/*
   *
   * 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.
   *
   * You should have received a copy of the GNU Lesser General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
   */
  
  
  
  #include <linux/errno.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/sched.h>
  #include <linux/string.h>
  #include <asm/uaccess.h>
  
  #include "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=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/circular-buffers.txt
  	 */
  	return (rbuf->pread == smp_load_acquire(&rbuf->pwrite));
  }
  
  
  
  ssize_t dvb_ringbuffer_free(struct dvb_ringbuffer *rbuf)
  {
  	ssize_t free;
  
  	/* ACCESS_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 = ACCESS_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 ACCESS_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 ACCESS_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) % 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);