/*
 *
 * dvb_ringbuffer.c: ring buffer implementation for the dvb driver
 *
 * Copyright (C) 2003 Oliver Endriss
 * Copyright (C) 2004 Andrew de Quincey
 *
 * based on code originally found in av7110.c & dvb_ci.c:
 * Copyright (C) 1999-2003 Ralph  Metzler
 *                       & Marcus Metzler for convergence integrated media GmbH
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1
 * of the License, or (at your option) any later version.
 *
 * 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 Lesser General Public License for more details.
 */



#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/uaccess.h>

#include <media/dvb_ringbuffer.h>

#define PKT_READY 0
#define PKT_DISPOSED 1


void dvb_ringbuffer_init(struct dvb_ringbuffer *rbuf, void *data, size_t len)
{
        rbuf->pread = 0;
        rbuf->pwrite = 0;
        rbuf->data = data;
        rbuf->size = len;
        rbuf->error = 0;

        init_waitqueue_head(&rbuf->queue);

        spin_lock_init(&(rbuf->lock));
}



int dvb_ringbuffer_empty(struct dvb_ringbuffer *rbuf)
{
        /* smp_load_acquire() to load write pointer on reader side
         * this pairs with smp_store_release() in dvb_ringbuffer_write(),
         * dvb_ringbuffer_write_user(), or dvb_ringbuffer_reset()
         *
         * for memory barriers also see Documentation/core-api/circular-buffers.rst
         */
        return (rbuf->pread == smp_load_acquire(&rbuf->pwrite));
}



ssize_t dvb_ringbuffer_free(struct dvb_ringbuffer *rbuf)
{
        ssize_t free;

        /* READ_ONCE() to load read pointer on writer side
         * this pairs with smp_store_release() in dvb_ringbuffer_read(),
         * dvb_ringbuffer_read_user(), dvb_ringbuffer_flush(),
         * or dvb_ringbuffer_reset()
         */
        free = READ_ONCE(rbuf->pread) - rbuf->pwrite;
        if (free <= 0)
                free += rbuf->size;
        return free-1;
}



ssize_t dvb_ringbuffer_avail(struct dvb_ringbuffer *rbuf)
{
        ssize_t avail;

        /* smp_load_acquire() to load write pointer on reader side
         * this pairs with smp_store_release() in dvb_ringbuffer_write(),
         * dvb_ringbuffer_write_user(), or dvb_ringbuffer_reset()
         */
        avail = smp_load_acquire(&rbuf->pwrite) - rbuf->pread;
        if (avail < 0)
                avail += rbuf->size;
        return avail;
}



void dvb_ringbuffer_flush(struct dvb_ringbuffer *rbuf)
{
        /* dvb_ringbuffer_flush() counts as read operation
         * smp_load_acquire() to load write pointer
         * smp_store_release() to update read pointer, this ensures that the
         * correct pointer is visible for subsequent dvb_ringbuffer_free()
         * calls on other cpu cores
         */
        smp_store_release(&rbuf->pread, smp_load_acquire(&rbuf->pwrite));
        rbuf->error = 0;
}
EXPORT_SYMBOL(dvb_ringbuffer_flush);

void dvb_ringbuffer_reset(struct dvb_ringbuffer *rbuf)
{
        /* dvb_ringbuffer_reset() counts as read and write operation
         * smp_store_release() to update read pointer
         */
        smp_store_release(&rbuf->pread, 0);
        /* smp_store_release() to update write pointer */
        smp_store_release(&rbuf->pwrite, 0);
        rbuf->error = 0;
}

void dvb_ringbuffer_flush_spinlock_wakeup(struct dvb_ringbuffer *rbuf)
{
        unsigned long flags;

        spin_lock_irqsave(&rbuf->lock, flags);
        dvb_ringbuffer_flush(rbuf);
        spin_unlock_irqrestore(&rbuf->lock, flags);

        wake_up(&rbuf->queue);
}

ssize_t dvb_ringbuffer_read_user(struct dvb_ringbuffer *rbuf, u8 __user *buf, size_t len)
{
        size_t todo = len;
        size_t split;

        split = (rbuf->pread + len > rbuf->size) ? rbuf->size - rbuf->pread : 0;
        if (split > 0) {
                if (copy_to_user(buf, rbuf->data+rbuf->pread, split))
                        return -EFAULT;
                buf += split;
                todo -= split;
                /* smp_store_release() for read pointer update to ensure
                 * that buf is not overwritten until read is complete,
                 * this pairs with READ_ONCE() in dvb_ringbuffer_free()
                 */
                smp_store_release(&rbuf->pread, 0);
        }
        if (copy_to_user(buf, rbuf->data+rbuf->pread, todo))
                return -EFAULT;

