/*
   * Copyright (c) 2006 Oracle.  All rights reserved.
   *
   * This software is available to you under a choice of one of two
   * licenses.  You may choose to be licensed under the terms of the GNU
   * General Public License (GPL) Version 2, available from the file
   * COPYING in the main directory of this source tree, or the
   * OpenIB.org BSD license below:
   *
   *     Redistribution and use in source and binary forms, with or
   *     without modification, are permitted provided that the following
   *     conditions are met:
   *
   *      - Redistributions of source code must retain the above
   *        copyright notice, this list of conditions and the following
   *        disclaimer.
   *
   *      - Redistributions in binary form must reproduce the above
   *        copyright notice, this list of conditions and the following
   *        disclaimer in the documentation and/or other materials
   *        provided with the distribution.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
   * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
   * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
   * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
   * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
   * SOFTWARE.
   *
   */
  #include <linux/kernel.h>
  
  #include "rds.h"
  #include "ib.h"
  
  /*
   * Locking for IB rings.
   * We assume that allocation is always protected by a mutex
   * in the caller (this is a valid assumption for the current
   * implementation).
   *
   * Freeing always happens in an interrupt, and hence only
   * races with allocations, but not with other free()s.
   *
   * The interaction between allocation and freeing is that
   * the alloc code has to determine the number of free entries.
   * To this end, we maintain two counters; an allocation counter
   * and a free counter. Both are allowed to run freely, and wrap
   * around.
   * The number of used entries is always (alloc_ctr - free_ctr) % NR.
   *
   * The current implementation makes free_ctr atomic. When the
   * caller finds an allocation fails, it should set an "alloc fail"
   * bit and retry the allocation. The "alloc fail" bit essentially tells
   * the CQ completion handlers to wake it up after freeing some
   * more entries.
   */
  
  /*
   * This only happens on shutdown.
   */
  DECLARE_WAIT_QUEUE_HEAD(rds_ib_ring_empty_wait);
  
  void rds_ib_ring_init(struct rds_ib_work_ring *ring, u32 nr)
  {
  	memset(ring, 0, sizeof(*ring));
  	ring->w_nr = nr;
  	rdsdebug("ring %p nr %u
  ", ring, ring->w_nr);
  }
  
  static inline u32 __rds_ib_ring_used(struct rds_ib_work_ring *ring)
  {
  	u32 diff;
  
  	/* This assumes that atomic_t has at least as many bits as u32 */
  	diff = ring->w_alloc_ctr - (u32) atomic_read(&ring->w_free_ctr);
  	BUG_ON(diff > ring->w_nr);
  
  	return diff;
  }
  
  void rds_ib_ring_resize(struct rds_ib_work_ring *ring, u32 nr)
  {
  	/* We only ever get called from the connection setup code,
  	 * prior to creating the QP. */
  	BUG_ON(__rds_ib_ring_used(ring));
  	ring->w_nr = nr;
  }
  
  static int __rds_ib_ring_empty(struct rds_ib_work_ring *ring)
  {
  	return __rds_ib_ring_used(ring) == 0;
  }
  
  u32 rds_ib_ring_alloc(struct rds_ib_work_ring *ring, u32 val, u32 *pos)
  {
  	u32 ret = 0, avail;
  
  	avail = ring->w_nr - __rds_ib_ring_used(ring);
  
  	rdsdebug("ring %p val %u next %u free %u
  ", ring, val,
  		 ring->w_alloc_ptr, avail);
  
  	if (val && avail) {
  		ret = min(val, avail);
  		*pos = ring->w_alloc_ptr;
  
  		ring->w_alloc_ptr = (ring->w_alloc_ptr + ret) % ring->w_nr;
  		ring->w_alloc_ctr += ret;
  	}
  
  	return ret;
  }
  
  void rds_ib_ring_free(struct rds_ib_work_ring *ring, u32 val)
  {
  	ring->w_free_ptr = (ring->w_free_ptr + val) % ring->w_nr;
  	atomic_add(val, &ring->w_free_ctr);
  
  	if (__rds_ib_ring_empty(ring) &&
  	    waitqueue_active(&rds_ib_ring_empty_wait))
  		wake_up(&rds_ib_ring_empty_wait);
  }
  
  void rds_ib_ring_unalloc(struct rds_ib_work_ring *ring, u32 val)
  {
  	ring->w_alloc_ptr = (ring->w_alloc_ptr - val) % ring->w_nr;
  	ring->w_alloc_ctr -= val;
  }
  
  int rds_ib_ring_empty(struct rds_ib_work_ring *ring)
  {
  	return __rds_ib_ring_empty(ring);
  }
  
  int rds_ib_ring_low(struct rds_ib_work_ring *ring)
  {
  	return __rds_ib_ring_used(ring) <= (ring->w_nr >> 1);
  }
  
  /*
   * returns the oldest alloced ring entry.  This will be the next one
   * freed.  This can't be called if there are none allocated.
   */
  u32 rds_ib_ring_oldest(struct rds_ib_work_ring *ring)
  {
  	return ring->w_free_ptr;
  }
  
  /*
   * returns the number of completed work requests.
   */
  
  u32 rds_ib_ring_completed(struct rds_ib_work_ring *ring, u32 wr_id, u32 oldest)
  {
  	u32 ret;
  
  	if (oldest <= (unsigned long long)wr_id)
  		ret = (unsigned long long)wr_id - oldest + 1;
  	else
  		ret = ring->w_nr - oldest + (unsigned long long)wr_id + 1;
  
  	rdsdebug("ring %p ret %u wr_id %u oldest %u
  ", ring, ret,
  		 wr_id, oldest);
  	return ret;
  }