/*
   * Copyright (C) 2008 Felix Fietkau <nbd@openwrt.org>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   *
   * Based on minstrel.c:
   *   Copyright (C) 2005-2007 Derek Smithies <derek@indranet.co.nz>
   *   Sponsored by Indranet Technologies Ltd
   *
   * Based on sample.c:
   *   Copyright (c) 2005 John Bicket
   *   All rights reserved.
   *
   *   Redistribution and use in source and binary forms, with or without
   *   modification, are permitted provided that the following conditions
   *   are met:
   *   1. Redistributions of source code must retain the above copyright
   *      notice, this list of conditions and the following disclaimer,
   *      without modification.
   *   2. Redistributions in binary form must reproduce at minimum a disclaimer
   *      similar to the "NO WARRANTY" disclaimer below ("Disclaimer") and any
   *      redistribution must be conditioned upon including a substantially
   *      similar Disclaimer requirement for further binary redistribution.
   *   3. Neither the names of the above-listed copyright holders nor the names
   *      of any contributors may be used to endorse or promote products derived
   *      from this software without specific prior written permission.
   *
   *   Alternatively, this software may be distributed under the terms of the
   *   GNU General Public License ("GPL") version 2 as published by the Free
   *   Software Foundation.
   *
   *   NO WARRANTY
   *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   *   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   *   LIMITED TO, THE IMPLIED WARRANTIES OF NONINFRINGEMENT, MERCHANTIBILITY
   *   AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
   *   THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY,
   *   OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   *   SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   *   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
   *   IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   *   ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
   *   THE POSSIBILITY OF SUCH DAMAGES.
   */
  #include <linux/netdevice.h>
  #include <linux/types.h>
  #include <linux/skbuff.h>
  #include <linux/debugfs.h>
  #include <linux/random.h>
  #include <linux/ieee80211.h>

  #include <linux/slab.h>

  #include <net/mac80211.h>
  #include "rate.h"
  #include "rc80211_minstrel.h"
  
  #define SAMPLE_COLUMNS	10
  #define SAMPLE_TBL(_mi, _idx, _col) \
  		_mi->sample_table[(_idx * SAMPLE_COLUMNS) + _col]
  
  /* convert mac80211 rate index to local array index */
  static inline int
  rix_to_ndx(struct minstrel_sta_info *mi, int rix)
  {
  	int i = rix;
  	for (i = rix; i >= 0; i--)
  		if (mi->r[i].rix == rix)
  			break;

  	return i;
  }

  static void
  minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
  {
  	u32 max_tp = 0, index_max_tp = 0, index_max_tp2 = 0;
  	u32 max_prob = 0, index_max_prob = 0;
  	u32 usecs;
  	u32 p;
  	int i;
  
  	mi->stats_update = jiffies;
  	for (i = 0; i < mi->n_rates; i++) {
  		struct minstrel_rate *mr = &mi->r[i];
  
  		usecs = mr->perfect_tx_time;
  		if (!usecs)
  			usecs = 1000000;
  
  		/* To avoid rounding issues, probabilities scale from 0 (0%)
  		 * to 18000 (100%) */
  		if (mr->attempts) {
  			p = (mr->success * 18000) / mr->attempts;
  			mr->succ_hist += mr->success;
  			mr->att_hist += mr->attempts;
  			mr->cur_prob = p;
  			p = ((p * (100 - mp->ewma_level)) + (mr->probability *
  				mp->ewma_level)) / 100;
  			mr->probability = p;
  			mr->cur_tp = p * (1000000 / usecs);
  		}
  
  		mr->last_success = mr->success;
  		mr->last_attempts = mr->attempts;
  		mr->success = 0;
  		mr->attempts = 0;
  
  		/* Sample less often below the 10% chance of success.
  		 * Sample less often above the 95% chance of success. */
  		if ((mr->probability > 17100) || (mr->probability < 1800)) {
  			mr->adjusted_retry_count = mr->retry_count >> 1;
  			if (mr->adjusted_retry_count > 2)
  				mr->adjusted_retry_count = 2;

  			mr->sample_limit = 4;