        /* smp_store_release() to update read pointer, see above */
        smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size);

        return len;
}

void dvb_ringbuffer_read(struct dvb_ringbuffer *rbuf, u8 *buf, size_t len)
{
        size_t todo = len;
        size_t split;

        split = (rbuf->pread + len > rbuf->size) ? rbuf->size - rbuf->pread : 0;
        if (split > 0) {
                memcpy(buf, rbuf->data+rbuf->pread, split);
                buf += split;
                todo -= split;
                /* smp_store_release() for read pointer update to ensure
                 * that buf is not overwritten until read is complete,
                 * this pairs with READ_ONCE() in dvb_ringbuffer_free()
                 */
                smp_store_release(&rbuf->pread, 0);
        }
        memcpy(buf, rbuf->data+rbuf->pread, todo);

        /* smp_store_release() to update read pointer, see above */
        smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size);
}


ssize_t dvb_ringbuffer_write(struct dvb_ringbuffer *rbuf, const u8 *buf, size_t len)
{
        size_t todo = len;
        size_t split;

        split = (rbuf->pwrite + len > rbuf->size) ? rbuf->size - rbuf->pwrite : 0;

        if (split > 0) {
                memcpy(rbuf->data+rbuf->pwrite, buf, split);
                buf += split;
                todo -= split;
                /* smp_store_release() for write pointer update to ensure that
                 * written data is visible on other cpu cores before the pointer
                 * update, this pairs with smp_load_acquire() in
                 * dvb_ringbuffer_empty() or dvb_ringbuffer_avail()
                 */
                smp_store_release(&rbuf->pwrite, 0);
        }
        memcpy(rbuf->data+rbuf->pwrite, buf, todo);
        /* smp_store_release() for write pointer update, see above */
        smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size);

        return len;
}

ssize_t dvb_ringbuffer_write_user(struct dvb_ringbuffer *rbuf,
                                  const u8 __user *buf, size_t len)
{
        int status;
        size_t todo = len;
        size_t split;

        split = (rbuf->pwrite + len > rbuf->size) ? rbuf->size - rbuf->pwrite : 0;

        if (split > 0) {
                status = copy_from_user(rbuf->data+rbuf->pwrite, buf, split);
                if (status)
                        return len - todo;
                buf += split;
                todo -= split;
                /* smp_store_release() for write pointer update to ensure that
                 * written data is visible on other cpu cores before the pointer
                 * update, this pairs with smp_load_acquire() in
                 * dvb_ringbuffer_empty() or dvb_ringbuffer_avail()
                 */
                smp_store_release(&rbuf->pwrite, 0);
        }
        status = copy_from_user(rbuf->data+rbuf->pwrite, buf, todo);
        if (status)
                return len - todo;
        /* smp_store_release() for write pointer update, see above */
        smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size);

        return len;
}

ssize_t dvb_ringbuffer_pkt_write(struct dvb_ringbuffer *rbuf, u8 *buf, size_t len)
{
        int status;
        ssize_t oldpwrite = rbuf->pwrite;

        DVB_RINGBUFFER_WRITE_BYTE(rbuf, len >> 8);
        DVB_RINGBUFFER_WRITE_BYTE(rbuf, len & 0xff);
        DVB_RINGBUFFER_WRITE_BYTE(rbuf, PKT_READY);
        status = dvb_ringbuffer_write(rbuf, buf, len);

        if (status < 0)
                rbuf->pwrite = oldpwrite;
        return status;
}

ssize_t dvb_ringbuffer_pkt_read_user(struct dvb_ringbuffer *rbuf, size_t idx,
                                int offset, u8 __user *buf, size_t len)
{
        size_t todo;
        size_t split;
        size_t pktlen;

        pktlen = rbuf->data[idx] << 8;
        pktlen |= rbuf->data[(idx + 1) % rbuf->size];
        if (offset > pktlen)
                return -EINVAL;
        if ((offset + len) > pktlen)
                len = pktlen - offset;

