->devno));
                wake_up_interruptible(&channel->wq);
                kfree(channel);
                return 0;
        }
        mutex_unlock(&channel->io_mutex);

        while (kfifo_out((struct kfifo *)&channel->fifo, &mbo, 1))
                most_put_mbo(mbo);
        if (channel->keep_mbo)
                most_put_mbo(channel->stacked_mbo);
        ret = most_stop_channel(channel->iface, channel->channel_id, &cdev_aim);
        atomic_dec(&channel->access_ref);
        wake_up_interruptible(&channel->wq);
        return ret;
}

/**
 * aim_write - implements the syscall to write to the device
 * @filp: file pointer
 * @buf: pointer to user buffer
 * @count: number of bytes to write
 * @offset: offset from where to start writing
 */
static ssize_t aim_write(struct file *filp, const char __user *buf,
                         size_t count, loff_t *offset)
{
        int ret, err;
        size_t actual_len = 0;
        size_t max_len = 0;
        ssize_t retval;
        struct mbo *mbo;
        struct aim_channel *channel = filp->private_data;

        mutex_lock(&channel->io_mutex);
        if (unlikely(!channel->dev)) {
                mutex_unlock(&channel->io_mutex);
                return -EPIPE;
        }
        mutex_unlock(&channel->io_mutex);

        mbo = most_get_mbo(channel->iface, channel->channel_id, &cdev_aim);

        if (!mbo) {
                if ((filp->f_flags & O_NONBLOCK))
                        return -EAGAIN;
                if (wait_event_interruptible(
                            channel->wq,
                            (mbo = most_get_mbo(channel->iface,
                                                channel->channel_id,
                                                &cdev_aim)) ||
                            (!channel->dev)))
                        return -ERESTARTSYS;
        }

        mutex_lock(&channel->io_mutex);
        if (unlikely(!channel->dev)) {
                mutex_unlock(&channel->io_mutex);
                err = -EPIPE;
                goto error;
        }
        mutex_unlock(&channel->io_mutex);

        max_len = channel->cfg->buffer_size;
        actual_len = min(count, max_len);
        mbo->buffer_length = actual_len;

        retval = copy_from_user(mbo->virt_address, buf, mbo->buffer_length);
        if (retval) {
                err = -EIO;
                goto error;
        }

        ret = most_submit_mbo(mbo);
        if (ret) {
                pr_info("submitting MBO to core failed\n");
                err = ret;
                goto error;
        }
        return actual_len - retval;
error:
        most_put_mbo(mbo);
        return err;
}

/**
 * aim_read - implements the syscall to read from the device
 * @filp: file pointer
 * @buf: pointer to user buffer
 * @count: number of bytes to read
 * @offset: offset from where to start reading
 */
static ssize_t
aim_read(struct file *filp, char __user *buf, size_t count, loff_t *offset)
{
        ssize_t retval;
        size_t not_copied, proc_len;
        struct mbo *mbo;
        struct aim_channel *channel = filp->private_data;

        if (channel->keep_mbo) {
                mbo = channel->stacked_mbo;
                channel->keep_mbo = false;
                goto start_copy;
        }
        while ((!kfifo_out(&channel->fifo, &mbo, 1)) && (channel->dev)) {
                if (filp->f_flags & O_NONBLOCK)
                        return -EAGAIN;
                if (wait_event_interruptible(channel->wq,
                                             (!kfifo_is_empty(&channel->fifo) ||
                                              (!channel->dev))))
                        return -ERESTARTSYS;
        }

start_copy:
        /* make sure we don't submit to gone devices */
        mutex_lock(&channel->io_mutex);
        if (unlikely(!channel->dev)) {
                mutex_unlock(&channel->io_mutex);
                return -EIO;
        }

        if (count < mbo->processed_length)
                channel->keep_mbo = true;

        proc_len = min((int)count,
                       (int)(mbo->processed_length - channel->mbo_offs));

        not_copied = copy_to_user(buf,
                                  mbo->virt_address + channel->mbo_offs,
                                  proc_len);

        retval = not_copied ? proc_len - not_copied : proc_len;

        if (channel->keep_mbo) {
                channel->mbo_offs = retval;
                channel->stacked_mbo = mbo;
        } else {
                most_put_mbo(mbo);
                channel->mbo_offs = 0;
        }
        mutex_unlock(&channel->io_mutex);
        return retval;
}