  		} else {

  			mr->sample_limit = -1;

  			mr->adjusted_retry_count = mr->retry_count;
  		}
  		if (!mr->adjusted_retry_count)
  			mr->adjusted_retry_count = 2;
  	}
  
  	for (i = 0; i < mi->n_rates; i++) {
  		struct minstrel_rate *mr = &mi->r[i];
  		if (max_tp < mr->cur_tp) {
  			index_max_tp = i;
  			max_tp = mr->cur_tp;
  		}
  		if (max_prob < mr->probability) {
  			index_max_prob = i;
  			max_prob = mr->probability;
  		}
  	}
  
  	max_tp = 0;
  	for (i = 0; i < mi->n_rates; i++) {
  		struct minstrel_rate *mr = &mi->r[i];
  
  		if (i == index_max_tp)
  			continue;
  
  		if (max_tp < mr->cur_tp) {
  			index_max_tp2 = i;
  			max_tp = mr->cur_tp;
  		}
  	}
  	mi->max_tp_rate = index_max_tp;
  	mi->max_tp_rate2 = index_max_tp2;
  	mi->max_prob_rate = index_max_prob;
  }
  
  static void
  minstrel_tx_status(void *priv, struct ieee80211_supported_band *sband,
                     struct ieee80211_sta *sta, void *priv_sta,
  		   struct sk_buff *skb)
  {
  	struct minstrel_sta_info *mi = priv_sta;
  	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);

  	struct ieee80211_tx_rate *ar = info->status.rates;
  	int i, ndx;
  	int success;

  	success = !!(info->flags & IEEE80211_TX_STAT_ACK);

  	for (i = 0; i < IEEE80211_TX_MAX_RATES; i++) {
  		if (ar[i].idx < 0)

  			break;

  		ndx = rix_to_ndx(mi, ar[i].idx);

  		if (ndx < 0)
  			continue;

  		mi->r[ndx].attempts += ar[i].count;

  		if ((i != IEEE80211_TX_MAX_RATES - 1) && (ar[i + 1].idx < 0))

  			mi->r[ndx].success += success;
  	}
  
  	if ((info->flags & IEEE80211_TX_CTL_RATE_CTRL_PROBE) && (i >= 0))
  		mi->sample_count++;
  
  	if (mi->sample_deferred > 0)
  		mi->sample_deferred--;
  }
  
  
  static inline unsigned int
  minstrel_get_retry_count(struct minstrel_rate *mr,
                           struct ieee80211_tx_info *info)
  {
  	unsigned int retry = mr->adjusted_retry_count;

  	if (info->control.rates[0].flags & IEEE80211_TX_RC_USE_RTS_CTS)

  		retry = max(2U, min(mr->retry_count_rtscts, retry));

  	else if (info->control.rates[0].flags & IEEE80211_TX_RC_USE_CTS_PROTECT)

  		retry = max(2U, min(mr->retry_count_cts, retry));
  	return retry;
  }
  
  
  static int
  minstrel_get_next_sample(struct minstrel_sta_info *mi)
  {
  	unsigned int sample_ndx;
  	sample_ndx = SAMPLE_TBL(mi, mi->sample_idx, mi->sample_column);
  	mi->sample_idx++;

  	if ((int) mi->sample_idx > (mi->n_rates - 2)) {

  		mi->sample_idx = 0;
  		mi->sample_column++;
  		if (mi->sample_column >= SAMPLE_COLUMNS)
  			mi->sample_column = 0;
  	}
  	return sample_ndx;
  }

  static void

  minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
  		  void *priv_sta, struct ieee80211_tx_rate_control *txrc)

  {

  	struct sk_buff *skb = txrc->skb;

  	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
  	struct minstrel_sta_info *mi = priv_sta;
  	struct minstrel_priv *mp = priv;

  	struct ieee80211_tx_rate *ar = info->control.rates;

  	unsigned int ndx, sample_ndx = 0;
  	bool mrr;
  	bool sample_slower = false;
  	bool sample = false;
  	int i, delta;
  	int mrr_ndx[3];
  	int sample_rate;

  	if (rate_control_send_low(sta, priv_sta, txrc))

  		return;

  	mrr = mp->has_mrr && !txrc->rts && !txrc->bss_conf->use_cts_prot;

  
  	if (time_after(jiffies, mi->stats_update + (mp->update_interval *
  			HZ) / 1000))
  		minstrel_update_stats(mp, mi);
  
  	ndx = mi->max_tp_rate;
  
  	if (mrr)
  		sample_rate = mp->lookaround_rate_mrr;
  	else
  		sample_rate = mp->lookaround_rate;
  
  	mi->packet_count++;
  	delta = (mi->packet_count * sample_rate / 100) -
  			(mi->sample_count + mi->sample_deferred / 2);
  
