/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 2005 MIPS Technologies, Inc.  All rights reserved.
 * Copyright (C) 2005, 06 Ralf Baechle (ralf@linux-mips.org)
 * Copyright (C) 2013 Imagination Technologies Ltd.
 */
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/syscalls.h>
#include <linux/moduleloader.h>
#include <linux/atomic.h>
#include <linux/sched/signal.h>

#include <asm/mipsmtregs.h>
#include <asm/mips_mt.h>
#include <asm/processor.h>
#include <asm/rtlx.h>
#include <asm/setup.h>
#include <asm/vpe.h>

static int sp_stopping;
struct rtlx_info *rtlx;
struct chan_waitqueues channel_wqs[RTLX_CHANNELS];
struct vpe_notifications rtlx_notify;
void (*aprp_hook)(void) = NULL;
EXPORT_SYMBOL(aprp_hook);

static void __used dump_rtlx(void)
{
        int i;

        pr_info("id 0x%lx state %d\n", rtlx->id, rtlx->state);

        for (i = 0; i < RTLX_CHANNELS; i++) {
                struct rtlx_channel *chan = &rtlx->channel[i];

                pr_info(" rt_state %d lx_state %d buffer_size %d\n",
                        chan->rt_state, chan->lx_state, chan->buffer_size);

                pr_info(" rt_read %d rt_write %d\n",
                        chan->rt_read, chan->rt_write);

                pr_info(" lx_read %d lx_write %d\n",
                        chan->lx_read, chan->lx_write);

                pr_info(" rt_buffer <%s>\n", chan->rt_buffer);
                pr_info(" lx_buffer <%s>\n", chan->lx_buffer);
        }
}

/* call when we have the address of the shared structure from the SP side. */
static int rtlx_init(struct rtlx_info *rtlxi)
{
        if (rtlxi->id != RTLX_ID) {
                pr_err("no valid RTLX id at 0x%p 0x%lx\n", rtlxi, rtlxi->id);
                return -ENOEXEC;
        }

        rtlx = rtlxi;

        return 0;
}

/* notifications */
void rtlx_starting(int vpe)
{
        int i;
        sp_stopping = 0;

        /* force a reload of rtlx */
        rtlx = NULL;

        /* wake up any sleeping rtlx_open's */
        for (i = 0; i < RTLX_CHANNELS; i++)
                wake_up_interruptible(&channel_wqs[i].lx_queue);
}

void rtlx_stopping(int vpe)
{
        int i;

        sp_stopping = 1;
        for (i = 0; i < RTLX_CHANNELS; i++)
                wake_up_interruptible(&channel_wqs[i].lx_queue);
}


int rtlx_open(int index, int can_sleep)
{
        struct rtlx_info **p;
        struct rtlx_channel *chan;
        enum rtlx_state state;
        int ret = 0;

        if (index >= RTLX_CHANNELS) {
                pr_debug("rtlx_open index out of range\n");
                return -ENOSYS;
        }

        if (atomic_inc_return(&channel_wqs[index].in_open) > 1) {
                pr_debug("rtlx_open channel %d already opened\n", index);
                ret = -EBUSY;
                goto out_fail;
        }

        if (rtlx == NULL) {
                p = vpe_get_shared(aprp_cpu_index());
                if (p == NULL) {
                        if (can_sleep) {
                                ret = __wait_event_interruptible(
                                        channel_wqs[index].lx_queue,
                                        (p = vpe_get_shared(aprp_cpu_index())));
                                if (ret)
                                        goto out_fail;
                        } else {
                                pr_debug("No SP program loaded, and device opened with O_NONBLOCK\n");
                                ret = -ENOSYS;
                                goto out_fail;
                        }
                }

                smp_rmb();
                if (*p == NULL) {
                        if (can_sleep) {
                                DEFINE_WAIT(wait);

                                for (;;) {
                                        prepare_to_wait(
                                                &channel_wqs[index].lx_queue,
                                                &wait, TASK_INTERRUPTIBLE);
                                        smp_rmb();
                                        if (*p != NULL)
                                                break;
                                        if (!signal_pending(current)) {
                                                schedule();
                                                continue;
                                        }
                                        ret = -ERESTARTSYS;
                                        goto out_fail;
                                }
                                finish_wait(&channel_wqs[index].lx_queue,
                                            &wait);
                        } else {
                                pr_err(" *vpe_get_shared is NULL. Has an SP program been loaded?\n");
                                ret = -ENOSYS;
                                goto out_fail;
                        }
                }

                if ((unsigned int)*p < KSEG0) {
                        pr_warn("vpe_get_shared returned an invalid pointer maybe an error code %d\n",
                                (int)*p);
                        ret = -ENOSYS;
                        goto out_fail;
                }

                ret = rtlx_init(*p);
                if (ret < 0)
                        goto out_ret;
        }

        chan = &rtlx->channel[index];

        state = xchg(&chan->lx_state, RTLX_STATE_OPENED);
        if (state == RTLX_STATE_OPENED) {
                ret = -EBUSY;
                goto out_fail;
        }

out_fail:
        smp_mb();
        atomic_dec(&channel_wqs[index].in_open);
        smp_mb();

out_ret:
        return ret;
}

int rtlx_release(int index)
{
        if (rtlx == NULL) {
                pr_err("rtlx_release() with null rtlx\n");
                return 0;
        }
        rtlx->channel[index].lx_state = RTLX_STATE_UNUSED;
        return 0;
}

unsigned int rtlx_read_poll(int index, int can_sleep)
{
        struct rtlx_channel *chan;

        if (rtlx == NULL)
                return 0;

        chan = &rtlx->channel[index];