static inline bool __must_check IS_ERR_OR_FALSE(int x)
{
        return x <= 0;
}

static unsigned int aim_poll(struct file *filp, poll_table *wait)
{
        struct aim_channel *c = filp->private_data;
        unsigned int mask = 0;

        poll_wait(filp, &c->wq, wait);

        if (c->cfg->direction == MOST_CH_RX) {
                if (!kfifo_is_empty(&c->fifo))
                        mask |= POLLIN | POLLRDNORM;
        } else {
                if (!IS_ERR_OR_FALSE(channel_has_mbo(c->iface, c->channel_id)))
                        mask |= POLLOUT | POLLWRNORM;
        }
        return mask;
}

/**
 * Initialization of struct file_operations
 */
static const struct file_operations channel_fops = {
        .owner = THIS_MODULE,
        .read = aim_read,
        .write = aim_write,
        .open = aim_open,
        .release = aim_close,
        .poll = aim_poll,
};

/**
 * aim_disconnect_channel - disconnect a channel
 * @iface: pointer to interface instance
 * @channel_id: channel index
 *
 * This frees allocated memory and removes the cdev that represents this
 * channel in user space.
 */
static int aim_disconnect_channel(struct most_interface *iface, int channel_id)
{
        struct aim_channel *channel;
        unsigned long flags;

        if (!iface) {
                pr_info("Bad interface pointer\n");
                return -EINVAL;
        }

        channel = get_channel(iface, channel_id);
        if (!channel)
                return -ENXIO;

        mutex_lock(&channel->io_mutex);
        channel->dev = NULL;
        mutex_unlock(&channel->io_mutex);

        if (atomic_read(&channel->access_ref)) {
                device_destroy(aim_class, channel->devno);
                cdev_del(&channel->cdev);
                kfifo_free(&channel->fifo);
                ida_simple_remove(&minor_id, MINOR(channel->devno));
                spin_lock_irqsave(&ch_list_lock, flags);
                list_del(&channel->list);
                spin_unlock_irqrestore(&ch_list_lock, flags);
                kfree(channel);
        } else {
                wake_up_interruptible(&channel->wq);
        }
        return 0;
}

/**
 * aim_rx_completion - completion handler for rx channels
 * @mbo: pointer to buffer object that has completed
 *
 * This searches for the channel linked to this MBO and stores it in the local
 * fifo buffer.
 */
static int aim_rx_completion(struct mbo *mbo)
{
        struct aim_channel *channel;

        if (!mbo)
                return -EINVAL;

        channel = get_channel(mbo->ifp, mbo->hdm_channel_id);
        if (!channel)
                return -ENXIO;

        kfifo_in(&channel->fifo, &mbo, 1);
#ifdef DEBUG_MESG
        if (kfifo_is_full(&channel->fifo))
                pr_info("WARN: Fifo is full\n");
#endif
        wake_up_interruptible(&channel->wq);
        return 0;
}

/**
 * aim_tx_completion - completion handler for tx channels
 * @iface: pointer to interface instance
 * @channel_id: channel index/ID
 *
 * This wakes sleeping processes in the wait-queue.
 */
static int aim_tx_completion(struct most_interface *iface, int channel_id)
{
        struct aim_channel *channel;

        if (!iface) {
                pr_info("Bad interface pointer\n");
                return -EINVAL;
        }
        if ((channel_id < 0) || (channel_id >= iface->num_channels)) {
                pr_info("Channel ID out of range\n");
                return -EINVAL;
        }

        channel = get_channel(iface, channel_id);
        if (!channel)
                return -ENXIO;
        wake_up_interruptible(&channel->wq);
        return 0;
}

static struct most_aim cdev_aim;