  	/* delta > 0: sampling required */

  	if ((delta > 0) && (mrr || !mi->prev_sample)) {
  		struct minstrel_rate *msr;

  		if (mi->packet_count >= 10000) {
  			mi->sample_deferred = 0;
  			mi->sample_count = 0;
  			mi->packet_count = 0;
  		} else if (delta > mi->n_rates * 2) {
  			/* With multi-rate retry, not every planned sample
  			 * attempt actually gets used, due to the way the retry
  			 * chain is set up - [max_tp,sample,prob,lowest] for
  			 * sample_rate < max_tp.
  			 *
  			 * If there's too much sampling backlog and the link
  			 * starts getting worse, minstrel would start bursting
  			 * out lots of sampling frames, which would result
  			 * in a large throughput loss. */
  			mi->sample_count += (delta - mi->n_rates * 2);
  		}
  
  		sample_ndx = minstrel_get_next_sample(mi);

  		msr = &mi->r[sample_ndx];

  		sample = true;

  		sample_slower = mrr && (msr->perfect_tx_time >

  			mi->r[ndx].perfect_tx_time);
  
  		if (!sample_slower) {

  			if (msr->sample_limit != 0) {
  				ndx = sample_ndx;
  				mi->sample_count++;
  				if (msr->sample_limit > 0)
  					msr->sample_limit--;
  			} else {
  				sample = false;
  			}

  		} else {
  			/* Only use IEEE80211_TX_CTL_RATE_CTRL_PROBE to mark
  			 * packets that have the sampling rate deferred to the
  			 * second MRR stage. Increase the sample counter only
  			 * if the deferred sample rate was actually used.
  			 * Use the sample_deferred counter to make sure that
  			 * the sampling is not done in large bursts */
  			info->flags |= IEEE80211_TX_CTL_RATE_CTRL_PROBE;
  			mi->sample_deferred++;
  		}
  	}

  	mi->prev_sample = sample;
  
  	/* If we're not using MRR and the sampling rate already
  	 * has a probability of >95%, we shouldn't be attempting
  	 * to use it, as this only wastes precious airtime */
  	if (!mrr && sample && (mi->r[ndx].probability > 17100))
  		ndx = mi->max_tp_rate;

  	ar[0].idx = mi->r[ndx].rix;
  	ar[0].count = minstrel_get_retry_count(&mi->r[ndx], info);

  
  	if (!mrr) {

  		if (!sample)
  			ar[0].count = mp->max_retry;

  		ar[1].idx = mi->lowest_rix;
  		ar[1].count = mp->max_retry;

  		return;
  	}
  
  	/* MRR setup */
  	if (sample) {
  		if (sample_slower)
  			mrr_ndx[0] = sample_ndx;
  		else
  			mrr_ndx[0] = mi->max_tp_rate;
  	} else {
  		mrr_ndx[0] = mi->max_tp_rate2;
  	}
  	mrr_ndx[1] = mi->max_prob_rate;
  	mrr_ndx[2] = 0;

  	for (i = 1; i < 4; i++) {
  		ar[i].idx = mi->r[mrr_ndx[i - 1]].rix;
  		ar[i].count = mi->r[mrr_ndx[i - 1]].adjusted_retry_count;

  	}
  }
  
  
  static void
  calc_rate_durations(struct minstrel_sta_info *mi, struct ieee80211_local *local,
                      struct minstrel_rate *d, struct ieee80211_rate *rate)
  {
  	int erp = !!(rate->flags & IEEE80211_RATE_ERP_G);
  
  	d->perfect_tx_time = ieee80211_frame_duration(local, 1200,
  			rate->bitrate, erp, 1);
  	d->ack_time = ieee80211_frame_duration(local, 10,
  			rate->bitrate, erp, 1);
  }
  
  static void
  init_sample_table(struct minstrel_sta_info *mi)
  {
  	unsigned int i, col, new_idx;
  	unsigned int n_srates = mi->n_rates - 1;
  	u8 rnd[8];
  