        /* data available to read? */
        if (chan->lx_read == chan->lx_write) {
                if (can_sleep) {
                        int ret = __wait_event_interruptible(
                                channel_wqs[index].lx_queue,
                                (chan->lx_read != chan->lx_write) ||
                                sp_stopping);
                        if (ret)
                                return ret;

                        if (sp_stopping)
                                return 0;
                } else
                        return 0;
        }

        return (chan->lx_write + chan->buffer_size - chan->lx_read)
               % chan->buffer_size;
}

static inline int write_spacefree(int read, int write, int size)
{
        if (read == write) {
                /*
                 * Never fill the buffer completely, so indexes are always
                 * equal if empty and only empty, or !equal if data available
                 */
                return size - 1;
        }

        return ((read + size - write) % size) - 1;
}

unsigned int rtlx_write_poll(int index)
{
        struct rtlx_channel *chan = &rtlx->channel[index];

        return write_spacefree(chan->rt_read, chan->rt_write,
                                chan->buffer_size);
}

ssize_t rtlx_read(int index, void __user *buff, size_t count)
{
        size_t lx_write, fl = 0L;
        struct rtlx_channel *lx;
        unsigned long failed;

        if (rtlx == NULL)
                return -ENOSYS;

        lx = &rtlx->channel[index];

        mutex_lock(&channel_wqs[index].mutex);
        smp_rmb();
        lx_write = lx->lx_write;

        /* find out how much in total */
        count = min(count,
                     (size_t)(lx_write + lx->buffer_size - lx->lx_read)
                     % lx->buffer_size);

        /* then how much from the read pointer onwards */
        fl = min(count, (size_t)lx->buffer_size - lx->lx_read);

        failed = copy_to_user(buff, lx->lx_buffer + lx->lx_read, fl);
        if (failed)
                goto out;

        /* and if there is anything left at the beginning of the buffer */
        if (count - fl)
                failed = copy_to_user(buff + fl, lx->lx_buffer, count - fl);

out:
        count -= failed;

        smp_wmb();
        lx->lx_read = (lx->lx_read + count) % lx->buffer_size;
        smp_wmb();
        mutex_unlock(&channel_wqs[index].mutex);

        return count;
}

ssize_t rtlx_write(int index, const void __user *buffer, size_t count)
{
        struct rtlx_channel *rt;
        unsigned long failed;
        size_t rt_read;
        size_t fl;

        if (rtlx == NULL)
                return -ENOSYS;

        rt = &rtlx->channel[index];

        mutex_lock(&channel_wqs[index].mutex);
        smp_rmb();
        rt_read = rt->rt_read;

        /* total number of bytes to copy */
        count = min_t(size_t, count, write_spacefree(rt_read, rt->rt_write,
                                                     rt->buffer_size));

        /* first bit from write pointer to the end of the buffer, or count */
        fl = min(count, (size_t) rt->buffer_size - rt->rt_write);

        failed = copy_from_user(rt->rt_buffer + rt->rt_write, buffer, fl);
        if (failed)
                goto out;

        /* if there's any left copy to the beginning of the buffer */
        if (count - fl)
                failed = copy_from_user(rt->rt_buffer, buffer + fl, count - fl);

out:
        count -= failed;

        smp_wmb();
        rt->rt_write = (rt->rt_write + count) % rt->buffer_size;
        smp_wmb();
        mutex_unlock(&channel_wqs[index].mutex);

        _interrupt_sp();

        return count;
}


static int file_open(struct inode *inode, struct file *filp)
{
        return rtlx_open(iminor(inode), (filp->f_flags & O_NONBLOCK) ? 0 : 1);
}

static int file_release(struct inode *inode, struct file *filp)
{
        return rtlx_release(iminor(inode));
}

static __poll_t file_poll(struct file *file, poll_table *wait)
{
        int minor = iminor(file_inode(file));
        __poll_t mask = 0;

        poll_wait(file, &channel_wqs[minor].rt_queue, wait);
        poll_wait(file, &channel_wqs[minor].lx_queue, wait);

        if (rtlx == NULL)
                return 0;

        /* data available to read? */
        if (rtlx_read_poll(minor, 0))
                mask |= EPOLLIN | EPOLLRDNORM;

        /* space to write */
        if (rtlx_write_poll(minor))
                mask |= EPOLLOUT | EPOLLWRNORM;

        return mask;
}

static ssize_t file_read(struct file *file, char __user *buffer, size_t count,
                         loff_t *ppos)
{
        int minor = iminor(file_inode(file));

        /* data available? */
        if (!rtlx_read_poll(minor, (file->f_flags & O_NONBLOCK) ? 0 : 1))
                return 0;       /* -EAGAIN makes 'cat' whine */

        return rtlx_read(minor, buffer, count);
}

static ssize_t file_write(struct file *file, const char __user *buffer,
                          size_t count, loff_t *ppos)
{
        int minor = iminor(file_inode(file));

        /* any space left... */
        if (!rtlx_write_poll(minor)) {
                int ret;

                if (file->f_flags & O_NONBLOCK)
                        return -EAGAIN;

                ret = __wait_event_interruptible(channel_wqs[minor].rt_queue,
                                           rtlx_write_poll(minor));
                if (ret)
                        return ret;
        }

        return rtlx_write(minor, buffer, count);
}

const struct file_operations rtlx_fops = {
        .owner =   THIS_MODULE,
        .open =    file_open,
        .release = file_release,
        .write =   file_write,
        .read =    file_read,
        .poll =    file_poll,
        .llseek =  noop_llseek,
};

module_init(rtlx_module_init);
module_exit(rtlx_module_exit);

MODULE_DESCRIPTION("MIPS RTLX");
MODULE_AUTHOR("Elizabeth Oldham, MIPS Technologies, Inc.");
MODULE_LICENSE("GPL");