/**
 * aim_probe - probe function of the driver module
 * @iface: pointer to interface instance
 * @channel_id: channel index/ID
 * @cfg: pointer to actual channel configuration
 * @parent: pointer to kobject (needed for sysfs hook-up)
 * @name: name of the device to be created
 *
 * This allocates achannel object and creates the device node in /dev
 *
 * Returns 0 on success or error code otherwise.
 */
static int aim_probe(struct most_interface *iface, int channel_id,
                     struct most_channel_config *cfg,
                     struct kobject *parent, char *name)
{
        struct aim_channel *channel;
        unsigned long cl_flags;
        int retval;
        int current_minor;

        if ((!iface) || (!cfg) || (!parent) || (!name)) {
                pr_info("Probing AIM with bad arguments");
                return -EINVAL;
        }
        channel = get_channel(iface, channel_id);
        if (channel)
                return -EEXIST;

        current_minor = ida_simple_get(&minor_id, 0, 0, GFP_KERNEL);
        if (current_minor < 0)
                return current_minor;

        channel = kzalloc(sizeof(*channel), GFP_KERNEL);
        if (!channel) {
                retval = -ENOMEM;
                goto error_alloc_channel;
        }

        channel->devno = MKDEV(major, current_minor);
        cdev_init(&channel->cdev, &channel_fops);
        channel->cdev.owner = THIS_MODULE;
        cdev_add(&channel->cdev, channel->devno, 1);
        channel->iface = iface;
        channel->cfg = cfg;
        channel->channel_id = channel_id;
        channel->mbo_offs = 0;
        atomic_set(&channel->access_ref, -1);
        INIT_KFIFO(channel->fifo);
        retval = kfifo_alloc(&channel->fifo, cfg->num_buffers, GFP_KERNEL);
        if (retval) {
                pr_info("failed to alloc channel kfifo");
                goto error_alloc_kfifo;
        }
        init_waitqueue_head(&channel->wq);
        mutex_init(&channel->io_mutex);
        spin_lock_irqsave(&ch_list_lock, cl_flags);
        list_add_tail(&channel->list, &channel_list);
        spin_unlock_irqrestore(&ch_list_lock, cl_flags);
        channel->dev = device_create(aim_class,
                                     NULL,
                                     channel->devno,
                                     NULL,
                                     "%s", name);

        retval = IS_ERR(channel->dev);
        if (retval) {
                pr_info("failed to create new device node %s\n", name);
                goto error_create_device;
        }
        kobject_uevent(&channel->dev->kobj, KOBJ_ADD);
        return 0;

error_create_device:
        kfifo_free(&channel->fifo);
        list_del(&channel->list);
error_alloc_kfifo:
        cdev_del(&channel->cdev);
        kfree(channel);
error_alloc_channel:
        ida_simple_remove(&minor_id, current_minor);
        return retval;
}

static struct most_aim cdev_aim = {
        .name = "cdev",
        .probe_channel = aim_probe,
        .disconnect_channel = aim_disconnect_channel,
        .rx_completion = aim_rx_completion,
        .tx_completion = aim_tx_completion,
};

static int __init mod_init(void)
{
        pr_info("init()\n");

        INIT_LIST_HEAD(&channel_list);
        spin_lock_init(&ch_list_lock);
        ida_init(&minor_id);

        if (alloc_chrdev_region(&aim_devno, 0, 50, "cdev") < 0)
                return -EIO;
        major = MAJOR(aim_devno);

        aim_class = class_create(THIS_MODULE, "most_cdev_aim");
        if (IS_ERR(aim_class)) {
                pr_err("no udev support\n");
                goto free_cdev;
        }

        if (most_register_aim(&cdev_aim))
                goto dest_class;
        return 0;

dest_class:
        class_destroy(aim_class);
free_cdev:
        unregister_chrdev_region(aim_devno, 1);
        return -EIO;
}

static void __exit mod_exit(void)
{
        struct aim_channel *channel, *tmp;

        pr_info("exit module\n");

        most_deregister_aim(&cdev_aim);

        list_for_each_entry_safe(channel, tmp, &channel_list, list) {
                device_destroy(aim_class, channel->devno);
                cdev_del(&channel->cdev);
                kfifo_free(&channel->fifo);
                list_del(&channel->list);
                ida_simple_remove(&minor_id, MINOR(channel->devno));
                kfree(channel);
        }
        class_destroy(aim_class);
        unregister_chrdev_region(aim_devno, 1);
        ida_destroy(&minor_id);
}

module_init(mod_init);
module_exit(mod_exit);
MODULE_AUTHOR("Christian Gromm <christian.gromm@microchip.com>");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("character device AIM for mostcore");