  	mi->sample_column = 0;
  	mi->sample_idx = 0;
  	memset(mi->sample_table, 0, SAMPLE_COLUMNS * mi->n_rates);
  
  	for (col = 0; col < SAMPLE_COLUMNS; col++) {
  		for (i = 0; i < n_srates; i++) {
  			get_random_bytes(rnd, sizeof(rnd));
  			new_idx = (i + rnd[i & 7]) % n_srates;
  
  			while (SAMPLE_TBL(mi, new_idx, col) != 0)
  				new_idx = (new_idx + 1) % n_srates;
  
  			/* Don't sample the slowest rate (i.e. slowest base
  			 * rate). We must presume that the slowest rate works
  			 * fine, or else other management frames will also be
  			 * failing and the link will break */
  			SAMPLE_TBL(mi, new_idx, col) = i + 1;
  		}
  	}
  }
  
  static void
  minstrel_rate_init(void *priv, struct ieee80211_supported_band *sband,
                 struct ieee80211_sta *sta, void *priv_sta)
  {
  	struct minstrel_sta_info *mi = priv_sta;
  	struct minstrel_priv *mp = priv;

  	struct ieee80211_local *local = hw_to_local(mp->hw);
  	struct ieee80211_rate *ctl_rate;

  	unsigned int i, n = 0;
  	unsigned int t_slot = 9; /* FIXME: get real slot time */
  
  	mi->lowest_rix = rate_lowest_index(sband, sta);

  	ctl_rate = &sband->bitrates[mi->lowest_rix];
  	mi->sp_ack_dur = ieee80211_frame_duration(local, 10, ctl_rate->bitrate,
  				!!(ctl_rate->flags & IEEE80211_RATE_ERP_G), 1);

  
  	for (i = 0; i < sband->n_bitrates; i++) {
  		struct minstrel_rate *mr = &mi->r[n];
  		unsigned int tx_time = 0, tx_time_cts = 0, tx_time_rtscts = 0;
  		unsigned int tx_time_single;
  		unsigned int cw = mp->cw_min;
  
  		if (!rate_supported(sta, sband->band, i))
  			continue;
  		n++;
  		memset(mr, 0, sizeof(*mr));
  
  		mr->rix = i;
  		mr->bitrate = sband->bitrates[i].bitrate / 5;

  		calc_rate_durations(mi, local, mr,

  				&sband->bitrates[i]);
  
  		/* calculate maximum number of retransmissions before
  		 * fallback (based on maximum segment size) */

  		mr->sample_limit = -1;

  		mr->retry_count = 1;
  		mr->retry_count_cts = 1;
  		mr->retry_count_rtscts = 1;
  		tx_time = mr->perfect_tx_time + mi->sp_ack_dur;
  		do {
  			/* add one retransmission */
  			tx_time_single = mr->ack_time + mr->perfect_tx_time;
  
  			/* contention window */

  			tx_time_single += (t_slot * cw) >> 1;
  			cw = min((cw << 1) | 1, mp->cw_max);

  
  			tx_time += tx_time_single;
  			tx_time_cts += tx_time_single + mi->sp_ack_dur;
  			tx_time_rtscts += tx_time_single + 2 * mi->sp_ack_dur;
  			if ((tx_time_cts < mp->segment_size) &&
  				(mr->retry_count_cts < mp->max_retry))
  				mr->retry_count_cts++;
  			if ((tx_time_rtscts < mp->segment_size) &&
  				(mr->retry_count_rtscts < mp->max_retry))
  				mr->retry_count_rtscts++;
  		} while ((tx_time < mp->segment_size) &&
  				(++mr->retry_count < mp->max_retry));
  		mr->adjusted_retry_count = mr->retry_count;
  	}
  
  	for (i = n; i < sband->n_bitrates; i++) {
  		struct minstrel_rate *mr = &mi->r[i];
  		mr->rix = -1;
  	}
  
  	mi->n_rates = n;
  	mi->stats_update = jiffies;
  