        idx = (idx + DVB_RINGBUFFER_PKTHDRSIZE + offset) % rbuf->size;
        todo = len;
        split = ((idx + len) > rbuf->size) ? rbuf->size - idx : 0;
        if (split > 0) {
                if (copy_to_user(buf, rbuf->data+idx, split))
                        return -EFAULT;
                buf += split;
                todo -= split;
                idx = 0;
        }
        if (copy_to_user(buf, rbuf->data+idx, todo))
                return -EFAULT;

        return len;
}

ssize_t dvb_ringbuffer_pkt_read(struct dvb_ringbuffer *rbuf, size_t idx,
                                int offset, u8 *buf, size_t len)
{
        size_t todo;
        size_t split;
        size_t pktlen;

        pktlen = rbuf->data[idx] << 8;
        pktlen |= rbuf->data[(idx + 1) % rbuf->size];
        if (offset > pktlen)
                return -EINVAL;
        if ((offset + len) > pktlen)
                len = pktlen - offset;

        idx = (idx + DVB_RINGBUFFER_PKTHDRSIZE + offset) % rbuf->size;
        todo = len;
        split = ((idx + len) > rbuf->size) ? rbuf->size - idx : 0;
        if (split > 0) {
                memcpy(buf, rbuf->data+idx, split);
                buf += split;
                todo -= split;
                idx = 0;
        }
        memcpy(buf, rbuf->data+idx, todo);
        return len;
}

void dvb_ringbuffer_pkt_dispose(struct dvb_ringbuffer *rbuf, size_t idx)
{
        size_t pktlen;

        rbuf->data[(idx + 2) % rbuf->size] = PKT_DISPOSED;

        // clean up disposed packets
        while (dvb_ringbuffer_avail(rbuf) > DVB_RINGBUFFER_PKTHDRSIZE) {
                if (DVB_RINGBUFFER_PEEK(rbuf, 2) == PKT_DISPOSED) {
                        pktlen = DVB_RINGBUFFER_PEEK(rbuf, 0) << 8;
                        pktlen |= DVB_RINGBUFFER_PEEK(rbuf, 1);
                        DVB_RINGBUFFER_SKIP(rbuf, pktlen + DVB_RINGBUFFER_PKTHDRSIZE);
                } else {
                        // first packet is not disposed, so we stop cleaning now
                        break;
                }
        }
}

ssize_t dvb_ringbuffer_pkt_next(struct dvb_ringbuffer *rbuf, size_t idx, size_t *pktlen)
{
        int consumed;
        int curpktlen;
        int curpktstatus;

        if (idx == -1) {
                idx = rbuf->pread;
        } else {
                curpktlen = rbuf->data[idx] << 8;
                curpktlen |= rbuf->data[(idx + 1) % rbuf->size];
                idx = (idx + curpktlen + DVB_RINGBUFFER_PKTHDRSIZE) % rbuf->size;
        }

        consumed = (idx - rbuf->pread);
        if (consumed < 0)
                consumed += rbuf->size;

        while ((dvb_ringbuffer_avail(rbuf) - consumed) > DVB_RINGBUFFER_PKTHDRSIZE) {

                curpktlen = rbuf->data[idx] << 8;
                curpktlen |= rbuf->data[(idx + 1) % rbuf->size];
                curpktstatus = rbuf->data[(idx + 2) % rbuf->size];

                if (curpktstatus == PKT_READY) {
                        *pktlen = curpktlen;
                        return idx;
                }

                consumed += curpktlen + DVB_RINGBUFFER_PKTHDRSIZE;
                idx = (idx + curpktlen + DVB_RINGBUFFER_PKTHDRSIZE) % rbuf->size;
        }

        // no packets available
        return -1;
}



EXPORT_SYMBOL(dvb_ringbuffer_init);
EXPORT_SYMBOL(dvb_ringbuffer_empty);
EXPORT_SYMBOL(dvb_ringbuffer_free);
EXPORT_SYMBOL(dvb_ringbuffer_avail);
EXPORT_SYMBOL(dvb_ringbuffer_flush_spinlock_wakeup);
EXPORT_SYMBOL(dvb_ringbuffer_read_user);
EXPORT_SYMBOL(dvb_ringbuffer_read);
EXPORT_SYMBOL(dvb_ringbuffer_write);
EXPORT_SYMBOL(dvb_ringbuffer_write_user);