  	init_sample_table(mi);
  }
  
  static void *
  minstrel_alloc_sta(void *priv, struct ieee80211_sta *sta, gfp_t gfp)
  {
  	struct ieee80211_supported_band *sband;
  	struct minstrel_sta_info *mi;
  	struct minstrel_priv *mp = priv;
  	struct ieee80211_hw *hw = mp->hw;
  	int max_rates = 0;
  	int i;
  
  	mi = kzalloc(sizeof(struct minstrel_sta_info), gfp);
  	if (!mi)
  		return NULL;
  
  	for (i = 0; i < IEEE80211_NUM_BANDS; i++) {

  		sband = hw->wiphy->bands[i];

  		if (sband && sband->n_bitrates > max_rates)

  			max_rates = sband->n_bitrates;
  	}
  
  	mi->r = kzalloc(sizeof(struct minstrel_rate) * max_rates, gfp);
  	if (!mi->r)
  		goto error;
  
  	mi->sample_table = kmalloc(SAMPLE_COLUMNS * max_rates, gfp);
  	if (!mi->sample_table)
  		goto error1;
  
  	mi->stats_update = jiffies;
  	return mi;
  
  error1:
  	kfree(mi->r);
  error:
  	kfree(mi);
  	return NULL;
  }
  
  static void
  minstrel_free_sta(void *priv, struct ieee80211_sta *sta, void *priv_sta)
  {
  	struct minstrel_sta_info *mi = priv_sta;
  
  	kfree(mi->sample_table);
  	kfree(mi->r);
  	kfree(mi);
  }

  static void *
  minstrel_alloc(struct ieee80211_hw *hw, struct dentry *debugfsdir)
  {
  	struct minstrel_priv *mp;
  
  	mp = kzalloc(sizeof(struct minstrel_priv), GFP_ATOMIC);
  	if (!mp)
  		return NULL;
  
  	/* contention window settings
  	 * Just an approximation. Using the per-queue values would complicate
  	 * the calculations and is probably unnecessary */
  	mp->cw_min = 15;
  	mp->cw_max = 1023;
  
  	/* number of packets (in %) to use for sampling other rates
  	 * sample less often for non-mrr packets, because the overhead
  	 * is much higher than with mrr */
  	mp->lookaround_rate = 5;
  	mp->lookaround_rate_mrr = 10;
  
  	/* moving average weight for EWMA */
  	mp->ewma_level = 75;
  
  	/* maximum time that the hw is allowed to stay in one MRR segment */
  	mp->segment_size = 6000;

  	if (hw->max_rate_tries > 0)
  		mp->max_retry = hw->max_rate_tries;

  	else
  		/* safe default, does not necessarily have to match hw properties */
  		mp->max_retry = 7;

  	if (hw->max_rates >= 4)

  		mp->has_mrr = true;
  
  	mp->hw = hw;
  	mp->update_interval = 100;

  #ifdef CONFIG_MAC80211_DEBUGFS
  	mp->fixed_rate_idx = (u32) -1;
  	mp->dbg_fixed_rate = debugfs_create_u32("fixed_rate_idx",
  			S_IRUGO | S_IWUGO, debugfsdir, &mp->fixed_rate_idx);
  #endif

  	return mp;
  }
  
  static void
  minstrel_free(void *priv)
  {

  #ifdef CONFIG_MAC80211_DEBUGFS
  	debugfs_remove(((struct minstrel_priv *)priv)->dbg_fixed_rate);
  #endif

  	kfree(priv);
  }

  struct rate_control_ops mac80211_minstrel = {

  	.name = "minstrel",
  	.tx_status = minstrel_tx_status,
  	.get_rate = minstrel_get_rate,
  	.rate_init = minstrel_rate_init,

  	.alloc = minstrel_alloc,
  	.free = minstrel_free,
  	.alloc_sta = minstrel_alloc_sta,
  	.free_sta = minstrel_free_sta,
  #ifdef CONFIG_MAC80211_DEBUGFS
  	.add_sta_debugfs = minstrel_add_sta_debugfs,
  	.remove_sta_debugfs = minstrel_remove_sta_debugfs,
  #endif
  };
  
  int __init
  rc80211_minstrel_init(void)
  {
  	return ieee80211_rate_control_register(&mac80211_minstrel);
  }
  
  void
  rc80211_minstrel_exit(void)
  {
  	ieee80211_rate_control_unregister(&mac80211_minstrel);
  }